Merge commit 'ddf105b646' into sync-from-ra

crates/salsa/tests/cycles.rs

@@ -0,0 +1,493 @@
+use std::panic::UnwindSafe;
+
+use expect_test::expect;
+use salsa::{Durability, ParallelDatabase, Snapshot};
+use test_log::test;
+
+// Axes:
+//
+// Threading
+// * Intra-thread
+// * Cross-thread -- part of cycle is on one thread, part on another
+//
+// Recovery strategies:
+// * Panic
+// * Fallback
+// * Mixed -- multiple strategies within cycle participants
+//
+// Across revisions:
+// * N/A -- only one revision
+// * Present in new revision, not old
+// * Present in old revision, not new
+// * Present in both revisions
+//
+// Dependencies
+// * Tracked
+// * Untracked -- cycle participant(s) contain untracked reads
+//
+// Layers
+// * Direct -- cycle participant is directly invoked from test
+// * Indirect -- invoked a query that invokes the cycle
+//
+//
+// | Thread | Recovery | Old, New | Dep style | Layers   | Test Name      |
+// | ------ | -------- | -------- | --------- | ------   | ---------      |
+// | Intra  | Panic    | N/A      | Tracked   | direct   | cycle_memoized |
+// | Intra  | Panic    | N/A      | Untracked | direct   | cycle_volatile |
+// | Intra  | Fallback | N/A      | Tracked   | direct   | cycle_cycle  |
+// | Intra  | Fallback | N/A      | Tracked   | indirect | inner_cycle |
+// | Intra  | Fallback | Both     | Tracked   | direct   | cycle_revalidate |
+// | Intra  | Fallback | New      | Tracked   | direct   | cycle_appears |
+// | Intra  | Fallback | Old      | Tracked   | direct   | cycle_disappears |
+// | Intra  | Fallback | Old      | Tracked   | direct   | cycle_disappears_durability |
+// | Intra  | Mixed    | N/A      | Tracked   | direct   | cycle_mixed_1 |
+// | Intra  | Mixed    | N/A      | Tracked   | direct   | cycle_mixed_2 |
+// | Cross  | Fallback | N/A      | Tracked   | both     | parallel/cycles.rs: recover_parallel_cycle |
+// | Cross  | Panic    | N/A      | Tracked   | both     | parallel/cycles.rs: panic_parallel_cycle |
+
+#[derive(PartialEq, Eq, Hash, Clone, Debug)]
+struct Error {
+    cycle: Vec<String>,
+}
+
+#[salsa::database(GroupStruct)]
+#[derive(Default)]
+struct DatabaseImpl {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for DatabaseImpl {}
+
+impl ParallelDatabase for DatabaseImpl {
+    fn snapshot(&self) -> Snapshot<Self> {
+        Snapshot::new(DatabaseImpl { storage: self.storage.snapshot() })
+    }
+}
+
+/// The queries A, B, and C in `Database` can be configured
+/// to invoke one another in arbitrary ways using this
+/// enum.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum CycleQuery {
+    None,
+    A,
+    B,
+    C,
+    AthenC,
+}
+
+#[salsa::query_group(GroupStruct)]
+trait Database: salsa::Database {
+    // `a` and `b` depend on each other and form a cycle
+    fn memoized_a(&self) -> ();
+    fn memoized_b(&self) -> ();
+    fn volatile_a(&self) -> ();
+    fn volatile_b(&self) -> ();
+
+    #[salsa::input]
+    fn a_invokes(&self) -> CycleQuery;
+
+    #[salsa::input]
+    fn b_invokes(&self) -> CycleQuery;
+
+    #[salsa::input]
+    fn c_invokes(&self) -> CycleQuery;
+
+    #[salsa::cycle(recover_a)]
+    fn cycle_a(&self) -> Result<(), Error>;
+
+    #[salsa::cycle(recover_b)]
+    fn cycle_b(&self) -> Result<(), Error>;
+
+    fn cycle_c(&self) -> Result<(), Error>;
+}
+
+fn recover_a(db: &dyn Database, cycle: &salsa::Cycle) -> Result<(), Error> {
+    Err(Error { cycle: cycle.all_participants(db) })
+}
+
+fn recover_b(db: &dyn Database, cycle: &salsa::Cycle) -> Result<(), Error> {
+    Err(Error { cycle: cycle.all_participants(db) })
+}
+
+fn memoized_a(db: &dyn Database) {
+    db.memoized_b()
+}
+
+fn memoized_b(db: &dyn Database) {
+    db.memoized_a()
+}
+
+fn volatile_a(db: &dyn Database) {
+    db.salsa_runtime().report_untracked_read();
+    db.volatile_b()
+}
+
+fn volatile_b(db: &dyn Database) {
+    db.salsa_runtime().report_untracked_read();
+    db.volatile_a()
+}
+
+impl CycleQuery {
+    fn invoke(self, db: &dyn Database) -> Result<(), Error> {
+        match self {
+            CycleQuery::A => db.cycle_a(),
+            CycleQuery::B => db.cycle_b(),
+            CycleQuery::C => db.cycle_c(),
+            CycleQuery::AthenC => {
+                let _ = db.cycle_a();
+                db.cycle_c()
+            }
+            CycleQuery::None => Ok(()),
+        }
+    }
+}
+
+fn cycle_a(db: &dyn Database) -> Result<(), Error> {
+    db.a_invokes().invoke(db)
+}
+
+fn cycle_b(db: &dyn Database) -> Result<(), Error> {
+    db.b_invokes().invoke(db)
+}
+
+fn cycle_c(db: &dyn Database) -> Result<(), Error> {
+    db.c_invokes().invoke(db)
+}
+
+#[track_caller]
+fn extract_cycle(f: impl FnOnce() + UnwindSafe) -> salsa::Cycle {
+    let v = std::panic::catch_unwind(f);
+    if let Err(d) = &v {
+        if let Some(cycle) = d.downcast_ref::<salsa::Cycle>() {
+            return cycle.clone();
+        }
+    }
+    panic!("unexpected value: {:?}", v)
+}
+
+#[test]
+fn cycle_memoized() {
+    let db = DatabaseImpl::default();
+    let cycle = extract_cycle(|| db.memoized_a());
+    expect![[r#"
+        [
+            "memoized_a(())",
+            "memoized_b(())",
+        ]
+    "#]]
+    .assert_debug_eq(&cycle.unexpected_participants(&db));
+}
+
+#[test]
+fn cycle_volatile() {
+    let db = DatabaseImpl::default();
+    let cycle = extract_cycle(|| db.volatile_a());
+    expect![[r#"
+        [
+            "volatile_a(())",
+            "volatile_b(())",
+        ]
+    "#]]
+    .assert_debug_eq(&cycle.unexpected_participants(&db));
+}
+
+#[test]
+fn cycle_cycle() {
+    let mut query = DatabaseImpl::default();
+
+    //     A --> B
+    //     ^     |
+    //     +-----+
+
+    query.set_a_invokes(CycleQuery::B);
+    query.set_b_invokes(CycleQuery::A);
+
+    assert!(query.cycle_a().is_err());
+}
+
+#[test]
+fn inner_cycle() {
+    let mut query = DatabaseImpl::default();
+
+    //     A --> B <-- C
+    //     ^     |
+    //     +-----+
+
+    query.set_a_invokes(CycleQuery::B);
+    query.set_b_invokes(CycleQuery::A);
+    query.set_c_invokes(CycleQuery::B);
+
+    let err = query.cycle_c();
+    assert!(err.is_err());
+    let cycle = err.unwrap_err().cycle;
+    expect![[r#"
+        [
+            "cycle_a(())",
+            "cycle_b(())",
+        ]
+    "#]]
+    .assert_debug_eq(&cycle);
+}
+
+#[test]
+fn cycle_revalidate() {
+    let mut db = DatabaseImpl::default();
+
+    //     A --> B
+    //     ^     |
+    //     +-----+
