cmd/compile/internal/types2: add a check for nil reason in assignableTo

A recent change to error message formatting was missing a nil check.

Fixes #49592

Change-Id: Ic1843e0277ba75eec0e8e41fe34b59c323d7ea31
Reviewed-on: https://go-review.googlesource.com/c/go/+/364034
Trust: Robert Findley <rfindley@google.com>
Trust: Dan Scales <danscales@google.com>
Trust: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

diff --git a/src/cmd/compile/internal/types2/operand.go b/src/cmd/compile/internal/types2/operand.go
index 8a905f3fd0017318cf53be1b6b900df7d438b6b5..6581d80323ba708c6be9105dc53bd236b84249ea 100644 (file)
--- a/src/cmd/compile/internal/types2/operand.go
+++ b/src/cmd/compile/internal/types2/operand.go
@@ -316,7 +316,9 @@ func (x *operand) assignableTo(check *Checker, T Type, reason *string) (bool, er
        // not an interface.
        if check != nil && check.conf.CompilerErrorMessages {
                if isInterfacePtr(Tu) {
-                       *reason = check.sprintf("%s does not implement %s (%s is pointer to interface, not interface)", x.typ, T, T)
+                       if reason != nil {
+                               *reason = check.sprintf("%s does not implement %s (%s is pointer to interface, not interface)", x.typ, T, T)
+                       }
                        return false, _InvalidIfaceAssign
                }
                if Vi, _ := Vu.(*Interface); Vi != nil && Vp == nil {

diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue49592.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue49592.go2
new file mode 100644 (file)
index 0000000..846deaa
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue49592.go2
@@ -0,0 +1,11 @@
+// Copyright 2021 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 _() {
+       var x *interface{}
+       var y interface{}
+       _ = x == y
+}

diff --git a/src/go/types/testdata/fixedbugs/issue49592.go2 b/src/go/types/testdata/fixedbugs/issue49592.go2
new file mode 100644 (file)
index 0000000..846deaa
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue49592.go2
@@ -0,0 +1,11 @@
+// Copyright 2021 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 _() {
+       var x *interface{}
+       var y interface{}
+       _ = x == y
+}

diff --git a/test/fixedbugs/issue49592.go b/test/fixedbugs/issue49592.go
new file mode 100644 (file)
index 0000000..8b56129
--- /dev/null
+++ b/test/fixedbugs/issue49592.go
@@ -0,0 +1,13 @@
+// compile
+
+// Copyright 2021 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 _() {
+       var x *interface{}
+       var y interface{}
+       _ = x == y
+}