cmd/go: support -json flag in go version

It supports features described in the issue:

* add -json flag for 'go version -m' to print json encoding of
  runtime/debug.BuildSetting to standard output.
* report an error when specifying -json flag without -m.
* print build settings on seperated line for each binary

Fixes #69712

Change-Id: I79cba2109f80f7459252d197a74959694c4eea1f
Reviewed-on: https://go-review.googlesource.com/c/go/+/619955
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/go/alldocs.go

@@ -1967,7 +1967,7 @@
 //
 // Usage:
 //
-//	go version [-m] [-v] [file ...]
+//	go version [-m] [-v] [-json] [file ...]
 //
 // Version prints the build information for Go binary files.
 //
@@ -1986,6 +1986,9 @@
 // information consists of multiple lines following the version line, each
 // indented by a leading tab character.
 //
+// The -json flag is similar to -m but outputs the runtime/debug.BuildInfo in JSON format.
+// If flag -json is specified without -m, go version reports an error.
+//
 // See also: go doc runtime/debug.BuildInfo.
 //
 // # Report likely mistakes in packages

src/cmd/go/internal/version/version.go

@@ -8,6 +8,7 @@ package version
 import (
 	"context"
 	"debug/buildinfo"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io/fs"
@@ -21,7 +22,7 @@ import (
 )
 
 var CmdVersion = &base.Command{
-	UsageLine: "go version [-m] [-v] [file ...]",
+	UsageLine: "go version [-m] [-v] [-json] [file ...]",
 	Short:     "print Go version",
 	Long: `Version prints the build information for Go binary files.
 
@@ -40,6 +41,9 @@ module version information, when available. In the output, the module
 information consists of multiple lines following the version line, each
 indented by a leading tab character.
 
+The -json flag is similar to -m but outputs the runtime/debug.BuildInfo in JSON format.
+If flag -json is specified without -m, go version reports an error.
+
 See also: go doc runtime/debug.BuildInfo.
 `,
 }
@@ -50,8 +54,9 @@ func init() {
 }
 
 var (
-	versionM = CmdVersion.Flag.Bool("m", false, "")
-	versionV = CmdVersion.Flag.Bool("v", false, "")
+	versionM    = CmdVersion.Flag.Bool("m", false, "")
+	versionV    = CmdVersion.Flag.Bool("v", false, "")
+	versionJson = CmdVersion.Flag.Bool("json", false, "")
 )
 
 func runVersion(ctx context.Context, cmd *base.Command, args []string) {
@@ -68,6 +73,11 @@ func runVersion(ctx context.Context, cmd *base.Command, args []string) {
 			argOnlyFlag = "-m"
 		} else if !base.InGOFLAGS("-v") && *versionV {
 			argOnlyFlag = "-v"
+		} else if !base.InGOFLAGS("-json") && *versionJson {
+			// Even though '-json' without '-m' should report an error,
+			// it reports 'no arguments' issue only because that error will be reported
+			// once the 'no arguments' issue is fixed by users.
+			argOnlyFlag = "-json"
 		}
 		if argOnlyFlag != "" {
 			fmt.Fprintf(os.Stderr, "go: 'go version' only accepts %s flag with arguments\n", argOnlyFlag)
@@ -82,6 +92,12 @@ func runVersion(ctx context.Context, cmd *base.Command, args []string) {
 		return
 	}
 
+	if !*versionM && *versionJson {
+		fmt.Fprintf(os.Stderr, "go: 'go version' with -json flag requires -m flag\n")
+		base.SetExitStatus(2)
+		return
+	}
+
 	for _, arg := range args {
 		info, err := os.Stat(arg)
 		if err != nil {
@@ -155,7 +171,6 @@ func scanFile(file string, info fs.FileInfo, mustPrint bool) bool {
 			if pathErr := (*os.PathError)(nil); errors.As(err, &pathErr) && filepath.Clean(pathErr.Path) == filepath.Clean(file) {
 				fmt.Fprintf(os.Stderr, "%v\n", file)
 			} else {
-
 				// Skip errors for non-Go binaries.
 				// buildinfo.ReadFile errors are not fine-grained enough
 				// to know if the file is a Go binary or not,
@@ -168,6 +183,15 @@ func scanFile(file string, info fs.FileInfo, mustPrint bool) bool {
 		return false
 	}
 