+    db.set_a_invokes(CycleQuery::B);
+    db.set_b_invokes(CycleQuery::A);
+
+    assert!(db.cycle_a().is_err());
+    db.set_b_invokes(CycleQuery::A); // same value as default
+    assert!(db.cycle_a().is_err());
+}
+
+#[test]
+fn cycle_revalidate_unchanged_twice() {
+    let mut db = DatabaseImpl::default();
+
+    //     A --> B
+    //     ^     |
+    //     +-----+
+    db.set_a_invokes(CycleQuery::B);
+    db.set_b_invokes(CycleQuery::A);
+
+    assert!(db.cycle_a().is_err());
+    db.set_c_invokes(CycleQuery::A); // force new revisi5on
+
+    // on this run
+    expect![[r#"
+        Err(
+            Error {
+                cycle: [
+                    "cycle_a(())",
+                    "cycle_b(())",
+                ],
+            },
+        )
+    "#]]
+    .assert_debug_eq(&db.cycle_a());
+}
+
+#[test]
+fn cycle_appears() {
+    let mut db = DatabaseImpl::default();
+
+    //     A --> B
+    db.set_a_invokes(CycleQuery::B);
+    db.set_b_invokes(CycleQuery::None);
+    assert!(db.cycle_a().is_ok());
+
+    //     A --> B
+    //     ^     |
+    //     +-----+
+    db.set_b_invokes(CycleQuery::A);
+    tracing::debug!("Set Cycle Leaf");
+    assert!(db.cycle_a().is_err());
+}
+
+#[test]
+fn cycle_disappears() {
+    let mut db = DatabaseImpl::default();
+
+    //     A --> B
+    //     ^     |
+    //     +-----+
+    db.set_a_invokes(CycleQuery::B);
+    db.set_b_invokes(CycleQuery::A);
+    assert!(db.cycle_a().is_err());
+
+    //     A --> B
+    db.set_b_invokes(CycleQuery::None);
+    assert!(db.cycle_a().is_ok());
+}
+
+/// A variant on `cycle_disappears` in which the values of
+/// `a_invokes` and `b_invokes` are set with durability values.
+/// If we are not careful, this could cause us to overlook
+/// the fact that the cycle will no longer occur.
+#[test]
+fn cycle_disappears_durability() {
+    let mut db = DatabaseImpl::default();
+    db.set_a_invokes_with_durability(CycleQuery::B, Durability::LOW);
+    db.set_b_invokes_with_durability(CycleQuery::A, Durability::HIGH);
+
+    let res = db.cycle_a();
+    assert!(res.is_err());
+
+    // At this point, `a` read `LOW` input, and `b` read `HIGH` input. However,
+    // because `b` participates in the same cycle as `a`, its final durability
+    // should be `LOW`.
+    //
+    // Check that setting a `LOW` input causes us to re-execute `b` query, and
+    // observe that the cycle goes away.
+    db.set_a_invokes_with_durability(CycleQuery::None, Durability::LOW);
+
+    let res = db.cycle_b();
+    assert!(res.is_ok());
+}
+
+#[test]
+fn cycle_mixed_1() {
+    let mut db = DatabaseImpl::default();
+    //     A --> B <-- C
+    //           |     ^
+    //           +-----+
+    db.set_a_invokes(CycleQuery::B);
+    db.set_b_invokes(CycleQuery::C);
+    db.set_c_invokes(CycleQuery::B);
+
+    let u = db.cycle_c();
+    expect![[r#"
+        Err(
+            Error {
+                cycle: [
+                    "cycle_b(())",
+                    "cycle_c(())",
+                ],
+            },
+        )
+    "#]]
+    .assert_debug_eq(&u);
+}
+
+#[test]
+fn cycle_mixed_2() {
+    let mut db = DatabaseImpl::default();
+
+    // Configuration:
+    //
+    //     A --> B --> C
+    //     ^           |
+    //     +-----------+
+    db.set_a_invokes(CycleQuery::B);
+    db.set_b_invokes(CycleQuery::C);
+    db.set_c_invokes(CycleQuery::A);
+
+    let u = db.cycle_a();
+    expect![[r#"
+        Err(
+            Error {
+                cycle: [
+                    "cycle_a(())",
+                    "cycle_b(())",
+                    "cycle_c(())",
+                ],
+            },
+        )
+    "#]]
+    .assert_debug_eq(&u);
+}
+
+#[test]
+fn cycle_deterministic_order() {
+    // No matter whether we start from A or B, we get the same set of participants:
+    let db = || {
+        let mut db = DatabaseImpl::default();
+        //     A --> B
+        //     ^     |
+        //     +-----+
+        db.set_a_invokes(CycleQuery::B);
+        db.set_b_invokes(CycleQuery::A);
+        db
+    };
+    let a = db().cycle_a();
+    let b = db().cycle_b();
+    expect![[r#"
+        (
+            Err(
+                Error {
+                    cycle: [
+                        "cycle_a(())",
+                        "cycle_b(())",
+                    ],
+                },
+            ),
+            Err(
+                Error {
+                    cycle: [
+                        "cycle_a(())",
+                        "cycle_b(())",
+                    ],
+                },
+            ),
+        )
+    "#]]
+    .assert_debug_eq(&(a, b));
+}
+
+#[test]
+fn cycle_multiple() {
+    // No matter whether we start from A or B, we get the same set of participants:
+    let mut db = DatabaseImpl::default();
+
+    // Configuration:
+    //
+    //     A --> B <-- C
+    //     ^     |     ^
+    //     +-----+     |
+    //           |     |
+    //           +-----+
+    //
+    // Here, conceptually, B encounters a cycle with A and then
+    // recovers.
+    db.set_a_invokes(CycleQuery::B);
+    db.set_b_invokes(CycleQuery::AthenC);
+    db.set_c_invokes(CycleQuery::B);
+
+    let c = db.cycle_c();
+    let b = db.cycle_b();
+    let a = db.cycle_a();
+    expect![[r#"
+        (
+            Err(
+                Error {
+                    cycle: [
+                        "cycle_a(())",
+                        "cycle_b(())",
+                    ],
+                },
+            ),
+            Err(
+                Error {
+                    cycle: [
+                        "cycle_a(())",
+                        "cycle_b(())",
+                    ],
+                },
+            ),
+            Err(
+                Error {
+                    cycle: [
+                        "cycle_a(())",
+                        "cycle_b(())",
+                    ],
+                },
+            ),
+        )
+    "#]]
+    .assert_debug_eq(&(a, b, c));
+}
+
+#[test]
+fn cycle_recovery_set_but_not_participating() {
+    let mut db = DatabaseImpl::default();
+
+    //     A --> C -+
+    //           ^  |
+    //           +--+
+    db.set_a_invokes(CycleQuery::C);
+    db.set_c_invokes(CycleQuery::C);
+
+    // Here we expect C to panic and A not to recover:
+    let r = extract_cycle(|| drop(db.cycle_a()));
+    expect![[r#"
+        [
+            "cycle_c(())",
+        ]
+    "#]]
+    .assert_debug_eq(&r.all_participants(&db));
+}

