go.tools/go/types: implement label checks

R=adonovan
CC=golang-dev
https://golang.org/cl/14036046

go/types/api.go

@@ -121,8 +121,6 @@ type Info struct {
 	// in package clauses, blank identifiers on the lhs of assignments, or
 	// symbolic variables t in t := x.(type) of type switch headers), the
 	// corresponding objects are nil.
-	// BUG(gri) Label identifiers in break, continue, or goto statements
-	// are not yet mapped.
 	Objects map[*ast.Ident]Object
 
 	// Implicits maps nodes to their implicitly declared objects, if any.
@@ -184,6 +182,5 @@ func IsAssignableTo(V, T Type) bool {
 }
 
 // BUG(gri): Some built-ins don't check parameters fully, yet (e.g. append).
-// BUG(gri): Use of labels is only partially checked.
 // BUG(gri): Interface vs non-interface comparisons are not correctly implemented.
 // BUG(gri): Switch statements don't check duplicate cases for all types for which it is required.

go/types/check_test.go

@@ -66,6 +66,8 @@ var tests = [][]string{
 	{"testdata/conversions.src"},
 	{"testdata/stmt0.src"},
 	{"testdata/stmt1.src"},
+	{"testdata/gotos.src"},
+	{"testdata/labels.src"},
 }
 
 var fset = token.NewFileSet()

