gc: use inferred type rather than original one when reporting non-assignability.

Fixes #2451

R=rsc, bradfitz
CC=golang-dev
https://golang.org/cl/5372105

src/cmd/gc/fmt.c

@@ -1278,13 +1278,17 @@ exprfmt(Fmt *f, Node *n, int prec)
 static int
 nodefmt(Fmt *f, Node *n)
 {
+	Type *t;
+
+	t = n->type;
+	if(n->orig != N)
+		n = n->orig;
 
-	if(f->flags&FmtLong && n->type != T) {
-		if(n->type->etype == TNIL)
+	if(f->flags&FmtLong && t != T) {
+		if(t->etype == TNIL)
 			return fmtprint(f, "nil");
 		else
-			return fmtprint(f, "%N (type %T)", n, n->type);
-
+			return fmtprint(f, "%N (type %T)", n, t);
 	}
 
 	// TODO inlining produces expressions with ninits. we can't print these yet.
@@ -1479,8 +1483,6 @@ Nconv(Fmt *fp)
 	switch(fmtmode) {
 	case FErr:
 	case FExp:
-		if(n->orig != N)
-			n = n->orig;
 		r = nodefmt(fp, n);
 		break;
 	case FDbg:

test/ddd1.go

@@ -15,7 +15,7 @@ var (
 	_ = sum()
 	_ = sum(1.0, 2.0)
 	_ = sum(1.5)      // ERROR "integer"
-	_ = sum("hello")  // ERROR ".hello. .type ideal string. as type int|incompatible"
+	_ = sum("hello")  // ERROR ".hello. .type string. as type int|incompatible"
 	_ = sum([]int{1}) // ERROR "\[\]int literal.*as type int|incompatible"
 )
 

test/fixedbugs/bug386.go

+// errchk $G $D/$F.go
+
+// 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.
+
+// Issue 2451, 2452 
+package foo
+
+func f() error { return 0 } // ERROR "cannot use 0 .type int."
+
+func g() error { return -1 }  // ERROR "cannot use -1 .type int."
\ No newline at end of file

test/named1.go

@@ -37,7 +37,7 @@ func main() {
 	asBool(true)
 	asBool(*&b)
 	asBool(Bool(true))
-	asBool(1 != 2) // ERROR "cannot use.*type ideal bool.*as type Bool"
+	asBool(1 != 2) // ERROR "cannot use.*type bool.*as type Bool"
 	asBool(i < j)  // ERROR "cannot use.*type bool.*as type Bool"
 
 	_, b = m[2] // ERROR "cannot .* bool.*type Bool"