Allow ConfigParseError to unwrap (#1433)

* Allow ConfigParseError to unwrap

* wip

* Avoid pointer type

.editorconfig

@@ -0,0 +1,15 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_size = 4
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.go]
+indent_style = tab
+
+[{Makefile,*.mk}]
+indent_style = tab

.github/.editorconfig

@@ -0,0 +1,2 @@
+[{*.yml,*.yaml}]
+indent_size = 2

.github/ISSUE_TEMPLATE/bug_report.yaml

@@ -0,0 +1,119 @@
+name: 🐛 Bug report
+description: Report a bug to help us improve Viper
+labels: [kind/bug]
+body:
+- type: markdown
+  attributes:
+    value: |
+      Thank you for submitting a bug report!
+
+      Please fill out the template below to make it easier to debug your problem.
+
+      If you are not sure if it is a bug or not, you can contact us via the available [support channels](https://github.com/spf13/viper/issues/new/choose).
+- type: checkboxes
+  attributes:
+    label: Preflight Checklist
+    description: Please ensure you've completed all of the following.
+    options:
+      - label: I have searched the [issue tracker](https://www.github.com/spf13/viper/issues) for an issue that matches the one I want to file, without success.
+        required: true
+      - label: I am not looking for support or already pursued the available [support channels](https://github.com/spf13/viper/issues/new/choose) without success.
+        required: true
+      - label: I have checked the [troubleshooting guide](https://github.com/spf13/viper/blob/master/TROUBLESHOOTING.md) for my problem, without success.
+        required: true
+- type: input
+  attributes:
+    label: Viper Version
+    description: What version of Viper are you using?
+    placeholder: 1.8.1
+  validations:
+    required: true
+- type: input
+  attributes:
+    label: Go Version
+    description: What version of Go are you using?
+    placeholder: "1.16"
+  validations:
+    required: true
+- type: dropdown
+  attributes:
+    label: Config Source
+    description: What sources do you load configuration from?
+    options:
+      - Manual set
+      - Flags
+      - Environment variables
+      - Files
+      - Remove K/V stores
+      - Defaults
+    multiple: true
+  validations:
+    required: true
+- type: dropdown
+  attributes:
+    label: Format
+    description: Which file formats do you use?
+    options:
+      - JSON
+      - YAML
+      - TOML
+      - Dotenv
+      - HCL
+      - Java properties
+      - INI
+      - Other (specify below)
+    multiple: true
+- type: input
+  attributes:
+    label: Repl.it link
+    description: Complete example on Repl.it reproducing the issue. [Here](https://repl.it/@sagikazarmark/Viper-example) is an example you can use.
+    placeholder: https://repl.it/@sagikazarmark/Viper-example
+- type: textarea
+  attributes:
+    label: Code reproducing the issue
+    description: Please provide a Repl.it link if possible.
+    render: go
+    placeholder: |
+      package main
+
+      import (
+        "github.com/spf13/viper"
+      )
+
+      func main() {
+        v := viper.New()
+
+        // ...
+
+        var config Config
+
+        err = v.Unmarshal(&config)
+        if err != nil {
+          panic(err)
+        }
+      }
+- type: textarea
+  attributes:
+    label: Expected Behavior
+    description: A clear and concise description of what you expected to happen.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Actual Behavior
+    description: A clear description of what actually happens.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Steps To Reproduce
+    description: Steps to reproduce the behavior if it is not self-explanatory.
+    placeholder: |
+      1. In this environment...
+      2. With this config...
+      3. Run '...'
+      4. See error...
+- type: textarea
+  attributes:
+    label: Additional Information
+    description: Links? References? Anything that will give us more context about the issue that you are encountering!

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,13 @@
+blank_issues_enabled: false
+contact_links:
+  - name: ❓ Ask a question
+    url: https://github.com/spf13/viper/discussions/new?category=q-a
+    about:  Ask and discuss questions with other Viper community members
+
+  - name: 📓 Reference
+    url: https://pkg.go.dev/mod/github.com/spf13/viper
+    about: Check the Go code reference
+
+  - name: 💬 Slack channel
+    url: https://gophers.slack.com/messages/viper
+    about: Please ask and answer questions here

.github/ISSUE_TEMPLATE/feature_request.yaml

@@ -0,0 +1,39 @@
+name: 🎉 Feature request
+description: Suggest an idea for Viper
+labels: [kind/enhancement]
+body:
+- type: markdown
+  attributes:
+    value: |
+      Thank you for submitting a feature request!
+
+      Please describe what you would like to change/add and why in detail by filling out the template below.
+
+      If you are not sure if your request fits into Viper, you can contact us via the available [support channels](https://github.com/spf13/viper/issues/new/choose).
+- type: checkboxes
+  attributes:
+    label: Preflight Checklist
+    description: Please ensure you've completed all of the following.
+    options:
+      - label: I have searched the [issue tracker](https://www.github.com/spf13/viper/issues) for an issue that matches the one I want to file, without success.
+        required: true
+- type: textarea
+  attributes:
+    label: Problem Description
+    description: A clear and concise description of the problem you are seeking to solve with this feature request.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Proposed Solution
+    description: A clear and concise description of what would you like to happen.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Alternatives Considered
+    description: A clear and concise description of any alternative solutions or features you've considered.
+- type: textarea
+  attributes:
+    label: Additional Information
+    description: Add any other context about the problem here.

.github/PULL_REQUEST_TEMPLATES.md

@@ -0,0 +1,20 @@
+<!--
+Thank you for sending a pull request! Here some tips for contributors:
+
+1. Fill the description template below.
+2. Include appropriate tests (if necessary). Make sure that all CI checks passed.
+3. If the Pull Request is a work in progress, make use of GitHub's "Draft PR" feature and mark it as such.
+-->
+
+**Overview**:
+<!-- Describe your changes briefly here. -->
+
+**What problem does it solve?**:
+<!--
+- Please state in detail why we need this PR and what it solves.
+- If your PR closes some of the existing issues, please add links to them here.
+  Mentioned issues will be automatically closed.
+  Usage: "Closes #<issue number>", or "Closes (paste link of issue)"
+-->
+
+**Special notes for a reviewer**:

.github/dependabot.yml

@@ -0,0 +1,16 @@
+version: 2
+
+updates:
+  - package-ecosystem: gomod
+    directory: /
+    labels:
+      - area/dependencies
+    schedule:
+      interval: daily
+
+  - package-ecosystem: github-actions
+    directory: /
+    labels:
+      - area/dependencies
+    schedule:
+      interval: daily

.github/release.yml

@@ -0,0 +1,30 @@
+changelog:
+  exclude:
+    labels:
+      - release-note/ignore
+  categories:
+    - title: Exciting New Features 🎉
+      labels:
+        - kind/feature
+        - release-note/new-feature
+    - title: Enhancements 🚀
+      labels:
+        - kind/enhancement
+        - release-note/enhancement
+    - title: Bug Fixes 🐛
+      labels:
+        - kind/bug
+        - release-note/bug-fix
+    - title: Breaking Changes 🛠
+      labels:
+        - release-note/breaking-change
+    - title: Deprecations ❌
+      labels:
+        - release-note/deprecation
+    - title: Dependency Updates ⬆️
+      labels:
+        - area/dependencies
+        - release-note/dependency-update
+    - title: Other Changes
+      labels:
+        - "*"

.github/workflows/.editorconfig

@@ -1,2 +0,0 @@
-[*.yml]
-indent_size = 2

.github/workflows/checks.yaml

@@ -0,0 +1,18 @@
+name: PR Checks
+
+on:
+  pull_request:
+    types: [opened, labeled, unlabeled, synchronize]
+
+jobs:
+  release-label:
+    name: Release note label
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check minimum labels
+        uses: mheap/github-action-required-labels@v4
+        with:
+          mode: minimum
+          count: 1
+          labels: "release-note/ignore, kind/feature, release-note/new-feature, kind/enhancement, release-note/enhancement, kind/bug, release-note/bug-fix, release-note/breaking-change, release-note/deprecation, area/dependencies, release-note/dependency-update"

.github/workflows/ci.yaml

@@ -0,0 +1,85 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - goos: js
+            goarch: wasm
+          - goos: aix
+            goarch: ppc64
+
+    steps:
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: '1.20'
+
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Build
+        run: go build .
+        env:
+          GOOS: ${{ matrix.goos }}
+          GOARCH: ${{ matrix.goarch }}
+
+  test:
+    name: Test
+    runs-on: ${{ matrix.os }}
+    strategy:
+      # Fail fast is disabled because there are Go version specific features and tests
+      # that should be able to fail independently.
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        go: ['1.17', '1.18', '1.19', '1.20']
+    env:
+      GOFLAGS: -mod=readonly
+
+    steps:
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: ${{ matrix.go }}
+
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Test
+        run: go test -race -v ./...
+        if: runner.os != 'Windows'
+
+      - name: Test (without race detector)
+        run: go test -v ./...
+        if: runner.os == 'Windows'
+
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+    env:
+      GOFLAGS: -mod=readonly
+
+    steps:
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: '1.20'
+
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Lint
+        uses: golangci/golangci-lint-action@v3
+        with:
+          version: v1.52.2

.github/workflows/ci.yml

@@ -1,34 +0,0 @@
-name: CI
-
-on:
-  push:
-    branches:
-      - master
-  pull_request:
-
-jobs:
-  build:
-    name: Build
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        go: ['1.11', '1.12', '1.13']
-    env:
-      VERBOSE: 1
-      GOFLAGS: -mod=readonly
-      GOPROXY: https://proxy.golang.org
-
-    steps:
-      - name: Set up Go
-        uses: actions/setup-go@v1
-        with:
-          go-version: ${{ matrix.go }}
-
-      - name: Checkout code
-        uses: actions/checkout@v2
-
-      - name: Run tests
-        run: make test
-
-      - name: Run linter
-        run: make lint

.github/workflows/codeql-analysis.yaml

@@ -0,0 +1,72 @@
+# For most projects, this workflow file will not need changing; you simply need
+# to commit it to your repository.
+#
+# You may wish to alter this file to override the set of languages analyzed,
+# or to provide custom queries or build logic.
+#
+# ******** NOTE ********
+# We have attempted to detect the languages in your repository. Please check
+# the `language` matrix defined below to confirm you have the correct set of
+# supported CodeQL languages.
+#
+name: "CodeQL"
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    # The branches below must be a subset of the branches above
+    branches: [ master ]
+  schedule:
+    - cron: '22 16 * * 3'
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [ 'go' ]
+        # CodeQL supports [ 'cpp', 'csharp', 'go', 'java', 'javascript', 'python' ]
+        # Learn more:
+        # https://docs.github.com/en/free-pro-team@latest/github/finding-security-vulnerabilities-and-errors-in-your-code/configuring-code-scanning#changing-the-languages-that-are-analyzed
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v3
+
+    # Initializes the CodeQL tools for scanning.
+    - name: Initialize CodeQL
+      uses: github/codeql-action/init@v2
+      with:
+        languages: ${{ matrix.language }}
+        # If you wish to specify custom queries, you can do so here or in a config file.
+        # By default, queries listed here will override any specified in a config file.
+        # Prefix the list here with "+" to use these queries and those in the config file.
+        # queries: ./path/to/local/query, your-org/your-repo/queries@main
+
+    # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
+    # If this step fails, then you should remove it and run the build manually (see below)
+    - name: Autobuild
+      uses: github/codeql-action/autobuild@v2
+
+    # ℹ️ Command-line programs to run using the OS shell.
+    # 📚 https://git.io/JvXDl
+
+    # ✏️ If the Autobuild fails above, remove it and uncomment the following three lines
+    #    and modify them (or add more) to build your code if your project
+    #    uses a compiled language
+
+    #- run: |
+    #   make bootstrap
+    #   make release
+
+    - name: Perform CodeQL Analysis
+      uses: github/codeql-action/analyze@v2
+

.github/workflows/feedback_issue.yaml

@@ -0,0 +1,32 @@
+on:
+  issues:
+    types: [opened]
+
+jobs:
+  comment:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/github-script@v6
+        with:
+          github-token: ${{secrets.GITHUB_TOKEN}}
+          script: |
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: `👋 Thanks for reporting!
+
+            A maintainer will take a look at your issue shortly. 👀
+
+            In the meantime: We are working on **Viper v2** and we would love to hear your thoughts about what you like or don't like about Viper, so we can improve or fix those issues.
+
+            ⏰ If you have a couple minutes, please take some time and share your thoughts: https://forms.gle/R6faU74qPRPAzchZ9
+
+            📣 If you've already given us your feedback, you can still help by spreading the news,
+            either by sharing the above link or telling people about this on Twitter:
+
+            https://twitter.com/sagikazarmark/status/1306904078967074816
+
+            **Thank you!** ❤️
+            `,
+            })