go/types/labels.go

@@ -0,0 +1,265 @@
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+// labels checks correct label use in body.
+func (check *checker) labels(body *ast.BlockStmt) {
+	// set of all labels in this body
+	all := NewScope(nil)
+
+	fwdJumps := check.blockBranches(all, nil, nil, body.List)
+
+	// If there are any forward jumps left, no label was found for
+	// the corresponding goto statements. Either those labels were
+	// never defined, or they are inside blocks and not reachable
+	// for the respective gotos.
+	for _, jmp := range fwdJumps {
+		var msg string
+		name := jmp.Label.Name
+		if alt := all.Lookup(name); alt != nil {
+			msg = "goto %s jumps into block"
+			alt.(*Label).used = true // avoid another error
+		} else {
+			msg = "label %s not declared"
+		}
+		check.errorf(jmp.Label.Pos(), msg, name)
+	}
+
+	// spec: "It is illegal to define a label that is never used."
+	for _, obj := range all.elems {
+		if lbl := obj.(*Label); !lbl.used {
+			check.errorf(lbl.pos, "label %s declared but not used", lbl.name)
+		}
+	}
+}
+
+// A block tracks label declarations in a block and its enclosing blocks.
+type block struct {
+	parent *block                      // enclosing block
+	lstmt  *ast.LabeledStmt            // labeled statement to which this block belongs, or nil
+	labels map[string]*ast.LabeledStmt // allocated lazily
+}
+
+// insert records a new label declaration for the current block.
+// The label must not have been declared before in any block.
+func (b *block) insert(s *ast.LabeledStmt) {
+	name := s.Label.Name
+	if debug {
+		assert(b.gotoTarget(name) == nil)
+	}
+	labels := b.labels
+	if labels == nil {
+		labels = make(map[string]*ast.LabeledStmt)
+		b.labels = labels
+	}
+	labels[name] = s
+}
+
+// gotoTarget returns the labeled statement in the current
+// or an enclosing block with the given label name, or nil.
+func (b *block) gotoTarget(name string) *ast.LabeledStmt {
+	for s := b; s != nil; s = s.parent {
+		if t := s.labels[name]; t != nil {
+			return t
+		}
+	}
+	return nil
+}
+
+// enclosingTarget returns the innermost enclosing labeled
+// statement with the given label name, or nil.
+func (b *block) enclosingTarget(name string) *ast.LabeledStmt {
+	for s := b; s != nil; s = s.parent {
+		if t := s.lstmt; t != nil && t.Label.Name == name {
+			return t
+		}
+	}
+	return nil
+}
+
+// blockBranches processes a block's statement list and returns the set of outgoing forward jumps.
+// all is the scope of all declared labels, parent the set of labels declared in the immediately
+// enclosing block, and lstmt is the labeled statement this block is associated with (or nil).
+func (check *checker) blockBranches(all *Scope, parent *block, lstmt *ast.LabeledStmt, list []ast.Stmt) []*ast.BranchStmt {
+	b := &block{parent: parent, lstmt: lstmt}
+
+	var (
+		varDeclPos         token.Pos
+		fwdJumps, badJumps []*ast.BranchStmt
+	)
+
+	// All forward jumps jumping over a variable declaration are possibly
+	// invalid (they may still jump out of the block and be ok).
+	// recordVarDecl records them for the given position.
+	recordVarDecl := func(pos token.Pos) {
+		varDeclPos = pos
+		badJumps = append(badJumps[:0], fwdJumps...) // copy fwdJumps to badJumps
+	}
+
+	jumpsOverVarDecl := func(jmp *ast.BranchStmt) bool {
+		if varDeclPos.IsValid() {
+			for _, bad := range badJumps {
+				if jmp == bad {
+					return true
+				}
+			}
+		}
+		return false
+	}
+
+	var stmtBranches func(ast.Stmt)
+	stmtBranches = func(s ast.Stmt) {
+		switch s := s.(type) {
+		case *ast.DeclStmt:
+			if d, _ := s.Decl.(*ast.GenDecl); d != nil && d.Tok == token.VAR {
+				recordVarDecl(d.Pos())
+			}
+
