cmd/compile: clearer error when non-bool used as "||" and "&&" operand

Fixes #41500

Change-Id: I658d8921b7769b6e4288ca781cbdca5ff14a84ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/255899
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index 12c99bf48f80cc83c97838894fb1151cb2cb5250..2c445567deeb7ab8f934660d96f4094be5465414 100644 (file)
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -630,6 +630,22 @@ func typecheck1(n *Node, top int) (res *Node) {
                        break
                }
 
+               // For "x == x && len(s)", it's better to report that "len(s)" (type int)
+               // can't be used with "&&" than to report that "x == x" (type untyped bool)
+               // can't be converted to int (see issue #41500).
+               if n.Op == OANDAND || n.Op == OOROR {
+                       if !n.Left.Type.IsBoolean() {
+                               yyerror("invalid operation: %v (operator %v not defined on %s)", n, n.Op, typekind(n.Left.Type))
+                               n.Type = nil
+                               return n
+                       }
+                       if !n.Right.Type.IsBoolean() {
+                               yyerror("invalid operation: %v (operator %v not defined on %s)", n, n.Op, typekind(n.Right.Type))
+                               n.Type = nil
+                               return n
+                       }
+               }
+
                // ideal mixed with non-ideal
                l, r = defaultlit2(l, r, false)
 

diff --git a/test/fixedbugs/issue41500.go b/test/fixedbugs/issue41500.go
new file mode 100644 (file)
index 0000000..d1e4efc
--- /dev/null
+++ b/test/fixedbugs/issue41500.go
@@ -0,0 +1,20 @@
+// errorcheck
+
+// Copyright 2020 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 s struct {
+       slice []int
+}
+
+func f() {
+       var x *s
+
+       _ = x == nil || len(x.slice) // ERROR "invalid operation: .+ \(operator \|\| not defined on int\)"
+       _ = len(x.slice) || x == nil // ERROR "invalid operation: .+ \(operator \|\| not defined on int\)"
+       _ = x == nil && len(x.slice) // ERROR "invalid operation: .+ \(operator && not defined on int\)"
+       _ = len(x.slice) && x == nil // ERROR "invalid operation: .+ \(operator && not defined on int\)"
+}