.github/workflows/feedback_pull_request.yaml

@@ -0,0 +1,32 @@
+on:
+  pull_request_target:
+    types: [opened]
+
+jobs:
+  comment:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/github-script@v6
+        with:
+          github-token: ${{secrets.GITHUB_TOKEN}}
+          script: |
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: `👋 Thanks for contributing to Viper! You are awesome! 🎉
+
+            A maintainer will take a look at your pull request shortly. 👀
+
+            In the meantime: We are working on **Viper v2** and we would love to hear your thoughts about what you like or don't like about Viper, so we can improve or fix those issues.
+
+            ⏰ If you have a couple minutes, please take some time and share your thoughts: https://forms.gle/R6faU74qPRPAzchZ9
+
+            📣 If you've already given us your feedback, you can still help by spreading the news,
+            either by sharing the above link or telling people about this on Twitter:
+
+            https://twitter.com/sagikazarmark/status/1306904078967074816
+
+            **Thank you!** ❤️
+            `,
+            })

.gitignore

@@ -1,20 +1,5 @@
+/.idea/
 /bin/
 /build/
 /var/
 /vendor/
-
-# IDE integration
-/.vscode/*
-!/.vscode/launch.json
-!/.vscode/tasks.json
-/.idea/*
-!/.idea/codeStyles/
-!/.idea/copyright/
-!/.idea/dataSources.xml
-!/.idea/*.iml
-!/.idea/externalDependencies.xml
-!/.idea/go.imports.xml
-!/.idea/modules.xml
-!/.idea/runConfigurations/
-!/.idea/scopes/
-!/.idea/sqldialects.xml

.golangci.yaml

@@ -0,0 +1,98 @@
+run:
+    timeout: 5m
+
+linters-settings:
+    gci:
+        sections:
+            - standard
+            - default
+            - prefix(github.com/spf13/viper)
+    golint:
+        min-confidence: 0
+    goimports:
+        local-prefixes: github.com/spf13/viper
+
+linters:
+    disable-all: true
+    enable:
+        - bodyclose
+        - dogsled
+        - dupl
+        - durationcheck
+        - exhaustive
+        - exportloopref
+        - gci
+        - gofmt
+        - gofumpt
+        - goimports
+        - gomoddirectives
+        - goprintffuncname
+        - govet
+        - importas
+        - ineffassign
+        - makezero
+        - misspell
+        - nakedret
+        - nilerr
+        - noctx
+        - nolintlint
+        - prealloc
+        - predeclared
+        - revive
+        - rowserrcheck
+        - sqlclosecheck
+        - staticcheck
+        - stylecheck
+        - tparallel
+        - typecheck
+        - unconvert
+        - unparam
+        - unused
+        - wastedassign
+        - whitespace
+
+        # fixme
+        # - cyclop
+        # - errcheck
+        # - errorlint
+        # - exhaustivestruct
+        # - forbidigo
+        # - forcetypeassert
+        # - gochecknoglobals
+        # - gochecknoinits
+        # - gocognit
+        # - goconst
+        # - gocritic
+        # - gocyclo
+        # - godot
+        # - gosec
+        # - gosimple
+        # - ifshort
+        # - lll
+        # - nlreturn
+        # - paralleltest
+        # - scopelint
+        # - thelper
+        # - wrapcheck
+
+        # unused
+        # - depguard
+        # - goheader
+        # - gomodguard
+
+        # deprecated
+        # - deadcode
+        # - structcheck
+        # - varcheck
+
+        # don't enable:
+        # - asciicheck
+        # - funlen
+        # - godox
+        # - goerr113
+        # - gomnd
+        # - interfacer
+        # - maligned
+        # - nestif
+        # - testpackage
+        # - wsl

.golangci.yml

@@ -1,24 +0,0 @@
-linters-settings:
-    golint:
-        min-confidence: 0.1
-    goimports:
-        local-prefixes: github.com/spf13/viper
-
-linters:
-    enable-all: true
-    disable:
-        - funlen
-        - maligned
-
-        # TODO: fix me
-        - wsl
-        - gochecknoinits
-        - gosimple
-        - gochecknoglobals
-        - errcheck
-        - lll
-        - godox
-        - scopelint
-        - gocyclo
-        - gocognit
-        - gocritic

.idea/externalDependencies.xml

@@ -1,7 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="ExternalDependencies">
-    <plugin id="name.kropp.intellij.makefile" />
-    <plugin id="org.jetbrains.plugins.go" />
-  </component>
-</project>

.idea/go.imports.xml

@@ -1,8 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="GoImports">
-    <option name="groupStdlibImports" value="true" />
-    <option name="importSorting" value="GOFMT" />
-    <option name="moveAllImportsInOneDeclaration" value="true" />
-  </component>
-</project>

.idea/modules.xml

@@ -1,8 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="ProjectModuleManager">
-    <modules>
-      <module fileurl="file://$PROJECT_DIR$/.idea/viper.iml" filepath="$PROJECT_DIR$/.idea/viper.iml" />
-    </modules>
-  </component>
-</project>

.idea/runConfigurations/Check.xml

@@ -1,7 +0,0 @@
-<component name="ProjectRunConfigurationManager">
-  <configuration default="false" name="Check" type="CompoundRunConfigurationType">
-    <toRun name="Tests" type="GoTestRunConfiguration" />
-    <toRun name="Lint" type="MAKEFILE_TARGET_RUN_CONFIGURATION" />
-    <method v="2" />
-  </configuration>
-</component>

.idea/runConfigurations/Lint.xml

@@ -1,8 +0,0 @@
-<component name="ProjectRunConfigurationManager">
-  <configuration default="false" name="Lint" type="MAKEFILE_TARGET_RUN_CONFIGURATION" factoryName="Makefile">
-    <makefile filename="$PROJECT_DIR$/Makefile" target="lint" workingDirectory="" arguments="">
-      <envs />
-    </makefile>
-    <method v="2" />
-  </configuration>
-</component>

.idea/runConfigurations/Tests.xml

@@ -1,23 +0,0 @@
-<component name="ProjectRunConfigurationManager">
-  <configuration default="false" name="Tests" type="GoTestRunConfiguration" factoryName="Go Test">
-    <module name="viper" />
-    <working_directory value="$PROJECT_DIR$/" />
-    <go_parameters value="-i" />
-    <EXTENSION ID="net.ashald.envfile">
-      <option name="IS_ENABLED" value="false" />
-      <option name="IS_SUBST" value="false" />
-      <option name="IS_PATH_MACRO_SUPPORTED" value="false" />
-      <option name="IS_IGNORE_MISSING_FILES" value="false" />
-      <option name="IS_ENABLE_EXPERIMENTAL_INTEGRATIONS" value="false" />
-      <ENTRIES>
-        <ENTRY IS_ENABLED="true" PARSER="runconfig" />
-      </ENTRIES>
-    </EXTENSION>
-    <framework value="gotest" />
-    <kind value="DIRECTORY" />
-    <package value="github.com/spf13/viper" />
-    <directory value="$PROJECT_DIR$/" />
-    <filePath value="$PROJECT_DIR$/" />
-    <method v="2" />
-  </configuration>
-</component>

.idea/viper.iml

@@ -1,9 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<module type="WEB_MODULE" version="4">
-  <component name="Go" enabled="true" />
-  <component name="NewModuleRootManager">
-    <content url="file://$MODULE_DIR$" />
-    <orderEntry type="inheritedJdk" />
-    <orderEntry type="sourceFolder" forTests="false" />
-  </component>
-</module>

.travis.yml

@@ -1,32 +0,0 @@
-go_import_path: github.com/spf13/viper
-
-language: go
-
-env:
-  global:
-    - GO111MODULE="on"
-    - GOFLAGS="-mod=readonly"
-
-go:
-  - 1.11.x
-  - 1.12.x
-  - 1.13.x
-  - tip
-
-os:
-  - linux
-  - osx
-
-matrix:
-  allow_failures:
-    - go: tip
-  fast_finish: true
-
-script:
-  - go install ./...
-  - diff -u <(echo -n) <(gofmt -d .)
-  - go test -v ./...
-
-after_success:
-  - go get -u -d github.com/spf13/hugo
-  - cd $GOPATH/src/github.com/spf13/hugo && make && ./hugo -s docs && cd -

Makefile

@@ -15,8 +15,8 @@ TEST_FORMAT = short-verbose
 endif
 
 # Dependency versions
-GOTESTSUM_VERSION = 0.4.0
-GOLANGCI_VERSION = 1.21.0
+GOTESTSUM_VERSION = 1.9.0
+GOLANGCI_VERSION = 1.52.2
 
 # Add the ability to override some variables
 # Use with care
@@ -48,8 +48,8 @@ bin/golangci-lint: bin/golangci-lint-${GOLANGCI_VERSION}
 	@ln -sf golangci-lint-${GOLANGCI_VERSION} bin/golangci-lint
 bin/golangci-lint-${GOLANGCI_VERSION}:
 	@mkdir -p bin
-	curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | bash -s -- -b ./bin/ v${GOLANGCI_VERSION}
-	@mv bin/golangci-lint $@
+	curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | bash -s -- -b ./bin/ v${GOLANGCI_VERSION}
+	@mv bin/golangci-lint "$@"
 
 .PHONY: lint
 lint: bin/golangci-lint ## Run linter

README.md

@@ -1,10 +1,20 @@
-![viper logo](https://cloud.githubusercontent.com/assets/173412/10886745/998df88a-8151-11e5-9448-4736db51020d.png)
+> ## Viper v2 feedback
+> Viper is heading towards v2 and we would love to hear what _**you**_ would like to see in it. Share your thoughts here: https://forms.gle/R6faU74qPRPAzchZ9
+>
+> **Thank you!**
 
-Go configuration with fangs!
+![Viper](.github/logo.png?raw=true)
 
-[![Actions](https://github.com/spf13/viper/workflows/CI/badge.svg)](https://github.com/spf13/viper)
+[![Mentioned in Awesome Go](https://awesome.re/mentioned-badge-flat.svg)](https://github.com/avelino/awesome-go#configuration)
+[![run on repl.it](https://repl.it/badge/github/sagikazarmark/Viper-example)](https://repl.it/@sagikazarmark/Viper-example#main.go)
+
+[![GitHub Workflow Status](https://img.shields.io/github/actions/workflow/status/spf13/viper/ci.yaml?branch=master&style=flat-square)](https://github.com/spf13/viper/actions?query=workflow%3ACI)
 [![Join the chat at https://gitter.im/spf13/viper](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/spf13/viper?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-[![GoDoc](https://godoc.org/github.com/spf13/viper?status.svg)](https://godoc.org/github.com/spf13/viper)
+[![Go Report Card](https://goreportcard.com/badge/github.com/spf13/viper?style=flat-square)](https://goreportcard.com/report/github.com/spf13/viper)
+![Go Version](https://img.shields.io/badge/go%20version-%3E=1.16-61CFDD.svg?style=flat-square)
+[![PkgGoDev](https://pkg.go.dev/badge/mod/github.com/spf13/viper)](https://pkg.go.dev/mod/github.com/spf13/viper)
+
+**Go configuration with fangs!**
 
 Many Go projects are built using Viper including:
 
@@ -17,19 +27,24 @@ Many Go projects are built using Viper including:
 * [doctl](https://github.com/digitalocean/doctl)
 * [Clairctl](https://github.com/jgsqware/clairctl)
 * [Mercure](https://mercure.rocks)
+* [Meshery](https://github.com/meshery/meshery)
+* [Bearer](https://github.com/bearer/bearer)
+* [Coder](https://github.com/coder/coder)
 
 
 ## Install
 
-```console
+```shell
 go get github.com/spf13/viper
 ```
 
+**Note:** Viper uses [Go Modules](https://github.com/golang/go/wiki/Modules) to manage dependencies.
+
 
 ## What is Viper?
 
-Viper is a complete configuration solution for Go applications including 12-Factor apps. It is designed
-to work within an application, and can handle all types of configuration needs
+Viper is a complete configuration solution for Go applications including [12-Factor apps](https://12factor.net/#the_twelve_factors).
+It is designed to work within an application, and can handle all types of configuration needs
 and formats. It supports:
 
 * setting defaults
@@ -107,7 +122,7 @@ viper.AddConfigPath("$HOME/.appname")  // call multiple times to add many search
 viper.AddConfigPath(".")               // optionally look for config in the working directory
 err := viper.ReadInConfig() // Find and read the config file
 if err != nil { // Handle errors reading the config file
-	panic(fmt.Errorf("Fatal error config file: %s \n", err))
+	panic(fmt.Errorf("fatal error config file: %w", err))
 }
 ```
 
