Merge pull request #2274 from MeteorsLiu/fix/goroot-authoritative-syntax-diagnostics

fix: prefer compiler syntax diagnostics

Author: cpunion

internal/packages/load.go

@@ -257,6 +257,20 @@ func loadPackageEx(dedup Deduper, ld *loader, lpkg *loaderPackage) {
 		return // not a source package, don't get syntax trees
 	}
 
+	// go list has already captured cmd/compile's authoritative diagnostics in
+	// this block. For example, an unexpected else stops gc before recovery AST
+	// errors are reported, so do not append the local parser/type follow-ons.
+	hasCompilerSyntaxError := false
+	for _, err := range lpkg.Errors {
+		if err.Kind != packages.ListError || !strings.HasPrefix(err.Msg, "# ") {
+			continue
+		}
+		if _, diagnostics, ok := strings.Cut(err.Msg, "\n"); ok && strings.Contains(diagnostics, ": syntax error: ") {
+			hasCompilerSyntaxError = true
+			break
+		}
+	}
+
 	appendError := func(err error) {
 		// Convert various error types into the one true Error.
 		var errs []packages.Error
@@ -275,6 +289,9 @@ func loadPackageEx(dedup Deduper, ld *loader, lpkg *loaderPackage) {
 
 		case scanner.ErrorList:
 			// from parser
+			if hasCompilerSyntaxError {
+				return
+			}
 			for _, err := range err {
 				errs = append(errs, packages.Error{
 					Pos:  err.Pos.String(),
@@ -285,6 +302,9 @@ func loadPackageEx(dedup Deduper, ld *loader, lpkg *loaderPackage) {
 
 		case types.Error:
 			// from type checker
+			if hasCompilerSyntaxError {
+				return
+			}
 			lpkg.TypeErrors = append(lpkg.TypeErrors, err)
 			errs = append(errs, packages.Error{
 				Pos:  err.Fset.Position(err.Pos).String(),

internal/packages/load_test.go

@@ -229,6 +229,34 @@ func TestEmbedDiagnosticHelperBoundaries(t *testing.T) {
 }
 
 func TestLoadExNormalizesFrontendDiagnostics(t *testing.T) {
+	t.Run("compiler syntax errors are authoritative", func(t *testing.T) {
+		dir := t.TempDir()
+		writeLoadTestFile(t, filepath.Join(dir, "go.mod"), "module example.com/syntaxerror\ngo 1.24\n")
+		writeLoadTestFile(t, filepath.Join(dir, "load.go"), `package syntaxerror
+func f() {
+	if missing {}
+	else {}
+}
+`)
+		cfg := loadTestConfig(dir)
+		cfg.BuildFlags = []string{"-gcflags=all=-e"}
+		cfg.ParseFile = func(fset *token.FileSet, filename string, src []byte) (*ast.File, error) {
+			return parser.ParseFile(fset, filename, src, parser.AllErrors|parser.ParseComments)
+		}
+		pkgs, err := LoadExWithGoVersion(nil, nil, cfg, "go1.24", ".")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(pkgs) != 1 {
+			t.Fatalf("load returned %d packages, want 1", len(pkgs))
+		}
+		pkg := pkgs[0]
+		assertPackageError(t, pkg, "syntax error:")
+		for _, secondary := range []string{"expected statement", "found 'EOF'", "undefined: missing"} {
+			assertPackageErrorAbsent(t, pkg, secondary)
+		}
+	})
+
 	t.Run("embed local var", func(t *testing.T) {
 		dir := t.TempDir()
 		writeLoadTestFile(t, filepath.Join(dir, "go.mod"), "module example.com/embedlocal\ngo 1.24\n")

test/goroot/xfail.yaml

@@ -1818,54 +1818,10 @@ flakes:
     case: fixedbugs/issue25897a.go
     reason: reflect-generated goroutines under a single-P continuous-GC loop can complete or exceed the 1m run timeout on darwin/arm64
 xfails:
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue23664.go
-    reason: llgo parser recovery emits additional malformed-declaration diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue33386.go
-    reason: llgo parser recovery emits additional malformed-go/defer diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/bug349.go
-    reason: llgo parser recovery emits additional return-value diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue23587.go
-    reason: llgo parser recovery emits additional invalid-tilde diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/semi7.go
-    reason: llgo parser recovery emits additional semicolon and else diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/bug274.go
-    reason: llgo parser recovery emits additional case and label diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue18092.go
-    reason: llgo parser recovery emits additional malformed-channel diagnostics
   - version: go1.26
     directive: errorcheck
     case: fixedbugs/issue4776.go
     reason: llgo parser uses a different missing-package-clause diagnostic
-  - version: go1.26
-    directive: errorcheck
-    case: switch2.go
-    reason: llgo parser recovery emits additional malformed-switch diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue13319.go
-    reason: llgo parser recovery emits additional malformed-call diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/semi5.go
-    reason: llgo parser recovery emits additional semicolon and end-of-file diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue13274.go
-    reason: llgo parser emits an additional end-of-file diagnostic
   - version: go1.26
     directive: errorcheck
     case: fixedbugs/issue4405.go