Merge pull request #10 from srosenberg/sr/capture_go_build_output

Couple of small internal "debug UX" improvements owing to [1],

gcassert.go

@@ -158,7 +158,7 @@ func GCAssert(w io.Writer, paths ...string) error {
 	// Next: invoke Go compiler with -m flags to get the compiler to print
 	// its optimization decisions.
 
-	args := []string{"build", "-gcflags=-m -m -d=ssa/check_bce/debug=1"}
+	args := []string{"build", "-gcflags=-m=2 -d=ssa/check_bce/debug=1"}
 	for i := range paths {
 		args = append(args, "./"+paths[i])
 	}
@@ -169,12 +169,23 @@ func GCAssert(w io.Writer, paths ...string) error {
 	}
 	cmd.Dir = cwd
 	pr, pw := io.Pipe()
-	cmd.Stdout = pw
-	cmd.Stderr = pw
+	// Create a temp file to log all diagnostic output.
+	f, err := os.CreateTemp("", "gcassert-*.log")
+	if err != nil {
+		return err
+	}
+	fmt.Printf("See %s for full output.\n", f.Name())
+	// Log full 'go build' command.
+	fmt.Fprintln(f, cmd)
+	mw := io.MultiWriter(pw, f)
+	cmd.Stdout = mw
+	cmd.Stderr = mw
 	cmdErr := make(chan error, 1)
+
 	go func() {
 		cmdErr <- cmd.Run()
-		pw.Close()
+		_ = pw.Close()
+		_ = f.Close()
 	}()
 
 	scanner := bufio.NewScanner(pr)
@@ -284,6 +295,10 @@ func GCAssert(w io.Writer, paths ...string) error {
 			}
 		}
 	}
+	// If 'go build' failed, return the error.
+	if err := <-cmdErr; err != nil {
+		return err
+	}
 	return nil
 }
 

gcassert_test.go

@@ -64,9 +64,9 @@ func TestParseDirectives(t *testing.T) {
 		"testdata/noescape.go": {
 			21: {directives: []assertDirective{noescape}},
 			28: {directives: []assertDirective{noescape}},
-			34: {directives: []assertDirective{noescape}},
-			41: {directives: []assertDirective{noescape}},
-			44: {directives: []assertDirective{noescape}},
+			35: {directives: []assertDirective{noescape}},
+			42: {directives: []assertDirective{noescape}},
+			45: {directives: []assertDirective{noescape}},
 		},
 		"testdata/issue5.go": {
 			4: {inlinableCallsites: []passInfo{{colNo: 14}}},
@@ -83,13 +83,14 @@ func TestGCAssert(t *testing.T) {
 	}
 
 	expectedOutput := `testdata/noescape.go:21:	foo := foo{a: 1, b: 2}: foo escapes to heap:
-testdata/noescape.go:34:	// This annotation should fail, because f will escape to the heap.
+testdata/noescape.go:35:	// This annotation should fail, because f will escape to the heap.
+//
 //gcassert:noescape
 func (f foo) setA(a int) *foo {
 	f.a = a
 	return &f
 }: f escapes to heap:
-testdata/noescape.go:44:	: a escapes to heap:
+testdata/noescape.go:45:	: a escapes to heap:
 testdata/bce.go:8:	fmt.Println(ints[5]): Found IsInBounds
 testdata/bce.go:17:	sum += notInlinable(ints[i]): call was not inlined
 testdata/bce.go:19:	sum += notInlinable(ints[i]): call was not inlined

testdata/issue5.go

@@ -13,6 +13,7 @@ func Gen() S {
 // Gen().Layout() has another inlined function in it, Gen().
 
 //gcassert:inline
+//go:noinline
 func (s S) Layout() {
 	select {}
 }

testdata/noescape.go

@@ -30,6 +30,7 @@ func returnsStackVar() foo {
 }
 
 // This annotation should fail, because f will escape to the heap.
+//
 //gcassert:noescape
 func (f foo) setA(a int) *foo {
     f.a = a