cgen: fix cast type changed before last stmt in stmts_with_tmp_var (#25915)

Author: Krchi

vlib/v/gen/c/cgen.v

@@ -2149,9 +2149,11 @@ fn (mut g Gen) stmts_with_tmp_var(stmts []ast.Stmt, tmp_var string) bool {
 	if g.inside_ternary > 0 {
 		g.write('(')
 	}
+	expected_cast_type := g.expected_cast_type
 	mut last_stmt_was_return := false
 	for i, stmt in stmts {
 		if i == stmts.len - 1 {
+			g.expected_cast_type = expected_cast_type
 			if stmt is ast.Return {
 				last_stmt_was_return = true
 			}

vlib/v/tests/return_match_expr_with_nest_match_expr_test.v

@@ -0,0 +1,31 @@
+struct Foo {
+}
+
+struct Bar {
+	b bool
+}
+
+type FooBar = Foo | Bar
+
+fn get_foobar(f FooBar) FooBar {
+	return match f {
+		Foo {
+			Foo{}
+		}
+		Bar {
+			b := match f.b {
+				true { false }
+				false { true }
+			}
+			Bar{
+				b: b
+			}
+		}
+	}
+}
+
+fn test_return_match_expr_with_nest_match_expr() {
+	assert get_foobar(Bar{}) == FooBar(Bar{
+		b: true
+	})
+}