gc: Better typechecks and errors in switches.

Allow any type in switch on interface value.
Statically check typeswitch early.

Fixes issue 2423.
Fixes issue 2424.

R=rsc, dsymonds
CC=golang-dev
http://codereview.appspot.com/5339045

1 files changed, 38 insertions, 0 deletions

diff --git a/test/switch3.go b/test/switch3.go
new file mode 100644
index 000000000..95ff6ec3c
--- /dev/null
+++ b/test/switch3.go
@@ -0,0 +1,38 @@
+// errchk $G -e $D/$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.
+
+package main
+
+
+type I interface {
+       M()
+}
+
+func bad() {
+	var i I
+	var s string
+
+	switch i {
+	case s:  // ERROR "mismatched types string and I"
+	}
+
+	switch s {
+	case i:  // ERROR "mismatched types I and string"
+	}
+}
+
+func good() {
+	var i interface{}
+	var s string
+
+	switch i {
+	case s:
+	}
+
+	switch s {
+	case i:
+	}
+}