@@ -115,11 +130,11 @@ You can handle the specific case where no config file is found like this:
 
 ```go
 if err := viper.ReadInConfig(); err != nil {
-    if _, ok := err.(viper.ConfigFileNotFoundError); ok {
-        // Config file not found; ignore error if desired
-    } else {
-        // Config file was found but another error was produced
-    }
+	if _, ok := err.(viper.ConfigFileNotFoundError); ok {
+		// Config file not found; ignore error if desired
+	} else {
+		// Config file was found but another error was produced
+	}
 }
 
 // Config file found and successfully parsed
@@ -163,10 +178,10 @@ Optionally you can provide a function for Viper to run each time a change occurs
 **Make sure you add all of the configPaths prior to calling `WatchConfig()`**
 
 ```go
-viper.WatchConfig()
 viper.OnConfigChange(func(e fsnotify.Event) {
 	fmt.Println("Config file changed:", e.Name)
 })
+viper.WatchConfig()
 ```
 
 ### Reading Config from io.Reader
@@ -242,9 +257,10 @@ using `SetEnvPrefix`, you can tell Viper to use a prefix while reading from
 the environment variables. Both `BindEnv` and `AutomaticEnv` will use this
 prefix.
 
-`BindEnv` takes one or two parameters. The first parameter is the key name, the
-second is the name of the environment variable. The name of the environment
-variable is case sensitive. If the ENV variable name is not provided, then
+`BindEnv` takes one or more parameters. The first parameter is the key name, the
+rest are the name of the environment variables to bind to this key. If more than
+one are provided, they will take precedence in the specified order. The name of
+the environment variable is case sensitive. If the ENV variable name is not provided, then
 Viper will automatically assume that the ENV variable matches the following format: prefix + "_" + the key name in ALL CAPS. When you explicitly provide the ENV variable name (the second parameter),
 it **does not** automatically add the prefix. For example if the second parameter is "id",
 Viper will look for the ENV variable "ID".
@@ -256,7 +272,7 @@ the `BindEnv` is called.
 `AutomaticEnv` is a powerful helper especially when combined with
 `SetEnvPrefix`. When called, Viper will check for an environment variable any
 time a `viper.Get` request is made. It will apply the following rules. It will
-check for a environment variable with a name matching the key uppercased and
+check for an environment variable with a name matching the key uppercased and
 prefixed with the `EnvPrefix` if set.
 
 `SetEnvKeyReplacer` allows you to use a `strings.Replacer` object to rewrite Env
@@ -341,7 +357,7 @@ func main() {
 
 	i := viper.GetInt("flagname") // retrieve value from viper
 
-	...
+	// ...
 }
 ```
 
@@ -400,7 +416,7 @@ in a Key/Value store such as etcd or Consul.  These values take precedence over
 default values, but are overridden by configuration values retrieved from disk,
 flags, or environment variables.
 
-Viper uses [crypt](https://github.com/xordataexchange/crypt) to retrieve
+Viper uses [crypt](https://github.com/bketelsen/crypt) to retrieve
 configuration from the K/V store, which means that you can store your
 configuration values encrypted and have them automatically decrypted if you have
 the correct gpg keyring.  Encryption is optional.
@@ -412,7 +428,7 @@ independently of it.
 K/V store. `crypt` defaults to etcd on http://127.0.0.1:4001.
 
 ```bash
-$ go get github.com/xordataexchange/crypt/bin/crypt
+$ go get github.com/bketelsen/crypt/bin/crypt
 $ crypt set -plaintext /config/hugo.json /Users/hugo/settings/config.json
 ```
 
@@ -434,8 +450,15 @@ viper.SetConfigType("json") // because there is no file extension in a stream of
 err := viper.ReadRemoteConfig()
 ```
 
+#### etcd3
+```go
+viper.AddRemoteProvider("etcd3", "http://127.0.0.1:4001","/config/hugo.json")
+viper.SetConfigType("json") // because there is no file extension in a stream of bytes, supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop", "env", "dotenv"
+err := viper.ReadRemoteConfig()
+```
+
 #### Consul
-You need to set a key to Consul key/value storage with JSON value containing your desired config.  
+You need to set a key to Consul key/value storage with JSON value containing your desired config.
 For example, create a Consul key/value store key `MY_CONSUL_KEY` with value:
 
 ```json
@@ -454,6 +477,16 @@ fmt.Println(viper.Get("port")) // 8080
 fmt.Println(viper.Get("hostname")) // myhostname.com
 ```
 
+#### Firestore
+
+```go
+viper.AddRemoteProvider("firestore", "google-cloud-project-id", "collection/document")
+viper.SetConfigType("json") // Config's format: "json", "toml", "yaml", "yml"
+err := viper.ReadRemoteConfig()
+```
+
+Of course, you're allowed to use `SecureRemoteProvider` also
+
 ### Remote Key/Value Store Example - Encrypted
 
 ```go
@@ -480,18 +513,18 @@ runtime_viper.Unmarshal(&runtime_conf)
 // open a goroutine to watch remote changes forever
 go func(){
 	for {
-	    time.Sleep(time.Second * 5) // delay after each request
+		time.Sleep(time.Second * 5) // delay after each request
 
-	    // currently, only tested with etcd support
-	    err := runtime_viper.WatchRemoteConfig()
-	    if err != nil {
-	        log.Errorf("unable to read remote config: %v", err)
-	        continue
-	    }
+		// currently, only tested with etcd support
+		err := runtime_viper.WatchRemoteConfig()
+		if err != nil {
+			log.Errorf("unable to read remote config: %v", err)
+			continue
+		}
 
-	    // unmarshal new config into our runtime config struct. you can also use channel
-	    // to implement a signal to notify the system of the changes
-	    runtime_viper.Unmarshal(&runtime_conf)
+		// unmarshal new config into our runtime config struct. you can also use channel
+		// to implement a signal to notify the system of the changes
+		runtime_viper.Unmarshal(&runtime_conf)
 	}
 }()
 ```
@@ -523,7 +556,7 @@ Example:
 ```go
 viper.GetString("logfile") // case-insensitive Setting & Getting
 if viper.GetBool("verbose") {
-    fmt.Println("verbose enabled")
+	fmt.Println("verbose enabled")
 }
 ```
 ### Accessing nested keys
@@ -569,10 +602,37 @@ the `Set()` method, …) with an immediate value, then all sub-keys of
 `datastore.metric` become undefined, they are “shadowed” by the higher-priority
 configuration level.
 
+Viper can access array indices by using numbers in the path. For example:
+
+```jsonc
+{
+    "host": {
+        "address": "localhost",
+        "ports": [
+            5799,
+            6029
+        ]
+    },
+    "datastore": {
+        "metric": {
+            "host": "127.0.0.1",
+            "port": 3099
+        },
+        "warehouse": {
+            "host": "198.0.0.1",
+            "port": 2112
+        }
+    }
+}
+
+GetInt("host.ports.1") // returns 6029
+
+```
+
 Lastly, if there exists a key that matches the delimited key path, its value
 will be returned instead. E.g.
 
-```json
+```jsonc
 {
     "datastore.metric.host": "0.0.0.0",
     "host": {
@@ -594,14 +654,15 @@ will be returned instead. E.g.
 GetString("datastore.metric.host") // returns "0.0.0.0"
 ```
 
-### Extract sub-tree
+### Extracting a sub-tree
 
-Extract sub-tree from Viper.
+When developing reusable modules, it's often useful to extract a subset of the configuration
+and pass it to a module. This way the module can be instantiated more than once, with different configurations.
 
-For example, `viper` represents:
+For example, an application might use multiple different cache stores for different purposes:
 
-```json
-app:
+```yaml
+cache:
   cache1:
     max-items: 100
     item-size: 64
@@ -610,35 +671,36 @@ app:
     item-size: 80
 ```
 
-After executing:
+We could pass the cache name to a module (eg. `NewCache("cache1")`),
+but it would require weird concatenation for accessing config keys and would be less separated from the global config.
+
+So instead of doing that let's pass a Viper instance to the constructor that represents a subset of the configuration:
 
 ```go
-subv := viper.Sub("app.cache1")
+cache1Config := viper.Sub("cache.cache1")
+if cache1Config == nil { // Sub returns nil if the key cannot be found
+	panic("cache configuration not found")
+}
+
+cache1 := NewCache(cache1Config)
 ```
 
-`subv` represents:
+**Note:** Always check the return value of `Sub`. It returns `nil` if a key cannot be found.
 
-```json
-max-items: 100
-item-size: 64
-```
-
-Suppose we have:
+Internally, the `NewCache` function can address `max-items` and `item-size` keys directly:
 
 ```go
-func NewCache(cfg *Viper) *Cache {...}
+func NewCache(v *Viper) *Cache {
+	return &Cache{
+		MaxItems: v.GetInt("max-items"),
+		ItemSize: v.GetInt("item-size"),
+	}
+}
 ```
 
-which creates a cache based on config information formatted as `subv`.
-Now it’s easy to create these 2 caches separately as:
+The resulting code is easy to test, since it's decoupled from the main config structure,
+and easier to reuse (for the same reason).
 
-```go
-cfg1 := viper.Sub("app.cache1")
-cache1 := NewCache(cfg1)
-
-cfg2 := viper.Sub("app.cache2")
-cache2 := NewCache(cfg2)
-```
 
 ### Unmarshaling
 
@@ -674,18 +736,18 @@ you have to change the delimiter:
 v := viper.NewWithOptions(viper.KeyDelimiter("::"))
 
 v.SetDefault("chart::values", map[string]interface{}{
-    "ingress": map[string]interface{}{
-        "annotations": map[string]interface{}{
-            "traefik.frontend.rule.type":                 "PathPrefix",
-            "traefik.ingress.kubernetes.io/ssl-redirect": "true",
-        },
-    },
+	"ingress": map[string]interface{}{
+		"annotations": map[string]interface{}{
+			"traefik.frontend.rule.type":                 "PathPrefix",
+			"traefik.ingress.kubernetes.io/ssl-redirect": "true",
+		},
+	},
 })
 
 type config struct {
 	Chart struct{
-        Values map[string]interface{}
-    }
+		Values map[string]interface{}
+	}
 }
 
 var C config
@@ -726,24 +788,33 @@ if err != nil {
 
 Viper uses [github.com/mitchellh/mapstructure](https://github.com/mitchellh/mapstructure) under the hood for unmarshaling values which uses `mapstructure` tags by default.
 
+### Decoding custom formats
+
+A frequently requested feature for Viper is adding more value formats and decoders.
+For example, parsing character (dot, comma, semicolon, etc) separated strings into slices.
+
+This is already available in Viper using mapstructure decode hooks.
+
+Read more about the details in [this blog post](https://sagikazarmark.hu/blog/decoding-custom-formats-with-viper/).
+
 ### Marshalling to string
 
-You may need to marshal all the settings held in viper into a string rather than write them to a file. 
+You may need to marshal all the settings held in viper into a string rather than write them to a file.
 You can use your favorite format's marshaller with the config returned by `AllSettings()`.
 
 ```go
 import (
-    yaml "gopkg.in/yaml.v2"
-    // ...
-) 
+	yaml "gopkg.in/yaml.v2"
+	// ...
+)
 
