From: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Date: Tue, 5 Oct 2021 15:59:49 +0000 (+0700)
Subject: cmd/compile: better error message for invalid untyped nil conversion
X-Git-Tag: go1.18beta1~995
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=375a1fba0eb733676698ac3a9fdd12e6a8dd6602;p=gostls13.git

cmd/compile: better error message for invalid untyped nil conversion

In case of an invalid untyped nil conversion, the compiler's original
type checker leaves it to the caller to report a suitable error message.
But types2 does not, it always reports the invalid conversion.

CL 328053 made types2 report a better error message, and match the
original compiler behavior. But it ignored the case of untyped nil.

This CL adds that missing case, by checking whether the two operands can
be mixed when untyped nil is present.

Fixes #48784

Change-Id: Idc7d86eb0245aa18ca428e278f4416d6b3679058
Reviewed-on: https://go-review.googlesource.com/c/go/+/354049
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
---

diff --git a/src/cmd/compile/internal/types2/expr.go b/src/cmd/compile/internal/types2/expr.go
index 90c80f9de0..3a3a139156 100644
--- a/src/cmd/compile/internal/types2/expr.go
+++ b/src/cmd/compile/internal/types2/expr.go
@@ -996,6 +996,12 @@ func (check *Checker) binary(x *operand, e syntax.Expr, lhs, rhs syntax.Expr, op
 		if isString(x.typ) != isString(y.typ) {
 			return false
 		}
+		if x.isNil() && !hasNil(y.typ) {
+			return false
+		}
+		if y.isNil() && !hasNil(x.typ) {
+			return false
+		}
 		return true
 	}
 	if canMix(x, &y) {
diff --git a/src/cmd/compile/internal/types2/testdata/check/expr2.src b/src/cmd/compile/internal/types2/testdata/check/expr2.src
index f9726b5de5..8e5862319e 100644
--- a/src/cmd/compile/internal/types2/testdata/check/expr2.src
+++ b/src/cmd/compile/internal/types2/testdata/check/expr2.src
@@ -29,7 +29,7 @@ func arrays() {
 	_ = a == b
 	_ = a != b
 	_ = a /* ERROR < not defined */ < b
-	_ = a == nil /* ERROR cannot convert */
+	_ = a == nil /* ERROR invalid operation.*mismatched types */
 
 	type C [10]int
 	var c C
@@ -53,7 +53,7 @@ func structs() {
 	_ = s == t
 	_ = s != t
 	_ = s /* ERROR < not defined */ < t
-	_ = s == nil /* ERROR cannot convert */
+	_ = s == nil /* ERROR invalid operation.*mismatched types */
 
 	type S struct {
 		x int
diff --git a/test/fixedbugs/issue48784.go b/test/fixedbugs/issue48784.go
new file mode 100644
index 0000000000..6048518df2
--- /dev/null
+++ b/test/fixedbugs/issue48784.go
@@ -0,0 +1,23 @@
+// errorcheck -e
+
+// 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
+
+type T struct{}
+
+var s string
+var b bool
+var i int
+var t T
+var a [1]int
+
+var (
+	_ = s == nil // ERROR "invalid operation:.*mismatched types string and untyped nil"
+	_ = b == nil // ERROR "invalid operation:.*mismatched types bool and untyped nil"
+	_ = i == nil // ERROR "invalid operation:.*mismatched types int and untyped nil"
+	_ = t == nil // ERROR "invalid operation:.*mismatched types T and untyped nil"
+	_ = a == nil // ERROR "invalid operation:.*mismatched types \[1\]int and untyped nil"
+)