cmd/go: track root failing Action

Currently, each Action tracks whether it failed, which is propagated
up from dependencies. Shortly, we'll need to know the root cause if a
test fails because of a build failure. To support this, replace the
Failed boolean with a Failed *Action that tracks the root Action that
failed and caused other Actions to fail.

For #62067.

Change-Id: I8f84a51067354043ae9531a4368c6f8b11d688d5
Reviewed-on: https://go-review.googlesource.com/c/go/+/536398
Reviewed-by: Russ Cox <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: aclements

src/cmd/go/internal/test/test.go

@@ -1387,9 +1387,9 @@ func (r *runTestActor) Act(b *work.Builder, ctx context.Context, a *work.Action)
 	// Release next test to start (test2json.NewConverter writes the start event).
 	close(r.next)
 
-	if a.Failed {
+	if a.Failed != nil {
 		// We were unable to build the binary.
-		a.Failed = false
+		a.Failed = nil
 		fmt.Fprintf(stdout, "FAIL\t%s [build failed]\n", a.Package.ImportPath)
 		// Tell the JSON converter that this was a failure, not a passing run.
 		err = errors.New("build failed")

src/cmd/go/internal/work/action.go

@@ -110,7 +110,7 @@ type Action struct {
 	// Execution state.
 	pending      int               // number of deps yet to complete
 	priority     int               // relative execution priority
-	Failed       bool              // whether the action failed
+	Failed       *Action           // set to root cause if the action failed
 	json         *actionJSON       // action graph information
 	nonGoOverlay map[string]string // map from non-.go source files to copied files in objdir. Nil if no overlay is used.
 	traceSpan    *trace.Span
@@ -218,7 +218,7 @@ func actionGraphJSON(a *Action) string {
 				Args:       a.Args,
 				Objdir:     a.Objdir,
 				Target:     a.Target,
-				Failed:     a.Failed,
+				Failed:     a.Failed != nil,
 				Priority:   a.priority,
 				Built:      a.built,
 				VetxOnly:   a.VetxOnly,

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

@@ -138,7 +138,7 @@ func (b *Builder) Do(ctx context.Context, root *Action) {
 			a.json.TimeStart = time.Now()
 		}
 		var err error
-		if a.Actor != nil && (!a.Failed || a.IgnoreFail) {
+		if a.Actor != nil && (a.Failed == nil || a.IgnoreFail) {
 			// TODO(matloob): Better action descriptions
 			desc := "Executing action (" + a.Mode
 			if a.Package != nil {
@@ -176,12 +176,14 @@ func (b *Builder) Do(ctx context.Context, root *Action) {
 				sh := b.Shell(a)
 				sh.Errorf("%s", err)
 			}
-			a.Failed = true
+			if a.Failed == nil {
+				a.Failed = a
+			}
 		}
 
 		for _, a0 := range a.triggers {
-			if a.Failed {
-				a0.Failed = true
+			if a.Failed != nil {
+				a0.Failed = a.Failed
 			}
 			if a0.pending--; a0.pending == 0 {
 				b.ready.push(a0)
@@ -1242,9 +1244,9 @@ func (b *Builder) vet(ctx context.Context, a *Action) error {
 	// a.Deps[0] is the build of the package being vetted.
 	// a.Deps[1] is the build of the "fmt" package.
 
-	a.Failed = false // vet of dependency may have failed but we can still succeed
+	a.Failed = nil // vet of dependency may have failed but we can still succeed
 
-	if a.Deps[0].Failed {
+	if a.Deps[0].Failed != nil {
 		// The build of the package has failed. Skip vet check.
 		// Vet could return export data for non-typecheck errors,
 		// but we ignore it because the package cannot be compiled.