+		case *ast.LabeledStmt:
+			// declare label
+			name := s.Label.Name
+			lbl := NewLabel(s.Label.Pos(), name)
+			if alt := all.Insert(lbl); alt != nil {
+				check.errorf(lbl.pos, "label %s already declared", name)
+				check.reportAltDecl(alt)
+				// ok to continue
+			} else {
+				b.insert(s)
+				check.recordObject(s.Label, lbl)
+			}
+			// resolve matching forward jumps and remove them from fwdJumps
+			i := 0
+			for _, jmp := range fwdJumps {
+				if jmp.Label.Name == name {
+					// match
+					lbl.used = true
+					check.recordObject(jmp.Label, lbl)
+					if jumpsOverVarDecl(jmp) {
+						check.errorf(
+							jmp.Label.Pos(),
+							"goto %s jumps over variable declaration at line %d",
+							name,
+							check.fset.Position(varDeclPos).Line,
+						)
+						// ok to continue
+					}
+				} else {
+					// no match - record new forward jump
+					fwdJumps[i] = jmp
+					i++
+				}
+			}
+			fwdJumps = fwdJumps[:i]
+			lstmt = s
+			stmtBranches(s.Stmt)
+
+		case *ast.BranchStmt:
+			if s.Label == nil {
+				return // checked in 1st pass (check.stmt)
+			}
+
+			// determine and validate target
+			name := s.Label.Name
+			switch s.Tok {
+			case token.BREAK:
+				// spec: "If there is a label, it must be that of an enclosing
+				// "for", "switch", or "select" statement, and that is the one
+				// whose execution terminates."
+				t := b.enclosingTarget(name)
+				if t == nil {
+					check.errorf(s.Label.Pos(), "break label not declared: %s", name)
+					return
+				}
+				switch t.Stmt.(type) {
+				case *ast.SwitchStmt, *ast.TypeSwitchStmt, *ast.SelectStmt, *ast.ForStmt, *ast.RangeStmt:
+					// ok
+				default:
+					check.errorf(s.Label.Pos(), "invalid break label %s", name)
+					// continue and mark label as used to avoid another error
+				}
+
+			case token.CONTINUE:
+				// spec: "If there is a label, it must be that of an enclosing
+				// "for" statement, and that is the one whose execution advances."
+				t := b.enclosingTarget(name)
+				if t == nil {
+					check.errorf(s.Label.Pos(), "continue label not declared: %s", name)
+					return
+				}
+				switch t.Stmt.(type) {
+				case *ast.ForStmt, *ast.RangeStmt:
+					// ok
+				default:
+					check.errorf(s.Label.Pos(), "invalid continue label %s", name)
+					// continue and mark label as used to avoid another error
+				}
+
+			case token.GOTO:
+				if b.gotoTarget(name) == nil {
+					// label may be declared later - add to forward jumps
+					fwdJumps = append(fwdJumps, s)
+					return
+				}
+
+			default:
+				check.invalidAST(s.Pos(), "branch statement: %s %s", s.Tok, name)
+				return
+			}
+
+			// record label use
+			obj := all.Lookup(name)
+			obj.(*Label).used = true
+			check.recordObject(s.Label, obj)
+
+		case *ast.AssignStmt:
+			if s.Tok == token.DEFINE {
+				recordVarDecl(s.Pos())
+			}
+
+		case *ast.BlockStmt:
+			// Unresolved forward jumps inside the nested block
+			// become forward jumps in the current block.
+			fwdJumps = append(fwdJumps, check.blockBranches(all, b, lstmt, s.List)...)
+
+		case *ast.IfStmt:
+			stmtBranches(s.Body)
+			if s.Else != nil {
+				stmtBranches(s.Else)
+			}
+
+		case *ast.CaseClause:
+			fwdJumps = append(fwdJumps, check.blockBranches(all, b, nil, s.Body)...)
+
+		case *ast.SwitchStmt:
+			stmtBranches(s.Body)
+
+		case *ast.TypeSwitchStmt:
+			stmtBranches(s.Body)
+
+		case *ast.CommClause:
+			fwdJumps = append(fwdJumps, check.blockBranches(all, b, nil, s.Body)...)
+
+		case *ast.SelectStmt:
+			stmtBranches(s.Body)
+
+		case *ast.ForStmt:
+			stmtBranches(s.Body)
+
+		case *ast.RangeStmt:
+			stmtBranches(s.Body)
+		}
+	}
+
+	for _, s := range list {
+		stmtBranches(s)
+	}
+
+	return fwdJumps
+}

