cgen: fix struct shared field with default init (#15040)

vlib/v/gen/c/cgen.v

@@ -5360,8 +5360,7 @@ fn (mut g Gen) type_default(typ_ ast.Type) string {
 			mut has_none_zero := false
 			mut init_str := '{'
 			info := sym.info as ast.Struct
-			typ_is_shared_f := typ.has_flag(.shared_f)
-			if sym.language == .v && !typ_is_shared_f {
+			if sym.language == .v {
 				for field in info.fields {
 					field_sym := g.table.sym(field.typ)
 					if field.has_default_expr
@@ -5392,8 +5391,10 @@ fn (mut g Gen) type_default(typ_ ast.Type) string {
 					}
 				}
 			}
+			typ_is_shared_f := typ.has_flag(.shared_f)
 			if has_none_zero {
 				init_str += '}'
+				if !typ_is_shared_f {
 					type_name := if info.is_anon {
 						// No name needed for anon structs, C figures it out on its own.
 						''
@@ -5401,10 +5402,11 @@ fn (mut g Gen) type_default(typ_ ast.Type) string {
 						'(${g.typ(typ)})'
 					}
 					init_str = type_name + init_str
+				}
 			} else {
 				init_str += '0}'
 			}
-			if typ.has_flag(.shared_f) {
+			if typ_is_shared_f {
 				styp := '__shared__${g.table.sym(typ).cname}'
 				return '($styp*)__dup${styp}(&($styp){.mtx = {0}, .val = $init_str}, sizeof($styp))'
 			} else {

vlib/v/tests/struct_shared_field_with_default_init_test.v

@@ -0,0 +1,23 @@
+struct App {
+	id string
+mut:
+	app_data shared AppData
+}
+
+struct AppData {
+	id           string
+	sub_app_data SubAppData
+}
+
+struct SubAppData {
+	id      string
+	message string = 'Default message'
+}
+
+fn test_struct_field_with_default_init() {
+	mut app := App{}
+	println(app)
+	rlock app.app_data {
+		assert app.app_data.sub_app_data.message == 'Default message'
+	}
+}