+	if *versionM && *versionJson {
+		bs, err := json.MarshalIndent(bi, "", "\t")
+		if err != nil {
+			base.Fatal(err)
+		}
+		fmt.Printf("%s\n", bs)
+		return true
+	}
+
 	fmt.Printf("%s: %s\n", file, bi.GoVersion)
 	bi.GoVersion = "" // suppress printing go version again
 	mod := bi.String()

src/cmd/go/testdata/script/version.txt

@@ -8,6 +8,8 @@ stdout '^go version'
 stderr 'with arguments'
 ! go version -v
 stderr 'with arguments'
+! go version -json
+stderr 'with arguments'
 
 # Check that 'go version' succeed even when it does not contain Go build info.
 # It should print an error if the file has a known Go binary extension.
@@ -22,8 +24,8 @@ stderr 'could not read Go build info'
 go version empty.dll
 stderr 'could not read Go build info'
 
-# Neither of the two flags above should be an issue via GOFLAGS.
-env GOFLAGS='-m -v'
+# Neither of the three flags above should be an issue via GOFLAGS.
+env GOFLAGS='-m -v -json'
 go version
 stdout '^go version'
 env GOFLAGS=
@@ -57,6 +59,23 @@ stdout '^test2json.exe: .+'
 stdout '^\tpath\tcmd/test2json$'
 ! stdout 'mod[^e]'
 
+# Check -json flag
+go build -o test2json.exe cmd/test2json
+go version -m -json test2json.exe
+stdout '"Path": "cmd/test2json"'
+! stdout 'null'
+
+# Check -json flag output with multiple binaries
+go build -o test2json.exe cmd/test2json
+go version -m -json test2json.exe test2json.exe
+stdout -count=2 '"Path": "cmd/test2json"'
+
+# Check -json flag without -m
+go build -o test2json.exe cmd/test2json
+! go version -json test2json.exe
+! stdout '"Path": "cmd/test2json"'
+stderr 'with -json flag requires -m flag'
+
 # Repeat the test with -buildmode=pie and default linking.
 [!buildmode:pie] stop
 [pielinkext] [!cgo] stop

src/runtime/debug/mod.go

@@ -41,29 +41,29 @@ func ReadBuildInfo() (info *BuildInfo, ok bool) {
 type BuildInfo struct {
 	// GoVersion is the version of the Go toolchain that built the binary
 	// (for example, "go1.19.2").
-	GoVersion string
+	GoVersion string `json:",omitempty"`
 
 	// Path is the package path of the main package for the binary
 	// (for example, "golang.org/x/tools/cmd/stringer").
-	Path string
+	Path string `json:",omitempty"`
 
 	// Main describes the module that contains the main package for the binary.
-	Main Module
+	Main Module `json:""`
 
 	// Deps describes all the dependency modules, both direct and indirect,
 	// that contributed packages to the build of this binary.
-	Deps []*Module
+	Deps []*Module `json:",omitempty"`
 
 	// Settings describes the build settings used to build the binary.
-	Settings []BuildSetting
+	Settings []BuildSetting `json:",omitempty"`
 }
 
 // A Module describes a single module included in a build.
 type Module struct {
-	Path    string  // module path
-	Version string  // module version
-	Sum     string  // checksum
-	Replace *Module // replaced by this module
+	Path    string  `json:",omitempty"` // module path
+	Version string  `json:",omitempty"` // module version
+	Sum     string  `json:",omitempty"` // checksum
+	Replace *Module `json:",omitempty"` // replaced by this module
 }
 
 // A BuildSetting is a key-value pair describing one setting that influenced a build.
@@ -89,8 +89,9 @@ type Module struct {
 type BuildSetting struct {
 	// Key and Value describe the build setting.
 	// Key must not contain an equals sign, space, tab, or newline.
+	Key string `json:",omitempty"`
 	// Value must not contain newlines ('\n').
-	Key, Value string
+	Value string `json:",omitempty"`
 }
 
 // quoteKey reports whether key is required to be quoted.