cmd/go: add BuildID to list -json -export

That is, the following two pieces of shell code are now equivalent:

	$ go tool buildid $(go list -export -f {{.Export}} strings)
	v_0VqA6yzwuMg2dn4u57/PXcIR2Pb8Mi9yRdcdkwe

	$ go list -export -f {{.BuildID}} strings
	v_0VqA6yzwuMg2dn4u57/PXcIR2Pb8Mi9yRdcdkwe

This does not expose any information that wasn't available before, but
makes this workflow simpler and faster. In the first example, we have to
execute two programs, and 'go tool buildid' has to re-open the export
data file to read the build ID.

With the new mechanism, 'go list -export' already has the build ID
ready, so we can simply print it out. Moreover, when listing lots of
related packages like './...', we can now obtain all their build IDs at
once.

Fixes #37281.

Change-Id: I8e2f65a08391b3df1a628c6e06e708b8c8cb7865
Reviewed-on: https://go-review.googlesource.com/c/go/+/263542
Trust: Daniel Martí <mvdan@mvdan.cc>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/alldocs.go

@@ -796,6 +796,7 @@
 //         BinaryOnly    bool     // binary-only package (no longer supported)
 //         ForTest       string   // package is only for use in named test
 //         Export        string   // file containing export data (when using -export)
+//         BuildID       string   // build ID of the export data (when using -export)
 //         Module        *Module  // info about package's containing module, if any (can be nil)
 //         Match         []string // command-line patterns matching this package
 //         DepOnly       bool     // package is only a dependency, not explicitly listed

src/cmd/go/go_test.go

@@ -1237,6 +1237,18 @@ func TestGoListExport(t *testing.T) {
 	if _, err := os.Stat(file); err != nil {
 		t.Fatalf("cannot find .Export result %s: %v", file, err)
 	}
+
+	tg.run("list", "-export", "-f", "{{.BuildID}}", "strings")
+	buildID := strings.TrimSpace(tg.stdout.String())
+	if buildID == "" {
+		t.Fatalf(".BuildID with -export was empty")
+	}
+
+	tg.run("tool", "buildid", file)
+	toolBuildID := strings.TrimSpace(tg.stdout.String())
+	if buildID != toolBuildID {
+		t.Fatalf(".BuildID with -export %q disagrees with 'go tool buildid' %q", buildID, toolBuildID)
+	}
 }
 
 // Issue 4096. Validate the output of unsuccessful go install foo/quxx.

src/cmd/go/internal/list/list.go

@@ -66,6 +66,7 @@ to -f '{{.ImportPath}}'. The struct being passed to the template is:
         BinaryOnly    bool     // binary-only package (no longer supported)
         ForTest       string   // package is only for use in named test
         Export        string   // file containing export data (when using -export)
+        BuildID       string   // build ID of the export data (when using -export)
         Module        *Module  // info about package's containing module, if any (can be nil)
         Match         []string // command-line patterns matching this package
         DepOnly       bool     // package is only a dependency, not explicitly listed

src/cmd/go/internal/load/pkg.go

@@ -60,6 +60,7 @@ type PackagePublic struct {
 	ConflictDir   string                `json:",omitempty"` // Dir is hidden by this other directory
 	ForTest       string                `json:",omitempty"` // package is only for use in named test
 	Export        string                `json:",omitempty"` // file containing export data (set by go list -export)
+	BuildID       string                `json:",omitempty"` // build ID of the export data (set by go list -export)
 	Module        *modinfo.ModulePublic `json:",omitempty"` // info about package's module, if any
 	Match         []string              `json:",omitempty"` // command-line patterns matching this package
 	Goroot        bool                  `json:",omitempty"` // is this package found in the Go root?

src/cmd/go/internal/work/buildid.go

@@ -713,6 +713,7 @@ func (b *Builder) updateBuildID(a *Action, target string, rewrite bool) error {
 					return err
 				}
 				a.Package.Export = c.OutputFile(outputID)
+				a.Package.BuildID = a.buildID
 			}
 		}
 	}

src/cmd/go/internal/work/exec.go

@@ -433,6 +433,7 @@ func (b *Builder) build(ctx context.Context, a *Action) (err error) {
 			need &^= needBuild
 			if b.NeedExport {
 				p.Export = a.built
+				p.BuildID = a.buildID
 			}
 			if need&needCompiledGoFiles != 0 {
 				if err := b.loadCachedSrcFiles(a); err == nil {