cmd/gc: fix defaultlit of shifts used in interface context.

Fixes #4545.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6937058

diff --git a/src/cmd/gc/const.c b/src/cmd/gc/const.c
index 5720efc8e92f3dd3264276c83cf3744e1040bb99..31ea3a251cdf2e443038212ff64469f625b0445a 100644 (file)
--- a/src/cmd/gc/const.c
+++ b/src/cmd/gc/const.c
@@ -1052,6 +1052,11 @@ defaultlit(Node **np, Type *t)
                // When compiling x := 1<<i + 3.14, this means we try to push
                // the float64 down into the 1<<i, producing the correct error
                // (cannot shift float64).
+               //
+               // If t is an interface type, we want the default type for the
+               // value, so just do as if no type was given.
+               if(t && t->etype == TINTER)
+                       t = T;
                if(t == T && (n->right->op == OLSH || n->right->op == ORSH)) {
                        defaultlit(&n->left, T);
                        defaultlit(&n->right, n->left->type);

diff --git a/test/fixedbugs/issue4545.go b/test/fixedbugs/issue4545.go
new file mode 100644 (file)
index 0000000..3f2de16
--- /dev/null
+++ b/test/fixedbugs/issue4545.go
@@ -0,0 +1,19 @@
+// errorcheck
+
+// Copyright 2012 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 4545: untyped constants are incorrectly coerced
+// to concrete types when used in interface{} context.
+
+package main
+
+import "fmt"
+
+func main() {
+       var s uint
+       fmt.Println(1.0 + 1<<s) // ERROR "invalid operation"
+       x := 1.0 + 1<<s         // ERROR "invalid operation"
+       _ = x
+}