go/types/resolver.go

@@ -385,6 +385,10 @@ func (check *checker) resolveFiles(files []*ast.File) {
 
 	// Note: funcList may grow while iterating through it - cannot use range clause.
 	for i := 0; i < len(check.funcList); i++ {
+		// TODO(gri) Factor out this code into a dedicated function
+		// with its own context so that it can be run concurrently
+		// eventually.
+
 		f := check.funcList[i]
 		if trace {
 			s := "<function literal>"
@@ -400,7 +404,7 @@ func (check *checker) resolveFiles(files []*ast.File) {
 		check.stmtList(0, f.body.List)
 
 		if check.hasLabel {
-			// TODO(gri) check label use
+			check.labels(f.body)
 		}
 
 		if f.sig.results.Len() > 0 && !check.isTerminating(f.body, "") {

go/types/resolver_test.go

@@ -60,6 +60,21 @@ var sources = []string{
 	func (T) _() {}
 	func (T) _() {}
 	`,
+	`
+	package p
+	func _() {
+	L0:
+	L1:
+		goto L0
+		for {
+			goto L1
+		}
+		if true {
+			goto L2
+		}
+	L2:
+	}
+	`,
 }
 
 var pkgnames = []string{

go/types/stdlib_test.go

@@ -117,8 +117,7 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 
 func TestStdtest(t *testing.T) {
 	testTestDir(t, filepath.Join(runtime.GOROOT(), "test"),
-		"cmplxdivide.go",                   // also needs file cmplxdivide1.go - ignore
+		"cmplxdivide.go",          // also needs file cmplxdivide1.go - ignore
-		"goto.go", "label.go", "label1.go", // TODO(gri) implement missing label checks
 		"mapnan.go", "sigchld.go", // don't work on Windows; testTestDir should consult build tags
 		"sizeof.go", "switch.go", // TODO(gri) tone down duplicate checking in expr switches
 		"typeswitch2.go", // TODO(gri) implement duplicate checking in type switches