crates/salsa/tests/dyn_trait.rs

@@ -0,0 +1,28 @@
+//! Test that you can implement a query using a `dyn Trait` setup.
+
+#[salsa::database(DynTraitStorage)]
+#[derive(Default)]
+struct DynTraitDatabase {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for DynTraitDatabase {}
+
+#[salsa::query_group(DynTraitStorage)]
+trait DynTrait {
+    #[salsa::input]
+    fn input(&self, x: u32) -> u32;
+
+    fn output(&self, x: u32) -> u32;
+}
+
+fn output(db: &dyn DynTrait, x: u32) -> u32 {
+    db.input(x) * 2
+}
+
+#[test]
+fn dyn_trait() {
+    let mut query = DynTraitDatabase::default();
+    query.set_input(22, 23);
+    assert_eq!(query.output(22), 46);
+}

crates/salsa/tests/incremental/constants.rs

@@ -0,0 +1,145 @@
+use crate::implementation::{TestContext, TestContextImpl};
+use salsa::debug::DebugQueryTable;
+use salsa::Durability;
+
+#[salsa::query_group(Constants)]
+pub(crate) trait ConstantsDatabase: TestContext {
+    #[salsa::input]
+    fn input(&self, key: char) -> usize;
+
+    fn add(&self, key1: char, key2: char) -> usize;
+
+    fn add3(&self, key1: char, key2: char, key3: char) -> usize;
+}
+
+fn add(db: &dyn ConstantsDatabase, key1: char, key2: char) -> usize {
+    db.log().add(format!("add({}, {})", key1, key2));
+    db.input(key1) + db.input(key2)
+}
+
+fn add3(db: &dyn ConstantsDatabase, key1: char, key2: char, key3: char) -> usize {
+    db.log().add(format!("add3({}, {}, {})", key1, key2, key3));
+    db.add(key1, key2) + db.input(key3)
+}
+
+// Test we can assign a constant and things will be correctly
+// recomputed afterwards.
+#[test]
+fn invalidate_constant() {
+    let db = &mut TestContextImpl::default();
+    db.set_input_with_durability('a', 44, Durability::HIGH);
+    db.set_input_with_durability('b', 22, Durability::HIGH);
+    assert_eq!(db.add('a', 'b'), 66);
+
+    db.set_input_with_durability('a', 66, Durability::HIGH);
+    assert_eq!(db.add('a', 'b'), 88);
+}
+
+#[test]
+fn invalidate_constant_1() {
+    let db = &mut TestContextImpl::default();
+
+    // Not constant:
+    db.set_input('a', 44);
+    assert_eq!(db.add('a', 'a'), 88);
+
+    // Becomes constant:
+    db.set_input_with_durability('a', 44, Durability::HIGH);
+    assert_eq!(db.add('a', 'a'), 88);
+
+    // Invalidates:
+    db.set_input_with_durability('a', 33, Durability::HIGH);
+    assert_eq!(db.add('a', 'a'), 66);
+}
+
+// Test cases where we assign same value to 'a' after declaring it a
+// constant.
+#[test]
+fn set_after_constant_same_value() {
+    let db = &mut TestContextImpl::default();
+    db.set_input_with_durability('a', 44, Durability::HIGH);
+    db.set_input_with_durability('a', 44, Durability::HIGH);
+    db.set_input('a', 44);
+}
+
+#[test]
+fn not_constant() {
+    let mut db = TestContextImpl::default();
+
+    db.set_input('a', 22);
+    db.set_input('b', 44);
+    assert_eq!(db.add('a', 'b'), 66);
+    assert_eq!(Durability::LOW, AddQuery.in_db(&db).durability(('a', 'b')));
+}
+
+#[test]
+fn durability() {
+    let mut db = TestContextImpl::default();
+
+    db.set_input_with_durability('a', 22, Durability::HIGH);
+    db.set_input_with_durability('b', 44, Durability::HIGH);
+    assert_eq!(db.add('a', 'b'), 66);
+    assert_eq!(Durability::HIGH, AddQuery.in_db(&db).durability(('a', 'b')));
+}
+
+#[test]
+fn mixed_constant() {
+    let mut db = TestContextImpl::default();
+
+    db.set_input_with_durability('a', 22, Durability::HIGH);
+    db.set_input('b', 44);
+    assert_eq!(db.add('a', 'b'), 66);
+    assert_eq!(Durability::LOW, AddQuery.in_db(&db).durability(('a', 'b')));
+}
+
+#[test]
+fn becomes_constant_with_change() {
+    let mut db = TestContextImpl::default();
+
+    db.set_input('a', 22);
+    db.set_input('b', 44);
+    assert_eq!(db.add('a', 'b'), 66);
+    assert_eq!(Durability::LOW, AddQuery.in_db(&db).durability(('a', 'b')));
+
+    db.set_input_with_durability('a', 23, Durability::HIGH);
+    assert_eq!(db.add('a', 'b'), 67);
+    assert_eq!(Durability::LOW, AddQuery.in_db(&db).durability(('a', 'b')));
+
+    db.set_input_with_durability('b', 45, Durability::HIGH);
+    assert_eq!(db.add('a', 'b'), 68);
+    assert_eq!(Durability::HIGH, AddQuery.in_db(&db).durability(('a', 'b')));
+
+    db.set_input_with_durability('b', 45, Durability::MEDIUM);
+    assert_eq!(db.add('a', 'b'), 68);
+    assert_eq!(Durability::MEDIUM, AddQuery.in_db(&db).durability(('a', 'b')));
+}
+
+// Test a subtle case in which an input changes from constant to
+// non-constant, but its value doesn't change. If we're not careful,
+// this can cause us to incorrectly consider derived values as still
+// being constant.
+#[test]
+fn constant_to_non_constant() {
+    let mut db = TestContextImpl::default();
+
+    db.set_input_with_durability('a', 11, Durability::HIGH);
+    db.set_input_with_durability('b', 22, Durability::HIGH);
+    db.set_input_with_durability('c', 33, Durability::HIGH);
+
+    // Here, `add3` invokes `add`, which yields 33. Both calls are
+    // constant.
+    assert_eq!(db.add3('a', 'b', 'c'), 66);
+
+    db.set_input('a', 11);
+
+    // Here, `add3` invokes `add`, which *still* yields 33, but which
+    // is no longer constant. Since value didn't change, we might
+    // preserve `add3` unchanged, not noticing that it is no longer
+    // constant.
+    assert_eq!(db.add3('a', 'b', 'c'), 66);
+
+    // In that case, we would not get the correct result here, when
+    // 'a' changes *again*.
+    db.set_input('a', 22);
+    assert_eq!(db.add3('a', 'b', 'c'), 77);
+}

crates/salsa/tests/incremental/counter.rs

@@ -0,0 +1,14 @@
+use std::cell::Cell;
+
+#[derive(Default)]
+pub(crate) struct Counter {
+    value: Cell<usize>,
+}
+
+impl Counter {
+    pub(crate) fn increment(&self) -> usize {
+        let v = self.value.get();
+        self.value.set(v + 1);
+        v
+    }
+}

crates/salsa/tests/incremental/implementation.rs

@@ -0,0 +1,59 @@
+use crate::constants;
+use crate::counter::Counter;
+use crate::log::Log;
+use crate::memoized_dep_inputs;
+use crate::memoized_inputs;
+use crate::memoized_volatile;
+
+pub(crate) trait TestContext: salsa::Database {
+    fn clock(&self) -> &Counter;
+    fn log(&self) -> &Log;
+}
+
+#[salsa::database(
+    constants::Constants,
+    memoized_dep_inputs::MemoizedDepInputs,
+    memoized_inputs::MemoizedInputs,
+    memoized_volatile::MemoizedVolatile
+)]
+#[derive(Default)]
+pub(crate) struct TestContextImpl {
+    storage: salsa::Storage<TestContextImpl>,
+    clock: Counter,
+    log: Log,
+}
+
+impl TestContextImpl {
+    #[track_caller]
+    pub(crate) fn assert_log(&self, expected_log: &[&str]) {
+        let expected_text = &format!("{:#?}", expected_log);
+        let actual_text = &format!("{:#?}", self.log().take());
+
+        if expected_text == actual_text {
+            return;
+        }
+
+        #[allow(clippy::print_stdout)]
+        for diff in dissimilar::diff(expected_text, actual_text) {
+            match diff {
+                dissimilar::Chunk::Delete(l) => println!("-{}", l),
+                dissimilar::Chunk::Equal(l) => println!(" {}", l),
+                dissimilar::Chunk::Insert(r) => println!("+{}", r),
+            }
+        }
+
+        panic!("incorrect log results");
+    }
+}
+
+impl TestContext for TestContextImpl {
+    fn clock(&self) -> &Counter {
+        &self.clock
+    }
+
+    fn log(&self) -> &Log {
+        &self.log
+    }
+}
+
+impl salsa::Database for TestContextImpl {}

crates/salsa/tests/incremental/log.rs

@@ -0,0 +1,16 @@
+use std::cell::RefCell;
+
+#[derive(Default)]
+pub(crate) struct Log {
+    data: RefCell<Vec<String>>,
+}
+
+impl Log {
+    pub(crate) fn add(&self, text: impl Into<String>) {
+        self.data.borrow_mut().push(text.into());
+    }
+
+    pub(crate) fn take(&self) -> Vec<String> {
+        self.data.take()
+    }
+}

crates/salsa/tests/incremental/main.rs

@@ -0,0 +1,9 @@
+mod constants;
+mod counter;
+mod implementation;
+mod log;
+mod memoized_dep_inputs;
+mod memoized_inputs;
+mod memoized_volatile;
+
+fn main() {}

crates/salsa/tests/incremental/memoized_dep_inputs.rs

@@ -0,0 +1,60 @@
+use crate::implementation::{TestContext, TestContextImpl};
+
+#[salsa::query_group(MemoizedDepInputs)]
+pub(crate) trait MemoizedDepInputsContext: TestContext {
+    fn dep_memoized2(&self) -> usize;
+    fn dep_memoized1(&self) -> usize;
+    #[salsa::dependencies]
+    fn dep_derived1(&self) -> usize;
+    #[salsa::input]
+    fn dep_input1(&self) -> usize;
+    #[salsa::input]
+    fn dep_input2(&self) -> usize;
+}
+
+fn dep_memoized2(db: &dyn MemoizedDepInputsContext) -> usize {
+    db.log().add("Memoized2 invoked");
+    db.dep_memoized1()
+}
+
+fn dep_memoized1(db: &dyn MemoizedDepInputsContext) -> usize {
+    db.log().add("Memoized1 invoked");
+    db.dep_derived1() * 2
+}
+
+fn dep_derived1(db: &dyn MemoizedDepInputsContext) -> usize {
+    db.log().add("Derived1 invoked");
+    db.dep_input1() / 2
+}
+
+#[test]
+fn revalidate() {
+    let db = &mut TestContextImpl::default();
+
+    db.set_dep_input1(0);
+
+    // Initial run starts from Memoized2:
+    let v = db.dep_memoized2();
+    assert_eq!(v, 0);
+    db.assert_log(&["Memoized2 invoked", "Memoized1 invoked", "Derived1 invoked"]);
+
+    // After that, we first try to validate Memoized1 but wind up
+    // running Memoized2. Note that we don't try to validate
+    // Derived1, so it is invoked by Memoized1.
+    db.set_dep_input1(44);
+    let v = db.dep_memoized2();
+    assert_eq!(v, 44);
+    db.assert_log(&["Memoized1 invoked", "Derived1 invoked", "Memoized2 invoked"]);
+
+    // Here validation of Memoized1 succeeds so Memoized2 never runs.
+    db.set_dep_input1(45);
+    let v = db.dep_memoized2();
+    assert_eq!(v, 44);
+    db.assert_log(&["Memoized1 invoked", "Derived1 invoked"]);
+
+    // Here, a change to input2 doesn't affect us, so nothing runs.
+    db.set_dep_input2(45);
+    let v = db.dep_memoized2();
+    assert_eq!(v, 44);
+    db.assert_log(&[]);
+}

