type switch bug involving function parameter names

R=ken
OCL=34232
CL=34232

src/cmd/gc/subr.c

@@ -1920,8 +1920,12 @@ typehash(Type *at, int addsym, int d)
 		break;
 
 	case TSTRUCT:
-		for(t=at->type; t!=T; t=t->down)
-			h += PRIME7 * typehash(t, addsym, d+1);
+		for(t=at->type; t!=T; t=t->down) {
+			if(at->funarg)	// walk into TFIELD in function argument struct
+				h += PRIME7 * typehash(t->type, addsym, d+1);
+			else
+				h += PRIME7 * typehash(t, addsym, d+1);
+		}
 		break;
 
 	case TFUNC:

src/cmd/gc/swt.c

@@ -387,7 +387,7 @@ mkcaselist(Node *sw, int arg)
 				continue;
 			setlineno(c1->link->node);
 			yyerror("duplicate case in switch");
-			print("    previous case at %L\n",
+			print("\tprevious case at %L\n",
 				c1->node->lineno);
 		}
 		break;
@@ -400,7 +400,7 @@ mkcaselist(Node *sw, int arg)
 				continue;
 			setlineno(c1->link->node);
 			yyerror("duplicate case in switch");
-			print("    previous case at %L\n",
+			print("\tprevious case at %L\n",
 				c1->node->lineno);
 		}
 		break;

test/fixedbugs/bug200.go

+// errchk $G $D/$F.go
+
+// Copyright 2009 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 main
+
+func main() {
+	// 6g used to compile these as two different
+	// hash codes so it missed the duplication
+	// and worse, compiled the wrong code
+	// for one of them.
+	var x interface{};
+	switch v := x.(type) {
+	case func(int):
+	case func(f int):	// ERROR "duplicate"
+	}
+}