 func yamlStringSettings() string {
-    c := viper.AllSettings()
-    bs, err := yaml.Marshal(c)
-    if err != nil {
-        log.Fatalf("unable to marshal config to YAML: %v", err)
-    }
-    return string(bs)
+	c := viper.AllSettings()
+	bs, err := yaml.Marshal(c)
+	if err != nil {
+		log.Fatalf("unable to marshal config to YAML: %v", err)
+	}
+	return string(bs)
 }
 ```
 
@@ -779,15 +850,35 @@ y.SetDefault("ContentDir", "foobar")
 When working with multiple vipers, it is up to the user to keep track of the
 different vipers.
 
+
 ## Q & A
 
-Q: Why is it called “Viper”?
+### Why is it called “Viper”?
 
 A: Viper is designed to be a [companion](http://en.wikipedia.org/wiki/Viper_(G.I._Joe))
 to [Cobra](https://github.com/spf13/cobra). While both can operate completely
 independently, together they make a powerful pair to handle much of your
 application foundation needs.
 
-Q: Why is it called “Cobra”?
+### Why is it called “Cobra”?
 
-A: Is there a better name for a [commander](http://en.wikipedia.org/wiki/Cobra_Commander)?
+Is there a better name for a [commander](http://en.wikipedia.org/wiki/Cobra_Commander)?
+
+### Does Viper support case sensitive keys?
+
+**tl;dr:** No.
+
+Viper merges configuration from various sources, many of which are either case insensitive or uses different casing than the rest of the sources (eg. env vars).
+In order to provide the best experience when using multiple sources, the decision has been made to make all keys case insensitive.
+
+There has been several attempts to implement case sensitivity, but unfortunately it's not that trivial. We might take a stab at implementing it in [Viper v2](https://github.com/spf13/viper/issues/772), but despite the initial noise, it does not seem to be requested that much.
+
+You can vote for case sensitivity by filling out this feedback form: https://forms.gle/R6faU74qPRPAzchZ9
+
+### Is it safe to concurrently read and write to a viper?
+
+No, you will need to synchronize access to the viper yourself (for example by using the `sync` package). Concurrent reads and writes can cause a panic.
+
+## Troubleshooting
+
+See [TROUBLESHOOTING.md](TROUBLESHOOTING.md).

TROUBLESHOOTING.md

@@ -0,0 +1,32 @@
+# Troubleshooting
+
+## Unmarshaling doesn't work
+
+The most common reason for this issue is improper use of struct tags (eg. `yaml` or `json`). Viper uses [github.com/mitchellh/mapstructure](https://github.com/mitchellh/mapstructure) under the hood for unmarshaling values which uses `mapstructure` tags by default. Please refer to the library's documentation for using other struct tags.
+
+## Cannot find package
+
+Viper installation seems to fail a lot lately with the following (or a similar) error:
+
+```
+cannot find package "github.com/hashicorp/hcl/tree/hcl1" in any of:
+/usr/local/Cellar/go/1.15.7_1/libexec/src/github.com/hashicorp/hcl/tree/hcl1 (from $GOROOT)
+/Users/user/go/src/github.com/hashicorp/hcl/tree/hcl1 (from $GOPATH)
+```
+
+As the error message suggests, Go tries to look up dependencies in `GOPATH` mode (as it's commonly called) from the `GOPATH`.
+Viper opted to use [Go Modules](https://github.com/golang/go/wiki/Modules) to manage its dependencies. While in many cases the two methods are interchangeable, once a dependency releases new (major) versions, `GOPATH` mode is no longer able to decide which version to use, so it'll either use one that's already present or pick a version (usually the `master` branch).
+
+The solution is easy: switch to using Go Modules.
+Please refer to the [wiki](https://github.com/golang/go/wiki/Modules) on how to do that.
+
+**tl;dr* `export GO111MODULE=on`
+
+## Unquoted 'y' and 'n' characters get replaced with _true_ and _false_ when reading a YAML file
+
+This is a YAML 1.1 feature according to [go-yaml/yaml#740](https://github.com/go-yaml/yaml/issues/740).
+
+Potential solutions are:
+
+1. Quoting values resolved as boolean
+1. Upgrading to YAML v3 (for the time being this is possible by passing the `viper_yaml3` tag to your build)

experimental_logger.go

@@ -0,0 +1,11 @@
+//go:build viper_logger
+// +build viper_logger
+
+package viper
+
+// WithLogger sets a custom logger.
+func WithLogger(l Logger) Option {
+	return optionFunc(func(v *Viper) {
+		v.logger = l
+	})
+}

flags_test.go

@@ -10,13 +10,13 @@ import (
 func TestBindFlagValueSet(t *testing.T) {
 	flagSet := pflag.NewFlagSet("test", pflag.ContinueOnError)
 
-	var testValues = map[string]*string{
+	testValues := map[string]*string{
 		"host":     nil,
 		"port":     nil,
 		"endpoint": nil,
 	}
 
-	var mutatedTestValues = map[string]string{
+	mutatedTestValues := map[string]string{
 		"host":     "localhost",
 		"port":     "6060",
 		"endpoint": "/public",
@@ -44,8 +44,8 @@ func TestBindFlagValueSet(t *testing.T) {
 }
 
 func TestBindFlagValue(t *testing.T) {
-	var testString = "testing"
-	var testValue = newStringValue(testString, &testString)
+	testString := "testing"
+	testValue := newStringValue(testString, &testString)
 
 	flag := &pflag.Flag{
 		Name:    "testflag",
@@ -59,7 +59,7 @@ func TestBindFlagValue(t *testing.T) {
 	assert.Equal(t, testString, Get("testvalue"))
 
 	flag.Value.Set("testing_mutate")
-	flag.Changed = true //hack for pflag usage
+	flag.Changed = true // hack for pflag usage
 
 	assert.Equal(t, "testing_mutate", Get("testvalue"))
 }

fs.go

@@ -0,0 +1,65 @@
+//go:build go1.16 && finder
+// +build go1.16,finder
+
+package viper
+
+import (
+	"errors"
+	"io/fs"
+	"path"
+)
+
+type finder struct {
+	paths      []string
+	fileNames  []string
+	extensions []string
+
+	withoutExtension bool
+}
+
+func (f finder) Find(fsys fs.FS) (string, error) {
+	for _, searchPath := range f.paths {
+		for _, fileName := range f.fileNames {
+			for _, extension := range f.extensions {
+				filePath := path.Join(searchPath, fileName+"."+extension)
+
+				ok, err := fileExists(fsys, filePath)
+				if err != nil {
+					return "", err
+				}
+
+				if ok {
+					return filePath, nil
+				}
+			}
+
+			if f.withoutExtension {
+				filePath := path.Join(searchPath, fileName)
+
+				ok, err := fileExists(fsys, filePath)
+				if err != nil {
+					return "", err
+				}
+
+				if ok {
+					return filePath, nil
+				}
+			}
+		}
+	}
+
+	return "", nil
+}
+
+func fileExists(fsys fs.FS, filePath string) (bool, error) {
+	fileInfo, err := fs.Stat(fsys, filePath)
+	if err == nil {
+		return !fileInfo.IsDir(), nil
+	}
+
+	if errors.Is(err, fs.ErrNotExist) {
+		return false, nil
+	}
+
+	return false, err
+}

fs_test.go

@@ -0,0 +1,100 @@
+//go:build go1.16 && finder
+// +build go1.16,finder
+
+package viper
+
+import (
+	"io/fs"
+	"testing"
+	"testing/fstest"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFinder(t *testing.T) {
+	t.Parallel()
+
+	fsys := fstest.MapFS{
+		"home/user/.config":            &fstest.MapFile{},
+		"home/user/config.json":        &fstest.MapFile{},
+		"home/user/config.yaml":        &fstest.MapFile{},
+		"home/user/data.json":          &fstest.MapFile{},
+		"etc/config/.config":           &fstest.MapFile{},
+		"etc/config/a_random_file.txt": &fstest.MapFile{},
+		"etc/config/config.json":       &fstest.MapFile{},
+		"etc/config/config.yaml":       &fstest.MapFile{},
+		"etc/config/config.xml":        &fstest.MapFile{},
+	}
+
+	testCases := []struct {
+		name   string
+		fsys   func() fs.FS
+		finder finder
+		result string
+	}{
+		{
+			name: "find file",
+			fsys: func() fs.FS { return fsys },
+			finder: finder{
+				paths:      []string{"etc/config"},
+				fileNames:  []string{"config"},
+				extensions: []string{"json"},
+			},
+			result: "etc/config/config.json",
+		},
+		{
+			name: "file not found",
+			fsys: func() fs.FS { return fsys },
+			finder: finder{
+				paths:      []string{"var/config"},
+				fileNames:  []string{"config"},
+				extensions: []string{"json"},
+			},
+			result: "",
+		},
+		{
+			name:   "empty search params",
+			fsys:   func() fs.FS { return fsys },
+			finder: finder{},
+			result: "",
+		},
+		{
+			name: "precedence",
+			fsys: func() fs.FS { return fsys },
+			finder: finder{
+				paths:      []string{"var/config", "home/user", "etc/config"},
+				fileNames:  []string{"aconfig", "config"},
+				extensions: []string{"zml", "xml", "json"},
+			},
+			result: "home/user/config.json",
+		},
+		{
+			name: "without extension",
+			fsys: func() fs.FS { return fsys },
+			finder: finder{
+				paths:      []string{"var/config", "home/user", "etc/config"},
+				fileNames:  []string{".config"},
+				extensions: []string{"zml", "xml", "json"},
+
+				withoutExtension: true,
+			},
+			result: "home/user/.config",
+		},
+	}
+
+	for _, testCase := range testCases {
+		testCase := testCase
+
+		t.Run(testCase.name, func(t *testing.T) {
+			t.Parallel()
+
+			fsys := testCase.fsys()
+
+			result, err := testCase.finder.Find(fsys)
+			require.NoError(t, err)
+
+			assert.Equal(t, testCase.result, result)
+		})
+	}
+}

go.mod

@@ -1,48 +1,76 @@
 module github.com/spf13/viper
 
-go 1.12
+go 1.17
 
 require (
-	github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6 // indirect
-	github.com/coreos/bbolt v1.3.2 // indirect
-	github.com/coreos/etcd v3.3.10+incompatible // indirect
-	github.com/coreos/go-semver v0.2.0 // indirect
-	github.com/coreos/go-systemd v0.0.0-20190321100706-95778dfbb74e // indirect
-	github.com/coreos/pkg v0.0.0-20180928190104-399ea9e2e55f // indirect
-	github.com/dgrijalva/jwt-go v3.2.0+incompatible // indirect
-	github.com/fsnotify/fsnotify v1.4.7
-	github.com/gogo/protobuf v1.2.1 // indirect
-	github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef // indirect
-	github.com/google/btree v1.0.0 // indirect
-	github.com/gorilla/websocket v1.4.0 // indirect
-	github.com/grpc-ecosystem/go-grpc-middleware v1.0.0 // indirect
-	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 // indirect
-	github.com/grpc-ecosystem/grpc-gateway v1.9.0 // indirect
+	github.com/fsnotify/fsnotify v1.6.0
 	github.com/hashicorp/hcl v1.0.0
-	github.com/jonboulle/clockwork v0.1.0 // indirect
-	github.com/magiconair/properties v1.8.1
-	github.com/mitchellh/mapstructure v1.1.2
-	github.com/pelletier/go-toml v1.2.0
-	github.com/prometheus/client_golang v0.9.3 // indirect
-	github.com/smartystreets/goconvey v1.6.4 // indirect
-	github.com/soheilhy/cmux v0.1.4 // indirect
-	github.com/spf13/afero v1.1.2
-	github.com/spf13/cast v1.3.0
-	github.com/spf13/jwalterweatherman v1.0.0
-	github.com/spf13/pflag v1.0.3
-	github.com/stretchr/testify v1.2.2
-	github.com/subosito/gotenv v1.2.0
-	github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5 // indirect
-	github.com/ugorji/go v1.1.4 // indirect
-	github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 // indirect
-	github.com/xordataexchange/crypt v0.0.3-0.20170626215501-b2862e3d0a77
-	go.etcd.io/bbolt v1.3.2 // indirect
-	go.uber.org/atomic v1.4.0 // indirect
-	go.uber.org/multierr v1.1.0 // indirect
-	go.uber.org/zap v1.10.0 // indirect
-	golang.org/x/net v0.0.0-20190522155817-f3200d17e092 // indirect
-	golang.org/x/time v0.0.0-20190308202827-9d24e82272b4 // indirect
-	google.golang.org/grpc v1.21.0 // indirect
-	gopkg.in/ini.v1 v1.51.0
-	gopkg.in/yaml.v2 v2.2.4
+	github.com/magiconair/properties v1.8.7
+	github.com/mitchellh/mapstructure v1.5.0
+	github.com/pelletier/go-toml/v2 v2.0.8
+	github.com/sagikazarmark/crypt v0.10.0
+	github.com/spf13/afero v1.9.5
+	github.com/spf13/cast v1.5.1
+	github.com/spf13/jwalterweatherman v1.1.0
+	github.com/spf13/pflag v1.0.5
+	github.com/stretchr/testify v1.8.3
+	github.com/subosito/gotenv v1.4.2
+	gopkg.in/ini.v1 v1.67.0
+	gopkg.in/yaml.v3 v3.0.1
+)
+
+require (
+	cloud.google.com/go v0.110.0 // indirect
+	cloud.google.com/go/compute v1.19.0 // indirect
+	cloud.google.com/go/compute/metadata v0.2.3 // indirect
+	cloud.google.com/go/firestore v1.9.0 // indirect
+	cloud.google.com/go/longrunning v0.4.1 // indirect
+	github.com/armon/go-metrics v0.4.0 // indirect
+	github.com/coreos/go-semver v0.3.0 // indirect
+	github.com/coreos/go-systemd/v22 v22.3.2 // indirect
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/fatih/color v1.13.0 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