crates/salsa/tests/incremental/memoized_inputs.rs

@@ -0,0 +1,76 @@
+use crate::implementation::{TestContext, TestContextImpl};
+
+#[salsa::query_group(MemoizedInputs)]
+pub(crate) trait MemoizedInputsContext: TestContext {
+    fn max(&self) -> usize;
+    #[salsa::input]
+    fn input1(&self) -> usize;
+    #[salsa::input]
+    fn input2(&self) -> usize;
+}
+
+fn max(db: &dyn MemoizedInputsContext) -> usize {
+    db.log().add("Max invoked");
+    std::cmp::max(db.input1(), db.input2())
+}
+
+#[test]
+fn revalidate() {
+    let db = &mut TestContextImpl::default();
+
+    db.set_input1(0);
+    db.set_input2(0);
+
+    let v = db.max();
+    assert_eq!(v, 0);
+    db.assert_log(&["Max invoked"]);
+
+    let v = db.max();
+    assert_eq!(v, 0);
+    db.assert_log(&[]);
+
+    db.set_input1(44);
+    db.assert_log(&[]);
+
+    let v = db.max();
+    assert_eq!(v, 44);
+    db.assert_log(&["Max invoked"]);
+
+    let v = db.max();
+    assert_eq!(v, 44);
+    db.assert_log(&[]);
+
+    db.set_input1(44);
+    db.assert_log(&[]);
+    db.set_input2(66);
+    db.assert_log(&[]);
+    db.set_input1(64);
+    db.assert_log(&[]);
+
+    let v = db.max();
+    assert_eq!(v, 66);
+    db.assert_log(&["Max invoked"]);
+
+    let v = db.max();
+    assert_eq!(v, 66);
+    db.assert_log(&[]);
+}
+
+/// Test that invoking `set` on an input with the same value still
+/// triggers a new revision.
+#[test]
+fn set_after_no_change() {
+    let db = &mut TestContextImpl::default();
+
+    db.set_input2(0);
+
+    db.set_input1(44);
+    let v = db.max();
+    assert_eq!(v, 44);
+    db.assert_log(&["Max invoked"]);
+
+    db.set_input1(44);
+    let v = db.max();
+    assert_eq!(v, 44);
+    db.assert_log(&["Max invoked"]);
+}

crates/salsa/tests/incremental/memoized_volatile.rs

@@ -0,0 +1,77 @@
+use crate::implementation::{TestContext, TestContextImpl};
+use salsa::{Database, Durability};
+
+#[salsa::query_group(MemoizedVolatile)]
+pub(crate) trait MemoizedVolatileContext: TestContext {
+    // Queries for testing a "volatile" value wrapped by
+    // memoization.
+    fn memoized2(&self) -> usize;
+    fn memoized1(&self) -> usize;
+    fn volatile(&self) -> usize;
+}
+
+fn memoized2(db: &dyn MemoizedVolatileContext) -> usize {
+    db.log().add("Memoized2 invoked");
+    db.memoized1()
+}
+
+fn memoized1(db: &dyn MemoizedVolatileContext) -> usize {
+    db.log().add("Memoized1 invoked");
+    let v = db.volatile();
+    v / 2
+}
+
+fn volatile(db: &dyn MemoizedVolatileContext) -> usize {
+    db.log().add("Volatile invoked");
+    db.salsa_runtime().report_untracked_read();
+    db.clock().increment()
+}
+
+#[test]
+fn volatile_x2() {
+    let query = TestContextImpl::default();
+
+    // Invoking volatile twice doesn't execute twice, because volatile
+    // queries are memoized by default.
+    query.volatile();
+    query.volatile();
+    query.assert_log(&["Volatile invoked"]);
+}
+
+/// Test that:
+///
+/// - On the first run of R0, we recompute everything.
+/// - On the second run of R1, we recompute nothing.
+/// - On the first run of R1, we recompute Memoized1 but not Memoized2 (since Memoized1 result
+///   did not change).
+/// - On the second run of R1, we recompute nothing.
+/// - On the first run of R2, we recompute everything (since Memoized1 result *did* change).
+#[test]
+fn revalidate() {
+    let mut query = TestContextImpl::default();
+
+    query.memoized2();
+    query.assert_log(&["Memoized2 invoked", "Memoized1 invoked", "Volatile invoked"]);
+
+    query.memoized2();
+    query.assert_log(&[]);
+
+    // Second generation: volatile will change (to 1) but memoized1
+    // will not (still 0, as 1/2 = 0)
+    query.salsa_runtime_mut().synthetic_write(Durability::LOW);
+    query.memoized2();
+    query.assert_log(&["Volatile invoked", "Memoized1 invoked"]);
+    query.memoized2();
+    query.assert_log(&[]);
+
+    // Third generation: volatile will change (to 2) and memoized1
+    // will too (to 1).  Therefore, after validating that Memoized1
+    // changed, we now invoke Memoized2.
+    query.salsa_runtime_mut().synthetic_write(Durability::LOW);
+
+    query.memoized2();
+    query.assert_log(&["Volatile invoked", "Memoized1 invoked", "Memoized2 invoked"]);
+
+    query.memoized2();
+    query.assert_log(&[]);
+}

crates/salsa/tests/interned.rs

@@ -0,0 +1,90 @@
+//! Test that you can implement a query using a `dyn Trait` setup.
+
+use salsa::InternId;
+
+#[salsa::database(InternStorage)]
+#[derive(Default)]
+struct Database {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for Database {}
+
+impl salsa::ParallelDatabase for Database {
+    fn snapshot(&self) -> salsa::Snapshot<Self> {
+        salsa::Snapshot::new(Database { storage: self.storage.snapshot() })
+    }
+}
+
+#[salsa::query_group(InternStorage)]
+trait Intern {
+    #[salsa::interned]
+    fn intern1(&self, x: String) -> InternId;
+
+    #[salsa::interned]
+    fn intern2(&self, x: String, y: String) -> InternId;
+
+    #[salsa::interned]
+    fn intern_key(&self, x: String) -> InternKey;
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct InternKey(InternId);
+
+impl salsa::InternKey for InternKey {
+    fn from_intern_id(v: InternId) -> Self {
+        InternKey(v)
+    }
+
+    fn as_intern_id(&self) -> InternId {
+        self.0
+    }
+}
+
+#[test]
+fn test_intern1() {
+    let db = Database::default();
+    let foo0 = db.intern1("foo".to_owned());
+    let bar0 = db.intern1("bar".to_owned());
+    let foo1 = db.intern1("foo".to_owned());
+    let bar1 = db.intern1("bar".to_owned());
+
+    assert_eq!(foo0, foo1);
+    assert_eq!(bar0, bar1);
+    assert_ne!(foo0, bar0);
+
+    assert_eq!("foo".to_owned(), db.lookup_intern1(foo0));
+    assert_eq!("bar".to_owned(), db.lookup_intern1(bar0));
+}
+
+#[test]
+fn test_intern2() {
+    let db = Database::default();
+    let foo0 = db.intern2("x".to_owned(), "foo".to_owned());
+    let bar0 = db.intern2("x".to_owned(), "bar".to_owned());
+    let foo1 = db.intern2("x".to_owned(), "foo".to_owned());
+    let bar1 = db.intern2("x".to_owned(), "bar".to_owned());
+
+    assert_eq!(foo0, foo1);
+    assert_eq!(bar0, bar1);
+    assert_ne!(foo0, bar0);
+
+    assert_eq!(("x".to_owned(), "foo".to_owned()), db.lookup_intern2(foo0));
+    assert_eq!(("x".to_owned(), "bar".to_owned()), db.lookup_intern2(bar0));
+}
+
+#[test]
+fn test_intern_key() {
+    let db = Database::default();
+    let foo0 = db.intern_key("foo".to_owned());
+    let bar0 = db.intern_key("bar".to_owned());
+    let foo1 = db.intern_key("foo".to_owned());
+    let bar1 = db.intern_key("bar".to_owned());
+
+    assert_eq!(foo0, foo1);
+    assert_eq!(bar0, bar1);
+    assert_ne!(foo0, bar0);
+
+    assert_eq!("foo".to_owned(), db.lookup_intern_key(foo0));
+    assert_eq!("bar".to_owned(), db.lookup_intern_key(bar0));
+}

