cgen: allow init shared field with default value (fix #25990) (#25991)

Author: kbkpbot

vlib/v/gen/c/struct.v

@@ -450,7 +450,15 @@ fn (mut g Gen) init_shared_field(field ast.StructField) {
 	field_typ := field.typ.deref()
 	shared_styp := g.styp(field_typ)
 	g.write('(${shared_styp}*)__dup${shared_styp}(&(${shared_styp}){.mtx= {0}, .val=')
-	g.write(g.type_default(field_typ.clear_flag(.shared_f)))
+	if field.has_default_expr {
+		// avoid generate shared assign inside expr
+		old_is_shared := g.is_shared
+		g.is_shared = false
+		g.expr(field.default_expr)
+		g.is_shared = old_is_shared
+	} else {
+		g.write(g.type_default(field_typ.clear_flag(.shared_f)))
+	}
 	g.write('}, sizeof(${shared_styp}))')
 }
 
@@ -538,6 +546,9 @@ fn (mut g Gen) zero_struct_field(field ast.StructField) bool {
 			g.fixed_array_var_init(tmp_var, false, final_sym.info.elem_type, final_sym.info.size)
 			g.inside_memset = old_inside_memset
 			return true
+		} else if field.typ.has_flag(.shared_f) {
+			g.init_shared_field(field)
+			return true
 		}
 		g.expr(field.default_expr)
 	} else if field.typ.has_flag(.option) {

vlib/v/tests/shared_int_default_val_test.v

@@ -0,0 +1,15 @@
+module main
+
+struct Foo {
+mut:
+	a shared int = 200
+}
+
+fn test_main() {
+	x := Foo{}
+
+	rlock x.a {
+		k := x.a
+		assert k == 200
+	}
+}