add some tests for constants (check for invalidation)

tests/incremental/constants.rs

@@ -0,0 +1,43 @@
+use crate::implementation::{TestContext, TestContextImpl};
+use salsa::Database;
+
+salsa::query_group! {
+    pub(crate) trait ConstantsDatabase: TestContext {
+        fn constants_input(key: usize) -> usize {
+            type ConstantsInput;
+            storage input;
+        }
+
+        fn constants_derived(key: usize) -> usize {
+            type ConstantsDerived;
+        }
+    }
+}
+
+fn constants_derived(db: &impl ConstantsDatabase, key: usize) -> usize {
+    db.log().add(format!("constants_derived({}) invoked", key));
+    db.constants_input(key) * 2
+}
+
+#[test]
+#[should_panic]
+fn invalidate_constant() {
+    let db = &TestContextImpl::default();
+    db.query(ConstantsInput).set_constant(22, 44);
+    db.query(ConstantsInput).set_constant(22, 66);
+}
+
+#[test]
+#[should_panic]
+fn invalidate_constant_1() {
+    let db = &TestContextImpl::default();
+
+    // Not constant:
+    db.query(ConstantsInput).set(22, 44);
+
+    // Becomes constant:
+    db.query(ConstantsInput).set_constant(22, 44);
+
+    // Invalidates:
+    db.query(ConstantsInput).set_constant(22, 66);
+}

tests/incremental/implementation.rs

@@ -1,3 +1,4 @@
+use crate::constants;
 use crate::counter::Counter;
 use crate::log::Log;
 use crate::memoized_dep_inputs;
@@ -43,6 +44,11 @@ impl TestContextImpl {
 
 salsa::database_storage! {
     pub(crate) struct TestContextImplStorage for TestContextImpl {
+        impl constants::ConstantsDatabase {
+            fn constants_input() for constants::ConstantsInput;
+            fn constants_derived() for constants::ConstantsDerived;
+        }
+
         impl memoized_dep_inputs::MemoizedDepInputsContext {
             fn dep_memoized2() for memoized_dep_inputs::Memoized2;
             fn dep_memoized1() for memoized_dep_inputs::Memoized1;

tests/incremental/main.rs

@@ -1,3 +1,4 @@
+mod constants;
 mod counter;
 mod implementation;
 mod log;