fix(packages): generalize go list diagnostic preference for Go sources

internal/packages/load.go

@@ -257,19 +257,10 @@ 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
-		}
-	}
+	// A go list build diagnostic for this package's Go source is authoritative,
+	// so do not append local parser/type follow-ons or process the recovery AST
+	// as a valid package.
+	hasCompilerDiagnostics := hasGoSourceListDiagnostics(lpkg.Errors, lpkg.CompiledGoFiles)
 
 	appendError := func(err error) {
 		// Convert various error types into the one true Error.
@@ -289,7 +280,7 @@ func loadPackageEx(dedup Deduper, ld *loader, lpkg *loaderPackage) {
 
 		case scanner.ErrorList:
 			// from parser
-			if hasCompilerSyntaxError {
+			if hasCompilerDiagnostics {
 				return
 			}
 			for _, err := range err {
@@ -302,7 +293,7 @@ func loadPackageEx(dedup Deduper, ld *loader, lpkg *loaderPackage) {
 
 		case types.Error:
 			// from type checker
-			if hasCompilerSyntaxError {
+			if hasCompilerDiagnostics {
 				return
 			}
 			lpkg.TypeErrors = append(lpkg.TypeErrors, err)
@@ -632,6 +623,54 @@ func diagnosticFileLine(pos string) (file string, line int, ok bool) {
 	return prefix, last, true
 }
 
+// hasGoSourceListDiagnostics reports whether go list returned a positioned
+// ListError for one of the package's compiled Go files. For example:
+//
+//	# example.com/p
+//	load.go:2: undefined: missing
+//
+// The caller treats that go list block as authoritative and suppresses local
+// parser/type follow-on errors. The CompiledGoFiles check matters because go
+// list also forwards child-tool failures: an asm.s diagnostic must not match a
+// package whose compiled Go source is asm.go.
+func hasGoSourceListDiagnostics(errs []packages.Error, compiledGoFiles []string) bool {
+	for _, err := range errs {
+		if err.Kind != packages.ListError || !strings.HasPrefix(err.Msg, "# ") {
+			continue
+		}
+		for diagnostic := range strings.Lines(err.Msg) {
+			pos, _, ok := strings.Cut(diagnostic, ": ")
+			if !ok {
+				continue
+			}
+			diagnosticFile, _, ok := diagnosticFileLine(pos)
+			if !ok {
+				continue
+			}
+			for _, compiledGoFile := range compiledGoFiles {
+				if sameDiagnosticFile(diagnosticFile, compiledGoFile) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+// sameDiagnosticFile accepts relative suffixes because go list diagnostics may
+// shorten an absolute CompiledGoFiles path. For example, example/load.go
+// matches /tmp/project/example/load.go. Requiring a path separator before the
+// suffix prevents load.go from matching myload.go.
+func sameDiagnosticFile(left, right string) bool {
+	left = filepath.Clean(left)
+	right = filepath.Clean(right)
+	if left == right {
+		return true
+	}
+	return !filepath.IsAbs(left) && strings.HasSuffix(right, string(filepath.Separator)+left) ||
+		!filepath.IsAbs(right) && strings.HasSuffix(left, string(filepath.Separator)+right)
+}
+
 func localVarHasDocComment(file *ast.File, comment *ast.Comment) bool {
 	found := false
 	ast.Inspect(file, func(node ast.Node) bool {

internal/packages/load_test.go

@@ -11,6 +11,8 @@ import (
 	"strconv"
 	"strings"
 	"testing"
+
+	xpackages "golang.org/x/tools/go/packages"
 )
 
 func TestLoadExWithGoVersion(t *testing.T) {
@@ -257,6 +259,28 @@ func f() {
 		}
 	})
 
+	t.Run("compiler type errors are authoritative", func(t *testing.T) {
+		dir := t.TempDir()
+		writeLoadTestFile(t, filepath.Join(dir, "go.mod"), "module example.com/typeerror\ngo 1.24\n")
+		writeLoadTestFile(t, filepath.Join(dir, "load.go"), `package typeerror
+var x = struct{ X int }{Y: 1}
+`)
+		cfg := loadTestConfig(dir)
+		cfg.BuildFlags = []string{"-gcflags=all=-e"}
+		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, "unknown field Y")
+		if len(pkg.Errors) != 1 {
+			t.Fatalf("load returned %d package errors, want the compiler diagnostic only: %+v", len(pkg.Errors), pkg.Errors)
+		}
+	})
+
 	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")
@@ -297,6 +321,68 @@ var x string`)
 