go/types/stmt.go

@@ -243,7 +243,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 	case *ast.BranchStmt:
 		if s.Label != nil {
 			check.hasLabel = true
-			return // checks handled in separate pass
+			return // checked in 2nd pass (check.labels)
 		}
 		switch s.Tok {
 		case token.BREAK:
@@ -254,14 +254,12 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 			if ctxt&inContinuable == 0 {
 				check.errorf(s.Pos(), "continue not in for statement")
 			}
-		case token.GOTO:
-			check.invalidAST(s.Pos(), "goto without label")
 		case token.FALLTHROUGH:
 			if ctxt&fallthroughOk == 0 {
 				check.errorf(s.Pos(), "fallthrough statement out of place")
 			}
 		default:
-			check.invalidAST(s.Pos(), "unknown branch statement (%s)", s.Tok)
+			check.invalidAST(s.Pos(), "branch statement: %s", s.Tok)
 		}
 
 	case *ast.BlockStmt:

go/types/testdata/gotos.src

@@ -0,0 +1,560 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is a modified copy of $GOROOT/test/goto.go.
+
+package gotos
+
+var (
+	i, n int
+	x    []int
+	c    chan int
+	m    map[int]int
+	s    string
+)
+
+// goto after declaration okay
+func _() {
+	x := 1
+	goto L
+L:
+	_ = x
+}
+
+// goto before declaration okay
+func _() {
+	goto L
+L:
+	x := 1
+	_ = x
+}
+
+// goto across declaration not okay
+func _() {
+	goto L /* ERROR "goto L jumps over variable declaration at line 36" */
+	x := 1
+	_ = x
+L:
+}
+
+// goto across declaration in inner scope okay
+func _() {
+	goto L
+	{
+		x := 1
+		_ = x
+	}
+L:
+}
+
+// goto across declaration after inner scope not okay
+func _() {
+	goto L /* ERROR "goto L jumps over variable declaration at line 58" */
+	{
+		x := 1
+		_ = x
+	}
+	x := 1
+	_ = x
+L:
+}
+
+// goto across declaration in reverse okay
+func _() {
+L:
+	x := 1
+	_ = x
+	goto L
+}
+
+func _() {
+L: L1:
+	x := 1
+	_ = x
+	goto L
+	goto L1
+}
+
+// error shows first offending variable
+func _() {
+	goto L /* ERROR "goto L jumps over variable declaration at line 84" */
+	x := 1
+	_ = x
+	y := 1
+	_ = y
+L:
+}
+
+// goto not okay even if code path is dead
+func _() {
+	goto L /* ERROR "goto L jumps over variable declaration" */
+	x := 1
+	_ = x
+	y := 1
+	_ = y
+	return
+L:
+}
+
+// goto into outer block okay
+func _() {
+	{
+		goto L
+	}
+L:
+}
+
+func _() {
+	{
+		goto L
+		goto L1
+	}
+L: L1:
+}
+
+// goto backward into outer block okay
+func _() {
+L:
+	{
+		goto L
+	}
+}
+
+func _() {
+L: L1:
+	{
+		goto L
+		goto L1
+	}
+}
+
+// goto into inner block not okay
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	{
+	L:
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	goto L1 /* ERROR "goto L1 jumps into block" */
+	{
+	L: L1:
+	}
+}
+
+// goto backward into inner block still not okay
+func _() {
+	{
+	L:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+}
+
+func _() {
+	{
+	L: L1:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+	goto L1 /* ERROR "goto L1 jumps into block" */
+}
+
+// error shows first (outermost) offending block
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	{
+		{
+			{
+			L:
+			}
+		}
+	}
+}
+
+// error prefers block diagnostic over declaration diagnostic
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	x := 1
+	_ = x
+	{
+	L:
+	}
+}
+
+// many kinds of blocks, all invalid to jump into or among,
+// but valid to jump out of
+
+// if
+
+func _() {
+L:
+	if true {
+		goto L
+	}
+}
+
+func _() {
+L:
+	if true {
+		goto L
+	} else {
+	}
+}
+
+func _() {
+L:
+	if false {
+	} else {
+		goto L
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	if true {
+	L:
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	if true {
+	L:
+	} else {
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	if true {
+	} else {
+	L:
+	}
+}
+
+func _() {
+	if false {
+	L:
+	} else {
+		goto L /* ERROR "goto L jumps into block" */
+	}
+}
+
+func _() {
+	if true {
+		goto L /* ERROR "goto L jumps into block" */
+	} else {
+	L:
+	}
+}
+
+func _() {
+	if true {
+		goto L /* ERROR "goto L jumps into block" */
+	} else if false {
+	L:
+	}
+}
+
+func _() {
+	if true {
+		goto L /* ERROR "goto L jumps into block" */
+	} else if false {
+	L:
+	} else {
+	}
+}
+
+func _() {
+	if true {
+		goto L /* ERROR "goto L jumps into block" */
+	} else if false {
+	} else {
+	L:
+	}
+}
+
+func _() {
+	if true {
+		goto L /* ERROR "goto L jumps into block" */
+	} else {
+		L:
+	}
+}
+
+func _() {
+	if true {
+		L:
+	} else {
+		goto L /* ERROR "goto L jumps into block" */
+	}
+}
+
+// for
+
+func _() {
+	for {
+		goto L
+	}
+L:
+}
+
+func _() {
+	for {
+		goto L
+	L:
+	}
+}
+
+func _() {
+	for {
+	L:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+}
+
+func _() {
+	for {
+		goto L
+	L1:
+	}
+L:
+	goto L1 /* ERROR "goto L1 jumps into block" */
+}
+
+func _() {
+	for i < n {
+	L:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+}
+
+func _() {
+	for i = 0; i < n; i++ {
+	L:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+}
+
+func _() {
+	for i = range x {
+	L:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+}
+
+func _() {
+	for i = range c {
+	L:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+}
+
+func _() {
+	for i = range m {
+	L:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+}
+
+func _() {
+	for i = range s {
+	L:
+	}
+	goto L /* ERROR "goto L jumps into block" */
+}
+
+// switch
+
+func _() {
+L:
+	switch i {
+	case 0:
+		goto L
+	}
+}
+
+func _() {
+L:
+	switch i {
+	case 0:
+
+	default:
+		goto L
+	}
+}
+
+func _() {
+	switch i {
+	case 0:
+
+	default:
+	L:
+		goto L
+	}
+}
+
+func _() {
+	switch i {
+	case 0:
+
+	default:
+		goto L
+	L:
+	}
+}
+
+func _() {
+	switch i {
+	case 0:
+		goto L
+	L:
+		;
+	default:
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	switch i {
+	case 0:
+	L:
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	switch i {
+	case 0:
+	L:
+		;
+	default:
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	switch i {
+	case 0:
+	default:
+	L:
+	}
+}
+
+func _() {
+	switch i {
+	default:
+		goto L /* ERROR "goto L jumps into block" */
+	case 0:
+	L:
+	}
+}
+
+func _() {
+	switch i {
+	case 0:
+	L:
+		;
+	default:
+		goto L /* ERROR "goto L jumps into block" */
+	}
+}
+
+// select
+// different from switch.  the statement has no implicit block around it.
+
+func _() {
+L:
+	select {
+	case <-c:
+		goto L
+	}
+}
+
+func _() {
+L:
+	select {
+	case c <- 1:
+
+	default:
+		goto L
+	}
+}
+
+func _() {
+	select {
+	case <-c:
+
+	default:
+	L:
+		goto L
+	}
+}
+
+func _() {
+	select {
+	case c <- 1:
+
+	default:
+		goto L
+	L:
+	}
+}
+
+func _() {
+	select {
+	case <-c:
+		goto L
+	L:
+		;
+	default:
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	select {
+	case c <- 1:
+	L:
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	select {
+	case c <- 1:
+	L:
+		;
+	default:
+	}
+}
+
+func _() {
+	goto L /* ERROR "goto L jumps into block" */
+	select {
+	case <-c:
+	default:
+	L:
+	}
+}
+
+func _() {
+	select {
+	default:
+		goto L /* ERROR "goto L jumps into block" */
+	case <-c:
+	L:
+	}
+}
+
+func _() {
+	select {
+	case <-c:
+	L:
+		;
+	default:
+		goto L /* ERROR "goto L jumps into block" */
+	}
+}