+	github.com/golang/protobuf v1.5.3 // indirect
+	github.com/google/go-cmp v0.5.9 // indirect
+	github.com/google/s2a-go v0.1.3 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.2.3 // indirect
+	github.com/googleapis/gax-go/v2 v2.8.0 // indirect
+	github.com/hashicorp/consul/api v1.20.0 // indirect
+	github.com/hashicorp/go-cleanhttp v0.5.2 // indirect
+	github.com/hashicorp/go-hclog v1.2.0 // indirect
+	github.com/hashicorp/go-immutable-radix v1.3.1 // indirect
+	github.com/hashicorp/go-rootcerts v1.0.2 // indirect
+	github.com/hashicorp/golang-lru v0.5.4 // indirect
+	github.com/hashicorp/serf v0.10.1 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/mattn/go-colorable v0.1.12 // indirect
+	github.com/mattn/go-isatty v0.0.14 // indirect
+	github.com/mitchellh/go-homedir v1.1.0 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	go.etcd.io/etcd/api/v3 v3.5.9 // indirect
+	go.etcd.io/etcd/client/pkg/v3 v3.5.9 // indirect
+	go.etcd.io/etcd/client/v2 v2.305.7 // indirect
+	go.etcd.io/etcd/client/v3 v3.5.9 // indirect
+	go.opencensus.io v0.24.0 // indirect
+	go.uber.org/atomic v1.9.0 // indirect
+	go.uber.org/multierr v1.8.0 // indirect
+	go.uber.org/zap v1.21.0 // indirect
+	golang.org/x/crypto v0.9.0 // indirect
+	golang.org/x/net v0.10.0 // indirect
+	golang.org/x/oauth2 v0.7.0 // indirect
+	golang.org/x/sync v0.1.0 // indirect
+	golang.org/x/sys v0.8.0 // indirect
+	golang.org/x/text v0.9.0 // indirect
+	golang.org/x/time v0.1.0 // indirect
+	golang.org/x/xerrors v0.0.0-20220907171357-04be3eba64a2 // indirect
+	google.golang.org/api v0.122.0 // indirect
+	google.golang.org/appengine v1.6.7 // indirect
+	google.golang.org/genproto v0.0.0-20230410155749-daa745c078e1 // indirect
+	google.golang.org/grpc v1.55.0 // indirect
+	google.golang.org/protobuf v1.30.0 // indirect
 )

internal/encoding/decoder.go

@@ -0,0 +1,61 @@
+package encoding
+
+import (
+	"sync"
+)
+
+// Decoder decodes the contents of b into v.
+// It's primarily used for decoding contents of a file into a map[string]interface{}.
+type Decoder interface {
+	Decode(b []byte, v map[string]interface{}) error
+}
+
+const (
+	// ErrDecoderNotFound is returned when there is no decoder registered for a format.
+	ErrDecoderNotFound = encodingError("decoder not found for this format")
+
+	// ErrDecoderFormatAlreadyRegistered is returned when an decoder is already registered for a format.
+	ErrDecoderFormatAlreadyRegistered = encodingError("decoder already registered for this format")
+)
+
+// DecoderRegistry can choose an appropriate Decoder based on the provided format.
+type DecoderRegistry struct {
+	decoders map[string]Decoder
+
+	mu sync.RWMutex
+}
+
+// NewDecoderRegistry returns a new, initialized DecoderRegistry.
+func NewDecoderRegistry() *DecoderRegistry {
+	return &DecoderRegistry{
+		decoders: make(map[string]Decoder),
+	}
+}
+
+// RegisterDecoder registers a Decoder for a format.
+// Registering a Decoder for an already existing format is not supported.
+func (e *DecoderRegistry) RegisterDecoder(format string, enc Decoder) error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	if _, ok := e.decoders[format]; ok {
+		return ErrDecoderFormatAlreadyRegistered
+	}
+
+	e.decoders[format] = enc
+
+	return nil
+}
+
+// Decode calls the underlying Decoder based on the format.
+func (e *DecoderRegistry) Decode(format string, b []byte, v map[string]interface{}) error {
+	e.mu.RLock()
+	decoder, ok := e.decoders[format]
+	e.mu.RUnlock()
+
+	if !ok {
+		return ErrDecoderNotFound
+	}
+
+	return decoder.Decode(b, v)
+}

internal/encoding/decoder_test.go

@@ -0,0 +1,81 @@
+package encoding
+
+import (
+	"reflect"
+	"testing"
+)
+
+type decoder struct {
+	v map[string]interface{}
+}
+
+func (d decoder) Decode(_ []byte, v map[string]interface{}) error {
+	for key, value := range d.v {
+		v[key] = value
+	}
+
+	return nil
+}
+
+func TestDecoderRegistry_RegisterDecoder(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		registry := NewDecoderRegistry()
+
+		err := registry.RegisterDecoder("myformat", decoder{})
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("AlreadyRegistered", func(t *testing.T) {
+		registry := NewDecoderRegistry()
+
+		err := registry.RegisterDecoder("myformat", decoder{})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		err = registry.RegisterDecoder("myformat", decoder{})
+		if err != ErrDecoderFormatAlreadyRegistered {
+			t.Fatalf("expected ErrDecoderFormatAlreadyRegistered, got: %v", err)
+		}
+	})
+}
+
+func TestDecoderRegistry_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		registry := NewDecoderRegistry()
+		decoder := decoder{
+			v: map[string]interface{}{
+				"key": "value",
+			},
+		}
+
+		err := registry.RegisterDecoder("myformat", decoder)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		v := map[string]interface{}{}
+
+		err = registry.Decode("myformat", []byte("key: value"), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(decoder.v, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %+v\nexpected: %+v", v, decoder.v)
+		}
+	})
+
+	t.Run("DecoderNotFound", func(t *testing.T) {
+		registry := NewDecoderRegistry()
+
+		v := map[string]interface{}{}
+
+		err := registry.Decode("myformat", nil, v)
+		if err != ErrDecoderNotFound {
+			t.Fatalf("expected ErrDecoderNotFound, got: %v", err)
+		}
+	})
+}

internal/encoding/dotenv/codec.go

@@ -0,0 +1,61 @@
+package dotenv
+
+import (
+	"bytes"
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/subosito/gotenv"
+)
+
+const keyDelimiter = "_"
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for encoding data containing environment variables
+// (commonly called as dotenv format).
+type Codec struct{}
+
+func (Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	flattened := map[string]interface{}{}
+
+	flattened = flattenAndMergeMap(flattened, v, "", keyDelimiter)
+
+	keys := make([]string, 0, len(flattened))
+
+	for key := range flattened {
+		keys = append(keys, key)
+	}
+
+	sort.Strings(keys)
+
+	var buf bytes.Buffer
+
+	for _, key := range keys {
+		_, err := buf.WriteString(fmt.Sprintf("%v=%v\n", strings.ToUpper(key), flattened[key]))
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	var buf bytes.Buffer
+
+	_, err := buf.Write(b)
+	if err != nil {
+		return err
+	}
+
+	env, err := gotenv.StrictParse(&buf)
+	if err != nil {
+		return err
+	}
+
+	for key, value := range env {
+		v[key] = value
+	}
+
+	return nil
+}

internal/encoding/dotenv/codec_test.go

@@ -0,0 +1,63 @@
+package dotenv
+
+import (
+	"reflect"
+	"testing"
+)
+
+// original form of the data
+const original = `# key-value pair
+KEY=value
+`
+
+// encoded form of the data
+const encoded = `KEY=value
+`
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"KEY": "value",
+}
+
+func TestCodec_Encode(t *testing.T) {
+	codec := Codec{}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if encoded != string(b) {
+		t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+	}
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(original), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(data, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, data)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(`invalid data`), v)
+		if err == nil {
+			t.Fatal("expected decoding to fail")
+		}
+
+		t.Logf("decoding failed as expected: %s", err)
+	})
+}

internal/encoding/dotenv/map_utils.go

@@ -0,0 +1,41 @@
+package dotenv
+
+import (
+	"strings"
+
+	"github.com/spf13/cast"
+)
+
+// flattenAndMergeMap recursively flattens the given map into a new map
+// Code is based on the function with the same name in tha main package.
+// TODO: move it to a common place
+func flattenAndMergeMap(shadow map[string]interface{}, m map[string]interface{}, prefix string, delimiter string) map[string]interface{} {
+	if shadow != nil && prefix != "" && shadow[prefix] != nil {
+		// prefix is shadowed => nothing more to flatten
+		return shadow
+	}
+	if shadow == nil {
+		shadow = make(map[string]interface{})
+	}
+
+	var m2 map[string]interface{}
+	if prefix != "" {
+		prefix += delimiter
+	}
+	for k, val := range m {
+		fullKey := prefix + k
+		switch val.(type) {
+		case map[string]interface{}:
+			m2 = val.(map[string]interface{})
+		case map[interface{}]interface{}:
+			m2 = cast.ToStringMap(val)
+		default:
+			// immediate value
+			shadow[strings.ToLower(fullKey)] = val
+			continue
+		}
+		// recursively merge to shadow map
+		shadow = flattenAndMergeMap(shadow, m2, fullKey, delimiter)
+	}
+	return shadow
+}

internal/encoding/encoder.go

@@ -0,0 +1,60 @@
+package encoding
+
+import (
+	"sync"
+)
+
+// Encoder encodes the contents of v into a byte representation.
+// It's primarily used for encoding a map[string]interface{} into a file format.
+type Encoder interface {
+	Encode(v map[string]interface{}) ([]byte, error)
+}
+
+const (
+	// ErrEncoderNotFound is returned when there is no encoder registered for a format.
+	ErrEncoderNotFound = encodingError("encoder not found for this format")
+
+	// ErrEncoderFormatAlreadyRegistered is returned when an encoder is already registered for a format.
+	ErrEncoderFormatAlreadyRegistered = encodingError("encoder already registered for this format")
+)
+
+// EncoderRegistry can choose an appropriate Encoder based on the provided format.
+type EncoderRegistry struct {
+	encoders map[string]Encoder
+
+	mu sync.RWMutex
+}
+
+// NewEncoderRegistry returns a new, initialized EncoderRegistry.
+func NewEncoderRegistry() *EncoderRegistry {
+	return &EncoderRegistry{
+		encoders: make(map[string]Encoder),
+	}
+}
+
+// RegisterEncoder registers an Encoder for a format.
+// Registering a Encoder for an already existing format is not supported.
+func (e *EncoderRegistry) RegisterEncoder(format string, enc Encoder) error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	if _, ok := e.encoders[format]; ok {
+		return ErrEncoderFormatAlreadyRegistered
+	}
+
+	e.encoders[format] = enc
+
+	return nil
+}
+
+func (e *EncoderRegistry) Encode(format string, v map[string]interface{}) ([]byte, error) {
+	e.mu.RLock()
+	encoder, ok := e.encoders[format]
+	e.mu.RUnlock()
+
+	if !ok {
+		return nil, ErrEncoderNotFound
+	}
+
+	return encoder.Encode(v)
+}

internal/encoding/encoder_test.go

@@ -0,0 +1,70 @@
+package encoding
+
+import (
+	"testing"
+)
+
+type encoder struct {
+	b []byte
+}
+
+func (e encoder) Encode(_ map[string]interface{}) ([]byte, error) {
+	return e.b, nil
+}
+
+func TestEncoderRegistry_RegisterEncoder(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		registry := NewEncoderRegistry()
+
+		err := registry.RegisterEncoder("myformat", encoder{})
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("AlreadyRegistered", func(t *testing.T) {
+		registry := NewEncoderRegistry()
+
+		err := registry.RegisterEncoder("myformat", encoder{})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		err = registry.RegisterEncoder("myformat", encoder{})
+		if err != ErrEncoderFormatAlreadyRegistered {
+			t.Fatalf("expected ErrEncoderFormatAlreadyRegistered, got: %v", err)
+		}
+	})
+}
+
+func TestEncoderRegistry_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		registry := NewEncoderRegistry()
+		encoder := encoder{
+			b: []byte("key: value"),
+		}
+
+		err := registry.RegisterEncoder("myformat", encoder)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		b, err := registry.Encode("myformat", map[string]interface{}{"key": "value"})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if string(b) != "key: value" {
+			t.Fatalf("expected 'key: value', got: %#v", string(b))
+		}
+	})
+
+	t.Run("EncoderNotFound", func(t *testing.T) {
+		registry := NewEncoderRegistry()
+
+		_, err := registry.Encode("myformat", map[string]interface{}{"key": "value"})
+		if err != ErrEncoderNotFound {
+			t.Fatalf("expected ErrEncoderNotFound, got: %v", err)
+		}
+	})
+}

internal/encoding/error.go

@@ -0,0 +1,7 @@
+package encoding
+
+type encodingError string
+
+func (e encodingError) Error() string {
+	return string(e)
+}

internal/encoding/hcl/codec.go

