From: Daniel Morsing <daniel.morsing@gmail.com>
Date: Wed, 15 Aug 2012 23:53:06 +0000 (-0700)
Subject: cmd/gc: Don't claim type assertion would help when it wont.
X-Git-Tag: go1.1rc2~2640
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=b04c890a89e00f52c11ccccf4c76db389ef57d16;p=gostls13.git

cmd/gc: Don't claim type assertion would help when it wont.

Fixes #3465.

R=golang-dev, rsc, remyoudompheng, iant
CC=golang-dev
https://golang.org/cl/6448097
---

diff --git a/src/cmd/gc/subr.c b/src/cmd/gc/subr.c
index dfb425efcf..0cd7e6c4b0 100644
--- a/src/cmd/gc/subr.c
+++ b/src/cmd/gc/subr.c
@@ -1219,7 +1219,7 @@ assignop(Type *src, Type *dst, char **why)
 		return 0;
 	}
 	if(src->etype == TINTER && dst->etype != TBLANK) {
-		if(why != nil)
+		if(why != nil && implements(dst, src, &missing, &have, &ptr))
 			*why = ": need type assertion";
 		return 0;
 	}
diff --git a/test/interface/explicit.go b/test/interface/explicit.go
index d19480a685..7822b88d08 100644
--- a/test/interface/explicit.go
+++ b/test/interface/explicit.go
@@ -40,7 +40,7 @@ func main() {
 	// because i has an extra method
 	// that t does not, so i cannot contain a t.
 	i = t // ERROR "incompatible|missing M method"
-	t = i // ERROR "incompatible|need type assertion"
+	t = i // ERROR "incompatible|assignment$"
 
 	i = i2 // ok
 	i2 = i // ERROR "incompatible|missing N method"