crates/salsa/tests/lru.rs

@@ -0,0 +1,102 @@
+//! Test setting LRU actually limits the number of things in the database;
+use std::sync::{
+    atomic::{AtomicUsize, Ordering},
+    Arc,
+};
+
+#[derive(Debug, PartialEq, Eq)]
+struct HotPotato(u32);
+
+static N_POTATOES: AtomicUsize = AtomicUsize::new(0);
+
+impl HotPotato {
+    fn new(id: u32) -> HotPotato {
+        N_POTATOES.fetch_add(1, Ordering::SeqCst);
+        HotPotato(id)
+    }
+}
+
+impl Drop for HotPotato {
+    fn drop(&mut self) {
+        N_POTATOES.fetch_sub(1, Ordering::SeqCst);
+    }
+}
+
+#[salsa::query_group(QueryGroupStorage)]
+trait QueryGroup: salsa::Database {
+    fn get(&self, x: u32) -> Arc<HotPotato>;
+    fn get_volatile(&self, x: u32) -> usize;
+}
+
+fn get(_db: &dyn QueryGroup, x: u32) -> Arc<HotPotato> {
+    Arc::new(HotPotato::new(x))
+}
+
+fn get_volatile(db: &dyn QueryGroup, _x: u32) -> usize {
+    static COUNTER: AtomicUsize = AtomicUsize::new(0);
+    db.salsa_runtime().report_untracked_read();
+    COUNTER.fetch_add(1, Ordering::SeqCst)
+}
+
+#[salsa::database(QueryGroupStorage)]
+#[derive(Default)]
+struct Database {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for Database {}
+
+#[test]
+fn lru_works() {
+    let mut db = Database::default();
+    GetQuery.in_db_mut(&mut db).set_lru_capacity(32);
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 0);
+
+    for i in 0..128u32 {
+        let p = db.get(i);
+        assert_eq!(p.0, i)
+    }
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 32);
+
+    for i in 0..128u32 {
+        let p = db.get(i);
+        assert_eq!(p.0, i)
+    }
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 32);
+
+    GetQuery.in_db_mut(&mut db).set_lru_capacity(32);
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 32);
+
+    GetQuery.in_db_mut(&mut db).set_lru_capacity(64);
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 32);
+    for i in 0..128u32 {
+        let p = db.get(i);
+        assert_eq!(p.0, i)
+    }
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 64);
+
+    // Special case: setting capacity to zero disables LRU
+    GetQuery.in_db_mut(&mut db).set_lru_capacity(0);
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 64);
+    for i in 0..128u32 {
+        let p = db.get(i);
+        assert_eq!(p.0, i)
+    }
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 128);
+
+    drop(db);
+    assert_eq!(N_POTATOES.load(Ordering::SeqCst), 0);
+}
+
+#[test]
+fn lru_doesnt_break_volatile_queries() {
+    let mut db = Database::default();
+    GetVolatileQuery.in_db_mut(&mut db).set_lru_capacity(32);
+    // Here, we check that we execute each volatile query at most once, despite
+    // LRU. That does mean that we have more values in DB than the LRU capacity,
+    // but it's much better than inconsistent results from volatile queries!
+    for i in (0..3).flat_map(|_| 0..128usize) {
+        let x = db.get_volatile(i as u32);
+        assert_eq!(x, i)
+    }
+}

crates/salsa/tests/macros.rs

@@ -0,0 +1,11 @@
+#[salsa::query_group(MyStruct)]
+trait MyDatabase: salsa::Database {
+    #[salsa::invoke(another_module::another_name)]
+    fn my_query(&self, key: ()) -> ();
+}
+
+mod another_module {
+    pub(crate) fn another_name(_: &dyn crate::MyDatabase, (): ()) {}
+}
+
+fn main() {}

crates/salsa/tests/no_send_sync.rs

@@ -0,0 +1,31 @@
+use std::rc::Rc;
+
+#[salsa::query_group(NoSendSyncStorage)]
+trait NoSendSyncDatabase: salsa::Database {
+    fn no_send_sync_value(&self, key: bool) -> Rc<bool>;
+    fn no_send_sync_key(&self, key: Rc<bool>) -> bool;
+}
+
+fn no_send_sync_value(_db: &dyn NoSendSyncDatabase, key: bool) -> Rc<bool> {
+    Rc::new(key)
+}
+
+fn no_send_sync_key(_db: &dyn NoSendSyncDatabase, key: Rc<bool>) -> bool {
+    *key
+}
+
+#[salsa::database(NoSendSyncStorage)]
+#[derive(Default)]
+struct DatabaseImpl {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for DatabaseImpl {}
+
+#[test]
+fn no_send_sync() {
+    let db = DatabaseImpl::default();
+
+    assert_eq!(db.no_send_sync_value(true), Rc::new(true));
+    assert!(!db.no_send_sync_key(Rc::new(false)));
+}

crates/salsa/tests/on_demand_inputs.rs

@@ -0,0 +1,147 @@
+//! Test that "on-demand" input pattern works.
+//!
+//! On-demand inputs are inputs computed lazily on the fly. They are simulated
+//! via a b query with zero inputs, which uses `add_synthetic_read` to
+//! tweak durability and `invalidate` to clear the input.
+
+#![allow(clippy::disallowed_types, clippy::type_complexity)]
+
+use std::{cell::RefCell, collections::HashMap, rc::Rc};
+
+use salsa::{Database as _, Durability, EventKind};
+
+#[salsa::query_group(QueryGroupStorage)]
+trait QueryGroup: salsa::Database + AsRef<HashMap<u32, u32>> {
+    fn a(&self, x: u32) -> u32;
+    fn b(&self, x: u32) -> u32;
+    fn c(&self, x: u32) -> u32;
+}
+
+fn a(db: &dyn QueryGroup, x: u32) -> u32 {
+    let durability = if x % 2 == 0 { Durability::LOW } else { Durability::HIGH };
+    db.salsa_runtime().report_synthetic_read(durability);
+    let external_state: &HashMap<u32, u32> = db.as_ref();
+    external_state[&x]
+}
+
+fn b(db: &dyn QueryGroup, x: u32) -> u32 {
+    db.a(x)
+}
+
+fn c(db: &dyn QueryGroup, x: u32) -> u32 {
+    db.b(x)
+}
+
+#[salsa::database(QueryGroupStorage)]
+#[derive(Default)]
+struct Database {
+    storage: salsa::Storage<Self>,
+    external_state: HashMap<u32, u32>,
+    on_event: Option<Box<dyn Fn(&Database, salsa::Event)>>,
+}
+
+impl salsa::Database for Database {
+    fn salsa_event(&self, event: salsa::Event) {
+        if let Some(cb) = &self.on_event {
+            cb(self, event)
+        }
+    }
+}
+
+impl AsRef<HashMap<u32, u32>> for Database {
+    fn as_ref(&self) -> &HashMap<u32, u32> {
+        &self.external_state
+    }
+}
+
+#[test]
+fn on_demand_input_works() {
+    let mut db = Database::default();
+
+    db.external_state.insert(1, 10);
+    assert_eq!(db.b(1), 10);
+    assert_eq!(db.a(1), 10);
+
+    // We changed external state, but haven't signaled about this yet,
+    // so we expect to see the old answer
+    db.external_state.insert(1, 92);
+    assert_eq!(db.b(1), 10);
+    assert_eq!(db.a(1), 10);
+
+    AQuery.in_db_mut(&mut db).invalidate(&1);
+    assert_eq!(db.b(1), 92);
+    assert_eq!(db.a(1), 92);
+
+    // Downstream queries should also be rerun if we call `a` first.
+    db.external_state.insert(1, 50);
+    AQuery.in_db_mut(&mut db).invalidate(&1);
+    assert_eq!(db.a(1), 50);
+    assert_eq!(db.b(1), 50);
+}
+
+#[test]
+fn on_demand_input_durability() {
+    let mut db = Database::default();
+
+    let events = Rc::new(RefCell::new(vec![]));
+    db.on_event = Some(Box::new({
+        let events = events.clone();
+        move |db, event| {
+            if let EventKind::WillCheckCancellation = event.kind {
+                // these events are not interesting
+            } else {
+                events.borrow_mut().push(format!("{:?}", event.debug(db)))
+            }
+        }
+    }));
+
+    events.replace(vec![]);
+    db.external_state.insert(1, 10);
+    db.external_state.insert(2, 20);
+    assert_eq!(db.b(1), 10);
+    assert_eq!(db.b(2), 20);
+    expect_test::expect![[r#"
+        RefCell {
+            value: [
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: b(1) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: a(1) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: b(2) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: a(2) } }",
+            ],
+        }
+    "#]].assert_debug_eq(&events);
+
+    db.salsa_runtime_mut().synthetic_write(Durability::LOW);
+    events.replace(vec![]);
+    assert_eq!(db.c(1), 10);
+    assert_eq!(db.c(2), 20);
+    // Re-execute `a(2)` because that has low durability, but not `a(1)`
+    expect_test::expect![[r#"
+        RefCell {
+            value: [
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: c(1) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: DidValidateMemoizedValue { database_key: b(1) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: c(2) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: a(2) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: DidValidateMemoizedValue { database_key: b(2) } }",
+            ],
+        }
+    "#]].assert_debug_eq(&events);
+
+    db.salsa_runtime_mut().synthetic_write(Durability::HIGH);
+    events.replace(vec![]);
+    assert_eq!(db.c(1), 10);
+    assert_eq!(db.c(2), 20);
+    // Re-execute both `a(1)` and `a(2)`, but we don't re-execute any `b` queries as the
+    // result didn't actually change.
+    expect_test::expect![[r#"
+        RefCell {
+            value: [
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: a(1) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: DidValidateMemoizedValue { database_key: c(1) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: WillExecute { database_key: a(2) } }",
+                "Event { runtime_id: RuntimeId { counter: 0 }, kind: DidValidateMemoizedValue { database_key: c(2) } }",
+            ],
+        }
+    "#]].assert_debug_eq(&events);
+}

