parser, checker, cgen: fix anon struct with default expr (#19257)

vlib/v/checker/struct.v

@@ -93,6 +93,10 @@ fn (mut c Checker) struct_decl(mut node ast.StructDecl) {
 					}
 				}
 			}
+			// check anon struct declaration
+			if field.anon_struct_decl.fields.len > 0 {
+				c.struct_decl(mut field.anon_struct_decl)
+			}
 		}
 		c.expected_type = old_expected_type
 		util.timing_measure_cumulative('Checker.struct setting default_expr_typ')

vlib/v/gen/c/struct.v

@@ -333,7 +333,7 @@ fn (mut g Gen) zero_struct_field(field ast.StructField) bool {
 					break
 				}
 			}
-			if has_option_field {
+			if has_option_field || field.anon_struct_decl.fields.len > 0 {
 				default_init := ast.StructInit{
 					typ: field.typ
 				}
@@ -379,7 +379,6 @@ fn (mut g Gen) zero_struct_field(field ast.StructField) bool {
 				tmp_var)
 			return true
 		}
-
 		g.expr(field.default_expr)
 	} else if field.typ.has_flag(.option) {
 		tmp_var := g.new_tmp_var()

vlib/v/parser/struct.v

@@ -314,7 +314,6 @@ fn (mut p Parser) struct_decl(is_anon bool) ast.StructDecl {
 					is_deprecated: is_field_deprecated
 					anon_struct_decl: p.anon_struct_decl
 				}
-				p.anon_struct_decl = ast.StructDecl{}
 			}
 			// save embeds as table fields too, it will be used in generation phase
 			fields << ast.StructField{
@@ -333,7 +332,9 @@ fn (mut p Parser) struct_decl(is_anon bool) ast.StructDecl {
 				is_global: is_field_global
 				is_volatile: is_field_volatile
 				is_deprecated: is_field_deprecated
+				anon_struct_decl: p.anon_struct_decl
 			}
+			p.anon_struct_decl = ast.StructDecl{}
 			p.attrs = prev_attrs
 			i++
 		}

vlib/v/tests/anon_struct_with_default_expr_test.v

@@ -0,0 +1,15 @@
+struct Bar {
+	anon struct {
+		foofoo Foo = Foo{'foofoo'}
+	}
+}
+
+struct Foo {
+	name string
+}
+
+fn test_anon_struct_with_default_expr() {
+	bar := Bar{}
+	println(bar.anon.foofoo.name)
+	assert bar.anon.foofoo.name == 'foofoo'
+}