cgen: fix initialising a map, using option type as value (#18540)

vlib/v/gen/c/cgen.v

@@ -1888,7 +1888,11 @@ fn (mut g Gen) expr_with_tmp_var(expr ast.Expr, expr_typ ast.Type, ret_typ ast.T
 		g.writeln('${g.typ(ret_typ)} ${tmp_var};')
 		if ret_typ.has_flag(.option) {
 			if expr_typ.has_flag(.option) && expr in [ast.StructInit, ast.ArrayInit, ast.MapInit] {
-				g.write('_option_none(&(${styp}[]) { ')
+				if expr is ast.StructInit && (expr as ast.StructInit).init_fields.len > 0 {
+					g.write('_option_ok(&(${styp}[]) { ')
+				} else {
+					g.write('_option_none(&(${styp}[]) { ')
+				}
 			} else {
 				is_ptr_to_ptr_assign = (expr is ast.SelectorExpr
 					|| (expr is ast.Ident && !(expr as ast.Ident).is_auto_heap()))
@@ -3989,6 +3993,8 @@ fn (mut g Gen) map_init(node ast.MapInit) {
 			}
 			if value_sym.kind == .sum_type {
 				g.expr_with_cast(expr, node.val_types[i], unwrap_val_typ)
+			} else if node.val_types[i].has_flag(.option) {
+				g.expr_with_opt(expr, node.val_types[i], unwrap_val_typ)
 			} else {
 				g.expr(expr)
 			}

vlib/v/gen/c/index.v

@@ -404,7 +404,7 @@ fn (mut g Gen) index_of_map(node ast.IndexExpr, sym ast.TypeSymbol) {
 		if g.inside_return {
 			g.typ(val_type)
 		} else {
-			g.typ(val_type.clear_flags(.option, .result))
+			g.typ(val_type.clear_flags(.result))
 		}
 	}
 	get_and_set_types := val_sym.kind in [.struct_, .map, .array]

vlib/v/tests/option_map_init_test.v

@@ -0,0 +1,25 @@
+struct MyStruct {
+	field int
+}
+
+fn empty() map[string]?MyStruct {
+	return {
+		'key1': ?MyStruct(none)
+		'key2': ?MyStruct{
+			field: 10
+		}
+	}
+}
+
+fn test_main() {
+	a := dump(empty())
+
+	b := dump(a['key2'])
+
+	assert b? == MyStruct{
+		field: 10
+	}
+
+	assert a['key1'] == none
+	assert a['key2'] != none
+}