crates/salsa/tests/panic_safely.rs

@@ -0,0 +1,93 @@
+use salsa::{Database, ParallelDatabase, Snapshot};
+use std::panic::{self, AssertUnwindSafe};
+use std::sync::atomic::{AtomicU32, Ordering::SeqCst};
+
+#[salsa::query_group(PanicSafelyStruct)]
+trait PanicSafelyDatabase: salsa::Database {
+    #[salsa::input]
+    fn one(&self) -> usize;
+
+    fn panic_safely(&self) -> ();
+
+    fn outer(&self) -> ();
+}
+
+fn panic_safely(db: &dyn PanicSafelyDatabase) {
+    assert_eq!(db.one(), 1);
+}
+
+static OUTER_CALLS: AtomicU32 = AtomicU32::new(0);
+
+fn outer(db: &dyn PanicSafelyDatabase) {
+    OUTER_CALLS.fetch_add(1, SeqCst);
+    db.panic_safely();
+}
+
+#[salsa::database(PanicSafelyStruct)]
+#[derive(Default)]
+struct DatabaseStruct {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for DatabaseStruct {}
+
+impl salsa::ParallelDatabase for DatabaseStruct {
+    fn snapshot(&self) -> Snapshot<Self> {
+        Snapshot::new(DatabaseStruct { storage: self.storage.snapshot() })
+    }
+}
+
+#[test]
+fn should_panic_safely() {
+    let mut db = DatabaseStruct::default();
+    db.set_one(0);
+
+    // Invoke `db.panic_safely() without having set `db.one`. `db.one` will
+    // return 0 and we should catch the panic.
+    let result = panic::catch_unwind(AssertUnwindSafe({
+        let db = db.snapshot();
+        move || db.panic_safely()
+    }));
+    assert!(result.is_err());
+
+    // Set `db.one` to 1 and assert ok
+    db.set_one(1);
+    let result = panic::catch_unwind(AssertUnwindSafe(|| db.panic_safely()));
+    assert!(result.is_ok());
+
+    // Check, that memoized outer is not invalidated by a panic
+    {
+        assert_eq!(OUTER_CALLS.load(SeqCst), 0);
+        db.outer();
+        assert_eq!(OUTER_CALLS.load(SeqCst), 1);
+
+        db.set_one(0);
+        let result = panic::catch_unwind(AssertUnwindSafe(|| db.outer()));
+        assert!(result.is_err());
+        assert_eq!(OUTER_CALLS.load(SeqCst), 1);
+
+        db.set_one(1);
+        db.outer();
+        assert_eq!(OUTER_CALLS.load(SeqCst), 2);
+    }
+}
+
+#[test]
+fn storages_are_unwind_safe() {
+    fn check_unwind_safe<T: std::panic::UnwindSafe>() {}
+    check_unwind_safe::<&DatabaseStruct>();
+}
+
+#[test]
+fn panics_clear_query_stack() {
+    let db = DatabaseStruct::default();
+
+    // Invoke `db.panic_if_not_one() without having set `db.input`. `db.input`
+    // will default to 0 and we should catch the panic.
+    let result = panic::catch_unwind(AssertUnwindSafe(|| db.panic_safely()));
+    assert!(result.is_err());
+
+    // The database has been poisoned and any attempt to increment the
+    // revision should panic.
+    assert_eq!(db.salsa_runtime().active_query(), None);
+}

crates/salsa/tests/parallel/cancellation.rs

@@ -0,0 +1,132 @@
+use crate::setup::{CancellationFlag, Knobs, ParDatabase, ParDatabaseImpl, WithValue};
+use salsa::{Cancelled, ParallelDatabase};
+
+macro_rules! assert_cancelled {
+    ($thread:expr) => {
+        match $thread.join() {
+            Ok(value) => panic!("expected cancellation, got {:?}", value),
+            Err(payload) => match payload.downcast::<Cancelled>() {
+                Ok(_) => {}
+                Err(payload) => ::std::panic::resume_unwind(payload),
+            },
+        }
+    };
+}
+
+/// Add test where a call to `sum` is cancelled by a simultaneous
+/// write. Check that we recompute the result in next revision, even
+/// though none of the inputs have changed.
+#[test]
+fn in_par_get_set_cancellation_immediate() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 100);
+    db.set_input('b', 10);
+    db.set_input('c', 1);
+    db.set_input('d', 0);
+
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            // This will not return until it sees cancellation is
+            // signaled.
+            db.knobs().sum_signal_on_entry.with_value(1, || {
+                db.knobs()
+                    .sum_wait_for_cancellation
+                    .with_value(CancellationFlag::Panic, || db.sum("abc"))
+            })
+        }
+    });
+
+    // Wait until we have entered `sum` in the other thread.
+    db.wait_for(1);
+
+    // Try to set the input. This will signal cancellation.
+    db.set_input('d', 1000);
+
+    // This should re-compute the value (even though no input has changed).
+    let thread2 = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.sum("abc")
+    });
+
+    assert_eq!(db.sum("d"), 1000);
+    assert_cancelled!(thread1);
+    assert_eq!(thread2.join().unwrap(), 111);
+}
+
+/// Here, we check that `sum`'s cancellation is propagated
+/// to `sum2` properly.
+#[test]
+fn in_par_get_set_cancellation_transitive() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 100);
+    db.set_input('b', 10);
+    db.set_input('c', 1);
+    db.set_input('d', 0);
+
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            // This will not return until it sees cancellation is
+            // signaled.
+            db.knobs().sum_signal_on_entry.with_value(1, || {
+                db.knobs()
+                    .sum_wait_for_cancellation
+                    .with_value(CancellationFlag::Panic, || db.sum2("abc"))
+            })
+        }
+    });
+
+    // Wait until we have entered `sum` in the other thread.
+    db.wait_for(1);
+
+    // Try to set the input. This will signal cancellation.
+    db.set_input('d', 1000);
+
+    // This should re-compute the value (even though no input has changed).
+    let thread2 = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.sum2("abc")
+    });
+
+    assert_eq!(db.sum2("d"), 1000);
+    assert_cancelled!(thread1);
+    assert_eq!(thread2.join().unwrap(), 111);
+}
+
+/// https://github.com/salsa-rs/salsa/issues/66
+#[test]
+fn no_back_dating_in_cancellation() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 1);
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            // Here we compute a long-chain of queries,
+            // but the last one gets cancelled.
+            db.knobs().sum_signal_on_entry.with_value(1, || {
+                db.knobs()
+                    .sum_wait_for_cancellation
+                    .with_value(CancellationFlag::Panic, || db.sum3("a"))
+            })
+        }
+    });
+
+    db.wait_for(1);
+
+    // Set unrelated input to bump revision
+    db.set_input('b', 2);
+
+    // Here we should recompuet the whole chain again, clearing the cancellation
+    // state. If we get `usize::max()` here, it is a bug!
+    assert_eq!(db.sum3("a"), 1);
+
+    assert_cancelled!(thread1);
+
+    db.set_input('a', 3);
+    db.set_input('a', 4);
+    assert_eq!(db.sum3("ab"), 6);
+}

crates/salsa/tests/parallel/frozen.rs

@@ -0,0 +1,57 @@
+use crate::setup::{ParDatabase, ParDatabaseImpl};
+use crate::signal::Signal;
+use salsa::{Database, ParallelDatabase};
+use std::{
+    panic::{catch_unwind, AssertUnwindSafe},
+    sync::Arc,
+};
+
+/// Add test where a call to `sum` is cancelled by a simultaneous
+/// write. Check that we recompute the result in next revision, even
+/// though none of the inputs have changed.
+#[test]
+fn in_par_get_set_cancellation() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 1);
+
+    let signal = Arc::new(Signal::default());
+
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        let signal = signal.clone();
+        move || {
+            // Check that cancellation flag is not yet set, because
+            // `set` cannot have been called yet.
+            catch_unwind(AssertUnwindSafe(|| db.unwind_if_cancelled())).unwrap();
+
+            // Signal other thread to proceed.
+            signal.signal(1);
+
+            // Wait for other thread to signal cancellation
+            catch_unwind(AssertUnwindSafe(|| loop {
+                db.unwind_if_cancelled();
+                std::thread::yield_now();
+            }))
+            .unwrap_err();
+        }
+    });
+
+    let thread2 = std::thread::spawn({
+        move || {
+            // Wait until thread 1 has asserted that they are not cancelled
+            // before we invoke `set.`
+            signal.wait_for(1);
+
+            // This will block until thread1 drops the revision lock.
+            db.set_input('a', 2);
+
+            db.input('a')
+        }
+    });
+
+    thread1.join().unwrap();
+
+    let c = thread2.join().unwrap();
+    assert_eq!(c, 2);
+}