 }
 
+func TestHasGoSourceListDiagnostics(t *testing.T) {
+	goFile := filepath.Join(string(filepath.Separator), "tmp", "example", "load.go")
+	cgoFile := filepath.Join(string(filepath.Separator), "tmp", "example", "cgoerr", "cgo.go")
+	tests := []struct {
+		name            string
+		err             xpackages.Error
+		compiledGoFiles []string
+		want            bool
+	}{
+		{
+			name:            "absolute Go source",
+			err:             xpackages.Error{Kind: xpackages.ListError, Msg: "# example.com/p\n" + goFile + ":2:3: undefined: missing"},
+			compiledGoFiles: []string{goFile},
+			want:            true,
+		},
+		{
+			name:            "relative Go source",
+			err:             xpackages.Error{Kind: xpackages.ListError, Msg: "# example.com/p\nload.go:2: undefined: missing"},
+			compiledGoFiles: []string{goFile},
+			want:            true,
+		},
+		{
+			name:            "different Go source",
+			err:             xpackages.Error{Kind: xpackages.ListError, Msg: "# example.com/p\nother.go:2: undefined: missing"},
+			compiledGoFiles: []string{goFile},
+		},
+		{
+			name: "cgo diagnostic in Go source",
+			err: xpackages.Error{Kind: xpackages.ListError, Msg: `# example.com/diagcompare/cgoerr
+cgoerr/cgo.go:4:2: error: "intentional cgo failure"
+#error "intentional cgo failure"
+ ^
+1 error generated.
+`},
+			compiledGoFiles: []string{cgoFile},
+			want:            true,
+		},
+		{
+			name:            "unpositioned build error",
+			err:             xpackages.Error{Kind: xpackages.ListError, Msg: "# example.com/p\ncompile: internal compiler error"},
+			compiledGoFiles: []string{goFile},
+		},
+		{
+			name:            "metadata list error",
+			err:             xpackages.Error{Kind: xpackages.ListError, Msg: "import cycle not allowed"},
+			compiledGoFiles: []string{goFile},
+		},
+		{
+			name:            "non-list error",
+			err:             xpackages.Error{Kind: xpackages.TypeError, Msg: "# example.com/p\nload.go:2: undefined: missing"},
+			compiledGoFiles: []string{goFile},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := hasGoSourceListDiagnostics([]xpackages.Error{tt.err}, tt.compiledGoFiles); got != tt.want {
+				t.Fatalf("hasGoSourceListDiagnostics() = %t, want %t", got, tt.want)
+			}
+		})
+	}
+}
+
 func loadOnePackage(t *testing.T, dir, goVersion string) *Package {
 	t.Helper()
 	pkgs, err := LoadExWithGoVersion(nil, nil, loadTestConfig(dir), goVersion, ".")

test/goroot/notapplicable.yaml

@@ -91,10 +91,6 @@ not_applicable:
     directive: errorcheck
     case: fixedbugs/issue18419.dir/test.go
     reason: "not applicable: this case asserts cmd/compile-specific -m optimization diagnostics; LLGo uses go/types plus LLVM and does not reproduce gc compiler diagnostic output; supporting this toolchain-specific behavior is not an LLGo compatibility goal"
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/bug388.go
-    reason: "not applicable: this case asserts gc runtime pseudo-type diagnostics; LLGo uses its own runtime and does not expose gc's private compiler diagnostics; supporting this toolchain-specific behavior is not an LLGo compatibility goal"
   - version: go1.26
     directive: errorcheck
     case: escape2.go
@@ -155,10 +151,6 @@ not_applicable:
     directive: errorcheck
     case: escape_map.go
     reason: "not applicable: this case asserts cmd/compile-specific -m escape-analysis diagnostics; LLGo uses go/types plus LLVM and does not reproduce gc compiler diagnostic output; supporting this toolchain-specific behavior is not an LLGo compatibility goal"
-  - version: go1.26
-    directive: errorcheck
-    case: runtime.go
-    reason: "not applicable: this case asserts gc runtime private-symbol compiler diagnostics; LLGo uses its own runtime and does not expose gc's private compiler diagnostics; supporting this toolchain-specific behavior is not an LLGo compatibility goal"
   - version: go1.26
     directive: errorcheck
     case: fixedbugs/notinheap.go

