reflect: omit anonymous field name from StructOf type string

This makes the reflect package match the compiler for StructOf
with an embedded field.

Fixes #24781

Change-Id: Ice64b167cbe0b9d30a953c5d8e2a86f3ad1158bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/567897
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Commit-Queue: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/reflect/all_test.go

@@ -6112,6 +6112,20 @@ func TestStructOfTooLarge(t *testing.T) {
 	}
 }
 
+func TestStructOfAnonymous(t *testing.T) {
+	var s any = struct{ D1 }{}
+	f := TypeOf(s).Field(0)
+	ds := StructOf([]StructField{f})
+	st := TypeOf(s)
+	dt := New(ds).Elem()
+	if st != dt.Type() {
+		t.Errorf("StructOf returned %s, want %s", dt.Type(), st)
+	}
+
+	// This should not panic.
+	_ = dt.Interface().(struct{ D1 })
+}
+
 func TestChanOf(t *testing.T) {
 	// check construction and use of type not in binary
 	type T string

src/reflect/type.go

@@ -2287,8 +2287,9 @@ func StructOf(fields []StructField) Type {
 		// Update string and hash
 		name := f.Name.Name()
 		hash = fnv1(hash, []byte(name)...)
-		repr = append(repr, (" " + name)...)
-		if f.Embedded() {
+		if !f.Embedded() {
+			repr = append(repr, (" " + name)...)
+		} else {
 			// Embedded field
 			if f.Typ.Kind() == abi.Pointer {
 				// Embedded ** and *interface{} are illegal