crates/salsa/tests/parallel/independent.rs

@@ -0,0 +1,29 @@
+use crate::setup::{ParDatabase, ParDatabaseImpl};
+use salsa::ParallelDatabase;
+
+/// Test two `sum` queries (on distinct keys) executing in different
+/// threads. Really just a test that `snapshot` etc compiles.
+#[test]
+fn in_par_two_independent_queries() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 100);
+    db.set_input('b', 10);
+    db.set_input('c', 1);
+    db.set_input('d', 200);
+    db.set_input('e', 20);
+    db.set_input('f', 2);
+
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.sum("abc")
+    });
+
+    let thread2 = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.sum("def")
+    });
+
+    assert_eq!(thread1.join().unwrap(), 111);
+    assert_eq!(thread2.join().unwrap(), 222);
+}

crates/salsa/tests/parallel/main.rs

@@ -0,0 +1,13 @@
+mod setup;
+
+mod cancellation;
+mod frozen;
+mod independent;
+mod parallel_cycle_all_recover;
+mod parallel_cycle_mid_recover;
+mod parallel_cycle_none_recover;
+mod parallel_cycle_one_recovers;
+mod race;
+mod signal;
+mod stress;
+mod true_parallel;

crates/salsa/tests/parallel/parallel_cycle_all_recover.rs

@@ -0,0 +1,110 @@
+//! Test for cycle recover spread across two threads.
+//! See `../cycles.rs` for a complete listing of cycle tests,
+//! both intra and cross thread.
+
+use crate::setup::{Knobs, ParDatabaseImpl};
+use salsa::ParallelDatabase;
+use test_log::test;
+
+// Recover cycle test:
+//
+// The pattern is as follows.
+//
+// Thread A                   Thread B
+// --------                   --------
+// a1                         b1
+// |                          wait for stage 1 (blocks)
+// signal stage 1             |
+// wait for stage 2 (blocks)  (unblocked)
+// |                          signal stage 2
+// (unblocked)                wait for stage 3 (blocks)
+// a2                         |
+// b1 (blocks -> stage 3)     |
+// |                          (unblocked)
+// |                          b2
+// |                          a1 (cycle detected, recovers)
+// |                          b2 completes, recovers
+// |                          b1 completes, recovers
+// a2 sees cycle, recovers
+// a1 completes, recovers
+
+#[test]
+fn parallel_cycle_all_recover() {
+    let db = ParDatabaseImpl::default();
+    db.knobs().signal_on_will_block.set(3);
+
+    let thread_a = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.a1(1)
+    });
+
+    let thread_b = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.b1(1)
+    });
+
+    assert_eq!(thread_a.join().unwrap(), 11);
+    assert_eq!(thread_b.join().unwrap(), 21);
+}
+
+#[salsa::query_group(ParallelCycleAllRecover)]
+pub(crate) trait TestDatabase: Knobs {
+    #[salsa::cycle(recover_a1)]
+    fn a1(&self, key: i32) -> i32;
+
+    #[salsa::cycle(recover_a2)]
+    fn a2(&self, key: i32) -> i32;
+
+    #[salsa::cycle(recover_b1)]
+    fn b1(&self, key: i32) -> i32;
+
+    #[salsa::cycle(recover_b2)]
+    fn b2(&self, key: i32) -> i32;
+}
+
+fn recover_a1(_db: &dyn TestDatabase, _cycle: &salsa::Cycle, key: &i32) -> i32 {
+    tracing::debug!("recover_a1");
+    key * 10 + 1
+}
+
+fn recover_a2(_db: &dyn TestDatabase, _cycle: &salsa::Cycle, key: &i32) -> i32 {
+    tracing::debug!("recover_a2");
+    key * 10 + 2
+}
+
+fn recover_b1(_db: &dyn TestDatabase, _cycle: &salsa::Cycle, key: &i32) -> i32 {
+    tracing::debug!("recover_b1");
+    key * 20 + 1
+}
+
+fn recover_b2(_db: &dyn TestDatabase, _cycle: &salsa::Cycle, key: &i32) -> i32 {
+    tracing::debug!("recover_b2");
+    key * 20 + 2
+}
+
+fn a1(db: &dyn TestDatabase, key: i32) -> i32 {
+    // Wait to create the cycle until both threads have entered
+    db.signal(1);
+    db.wait_for(2);
+
+    db.a2(key)
+}
+
+fn a2(db: &dyn TestDatabase, key: i32) -> i32 {
+    db.b1(key)
+}
+
+fn b1(db: &dyn TestDatabase, key: i32) -> i32 {
+    // Wait to create the cycle until both threads have entered
+    db.wait_for(1);
+    db.signal(2);
+
+    // Wait for thread A to block on this thread
+    db.wait_for(3);
+
+    db.b2(key)
+}
+
+fn b2(db: &dyn TestDatabase, key: i32) -> i32 {
+    db.a1(key)
+}

crates/salsa/tests/parallel/parallel_cycle_mid_recover.rs

@@ -0,0 +1,110 @@
+//! Test for cycle recover spread across two threads.
+//! See `../cycles.rs` for a complete listing of cycle tests,
+//! both intra and cross thread.
+
+use crate::setup::{Knobs, ParDatabaseImpl};
+use salsa::ParallelDatabase;
+use test_log::test;
+
+// Recover cycle test:
+//
+// The pattern is as follows.
+//
+// Thread A                   Thread B
+// --------                   --------
+// a1                         b1
+// |                          wait for stage 1 (blocks)
+// signal stage 1             |
+// wait for stage 2 (blocks)  (unblocked)
+// |                          |
+// |                          b2
+// |                          b3
+// |                          a1 (blocks -> stage 2)
+// (unblocked)                |
+// a2 (cycle detected)        |
+//                            b3 recovers
+//                            b2 resumes
+//                            b1 panics because bug
+
+#[test]
+fn parallel_cycle_mid_recovers() {
+    let db = ParDatabaseImpl::default();
+    db.knobs().signal_on_will_block.set(2);
+
+    let thread_a = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.a1(1)
+    });
+
+    let thread_b = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.b1(1)
+    });
+
+    // We expect that the recovery function yields
+    // `1 * 20 + 2`, which is returned (and forwarded)
+    // to b1, and from there to a2 and a1.
+    assert_eq!(thread_a.join().unwrap(), 22);
+    assert_eq!(thread_b.join().unwrap(), 22);
+}
+
+#[salsa::query_group(ParallelCycleMidRecovers)]
+pub(crate) trait TestDatabase: Knobs {
+    fn a1(&self, key: i32) -> i32;
+
+    fn a2(&self, key: i32) -> i32;
+
+    #[salsa::cycle(recover_b1)]
+    fn b1(&self, key: i32) -> i32;
+
+    fn b2(&self, key: i32) -> i32;
+
+    #[salsa::cycle(recover_b3)]
+    fn b3(&self, key: i32) -> i32;
+}
+
+fn recover_b1(_db: &dyn TestDatabase, _cycle: &salsa::Cycle, key: &i32) -> i32 {
+    tracing::debug!("recover_b1");
+    key * 20 + 2
+}
+
+fn recover_b3(_db: &dyn TestDatabase, _cycle: &salsa::Cycle, key: &i32) -> i32 {
+    tracing::debug!("recover_b1");
+    key * 200 + 2
+}
+
+fn a1(db: &dyn TestDatabase, key: i32) -> i32 {
+    // tell thread b we have started
+    db.signal(1);
+
+    // wait for thread b to block on a1
+    db.wait_for(2);
+
+    db.a2(key)
+}
+
+fn a2(db: &dyn TestDatabase, key: i32) -> i32 {
+    // create the cycle
+    db.b1(key)
+}
+
+fn b1(db: &dyn TestDatabase, key: i32) -> i32 {
+    // wait for thread a to have started
+    db.wait_for(1);
+
+    db.b2(key);
+
+    0
+}
+
+fn b2(db: &dyn TestDatabase, key: i32) -> i32 {
+    // will encounter a cycle but recover
+    db.b3(key);
+    db.b1(key); // hasn't recovered yet
+    0
+}
+
+fn b3(db: &dyn TestDatabase, key: i32) -> i32 {
+    // will block on thread a, signaling stage 2
+    db.a1(key)
+}

