[release-branch.go1.8] cmd/compile: don't crash when slicing non-slice

Fixes #19323
Fixes #19638 (backport)

Change-Id: I92d1bdefb15de6178a577a4fa0f0dc004f791904
Reviewed-on: https://go-review.googlesource.com/39601
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index 5ec1c9e2f23e3845abcf61ac74629cff3c4b7bf7..7cfd951fde1d77c176e61f279d9a20ac96d276c1 100644 (file)
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -1107,7 +1107,7 @@ OpSwitch:
 
        case OSLICE, OSLICE3:
                ok |= Erv
-               n.Left = typecheck(n.Left, top)
+               n.Left = typecheck(n.Left, Erv)
                low, high, max := n.SliceBounds()
                hasmax := n.Op.IsSlice3()
                low = typecheck(low, Erv)
@@ -1119,6 +1119,10 @@ OpSwitch:
                max = indexlit(max)
                n.SetSliceBounds(low, high, max)
                l := n.Left
+               if l.Type == nil {
+                       n.Type = nil
+                       return n
+               }
                if l.Type.IsArray() {
                        if !islvalue(n.Left) {
                                yyerror("invalid operation %v (slice of unaddressable value)", n)
@@ -1131,12 +1135,7 @@ OpSwitch:
                        n.Left = typecheck(n.Left, Erv)
                        l = n.Left
                }
-
                t := l.Type
-               if t == nil {
-                       n.Type = nil
-                       return n
-               }
                var tp *Type
                if t.IsString() {
                        if hasmax {

diff --git a/test/fixedbugs/issue19323.go b/test/fixedbugs/issue19323.go
new file mode 100644 (file)
index 0000000..f90af66
--- /dev/null
+++ b/test/fixedbugs/issue19323.go
@@ -0,0 +1,19 @@
+// 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.
+
+package p
+
+func g() {}
+
+func f() {
+       g()[:] // ERROR "g.. used as value"
+}
+
+func g2() ([]byte, []byte) { return nil, nil }
+
+func f2() {
+       g2()[:] // ERROR "multiple-value g2.. in single-value context"
+}