@@ -0,0 +1,40 @@
+package hcl
+
+import (
+	"bytes"
+	"encoding/json"
+
+	"github.com/hashicorp/hcl"
+	"github.com/hashicorp/hcl/hcl/printer"
+)
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for HCL encoding.
+// TODO: add printer config to the codec?
+type Codec struct{}
+
+func (Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	b, err := json.Marshal(v)
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO: use printer.Format? Is the trailing newline an issue?
+
+	ast, err := hcl.Parse(string(b))
+	if err != nil {
+		return nil, err
+	}
+
+	var buf bytes.Buffer
+
+	err = printer.Fprint(&buf, ast.Node)
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	return hcl.Unmarshal(b, &v)
+}

internal/encoding/hcl/codec_test.go

@@ -0,0 +1,140 @@
+package hcl
+
+import (
+	"reflect"
+	"testing"
+)
+
+// original form of the data
+const original = `# key-value pair
+"key" = "value"
+
+// list
+"list" = ["item1", "item2", "item3"]
+
+/* map */
+"map" = {
+  "key" = "value"
+}
+
+/*
+nested map
+*/
+"nested_map" "map" {
+  "key" = "value"
+
+  "list" = ["item1", "item2", "item3"]
+}`
+
+// encoded form of the data
+const encoded = `"key" = "value"
+
+"list" = ["item1", "item2", "item3"]
+
+"map" = {
+  "key" = "value"
+}
+
+"nested_map" "map" {
+  "key" = "value"
+
+  "list" = ["item1", "item2", "item3"]
+}`
+
+// decoded form of the data
+//
+// in case of HCL it's slightly different from Viper's internal representation
+// (eg. map is decoded into a list of maps)
+var decoded = map[string]interface{}{
+	"key": "value",
+	"list": []interface{}{
+		"item1",
+		"item2",
+		"item3",
+	},
+	"map": []map[string]interface{}{
+		{
+			"key": "value",
+		},
+	},
+	"nested_map": []map[string]interface{}{
+		{
+			"map": []map[string]interface{}{
+				{
+					"key": "value",
+					"list": []interface{}{
+						"item1",
+						"item2",
+						"item3",
+					},
+				},
+			},
+		},
+	},
+}
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"key": "value",
+	"list": []interface{}{
+		"item1",
+		"item2",
+		"item3",
+	},
+	"map": map[string]interface{}{
+		"key": "value",
+	},
+	"nested_map": map[string]interface{}{
+		"map": map[string]interface{}{
+			"key": "value",
+			"list": []interface{}{
+				"item1",
+				"item2",
+				"item3",
+			},
+		},
+	},
+}
+
+func TestCodec_Encode(t *testing.T) {
+	codec := Codec{}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if encoded != string(b) {
+		t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+	}
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(original), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(decoded, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, decoded)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(`invalid data`), v)
+		if err == nil {
+			t.Fatal("expected decoding to fail")
+		}
+
+		t.Logf("decoding failed as expected: %s", err)
+	})
+}

internal/encoding/ini/codec.go

@@ -0,0 +1,99 @@
+package ini
+
+import (
+	"bytes"
+	"sort"
+	"strings"
+
+	"github.com/spf13/cast"
+	"gopkg.in/ini.v1"
+)
+
+// LoadOptions contains all customized options used for load data source(s).
+// This type is added here for convenience: this way consumers can import a single package called "ini".
+type LoadOptions = ini.LoadOptions
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for INI encoding.
+type Codec struct {
+	KeyDelimiter string
+	LoadOptions  LoadOptions
+}
+
+func (c Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	cfg := ini.Empty()
+	ini.PrettyFormat = false
+
+	flattened := map[string]interface{}{}
+
+	flattened = flattenAndMergeMap(flattened, v, "", c.keyDelimiter())
+
+	keys := make([]string, 0, len(flattened))
+
+	for key := range flattened {
+		keys = append(keys, key)
+	}
+
+	sort.Strings(keys)
+
+	for _, key := range keys {
+		sectionName, keyName := "", key
+
+		lastSep := strings.LastIndex(key, ".")
+		if lastSep != -1 {
+			sectionName = key[:(lastSep)]
+			keyName = key[(lastSep + 1):]
+		}
+
+		// TODO: is this a good idea?
+		if sectionName == "default" {
+			sectionName = ""
+		}
+
+		cfg.Section(sectionName).Key(keyName).SetValue(cast.ToString(flattened[key]))
+	}
+
+	var buf bytes.Buffer
+
+	_, err := cfg.WriteTo(&buf)
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (c Codec) Decode(b []byte, v map[string]interface{}) error {
+	cfg := ini.Empty(c.LoadOptions)
+
+	err := cfg.Append(b)
+	if err != nil {
+		return err
+	}
+
+	sections := cfg.Sections()
+
+	for i := 0; i < len(sections); i++ {
+		section := sections[i]
+		keys := section.Keys()
+
+		for j := 0; j < len(keys); j++ {
+			key := keys[j]
+			value := cfg.Section(section.Name()).Key(key.Name()).String()
+
+			deepestMap := deepSearch(v, strings.Split(section.Name(), c.keyDelimiter()))
+
+			// set innermost value
+			deepestMap[key.Name()] = value
+		}
+	}
+
+	return nil
+}
+
+func (c Codec) keyDelimiter() string {
+	if c.KeyDelimiter == "" {
+		return "."
+	}
+
+	return c.KeyDelimiter
+}

internal/encoding/ini/codec_test.go

@@ -0,0 +1,111 @@
+package ini
+
+import (
+	"reflect"
+	"testing"
+)
+
+// original form of the data
+const original = `; key-value pair
+key=value ; key-value pair
+
+# map
+[map] # map
+key=%(key)s
+
+`
+
+// encoded form of the data
+const encoded = `key=value
+
+[map]
+key=value
+`
+
+// decoded form of the data
+//
+// in case of INI it's slightly different from Viper's internal representation
+// (eg. top level keys land in a section called default)
+var decoded = map[string]interface{}{
+	"DEFAULT": map[string]interface{}{
+		"key": "value",
+	},
+	"map": map[string]interface{}{
+		"key": "value",
+	},
+}
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"key": "value",
+	"map": map[string]interface{}{
+		"key": "value",
+	},
+}
+
+func TestCodec_Encode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		b, err := codec.Encode(data)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if encoded != string(b) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+		}
+	})
+
+	t.Run("Default", func(t *testing.T) {
+		codec := Codec{}
+
+		data := map[string]interface{}{
+			"default": map[string]interface{}{
+				"key": "value",
+			},
+			"map": map[string]interface{}{
+				"key": "value",
+			},
+		}
+
+		b, err := codec.Encode(data)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if encoded != string(b) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+		}
+	})
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(original), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(decoded, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, decoded)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(`invalid data`), v)
+		if err == nil {
+			t.Fatal("expected decoding to fail")
+		}
+
+		t.Logf("decoding failed as expected: %s", err)
+	})
+}

internal/encoding/ini/map_utils.go

@@ -0,0 +1,74 @@
+package ini
+
+import (
+	"strings"
+
+	"github.com/spf13/cast"
+)
+
+// THIS CODE IS COPIED HERE: IT SHOULD NOT BE MODIFIED
+// AT SOME POINT IT WILL BE MOVED TO A COMMON PLACE
+// deepSearch scans deep maps, following the key indexes listed in the
+// sequence "path".
+// The last value is expected to be another map, and is returned.
+//
+// In case intermediate keys do not exist, or map to a non-map value,
+// a new map is created and inserted, and the search continues from there:
+// the initial map "m" may be modified!
+func deepSearch(m map[string]interface{}, path []string) map[string]interface{} {
+	for _, k := range path {
+		m2, ok := m[k]
+		if !ok {
+			// intermediate key does not exist
+			// => create it and continue from there
+			m3 := make(map[string]interface{})
+			m[k] = m3
+			m = m3
+			continue
+		}
+		m3, ok := m2.(map[string]interface{})
+		if !ok {
+			// intermediate key is a value
+			// => replace with a new map
+			m3 = make(map[string]interface{})
+			m[k] = m3
+		}
+		// continue search from here
+		m = m3
+	}
+	return m
+}
+
+// flattenAndMergeMap recursively flattens the given map into a new map
+// Code is based on the function with the same name in tha main package.
+// TODO: move it to a common place
+func flattenAndMergeMap(shadow map[string]interface{}, m map[string]interface{}, prefix string, delimiter string) map[string]interface{} {
+	if shadow != nil && prefix != "" && shadow[prefix] != nil {
+		// prefix is shadowed => nothing more to flatten
+		return shadow
+	}
+	if shadow == nil {
+		shadow = make(map[string]interface{})
+	}
+
+	var m2 map[string]interface{}
+	if prefix != "" {
+		prefix += delimiter
+	}
+	for k, val := range m {
+		fullKey := prefix + k
+		switch val.(type) {
+		case map[string]interface{}:
+			m2 = val.(map[string]interface{})
+		case map[interface{}]interface{}:
+			m2 = cast.ToStringMap(val)
+		default:
+			// immediate value
+			shadow[strings.ToLower(fullKey)] = val
+			continue
+		}
+		// recursively merge to shadow map
+		shadow = flattenAndMergeMap(shadow, m2, fullKey, delimiter)
+	}
+	return shadow
+}

internal/encoding/javaproperties/codec.go

@@ -0,0 +1,86 @@
+package javaproperties
+
+import (
+	"bytes"
+	"sort"
+	"strings"
+
+	"github.com/magiconair/properties"
+	"github.com/spf13/cast"
+)
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for Java properties encoding.
+type Codec struct {
+	KeyDelimiter string
+
+	// Store read properties on the object so that we can write back in order with comments.
+	// This will only be used if the configuration read is a properties file.
+	// TODO: drop this feature in v2
+	// TODO: make use of the global properties object optional
+	Properties *properties.Properties
+}
+
+func (c *Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	if c.Properties == nil {
+		c.Properties = properties.NewProperties()
+	}
+
+	flattened := map[string]interface{}{}
+
+	flattened = flattenAndMergeMap(flattened, v, "", c.keyDelimiter())
+
+	keys := make([]string, 0, len(flattened))
+
+	for key := range flattened {
+		keys = append(keys, key)
+	}
+
+	sort.Strings(keys)
+
+	for _, key := range keys {
+		_, _, err := c.Properties.Set(key, cast.ToString(flattened[key]))
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	var buf bytes.Buffer
+
+	_, err := c.Properties.WriteComment(&buf, "#", properties.UTF8)
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (c *Codec) Decode(b []byte, v map[string]interface{}) error {
+	var err error
+	c.Properties, err = properties.Load(b, properties.UTF8)
+	if err != nil {
+		return err
+	}
+
+	for _, key := range c.Properties.Keys() {
+		// ignore existence check: we know it's there
+		value, _ := c.Properties.Get(key)
+
+		// recursively build nested maps
+		path := strings.Split(key, c.keyDelimiter())
+		lastKey := strings.ToLower(path[len(path)-1])
+		deepestMap := deepSearch(v, path[0:len(path)-1])
+
+		// set innermost value
+		deepestMap[lastKey] = value
+	}
+
+	return nil
+}
+
+func (c Codec) keyDelimiter() string {
+	if c.KeyDelimiter == "" {
+		return "."
+	}
+
+	return c.KeyDelimiter
+}

internal/encoding/javaproperties/codec_test.go

@@ -0,0 +1,89 @@
+package javaproperties
+
+import (
+	"reflect"
+	"testing"
+)
+
+// original form of the data
+const original = `#key-value pair
+key = value
+map.key = value
+`
+
+// encoded form of the data
+const encoded = `key = value
+map.key = value
+`
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"key": "value",
+	"map": map[string]interface{}{
+		"key": "value",
+	},
+}
+
+func TestCodec_Encode(t *testing.T) {
+	codec := Codec{}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if encoded != string(b) {
+		t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+	}
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(original), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(data, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, data)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		t.Skip("TODO: needs invalid data example")
+
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		codec.Decode([]byte(``), v)
+
+		if len(v) > 0 {
+			t.Fatalf("expected map to be empty when data is invalid\nactual: %#v", v)
+		}
+	})
+}
+
