cgen: fix struct initialization with option value (#17539)

vlib/v/gen/c/assign.v

@@ -70,7 +70,7 @@ fn (mut g Gen) expr_opt_with_cast(expr ast.Expr, expr_typ ast.Type, ret_typ ast.
 		} else {
 			old_inside_opt_or_res := g.inside_opt_or_res
 			g.inside_opt_or_res = false
-			g.expr(expr)
+			g.expr_with_cast(expr, expr_typ, ret_typ)
 			g.inside_opt_or_res = old_inside_opt_or_res
 		}
 		g.writeln(' }, (${option_name}*)(&${tmp_var}), sizeof(${styp}));')

vlib/v/gen/c/cgen.v

@@ -2260,8 +2260,7 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 		return
 	}
 	if got_sym.info !is ast.Interface && exp_sym.info is ast.Interface
-		&& got_type.idx() != expected_type.idx() && !expected_type.has_flag(.option)
-		&& !expected_type.has_flag(.result) {
+		&& got_type.idx() != expected_type.idx() && !expected_type.has_flag(.result) {
 		if expr is ast.StructInit && !got_type.is_ptr() {
 			g.inside_cast_in_heap++
 			got_styp := g.cc_type(got_type.ref(), true)

vlib/v/gen/c/struct.v

@@ -336,12 +336,21 @@ fn (mut g Gen) zero_struct_field(field ast.StructField) bool {
 	g.write('.${field_name} = ')
 	if field.has_default_expr {
 		if sym.kind in [.sum_type, .interface_] {
-			g.expr_with_cast(field.default_expr, field.default_expr_typ, field.typ)
+			if field.typ.has_flag(.option) {
+				g.expr_opt_with_cast(field.default_expr, field.default_expr_typ.set_flag(.option),
+					field.typ)
+			} else {
+				g.expr_with_cast(field.default_expr, field.default_expr_typ, field.typ)
+			}
 			return true
 		}
 
-		if (field.typ.has_flag(.option) && !field.default_expr_typ.has_flag(.option))
-			|| (field.typ.has_flag(.result) && !field.default_expr_typ.has_flag(.result)) {
+		if field.typ.has_flag(.option) {
+			tmp_var := g.new_tmp_var()
+			g.expr_with_tmp_var(field.default_expr, field.default_expr_typ, field.typ,
+				tmp_var)
+			return true
+		} else if field.typ.has_flag(.result) && !field.default_expr_typ.has_flag(.result) {
 			tmp_var := g.new_tmp_var()
 			g.expr_with_tmp_var(field.default_expr, field.default_expr_typ, field.typ,
 				tmp_var)
@@ -538,10 +547,9 @@ fn (mut g Gen) struct_init_field(sfield ast.StructInitField, language ast.Langua
 				g.write('/* autoref */&')
 			}
 
-			if (sfield.expected_type.has_flag(.option) && !sfield.typ.has_flag(.option))
+			if sfield.expected_type.has_flag(.option)
 				|| (sfield.expected_type.has_flag(.result) && !sfield.typ.has_flag(.result)) {
-				tmp_var := g.new_tmp_var()
-				g.expr_with_tmp_var(sfield.expr, sfield.typ, sfield.expected_type, tmp_var)
+				g.expr_with_opt(sfield.expr, sfield.typ, sfield.expected_type)
 			} else {
 				g.expr_with_cast(sfield.expr, sfield.typ, sfield.expected_type)
 			}

vlib/v/tests/option_struct_init_interface_test.v

@@ -0,0 +1,18 @@
+interface IPerson {
+	name string
+	age int
+}
+
+struct PersonImpl {
+	name string
+	age  int
+}
+
+struct Person {
+	other ?IPerson = PersonImpl{}
+}
+
+fn test_main() {
+	a := Person{}
+	assert a.other != none
+}

vlib/v/tests/option_struct_init_with_opt_test.v

@@ -0,0 +1,19 @@
+struct Foo {
+	x ?string
+}
+
+fn test_main() {
+	x := ?string('hi')
+	foo := Foo{
+		x: x
+	}
+	assert foo.x? == 'hi'
+}
+
+fn test_none() {
+	x := ?string(none)
+	foo := Foo{
+		x: x
+	}
+	assert foo.x == none
+}