add a test for specify

`specify` only works if the key is created in the current query.

salsa-2022-tests/tests/specify-only-works-if-the-key-is-created-in-the-current-query.rs

@@ -0,0 +1,57 @@
+//! Test that `specify` only works if the key is a tracked struct created in the current query.
+//! compilation succeeds but execution panics
+#![allow(warnings)]
+
+#[salsa::jar(db = Db)]
+struct Jar(MyInput, MyTracked, tracked_fn, tracked_fn_extra, tracked_struct_created_in_another_query);
+
+trait Db: salsa::DbWithJar<Jar> {}
+
+#[salsa::input(jar = Jar)]
+struct MyInput {
+    field: u32,
+}
+
+#[salsa::tracked(jar = Jar)]
+struct MyTracked {
+    field: u32,
+}
+
+#[salsa::tracked(jar = Jar)]
+fn tracked_struct_created_in_another_query(db: &dyn Db, input: MyInput) -> MyTracked {
+     MyTracked::new(db, input.field(db) * 2)
+}
+
+#[salsa::tracked(jar = Jar)]
+fn tracked_fn(db: &dyn Db, input: MyInput) -> MyTracked {
+    let t = tracked_struct_created_in_another_query(db, input);
+    if input.field(db) != 0 {
+        tracked_fn_extra::specify(db, t, 2222);
+    }
+    t
+}
+
+#[salsa::tracked(jar = Jar, specify)]
+fn tracked_fn_extra(_db: &dyn Db, _input: MyTracked) -> u32 {
+    0
+}
+
+#[salsa::db(Jar)]
+#[derive(Default)]
+struct Database {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for Database {}
+
+impl Db for Database {}
+
+#[test]
+#[should_panic]
+fn execute_when_specified() {
+    let mut db = Database::default();
+    let input = MyInput::new(&mut db, 22);
+    let tracked = tracked_fn(&db, input);
+}
+
+