cmd/compile: fix error when typeswitching on untyped

Fixes #20185
Fixes #19977

Change-Id: I8434713d20616ff0c0bc8f33f017e2548a5cccfa
Reviewed-on: https://go-review.googlesource.com/42210
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

diff --git a/src/cmd/compile/internal/gc/swt.go b/src/cmd/compile/internal/gc/swt.go
index 7fd0fe0dbcb9227a6927dc032459300f5404d9fb..871cb5b8b1d18b498637d50d0f5508c8ab772c7d 100644 (file)
--- a/src/cmd/compile/internal/gc/swt.go
+++ b/src/cmd/compile/internal/gc/swt.go
@@ -177,7 +177,14 @@ func typecheckswitch(n *Node) {
                        }
                }
 
-               if top == Etype && n.Type != nil {
+               if n.Type == nil || n.Type.IsUntyped() {
+                       // if the value we're switching on has no type or is untyped,
+                       // we've already printed an error and don't need to continue
+                       // typechecking the body
+                       return
+               }
+
+               if top == Etype {
                        ll := ncase.List
                        if ncase.Rlist.Len() != 0 {
                                nvar := ncase.Rlist.First()

diff --git a/test/fixedbugs/issue19977.go b/test/fixedbugs/issue19977.go
new file mode 100644 (file)
index 0000000..3db1dfd
--- /dev/null
+++ b/test/fixedbugs/issue19977.go
@@ -0,0 +1,16 @@
+// errorcheck
+
+// Copyright 2017 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 19977: multiple error messages when type switching on an undefined
+
+package foo
+
+func Foo() {
+       switch x := a.(type) { // ERROR "undefined: a"
+       default:
+               _ = x
+       }
+}

diff --git a/test/fixedbugs/issue20185.go b/test/fixedbugs/issue20185.go
new file mode 100644 (file)
index 0000000..00c23f6
--- /dev/null
+++ b/test/fixedbugs/issue20185.go
@@ -0,0 +1,25 @@
+// errorcheck
+
+// Copyright 2017 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 20185: type switching on untyped values (e.g. nil or consts)
+// caused an internal compiler error.
+
+package p
+
+func F() {
+       switch t := nil.(type) { // ERROR "cannot type switch on non-interface value nil"
+       default:
+               _ = t
+       }
+}
+
+const x = 1
+
+func G() {
+       switch t := x.(type) { // ERROR "cannot type switch on non-interface value x \(type untyped number\)"
+       default:
+       }
+}