reflect: handle zero-sized fields of directly-stored structures correctly

type W struct {
	E struct{}
	X *byte
}

type W is a "direct" type. That is, it is a pointer-ish type that can
be stored directly as the second word of an interface.

But if we ask reflect for W's first field, that value must *not* be
direct, as zero-sized things cannot be stored directly.

This was a problem introduced in CL 681937. Before that, types like W
were not eligible for directness.

Fixes #74935

Change-Id: Idefb55c23eaa59153009f863bad611593981e5cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/694195
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/test/fixedbugs/issue74935.go b/test/fixedbugs/issue74935.go
new file mode 100644
index 0000000000..1f6f718b02
--- /dev/null
+++ b/test/fixedbugs/issue74935.go
@@ -0,0 +1,19 @@
+// run
+
+// Copyright 2025 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"
+
+type W struct {
+	E struct{}
+	X *byte
+}
+
+func main() {
+	w := reflect.ValueOf(W{})
+	_ = w.Field(0).Interface()
+}