checker: allow embed of type alias anon struct (#21928)

vlib/v/checker/checker.v

@@ -571,9 +571,12 @@ fn (mut c Checker) alias_type_decl(node ast.AliasTypeDecl) {
 				}
 				if parent_typ_sym.info.is_anon {
 					for field in parent_typ_sym.info.fields {
-						if c.table.final_sym(field.typ).kind != .struct_ {
-							c.error('cannot embed non-struct `${c.table.sym(field.typ).name}`',
-								field.type_pos)
+						field_sym := c.table.sym(field.typ)
+						if field_sym.info is ast.Alias {
+							if c.table.sym(field_sym.info.parent_type).kind != .struct_ {
+								c.error('cannot embed non-struct `${field_sym.name}`',
+									field.type_pos)
+							}
 						}
 					}
 				}

vlib/v/checker/struct.v

@@ -26,7 +26,13 @@ fn (mut c Checker) struct_decl(mut node ast.StructDecl) {
 		}
 		for embed in node.embeds {
 			embed_sym := c.table.sym(embed.typ)
-			if embed_sym.kind != .struct_ {
+			if embed_sym.info is ast.Alias {
+				parent_sym := c.table.sym(embed_sym.info.parent_type)
+				if parent_sym.kind != .struct_ {
+					c.error('`${embed_sym.name}` (alias of `${parent_sym.name}`) is not a struct',
+						embed.pos)
+				}
+			} else if embed_sym.kind != .struct_ {
 				c.error('`${embed_sym.name}` is not a struct', embed.pos)
 			} else if (embed_sym.info as ast.Struct).is_heap && !embed.typ.is_ptr() {
 				struct_sym.info.is_heap = true

vlib/v/checker/tests/struct_embed_invalid_type.out

@@ -1,6 +1,6 @@
-vlib/v/checker/tests/struct_embed_invalid_type.vv:4:2: error: `Foo` is not a struct
-    2 |
+vlib/v/checker/tests/struct_embed_invalid_type.vv:4:2: error: `Foo` (alias of `int`) is not a struct
+    2 | 
     3 | struct Bar {
     4 |     Foo
       |     ~~~
-    5 | }
+    5 | }

vlib/v/tests/anon_struct_alias_type_decl_embed_test.v

@@ -0,0 +1,20 @@
+type AnonStruct = struct {
+	a int
+	b int
+	c int
+}
+
+struct Abc {
+	AnonStruct
+}
+
+fn test_anon_struct_type_alias_decl_embed() {
+	abc := Abc{AnonStruct(struct {10, 20, 30})}
+	assert abc.a == 10
+	assert abc.b == 20
+	assert abc.c == 30
+
+	assert abc.AnonStruct.a == 10
+	assert abc.AnonStruct.b == 20
+	assert abc.AnonStruct.c == 30
+}