go/types/testdata/labels.src

@@ -0,0 +1,144 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is a modified concatenation of the files
+// $GOROOT/test/label.go and $GOROOT/test/label1.go.
+
+package labels
+
+var x int
+
+func f0() {
+L1 /* ERROR "label L1 declared but not used" */ :
+	for {
+	}
+L2 /* ERROR "label L2 declared but not used" */ :
+	select {
+	}
+L3 /* ERROR "label L3 declared but not used" */ :
+	switch {
+	}
+L4 /* ERROR "label L4 declared but not used" */ :
+	if true {
+	}
+L5 /* ERROR "label L5 declared but not used" */ :
+	f0()
+L6:
+	f0()
+L6 /* ERROR "label L6 already declared" */ :
+	f0()
+	if x == 20 {
+		goto L6
+	}
+
+L7:
+	for {
+		break L7
+	}
+
+L8:
+	for {
+		if x == 21 {
+			continue L8
+		}
+	}
+
+L9:
+	switch {
+	case true:
+		break L9
+	defalt /* ERROR "label defalt declared but not used" */ :
+	}
+
+L10:
+	select {
+	default:
+		break L10
+	}
+}
+
+func f1() {
+L1:
+	for {
+		if x == 0 {
+			break L1
+		}
+		if x == 1 {
+			continue L1
+		}
+		goto L1
+	}
+
+L2:
+	select {
+	default:
+		if x == 0 {
+			break L2
+		}
+		if x == 1 {
+			continue L2 /* ERROR "invalid continue label L2" */
+		}
+		goto L2
+	}
+
+L3:
+	switch {
+	case x > 10:
+		if x == 11 {
+			break L3
+		}
+		if x == 12 {
+			continue L3 /* ERROR "invalid continue label L3" */
+		}
+		goto L3
+	}
+
+L4:
+	if true {
+		if x == 13 {
+			break L4 /* ERROR "invalid break label L4" */
+		}
+		if x == 14 {
+			continue L4 /* ERROR "invalid continue label L4" */
+		}
+		if x == 15 {
+			goto L4
+		}
+	}
+
+L5:
+	f1()
+	if x == 16 {
+		break L5 /* ERROR "invalid break label L5" */
+	}
+	if x == 17 {
+		continue L5 /* ERROR "invalid continue label L5" */
+	}
+	if x == 18 {
+		goto L5
+	}
+
+	for {
+		if x == 19 {
+			break L1 /* ERROR "break label not declared: L1" */
+		}
+		if x == 20 {
+			continue L1 /* ERROR "continue label not declared: L1" */
+		}
+		if x == 21 {
+			goto L1
+		}
+	}
+}
+
+// Additional tests not in the original files.
+
+func f2() {
+L1:
+	if x == 0 {
+		for {
+			continue L1 /* ERROR "invalid continue label L1" */
+		}
+	}
+}

go/types/testdata/stmt0.src

@@ -378,16 +378,24 @@ func switches1() {
 
 	switch x {
 	case 0:
+		goto L1
 		L1: fallthrough
 	case 1:
+		goto L2
+		goto L3
+		goto L4
 		L2: L3: L4: fallthrough
 	default:
 	}
 
 	switch x {
 	case 0:
+		goto L5
 		L5: fallthrough
 	default:
+		goto L6
+		goto L7
+		goto L8
 		L6: L7: L8: fallthrough /* ERROR "fallthrough statement out of place" */
 	}
 
@@ -605,14 +613,20 @@ func rangeloops() {
 }
 
 func labels0() {
+	goto L0
+	goto L1
 	L0:
 	L1:
-	L1:
+	L1 /* ERROR "already declared" */ :
 	if true {
+		goto L2		
 		L2:
-		L0:
+		L0 /* ERROR "already declared" */ :
 	}
 	_ = func() {
+		goto L0
+		goto L1
+		goto L2
 		L0:
 		L1:
 		L2: