gc: fix handling of types inside function bodies

Fixes #849.
Fixes #920.

R=ken2
CC=golang-dev
https://golang.org/cl/1841042

src/cmd/gc/align.c

@@ -351,8 +351,8 @@ void
 defercheckwidth(void)
 {
 	// we get out of sync on syntax errors, so don't be pedantic.
-	// if(defercalc)
-	//	fatal("defercheckwidth");
+	if(defercalc && nerrors == 0)
+		fatal("defercheckwidth");
 	defercalc = 1;
 }
 

src/cmd/gc/walk.c

@@ -292,10 +292,14 @@ walkdef(Node *n)
 		break;
 
 	case OTYPE:
+		if(curfn)
+			defercheckwidth();
 		n->walkdef = 1;
 		n->type = typ(TFORW);
 		n->type->sym = n->sym;
 		walkdeftype(n);
+		if(curfn)
+			resumecheckwidth();
 		break;
 
 	case OPACK:

test/fixedbugs/bug290.go

+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2010 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.
+
+// http://code.google.com/p/go/issues/detail?id=920
+
+package main
+
+type X struct { x []X }
+
+func main() {
+	type Y struct { x []Y }	// used to get invalid recursive type
+}

test/golden.out

@@ -180,10 +180,3 @@ BUG: bug260 failed
 
 =========== bugs/bug274.go
 BUG: errchk: command succeeded unexpectedly
-
-=========== bugs/bug286.go
-test2 called g
-panic: wrong method called
-
-panic PC=xxx
-BUG: bug286 failed