cmd/go: stamp VCS revision and uncommitted status into binaries

When the go command builds a binary, it will now stamp the current
revision from the local Git or Mercurial repository, and it will also
stamp whether there are uncommitted edited or untracked files. Only
Git and Mercurial are supported for now.

If no repository is found containing the current working directory
(where the go command was started), or if either the main package
directory or the containing module's root directory is outside the
repository, no VCS information will be stamped. If the VCS tool is
missing or returns an error, that error is reported on the main
package (hinting that -buildvcs may be disabled).

This change introduces the -buildvcs flag, which is enabled by
default. When disabled, VCS information won't be stamped when it would
be otherwise.

Stamped information may be read using 'go version -m file' or
debug.ReadBuildInfo.

For #37475

Change-Id: I4e7d3159e1c270d85869ad99f10502e546e7582d
Reviewed-on: https://go-review.googlesource.com/c/go/+/353930
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 36 insertions, 10 deletions

diff --git a/src/runtime/debug/mod.go b/src/runtime/debug/mod.go
index 0c6488753b..14b99f5735 100644
--- a/src/runtime/debug/mod.go
+++ b/src/runtime/debug/mod.go
@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"fmt"
 	"runtime"
+	"strings"
 )
 
 // exported from runtime
@@ -38,10 +39,11 @@ func ReadBuildInfo() (info *BuildInfo, ok bool) {
 
 // BuildInfo represents the build information read from a Go binary.
 type BuildInfo struct {
-	GoVersion string    // Version of Go that produced this binary.
-	Path      string    // The main package path
-	Main      Module    // The module containing the main package
-	Deps      []*Module // Module dependencies
+	GoVersion string         // Version of Go that produced this binary.
+	Path      string         // The main package path
+	Main      Module         // The module containing the main package
+	Deps      []*Module      // Module dependencies
+	Settings  []BuildSetting // Other information about the build.
 }
 
 // Module represents a module.
@@ -52,6 +54,14 @@ type Module struct {
 	Replace *Module // replaced by this module
 }
 
+// BuildSetting describes a setting that may be used to understand how the
+// binary was built. For example, VCS commit and dirty status is stored here.
+type BuildSetting struct {
+	// Key and Value describe the build setting. They must not contain tabs
+	// or newlines.
+	Key, Value string
+}
+
 func (bi *BuildInfo) MarshalText() ([]byte, error) {
 	buf := &bytes.Buffer{}
 	if bi.GoVersion != "" {
@@ -86,6 +96,12 @@ func (bi *BuildInfo) MarshalText() ([]byte, error) {
 	for _, dep := range bi.Deps {
 		formatMod("dep", *dep)
 	}
+	for _, s := range bi.Settings {
+		if strings.ContainsAny(s.Key, "\n\t") || strings.ContainsAny(s.Value, "\n\t") {
+			return nil, fmt.Errorf("build setting %q contains tab or newline", s.Key)
+		}
+		fmt.Fprintf(buf, "build\t%s\t%s\n", s.Key, s.Value)
+	}
 
 	return buf.Bytes(), nil
 }
@@ -100,12 +116,13 @@ func (bi *BuildInfo) UnmarshalText(data []byte) (err error) {
 	}()
 
 	var (
-		pathLine = []byte("path\t")
-		modLine  = []byte("mod\t")
-		depLine  = []byte("dep\t")
-		repLine  = []byte("=>\t")
-		newline  = []byte("\n")
-		tab      = []byte("\t")
+		pathLine  = []byte("path\t")
+		modLine   = []byte("mod\t")
+		depLine   = []byte("dep\t")
+		repLine   = []byte("=>\t")
+		buildLine = []byte("build\t")
+		newline   = []byte("\n")
+		tab       = []byte("\t")
 	)
 
 	readModuleLine := func(elem [][]byte) (Module, error) {
@@ -167,6 +184,15 @@ func (bi *BuildInfo) UnmarshalText(data []byte) (err error) {
 				Sum:     string(elem[2]),
 			}
 			last = nil
+		case bytes.HasPrefix(line, buildLine):
+			elem := bytes.Split(line[len(buildLine):], tab)
+			if len(elem) != 2 {
+				return fmt.Errorf("expected 2 columns for build setting; got %d", len(elem))
+			}
+			if len(elem[0]) == 0 {
+				return fmt.Errorf("empty key")
+			}
+			bi.Settings = append(bi.Settings, BuildSetting{Key: string(elem[0]), Value: string(elem[1])})
 		}
 		lineNum++
 	}