cmd/go: don't print cached output for non-build list commands

If a user is running a go list command that wouldn't trigger a build
(for example if -export was passed), don't print the cached stdout
outputs for previous builds of the artifacts.

Fixes #56375

Change-Id: I1d3e6c01d0eb3dada941bb2783ce2ac69aa3d5d2
Reviewed-on: https://go-review.googlesource.com/c/go/+/444836
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>

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

@@ -397,7 +397,7 @@ func (b *Builder) fileHash(file string) string {
 // during a's work. The caller should defer b.flushOutput(a), to make sure
 // that flushOutput is eventually called regardless of whether the action
 // succeeds. The flushOutput call must happen after updateBuildID.
-func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string) bool {
+func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string, printOutput bool) bool {
 	// The second half of the build ID here is a placeholder for the content hash.
 	// It's important that the overall buildID be unlikely verging on impossible
 	// to appear in the output by chance, but that should be taken care of by
@@ -462,10 +462,12 @@ func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string)
 					// Best effort attempt to display output from the compile and link steps.
 					// If it doesn't work, it doesn't work: reusing the cached binary is more
 					// important than reprinting diagnostic information.
+					if printOutput {
 						if c := cache.Default(); c != nil {
 							showStdout(b, c, a.actionID, "stdout")      // compile output
 							showStdout(b, c, a.actionID, "link-stdout") // link output
 						}
+					}
 
 					// Poison a.Target to catch uses later in the build.
 					a.Target = "DO NOT USE - main build pseudo-cache Target"
@@ -490,10 +492,12 @@ func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string)
 		// Best effort attempt to display output from the compile and link steps.
 		// If it doesn't work, it doesn't work: reusing the test result is more
 		// important than reprinting diagnostic information.
+		if printOutput {
 			if c := cache.Default(); c != nil {
 				showStdout(b, c, a.Deps[0].actionID, "stdout")      // compile output
 				showStdout(b, c, a.Deps[0].actionID, "link-stdout") // link output
 			}
+		}
 
 		// Poison a.Target to catch uses later in the build.
 		a.Target = "DO NOT USE -  pseudo-cache Target"
@@ -536,7 +540,9 @@ func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string)
 		if !cfg.BuildA {
 			if file, _, err := c.GetFile(actionHash); err == nil {
 				if buildID, err := buildid.ReadFile(file); err == nil {
-					if err := showStdout(b, c, a.actionID, "stdout"); err == nil {
+					if printOutput {
+						showStdout(b, c, a.actionID, "stdout")
+					}
 					a.built = file
 					a.Target = "DO NOT USE - using cache"
 					a.buildID = buildID
@@ -551,7 +557,6 @@ func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string)
 				}
 			}
 		}
-		}
 
 		// Begin saving output for later writing to cache.
 		a.output = []byte{}

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

@@ -479,7 +479,7 @@ func (b *Builder) build(ctx context.Context, a *Action) (err error) {
 		bit(needCompiledGoFiles, b.NeedCompiledGoFiles)
 
 	if !p.BinaryOnly {
-		if b.useCache(a, b.buildActionID(a), p.Target) {
+		if b.useCache(a, b.buildActionID(a), p.Target, need&needBuild != 0) {
 			// We found the main output in the cache.
 			// If we don't need any other outputs, we can stop.
 			// Otherwise, we need to write files to a.Objdir (needVet, needCgoHdr).
@@ -1384,7 +1384,7 @@ func (b *Builder) printLinkerConfig(h io.Writer, p *load.Package) {
 // link is the action for linking a single command.
 // Note that any new influence on this logic must be reported in b.linkActionID above as well.
 func (b *Builder) link(ctx context.Context, a *Action) (err error) {
-	if b.useCache(a, b.linkActionID(a), a.Package.Target) || b.IsCmdList {
+	if b.useCache(a, b.linkActionID(a), a.Package.Target, !b.IsCmdList) || b.IsCmdList {
 		return nil
 	}
 	defer b.flushOutput(a)
@@ -1626,7 +1626,7 @@ func (b *Builder) linkSharedActionID(a *Action) cache.ActionID {
 }
 
 func (b *Builder) linkShared(ctx context.Context, a *Action) (err error) {
-	if b.useCache(a, b.linkSharedActionID(a), a.Target) || b.IsCmdList {
+	if b.useCache(a, b.linkSharedActionID(a), a.Target, !b.IsCmdList) || b.IsCmdList {
 		return nil
 	}
 	defer b.flushOutput(a)

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

@@ -0,0 +1,16 @@
+[short] skip
+
+go install -gcflags=-m .
+stderr 'can inline main'
+go list -gcflags=-m -f '{{.Stale}}' .
+stdout 'false'
+! stderr 'can inline main'
+
+-- go.mod --
+module example.com/foo
+
+go 1.20
+-- main.go --
+package main
+
+func main() {}