cmd/compile: fix invalid switch case value panic

This is a regression introduced by myself in golang.org/cl/41852,
confirmed by the program that reproduces the crash that can be seen in
the added test.

Fixes #21988.

Change-Id: I18d5b2b3de63ced84db705b18490b00b16b59e02
Reviewed-on: https://go-review.googlesource.com/65655
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/cmd/compile/internal/gc/swt.go b/src/cmd/compile/internal/gc/swt.go
index 469af86aa63a5e36d76e07c11efbb376b929a7f2..dc285ae91cd5bed2d1bd5f1f7e5a448f560cfc82 100644 (file)
--- a/src/cmd/compile/internal/gc/swt.go
+++ b/src/cmd/compile/internal/gc/swt.go
@@ -610,6 +610,11 @@ func checkDupExprCases(exprname *Node, clauses []*Node) {
                                if ct := consttype(n); ct < 0 || ct == CTBOOL {
                                        continue
                                }
+                               // If the value has no type, we have
+                               // already printed an error about it.
+                               if n.Type == nil {
+                                       continue
+                               }
 
                                val := n.Val().Interface()
                                prev, dup := seen[val]

diff --git a/test/fixedbugs/issue21988.go b/test/fixedbugs/issue21988.go
new file mode 100644 (file)
index 0000000..850e039
--- /dev/null
+++ b/test/fixedbugs/issue21988.go
@@ -0,0 +1,17 @@
+// 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 21988: panic on switch case with invalid value
+
+package p
+
+const X = Wrong(0) // ERROR "undefined: Wrong"
+
+func _() {
+       switch 0 {
+       case X:
+       }
+}