test/goroot/xfail.yaml

@@ -1820,112 +1820,28 @@ flakes:
 xfails:
   - 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: fixedbugs/issue4405.go
-    reason: llgo parser recovery emits additional malformed-statement diagnostics
+    case: fixedbugs/bug299.go
+    reason: preload traverses a malformed parenthesized receiver AST and panics before the authoritative go list diagnostics are emitted
   - version: go1.26
     directive: errorcheck
-    case: syntax/semi4.go
-    reason: llgo parser recovery emits additional semicolon and brace diagnostics
+    case: fixedbugs/issue20789.go
+    reason: preload traverses a parser-recovery receiver AST and panics before the authoritative go list diagnostic is emitted
   - version: go1.26
     directive: errorcheck
-    case: fixedbugs/issue13273.go
-    reason: llgo parser and type checker emit additional channel-direction diagnostics
+    case: fixedbugs/issue5089.go
+    reason: preload assumes the non-local selector receiver is a local named type and panics before the authoritative go list diagnostic is emitted
   - version: go1.26
     directive: errorcheck
-    case: syntax/semi3.go
-    reason: llgo parser recovery emits additional semicolon and end-of-file diagnostics
+    case: fixedbugs/issue4776.go
+    reason: llgo parser uses a different missing-package-clause diagnostic
   - version: go1.26
     directive: errorcheck
     case: fixedbugs/issue13266.go
     reason: llgo parser uses a different malformed-package-clause diagnostic
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue19667.go
-    reason: llgo parser recovery emits additional malformed-call diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/semi2.go
-    reason: llgo parser recovery emits additional semicolon and brace diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue13248.go
-    reason: llgo parser recovery emits additional malformed-expression diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue17328.go
-    reason: llgo parser recovery emits additional end-of-file diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/semi1.go
-    reason: llgo parser recovery emits additional semicolon and end-of-file diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue20789.go
-    reason: llgo parser does not emit the expected malformed-name diagnostic
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/initvar.go
-    reason: llgo parser recovery emits additional invalid-initializer diagnostics
   - version: go1.26
     directive: errorcheck
     case: fixedbugs/bug050.go
     reason: llgo parser emits an additional malformed-declaration diagnostic
-  - version: go1.26
-    directive: errorcheck
-    case: bombad.go
-    reason: llgo parser recovery emits additional byte-order-mark diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/bug435.go
-    reason: llgo parser recovery emits additional end-of-file diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue14006.go
-    reason: llgo parser recovery emits additional malformed-label diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue22581.go
-    reason: llgo parser recovery emits additional malformed-control-clause diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/ddd.go
-    reason: llgo parser recovery emits additional malformed-selector diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/bug121.go
-    reason: llgo parser recovery emits additional malformed-declaration diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/bug228.go
-    reason: llgo parser emits an additional malformed-parameter diagnostic
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/chan1.go
-    reason: llgo parser recovery emits additional malformed-channel diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue18747.go
-    reason: llgo parser recovery emits additional undefined-name diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue11610.go
-    reason: llgo parser reports additional illegal-character diagnostics
-  - version: go1.26
-    directive: errorcheck
-    case: fixedbugs/issue22164.go
-    reason: llgo parser recovery emits additional diagnostics for a malformed argument list
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/vareq1.go
-    reason: llgo parser recovery emits an additional diagnostic after the expected syntax error
-  - version: go1.26
-    directive: errorcheck
-    case: syntax/vareq.go
-    reason: llgo parser recovery emits additional diagnostics after the expected syntax error
   - version: go1.24
     platform: darwin/arm64
     directive: run