+func TestCodec_DecodeEncode(t *testing.T) {
+	codec := Codec{}
+
+	v := map[string]interface{}{}
+
+	err := codec.Decode([]byte(original), v)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if original != string(b) {
+		t.Fatalf("encoded value does not match the original\nactual:   %#v\nexpected: %#v", string(b), original)
+	}
+}

internal/encoding/javaproperties/map_utils.go

@@ -0,0 +1,74 @@
+package javaproperties
+
+import (
+	"strings"
+
+	"github.com/spf13/cast"
+)
+
+// THIS CODE IS COPIED HERE: IT SHOULD NOT BE MODIFIED
+// AT SOME POINT IT WILL BE MOVED TO A COMMON PLACE
+// deepSearch scans deep maps, following the key indexes listed in the
+// sequence "path".
+// The last value is expected to be another map, and is returned.
+//
+// In case intermediate keys do not exist, or map to a non-map value,
+// a new map is created and inserted, and the search continues from there:
+// the initial map "m" may be modified!
+func deepSearch(m map[string]interface{}, path []string) map[string]interface{} {
+	for _, k := range path {
+		m2, ok := m[k]
+		if !ok {
+			// intermediate key does not exist
+			// => create it and continue from there
+			m3 := make(map[string]interface{})
+			m[k] = m3
+			m = m3
+			continue
+		}
+		m3, ok := m2.(map[string]interface{})
+		if !ok {
+			// intermediate key is a value
+			// => replace with a new map
+			m3 = make(map[string]interface{})
+			m[k] = m3
+		}
+		// continue search from here
+		m = m3
+	}
+	return m
+}
+
+// flattenAndMergeMap recursively flattens the given map into a new map
+// Code is based on the function with the same name in tha main package.
+// TODO: move it to a common place
+func flattenAndMergeMap(shadow map[string]interface{}, m map[string]interface{}, prefix string, delimiter string) map[string]interface{} {
+	if shadow != nil && prefix != "" && shadow[prefix] != nil {
+		// prefix is shadowed => nothing more to flatten
+		return shadow
+	}
+	if shadow == nil {
+		shadow = make(map[string]interface{})
+	}
+
+	var m2 map[string]interface{}
+	if prefix != "" {
+		prefix += delimiter
+	}
+	for k, val := range m {
+		fullKey := prefix + k
+		switch val.(type) {
+		case map[string]interface{}:
+			m2 = val.(map[string]interface{})
+		case map[interface{}]interface{}:
+			m2 = cast.ToStringMap(val)
+		default:
+			// immediate value
+			shadow[strings.ToLower(fullKey)] = val
+			continue
+		}
+		// recursively merge to shadow map
+		shadow = flattenAndMergeMap(shadow, m2, fullKey, delimiter)
+	}
+	return shadow
+}

internal/encoding/json/codec.go

@@ -0,0 +1,17 @@
+package json
+
+import (
+	"encoding/json"
+)
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for JSON encoding.
+type Codec struct{}
+
+func (Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	// TODO: expose prefix and indent in the Codec as setting?
+	return json.MarshalIndent(v, "", "  ")
+}
+
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	return json.Unmarshal(b, &v)
+}

internal/encoding/json/codec_test.go

@@ -0,0 +1,95 @@
+package json
+
+import (
+	"reflect"
+	"testing"
+)
+
+// encoded form of the data
+const encoded = `{
+  "key": "value",
+  "list": [
+    "item1",
+    "item2",
+    "item3"
+  ],
+  "map": {
+    "key": "value"
+  },
+  "nested_map": {
+    "map": {
+      "key": "value",
+      "list": [
+        "item1",
+        "item2",
+        "item3"
+      ]
+    }
+  }
+}`
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"key": "value",
+	"list": []interface{}{
+		"item1",
+		"item2",
+		"item3",
+	},
+	"map": map[string]interface{}{
+		"key": "value",
+	},
+	"nested_map": map[string]interface{}{
+		"map": map[string]interface{}{
+			"key": "value",
+			"list": []interface{}{
+				"item1",
+				"item2",
+				"item3",
+			},
+		},
+	},
+}
+
+func TestCodec_Encode(t *testing.T) {
+	codec := Codec{}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if encoded != string(b) {
+		t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+	}
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(encoded), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(data, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, data)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(`invalid data`), v)
+		if err == nil {
+			t.Fatal("expected decoding to fail")
+		}
+
+		t.Logf("decoding failed as expected: %s", err)
+	})
+}

internal/encoding/toml/codec.go

@@ -0,0 +1,16 @@
+package toml
+
+import (
+	"github.com/pelletier/go-toml/v2"
+)
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for TOML encoding.
+type Codec struct{}
+
+func (Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	return toml.Marshal(v)
+}
+
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	return toml.Unmarshal(b, &v)
+}

internal/encoding/toml/codec_test.go

@@ -0,0 +1,105 @@
+package toml
+
+import (
+	"reflect"
+	"testing"
+)
+
+// original form of the data
+const original = `# key-value pair
+key = "value"
+list = ["item1", "item2", "item3"]
+
+[map]
+key = "value"
+
+# nested
+# map
+[nested_map]
+[nested_map.map]
+key = "value"
+list = [
+  "item1",
+  "item2",
+  "item3",
+]
+`
+
+// encoded form of the data
+const encoded = `key = 'value'
+list = ['item1', 'item2', 'item3']
+
+[map]
+key = 'value'
+
+[nested_map]
+[nested_map.map]
+key = 'value'
+list = ['item1', 'item2', 'item3']
+`
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"key": "value",
+	"list": []interface{}{
+		"item1",
+		"item2",
+		"item3",
+	},
+	"map": map[string]interface{}{
+		"key": "value",
+	},
+	"nested_map": map[string]interface{}{
+		"map": map[string]interface{}{
+			"key": "value",
+			"list": []interface{}{
+				"item1",
+				"item2",
+				"item3",
+			},
+		},
+	},
+}
+
+func TestCodec_Encode(t *testing.T) {
+	codec := Codec{}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if encoded != string(b) {
+		t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+	}
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(original), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(data, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, data)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(`invalid data`), v)
+		if err == nil {
+			t.Fatal("expected decoding to fail")
+		}
+
+		t.Logf("decoding failed as expected: %s", err)
+	})
+}

internal/encoding/yaml/codec.go

@@ -0,0 +1,14 @@
+package yaml
+
+import "gopkg.in/yaml.v3"
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for YAML encoding.
+type Codec struct{}
+
+func (Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	return yaml.Marshal(v)
+}
+
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	return yaml.Unmarshal(b, &v)
+}

internal/encoding/yaml/codec_test.go

@@ -0,0 +1,136 @@
+package yaml
+
+import (
+	"reflect"
+	"testing"
+)
+
+// original form of the data
+const original = `# key-value pair
+key: value
+list:
+    - item1
+    - item2
+    - item3
+map:
+    key: value
+
+# nested
+# map
+nested_map:
+    map:
+        key: value
+        list:
+            - item1
+            - item2
+            - item3
+`
+
+// encoded form of the data
+const encoded = `key: value
+list:
+    - item1
+    - item2
+    - item3
+map:
+    key: value
+nested_map:
+    map:
+        key: value
+        list:
+            - item1
+            - item2
+            - item3
+`
+
+// decoded form of the data
+//
+// in case of YAML it's slightly different from Viper's internal representation
+// (eg. map is decoded into a map with interface key)
+var decoded = map[string]interface{}{
+	"key": "value",
+	"list": []interface{}{
+		"item1",
+		"item2",
+		"item3",
+	},
+	"map": map[string]interface{}{
+		"key": "value",
+	},
+	"nested_map": map[string]interface{}{
+		"map": map[string]interface{}{
+			"key": "value",
+			"list": []interface{}{
+				"item1",
+				"item2",
+				"item3",
+			},
+		},
+	},
+}
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"key": "value",
+	"list": []interface{}{
+		"item1",
+		"item2",
+		"item3",
+	},
+	"map": map[string]interface{}{
+		"key": "value",
+	},
+	"nested_map": map[string]interface{}{
+		"map": map[string]interface{}{
+			"key": "value",
+			"list": []interface{}{
+				"item1",
+				"item2",
+				"item3",
+			},
+		},
+	},
+}
+
+func TestCodec_Encode(t *testing.T) {
+	codec := Codec{}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if encoded != string(b) {
+		t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+	}
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(original), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(decoded, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, decoded)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(`invalid data`), v)
+		if err == nil {
+			t.Fatal("expected decoding to fail")
+		}
+
+		t.Logf("decoding failed as expected: %s", err)
+	})
+}

internal/testutil/env_go1_16.go

@@ -0,0 +1,40 @@
+//go:build !go1.17
+// +build !go1.17
+
+package testutil
+
+import (
+	"os"
+	"testing"
+)
+
+// Based on https://github.com/frankban/quicktest/blob/577841610793d24f99e31cc2c0ef3a541fefd7c7/patch.go#L34-L64
+// Licensed under the MIT license
+// Copyright (c) 2017 Canonical Ltd.
+
+// Setenv sets an environment variable to a temporary value for the
+// duration of the test.
+//
+// At the end of the test (see "Deferred execution" in the package docs), the
+// environment variable is returned to its original value.
+func Setenv(t *testing.T, name, val string) {
+	setenv(t, name, val, true)
+}
+
+// setenv sets or unsets an environment variable to a temporary value for the
+// duration of the test
+func setenv(t *testing.T, name, val string, valOK bool) {
+	oldVal, oldOK := os.LookupEnv(name)
+	if valOK {
+		os.Setenv(name, val)
+	} else {
+		os.Unsetenv(name)
+	}
+	t.Cleanup(func() {
+		if oldOK {
+			os.Setenv(name, oldVal)
+		} else {
+			os.Unsetenv(name)
+		}
+	})
+}

internal/testutil/env_go1_17.go

@@ -0,0 +1,18 @@
+//go:build go1.17
+// +build go1.17
+
+package testutil
+
+import (
+	"testing"
+)
+
+// Setenv sets an environment variable to a temporary value for the
+// duration of the test.
+//
+// This shim can be removed once support for Go <1.17 is dropped.
+func Setenv(t *testing.T, name, val string) {
+	t.Helper()
+
+	t.Setenv(name, val)
+}

internal/testutil/filepath.go

@@ -0,0 +1,18 @@
+package testutil
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+// AbsFilePath calls filepath.Abs on path.
+func AbsFilePath(t *testing.T, path string) string {
+	t.Helper()
+
+	s, err := filepath.Abs(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return s
+}

logger.go

@@ -0,0 +1,77 @@
+package viper
+
+import (
+	"fmt"
+
+	jww "github.com/spf13/jwalterweatherman"
+)
+
+// Logger is a unified interface for various logging use cases and practices, including:
+//   - leveled logging
+//   - structured logging
+type Logger interface {
+	// Trace logs a Trace event.
+	//
+	// Even more fine-grained information than Debug events.
+	// Loggers not supporting this level should fall back to Debug.
+	Trace(msg string, keyvals ...interface{})
+
+	// Debug logs a Debug event.
+	//
+	// A verbose series of information events.
+	// They are useful when debugging the system.
+	Debug(msg string, keyvals ...interface{})
+
+	// Info logs an Info event.
+	//
+	// General information about what's happening inside the system.
+	Info(msg string, keyvals ...interface{})
+
+	// Warn logs a Warn(ing) event.
+	//
+	// Non-critical events that should be looked at.
+	Warn(msg string, keyvals ...interface{})
+
+	// Error logs an Error event.
+	//
+	// Critical events that require immediate attention.
+	// Loggers commonly provide Fatal and Panic levels above Error level,
+	// but exiting and panicing is out of scope for a logging library.
+	Error(msg string, keyvals ...interface{})
+}
+
+type jwwLogger struct{}
+
+func (jwwLogger) Trace(msg string, keyvals ...interface{}) {
+	jww.TRACE.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func (jwwLogger) Debug(msg string, keyvals ...interface{}) {
+	jww.DEBUG.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func (jwwLogger) Info(msg string, keyvals ...interface{}) {
+	jww.INFO.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func (jwwLogger) Warn(msg string, keyvals ...interface{}) {
+	jww.WARN.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func (jwwLogger) Error(msg string, keyvals ...interface{}) {
+	jww.ERROR.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func jwwLogMessage(msg string, keyvals ...interface{}) string {
+	out := msg
+
+	if len(keyvals) > 0 && len(keyvals)%2 == 1 {
+		keyvals = append(keyvals, nil)
+	}
+
+	for i := 0; i <= len(keyvals)-2; i += 2 {
+		out = fmt.Sprintf("%s %v=%v", out, keyvals[i], keyvals[i+1])
+	}
+
+	return out
+}

overrides_test.go

@@ -78,6 +78,7 @@ func TestNestedOverrides(t *testing.T) {
 func overrideDefault(assert *assert.Assertions, firstPath string, firstValue interface{}, secondPath string, secondValue interface{}) *Viper {
 	return overrideFromLayer(defaultLayer, assert, firstPath, firstValue, secondPath, secondValue)
 }
+
 func override(assert *assert.Assertions, firstPath string, firstValue interface{}, secondPath string, secondValue interface{}) *Viper {
 	return overrideFromLayer(overrideLayer, assert, firstPath, firstValue, secondPath, secondValue)
 }

remote/remote.go

@@ -10,10 +10,11 @@ import (
 	"bytes"
 	"io"
 	"os"
+	"strings"
+
+	crypt "github.com/sagikazarmark/crypt/config"
 
 	"github.com/spf13/viper"
-
-	crypt "github.com/xordataexchange/crypt/config"
 )
 
 type remoteConfigProvider struct{}
@@ -75,6 +76,7 @@ func getConfigManager(rp viper.RemoteProvider) (crypt.ConfigManager, error) {
 	var cm crypt.ConfigManager
 	var err error
 
+	endpoints := strings.Split(rp.Endpoint(), ";")
 	if rp.SecretKeyring() != "" {
 		var kr *os.File
 		kr, err = os.Open(rp.SecretKeyring())
@@ -82,16 +84,26 @@ func getConfigManager(rp viper.RemoteProvider) (crypt.ConfigManager, error) {
 			return nil, err
 		}
 		defer kr.Close()
-		if rp.Provider() == "etcd" {
-			cm, err = crypt.NewEtcdConfigManager([]string{rp.Endpoint()}, kr)
-		} else {
-			cm, err = crypt.NewConsulConfigManager([]string{rp.Endpoint()}, kr)
+		switch rp.Provider() {
+		case "etcd":
+			cm, err = crypt.NewEtcdConfigManager(endpoints, kr)
+		case "etcd3":
+			cm, err = crypt.NewEtcdV3ConfigManager(endpoints, kr)
+		case "firestore":
+			cm, err = crypt.NewFirestoreConfigManager(endpoints, kr)
+		default:
+			cm, err = crypt.NewConsulConfigManager(endpoints, kr)
 		}
 	} else {
-		if rp.Provider() == "etcd" {
-			cm, err = crypt.NewStandardEtcdConfigManager([]string{rp.Endpoint()})
-		} else {
-			cm, err = crypt.NewStandardConsulConfigManager([]string{rp.Endpoint()})
+		switch rp.Provider() {
+		case "etcd":
+			cm, err = crypt.NewStandardEtcdConfigManager(endpoints)
+		case "etcd3":
+			cm, err = crypt.NewStandardEtcdV3ConfigManager(endpoints)
+		case "firestore":
+			cm, err = crypt.NewStandardFirestoreConfigManager(endpoints)
+		default:
+			cm, err = crypt.NewStandardConsulConfigManager(endpoints)
 		}
 	}
 	if err != nil {

util.go

@@ -18,9 +18,7 @@ import (
 	"strings"
 	"unicode"
 
-	"github.com/spf13/afero"
 	"github.com/spf13/cast"
-	jww "github.com/spf13/jwalterweatherman"
 )
 
 // ConfigParseError denotes failing to parse configuration file.
@@ -33,6 +31,11 @@ func (pe ConfigParseError) Error() string {
 	return fmt.Sprintf("While parsing config: %s", pe.err.Error())
 }
 
+// Unwrap returns the wrapped error.
+func (pe ConfigParseError) Unwrap() error {
+	return pe.err
+}
+
 // toCaseInsensitiveValue checks if the value is a  map;
 // if so, create a copy and lower-case the keys recursively.
 func toCaseInsensitiveValue(value interface{}) interface{} {
@@ -66,18 +69,25 @@ func copyAndInsensitiviseMap(m map[string]interface{}) map[string]interface{} {
 	return nm
 }
 
+func insensitiviseVal(val interface{}) interface{} {
+	switch val.(type) {
+	case map[interface{}]interface{}:
+		// nested map: cast and recursively insensitivise
+		val = cast.ToStringMap(val)
+		insensitiviseMap(val.(map[string]interface{}))
+	case map[string]interface{}:
+		// nested map: recursively insensitivise
+		insensitiviseMap(val.(map[string]interface{}))
+	case []interface{}:
+		// nested array: recursively insensitivise
+		insensitiveArray(val.([]interface{}))
+	}
+	return val
+}
+
 func insensitiviseMap(m map[string]interface{}) {
 	for key, val := range m {
-		switch val.(type) {
-		case map[interface{}]interface{}:
-			// nested map: cast and recursively insensitivise
-			val = cast.ToStringMap(val)
-			insensitiviseMap(val.(map[string]interface{}))
-		case map[string]interface{}:
-			// nested map: recursively insensitivise
-			insensitiviseMap(val.(map[string]interface{}))
-		}
-
+		val = insensitiviseVal(val)
 		lower := strings.ToLower(key)
 		if key != lower {
 			// remove old key (not lower-cased)
@@ -88,17 +98,20 @@ func insensitiviseMap(m map[string]interface{}) {
 	}
 }
 
-func absPathify(inPath string) string {
-	jww.INFO.Println("Trying to resolve absolute path to", inPath)
+func insensitiveArray(a []interface{}) {
+	for i, val := range a {
+		a[i] = insensitiviseVal(val)
+	}
+}
 
-	if strings.HasPrefix(inPath, "$HOME") {
+func absPathify(logger Logger, inPath string) string {
+	logger.Info("trying to resolve absolute path", "path", inPath)
+
+	if inPath == "$HOME" || strings.HasPrefix(inPath, "$HOME"+string(os.PathSeparator)) {
 		inPath = userHomeDir() + inPath[5:]
 	}
 
-	if strings.HasPrefix(inPath, "$") {
-		end := strings.Index(inPath, string(os.PathSeparator))
-		inPath = os.Getenv(inPath[1:end]) + inPath[end:]
-	}
+	inPath = os.ExpandEnv(inPath)
 
 	if filepath.IsAbs(inPath) {
 		return filepath.Clean(inPath)
@@ -109,21 +122,9 @@ func absPathify(inPath string) string {
 		return filepath.Clean(p)
 	}
 
-	jww.ERROR.Println("Couldn't discover absolute path")
-	jww.ERROR.Println(err)
-	return ""
-}
+	logger.Error(fmt.Errorf("could not discover absolute path: %w", err).Error())
 
-// Check if file Exists
-func exists(fs afero.Fs, path string) (bool, error) {
-	stat, err := fs.Stat(path)
-	if err == nil {
-		return !stat.IsDir(), nil
-	}
-	if os.IsNotExist(err) {
-		return false, nil
-	}
-	return false, err
+	return ""
 }
 
 func stringInSlice(a string, list []string) bool {

util_test.go

@@ -11,25 +11,29 @@
 package viper
 
 import (
+	"os"
+	"path/filepath"
 	"reflect"
 	"testing"
+
+	"github.com/spf13/viper/internal/testutil"
 )
 
 func TestCopyAndInsensitiviseMap(t *testing.T) {
 	var (
 		given = map[string]interface{}{
 			"Foo": 32,
-			"Bar": map[interface{}]interface {
-			}{
+			"Bar": map[interface{}]interface{}{
 				"ABc": "A",
-				"cDE": "B"},
+				"cDE": "B",
+			},
 		}
 		expected = map[string]interface{}{
 			"foo": 32,
-			"bar": map[string]interface {
-			}{
+			"bar": map[string]interface{}{
 				"abc": "A",
-				"cde": "B"},
+				"cde": "B",
+			},
 		}
 	)
 
@@ -52,3 +56,40 @@ func TestCopyAndInsensitiviseMap(t *testing.T) {
 		t.Fatal("Input map changed")
 	}
 }
+
+func TestAbsPathify(t *testing.T) {
+	skipWindows(t)
+
+	home := userHomeDir()
+	homer := filepath.Join(home, "homer")
+	wd, _ := os.Getwd()
+
+	testutil.Setenv(t, "HOMER_ABSOLUTE_PATH", homer)
+	testutil.Setenv(t, "VAR_WITH_RELATIVE_PATH", "relative")
+
+	tests := []struct {
+		input  string
+		output string
+	}{
+		{"", wd},
+		{"sub", filepath.Join(wd, "sub")},
+		{"./", wd},
+		{"./sub", filepath.Join(wd, "sub")},
+		{"$HOME", home},
+		{"$HOME/", home},
+		{"$HOME/sub", filepath.Join(home, "sub")},
+		{"$HOMER_ABSOLUTE_PATH", homer},
+		{"$HOMER_ABSOLUTE_PATH/", homer},
+		{"$HOMER_ABSOLUTE_PATH/sub", filepath.Join(homer, "sub")},
+		{"$VAR_WITH_RELATIVE_PATH", filepath.Join(wd, "relative")},
+		{"$VAR_WITH_RELATIVE_PATH/", filepath.Join(wd, "relative")},
+		{"$VAR_WITH_RELATIVE_PATH/sub", filepath.Join(wd, "relative", "sub")},
+	}
+
+	for _, test := range tests {
+		got := absPathify(jwwLogger{}, test.input)
+		if got != test.output {
+			t.Errorf("Got %v\nexpected\n%q", got, test.output)
+		}
+	}
+}

viper_go1_15.go

@@ -0,0 +1,57 @@
+//go:build !go1.16 || !finder
+// +build !go1.16 !finder
+
+package viper
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/spf13/afero"
+)
+
+// Search all configPaths for any config file.
+// Returns the first path that exists (and is a config file).
+func (v *Viper) findConfigFile() (string, error) {
+	v.logger.Info("searching for config in paths", "paths", v.configPaths)
+
+	for _, cp := range v.configPaths {
+		file := v.searchInPath(cp)
+		if file != "" {
+			return file, nil
+		}
+	}
+	return "", ConfigFileNotFoundError{v.configName, fmt.Sprintf("%s", v.configPaths)}
+}
+
+func (v *Viper) searchInPath(in string) (filename string) {
+	v.logger.Debug("searching for config in path", "path", in)
+	for _, ext := range SupportedExts {
+		v.logger.Debug("checking if file exists", "file", filepath.Join(in, v.configName+"."+ext))
+		if b, _ := exists(v.fs, filepath.Join(in, v.configName+"."+ext)); b {
+			v.logger.Debug("found file", "file", filepath.Join(in, v.configName+"."+ext))
+			return filepath.Join(in, v.configName+"."+ext)
+		}
+	}
+
+	if v.configType != "" {
+		if b, _ := exists(v.fs, filepath.Join(in, v.configName)); b {
+			return filepath.Join(in, v.configName)
+		}
+	}
+
+	return ""
+}
+
+// Check if file Exists
+func exists(fs afero.Fs, path string) (bool, error) {
+	stat, err := fs.Stat(path)
+	if err == nil {
+		return !stat.IsDir(), nil
+	}
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	return false, err
+}

viper_go1_16.go

@@ -0,0 +1,32 @@
+//go:build go1.16 && finder
+// +build go1.16,finder
+
+package viper
+
+import (
+	"fmt"
+
+	"github.com/spf13/afero"
+)
+
+// Search all configPaths for any config file.
+// Returns the first path that exists (and is a config file).
+func (v *Viper) findConfigFile() (string, error) {
+	finder := finder{
+		paths:            v.configPaths,
+		fileNames:        []string{v.configName},
+		extensions:       SupportedExts,
+		withoutExtension: v.configType != "",
+	}
+
+	file, err := finder.Find(afero.NewIOFS(v.fs))
+	if err != nil {
+		return "", err
+	}
+
+	if file == "" {
+		return "", ConfigFileNotFoundError{v.configName, fmt.Sprintf("%s", v.configPaths)}
+	}
+
+	return file, nil
+}

viper_yaml_test.go

@@ -0,0 +1,53 @@
+package viper
+
+var yamlExample = []byte(`Hacker: true
+name: steve
+hobbies:
+    - skateboarding
+    - snowboarding
+    - go
+clothing:
+    jacket: leather
+    trousers: denim
+    pants:
+        size: large
+age: 35
+eyes : brown
+beard: true
+`)
+
+var yamlWriteExpected = []byte(`age: 35
+beard: true
+clothing:
+    jacket: leather
+    pants:
+        size: large
+    trousers: denim
+eyes: brown
+hacker: true
+hobbies:
+    - skateboarding
+    - snowboarding
+    - go
+name: steve
+`)
+
+var yamlExampleWithDot = []byte(`Hacker: true
+name: steve
+hobbies:
+    - skateboarding
+    - snowboarding
+    - go
+clothing:
+    jacket: leather
+    trousers: denim
+    pants:
+        size: large
+age: 35
+eyes : brown
+beard: true
+emails:
+    steve@hacker.com:
+        created: 01/02/03
+        active: true
+`)

watch.go

@@ -0,0 +1,12 @@
+//go:build darwin || dragonfly || freebsd || openbsd || linux || netbsd || solaris || windows
+// +build darwin dragonfly freebsd openbsd linux netbsd solaris windows
+
+package viper
+
+import "github.com/fsnotify/fsnotify"
+
+type watcher = fsnotify.Watcher
+
+func newWatcher() (*watcher, error) {
+	return fsnotify.NewWatcher()
+}

watch_unsupported.go

@@ -0,0 +1,32 @@
+//go:build appengine || (!darwin && !dragonfly && !freebsd && !openbsd && !linux && !netbsd && !solaris && !windows)
+// +build appengine !darwin,!dragonfly,!freebsd,!openbsd,!linux,!netbsd,!solaris,!windows
+
+package viper
+
+import (
+	"fmt"
+	"runtime"
+
+	"github.com/fsnotify/fsnotify"
+)
+
+func newWatcher() (*watcher, error) {
+	return &watcher{}, fmt.Errorf("fsnotify not supported on %s", runtime.GOOS)
+}
+
+type watcher struct {
+	Events chan fsnotify.Event
+	Errors chan error
+}
+
+func (*watcher) Close() error {
+	return nil
+}
+
+func (*watcher) Add(name string) error {
+	return nil
+}
+
+func (*watcher) Remove(name string) error {
+	return nil
+}