reflect: skip duplicate check in StructOf when the name of a field is…

… "_"

Fixes #49110

Change-Id: I32c2cb26cca067a4a676ce4bbc3e51f1e0cdb259
Reviewed-on: https://go-review.googlesource.com/c/go/+/357959
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dan Kortschak <dan@kortschak.io>
Reviewed-by: Sebastien Binet <s@sbinet.org>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/reflect/type.go

@@ -2606,7 +2606,7 @@ func StructOf(fields []StructField) Type {
 				}
 			}
 		}
-		if _, dup := fset[name]; dup {
+		if _, dup := fset[name]; dup && name != "_" {
 			panic("reflect.StructOf: duplicate field " + name)
 		}
 		fset[name] = struct{}{}

test/fixedbugs/issue49110.go

@@ -0,0 +1,16 @@
+// run
+
+// 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 main
+
+import "reflect"
+
+func main() {
+	_ = reflect.StructOf([]reflect.StructField{
+		{Name: "_", PkgPath: "main", Type: reflect.TypeOf(int(0))},
+		{Name: "_", PkgPath: "main", Type: reflect.TypeOf(int(0))},
+	})
+}