Use Go generate instead of a makefile (#279)

* Use Go generate instead of a makefile

* Meet the go generate specifications

internal/gen-known-logs/Makefile

@@ -1,5 +0,0 @@
-.PHONY: ctlogs
-
-ctlogs:
-	go run github.com/square/certigo/internal/gen-known-logs --package lib > ../../lib/ctlogs.go
-	go fmt ../../lib/ctlogs.go

internal/gen-known-logs/README.md

@@ -6,4 +6,4 @@ Logs are fetched parsed from https://www.gstatic.com/ct/log_list/v2/all_logs_lis
 
 ## Usage
 
-From the current directory (`certigo/internal/gen-known-logs`), run `make ctlogs`. This will fetch the list of logs and place generated code in [lib/ctlogs.go](../../lib/ctlogs.go).
+Run `go generate ./...` to regenerate known logs.

internal/gen-known-logs/main.go

@@ -6,10 +6,13 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"os"
 	"time"
 )
 
-var packageName = flag.String("package", "lib", "Package for the generated code")
+var (
+	out = flag.String("out", "", "Output file")
+)
 
 // https://github.com/google/certificate-transparency-community-site/blob/master/docs/google/known-logs.md
 const knownLogsAddr = "https://www.gstatic.com/ct/log_list/v2/all_logs_list.json"
@@ -24,8 +27,7 @@ func main() {
 
 	resp, err := http.Get(knownLogsAddr)
 	if err != nil {
-		log.Printf("Failed to fetch the list of known CT logs: %v", err)
-		return
+		log.Fatalf("Failed to fetch the list of known CT logs: %v", err)
 	}
 	defer resp.Body.Close()
 
@@ -40,11 +42,16 @@ func main() {
 	}
 
 	if err := json.NewDecoder(resp.Body).Decode(&logs); err != nil {
-		log.Printf("Failed to parse the list of known CT logs: %v", err)
-		return
+		log.Fatalf("Failed to parse the list of known CT logs: %v", err)
 	}
 
-	fmt.Printf(`// Autogenerated with github.com/square/certigo/internal/gen-known-logs
+	f, err := os.Create(*out)
+	if err != nil {
+		log.Fatalf("Failed to open file %s", *out)
+	}
+	defer f.Close()
+
+	fmt.Fprintf(f, `// Code generated by github.com/square/certigo/internal/gen-known-logs; DO NOT EDIT
 // Generated at %s
 package %s
 
@@ -54,16 +61,16 @@ type ctLog struct {
 }
 
 var knownLogs = map[string]*ctLog{
-`, time.Now().Format(time.RFC3339), *packageName)
+`, time.Now().Format(time.RFC3339), os.Getenv("GOPACKAGE"))
 	knownLogs := make(map[string]*ctLog)
 	for _, op := range logs.Operators {
 		for _, l := range op.Logs {
-			fmt.Printf("\t%q: {operator: %q, url: %q},\n", l.ID, op.Name, l.URL)
+			fmt.Fprintf(f, "\t%q: {operator: %q, url: %q},\n", l.ID, op.Name, l.URL)
 			knownLogs[l.ID] = &ctLog{
 				operator: op.Name,
 				url:      l.URL,
 			}
 		}
 	}
-	fmt.Println("}")
+	fmt.Fprintln(f, "}")
 }

lib/ct.go

@@ -11,6 +11,9 @@ import (
 	ctutil "github.com/google/certificate-transparency-go/x509util"
 )
 
+//go:generate go run github.com/square/certigo/internal/gen-known-logs --out ctlogs.go
+//go:generate go fmt ctlogs.go
+
 func parseSCTList(cert *x509.Certificate) []*simpleSCT {
 	// ctutil contains a fork of crypto/x509 with support for SCTs. We must re-parse the
 	// whole certificate to get at them, so do a quick check to see if the SCT extension

lib/ctlogs.go

@@ -1,5 +1,5 @@
-// Autogenerated with github.com/square/certigo/internal/gen-known-logs
-// Generated at 2022-06-29T17:31:27-07:00
+// Code generated by github.com/square/certigo/internal/gen-known-logs; DO NOT EDIT
+// Generated at 2022-06-29T22:18:11-07:00
 package lib
 
 type ctLog struct {