cmd/internal/gc: ignore declarations of types for goto validation

Fixes #8042.

Change-Id: I75080f24104256065fd73b07a13c5b8e7d6da94c
Reviewed-on: https://go-review.googlesource.com/9442Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/internal/gc/dcl.go

@@ -65,6 +65,9 @@ func popdcl() {
 		}
 		s = Pkglookup(d.Name, d.Pkg)
 		lno = int(s.Lastlineno)
+		if s.Def != nil {
+			d.whyPushed = s.Def.Op
+		}
 		dcopy(s, d)
 		d.Lastlineno = int32(lno)
 		if dflag() {

src/cmd/internal/gc/gen.go

@@ -159,6 +159,21 @@ func checkgoto(from *Node, to *Node) {
 		fs = fs.Link
 	}
 	if fs != to.Sym {
+		// more declarations at label than at goto.
+		// figure out if they are all types.
+		ts := to.Sym
+		ntt := nt
+		for ; ntt > nf; ntt-- {
+			if ts.whyPushed != OTYPE {
+				break
+			}
+			ts = ts.Link
+		}
+		// all types, nothing to see here.
+		if ntt == nf {
+			return
+		}
+
 		lno := int(lineno)
 		setlineno(from)
 
@@ -168,11 +183,11 @@ func checkgoto(from *Node, to *Node) {
 		var block *Sym
 
 		var dcl *Sym
-		ts := to.Sym
+		ts = to.Sym
 		for ; nt > nf; nt-- {
 			if ts.Pkg == nil {
 				block = ts
-			} else {
+			} else if ts.whyPushed != OTYPE {
 				dcl = ts
 			}
 			ts = ts.Link
@@ -181,7 +196,7 @@ func checkgoto(from *Node, to *Node) {
 		for ts != fs {
 			if ts.Pkg == nil {
 				block = ts
-			} else {
+			} else if ts.whyPushed != OTYPE {
 				dcl = ts
 			}
 			ts = ts.Link

src/cmd/internal/gc/go.go

@@ -111,6 +111,7 @@ type Sym struct {
 	Uniqgen   uint32
 	Importdef *Pkg   // where imported definition was found
 	Linkname  string // link name
+	whyPushed uint8  // why this symbol pushed onto dclstack. Same as Node.Op. Used by goto validation
 
 	// saved and restored by dcopy
 	Pkg        *Pkg

test/goto.go

@@ -536,3 +536,19 @@ func _() {
 		goto L // ERROR "goto L jumps into block starting at LINE-4|goto jumps into block"
 	}
 }
+
+// issue 8042
+func _() {
+	goto L
+	type a int
+	L:
+}
+
+// make sure we only complain about variable declarations.
+func _() {
+	goto L // ERROR "goto L jumps over declaration of x at LINE+2|goto jumps over declaration"
+	type a int
+	x := 1	// GCCGO_ERROR "defined here"
+	_ = x
+L:
+}