crates/salsa/tests/parallel/parallel_cycle_none_recover.rs

@@ -0,0 +1,69 @@
+//! Test a cycle where no queries recover that occurs across threads.
+//! See the `../cycles.rs` for a complete listing of cycle tests,
+//! both intra and cross thread.
+
+use crate::setup::{Knobs, ParDatabaseImpl};
+use expect_test::expect;
+use salsa::ParallelDatabase;
+use test_log::test;
+
+#[test]
+fn parallel_cycle_none_recover() {
+    let db = ParDatabaseImpl::default();
+    db.knobs().signal_on_will_block.set(3);
+
+    let thread_a = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.a(-1)
+    });
+
+    let thread_b = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.b(-1)
+    });
+
+    // We expect B to panic because it detects a cycle (it is the one that calls A, ultimately).
+    // Right now, it panics with a string.
+    let err_b = thread_b.join().unwrap_err();
+    if let Some(c) = err_b.downcast_ref::<salsa::Cycle>() {
+        expect![[r#"
+            [
+                "a(-1)",
+                "b(-1)",
+            ]
+        "#]]
+        .assert_debug_eq(&c.unexpected_participants(&db));
+    } else {
+        panic!("b failed in an unexpected way: {:?}", err_b);
+    }
+
+    // We expect A to propagate a panic, which causes us to use the sentinel
+    // type `Canceled`.
+    assert!(thread_a.join().unwrap_err().downcast_ref::<salsa::Cycle>().is_some());
+}
+
+#[salsa::query_group(ParallelCycleNoneRecover)]
+pub(crate) trait TestDatabase: Knobs {
+    fn a(&self, key: i32) -> i32;
+    fn b(&self, key: i32) -> i32;
+}
+
+fn a(db: &dyn TestDatabase, key: i32) -> i32 {
+    // Wait to create the cycle until both threads have entered
+    db.signal(1);
+    db.wait_for(2);
+
+    db.b(key)
+}
+
+fn b(db: &dyn TestDatabase, key: i32) -> i32 {
+    // Wait to create the cycle until both threads have entered
+    db.wait_for(1);
+    db.signal(2);
+
+    // Wait for thread A to block on this thread
+    db.wait_for(3);
+
+    // Now try to execute A
+    db.a(key)
+}

crates/salsa/tests/parallel/parallel_cycle_one_recovers.rs

@@ -0,0 +1,95 @@
+//! Test for cycle recover spread across two threads.
+//! See `../cycles.rs` for a complete listing of cycle tests,
+//! both intra and cross thread.
+
+use crate::setup::{Knobs, ParDatabaseImpl};
+use salsa::ParallelDatabase;
+use test_log::test;
+
+// Recover cycle test:
+//
+// The pattern is as follows.
+//
+// Thread A                   Thread B
+// --------                   --------
+// a1                         b1
+// |                          wait for stage 1 (blocks)
+// signal stage 1             |
+// wait for stage 2 (blocks)  (unblocked)
+// |                          signal stage 2
+// (unblocked)                wait for stage 3 (blocks)
+// a2                         |
+// b1 (blocks -> stage 3)     |
+// |                          (unblocked)
+// |                          b2
+// |                          a1 (cycle detected)
+// a2 recovery fn executes    |
+// a1 completes normally      |
+//                            b2 completes, recovers
+//                            b1 completes, recovers
+
+#[test]
+fn parallel_cycle_one_recovers() {
+    let db = ParDatabaseImpl::default();
+    db.knobs().signal_on_will_block.set(3);
+
+    let thread_a = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.a1(1)
+    });
+
+    let thread_b = std::thread::spawn({
+        let db = db.snapshot();
+        move || db.b1(1)
+    });
+
+    // We expect that the recovery function yields
+    // `1 * 20 + 2`, which is returned (and forwarded)
+    // to b1, and from there to a2 and a1.
+    assert_eq!(thread_a.join().unwrap(), 22);
+    assert_eq!(thread_b.join().unwrap(), 22);
+}
+
+#[salsa::query_group(ParallelCycleOneRecovers)]
+pub(crate) trait TestDatabase: Knobs {
+    fn a1(&self, key: i32) -> i32;
+
+    #[salsa::cycle(recover)]
+    fn a2(&self, key: i32) -> i32;
+
+    fn b1(&self, key: i32) -> i32;
+
+    fn b2(&self, key: i32) -> i32;
+}
+
+fn recover(_db: &dyn TestDatabase, _cycle: &salsa::Cycle, key: &i32) -> i32 {
+    tracing::debug!("recover");
+    key * 20 + 2
+}
+
+fn a1(db: &dyn TestDatabase, key: i32) -> i32 {
+    // Wait to create the cycle until both threads have entered
+    db.signal(1);
+    db.wait_for(2);
+
+    db.a2(key)
+}
+
+fn a2(db: &dyn TestDatabase, key: i32) -> i32 {
+    db.b1(key)
+}
+
+fn b1(db: &dyn TestDatabase, key: i32) -> i32 {
+    // Wait to create the cycle until both threads have entered
+    db.wait_for(1);
+    db.signal(2);
+
+    // Wait for thread A to block on this thread
+    db.wait_for(3);
+
+    db.b2(key)
+}
+
+fn b2(db: &dyn TestDatabase, key: i32) -> i32 {
+    db.a1(key)
+}

crates/salsa/tests/parallel/race.rs

@@ -0,0 +1,37 @@
+use std::panic::AssertUnwindSafe;
+
+use crate::setup::{ParDatabase, ParDatabaseImpl};
+use salsa::{Cancelled, ParallelDatabase};
+
+/// Test where a read and a set are racing with one another.
+/// Should be atomic.
+#[test]
+fn in_par_get_set_race() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 100);
+    db.set_input('b', 10);
+    db.set_input('c', 1);
+
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || Cancelled::catch(AssertUnwindSafe(|| db.sum("abc")))
+    });
+
+    let thread2 = std::thread::spawn(move || {
+        db.set_input('a', 1000);
+        db.sum("a")
+    });
+
+    // If the 1st thread runs first, you get 111, otherwise you get
+    // 1011; if they run concurrently and the 1st thread observes the
+    // cancellation, it'll unwind.
+    let result1 = thread1.join().unwrap();
+    if let Ok(value1) = result1 {
+        assert!(value1 == 111 || value1 == 1011, "illegal result {}", value1);
+    }
+
+    // thread2 can not observe a cancellation because it performs a
+    // database write before running any other queries.
+    assert_eq!(thread2.join().unwrap(), 1000);
+}

crates/salsa/tests/parallel/setup.rs

@@ -0,0 +1,197 @@
+use crate::signal::Signal;
+use salsa::Database;
+use salsa::ParallelDatabase;
+use salsa::Snapshot;
+use std::sync::Arc;
+use std::{
+    cell::Cell,
+    panic::{catch_unwind, resume_unwind, AssertUnwindSafe},
+};
+
+#[salsa::query_group(Par)]
+pub(crate) trait ParDatabase: Knobs {
+    #[salsa::input]
+    fn input(&self, key: char) -> usize;
+
+    fn sum(&self, key: &'static str) -> usize;
+
+    /// Invokes `sum`
+    fn sum2(&self, key: &'static str) -> usize;
+
+    /// Invokes `sum` but doesn't really care about the result.
+    fn sum2_drop_sum(&self, key: &'static str) -> usize;
+
+    /// Invokes `sum2`
+    fn sum3(&self, key: &'static str) -> usize;
+
+    /// Invokes `sum2_drop_sum`
+    fn sum3_drop_sum(&self, key: &'static str) -> usize;
+}
+
+/// Various "knobs" and utilities used by tests to force
+/// a certain behavior.
+pub(crate) trait Knobs {
+    fn knobs(&self) -> &KnobsStruct;
+
+    fn signal(&self, stage: usize);
+
+    fn wait_for(&self, stage: usize);
+}
+
+pub(crate) trait WithValue<T> {
+    fn with_value<R>(&self, value: T, closure: impl FnOnce() -> R) -> R;
+}
+
+impl<T> WithValue<T> for Cell<T> {
+    fn with_value<R>(&self, value: T, closure: impl FnOnce() -> R) -> R {
+        let old_value = self.replace(value);
+
+        let result = catch_unwind(AssertUnwindSafe(closure));
+
+        self.set(old_value);
+
+        match result {
+            Ok(r) => r,
+            Err(payload) => resume_unwind(payload),
+        }
+    }
+}
+
+#[derive(Default, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum CancellationFlag {
+    #[default]
+    Down,
+    Panic,
+}
+
+/// Various "knobs" that can be used to customize how the queries
+/// behave on one specific thread. Note that this state is
+/// intentionally thread-local (apart from `signal`).
+#[derive(Clone, Default)]
+pub(crate) struct KnobsStruct {
+    /// A kind of flexible barrier used to coordinate execution across
+    /// threads to ensure we reach various weird states.
+    pub(crate) signal: Arc<Signal>,
+
+    /// When this database is about to block, send a signal.
+    pub(crate) signal_on_will_block: Cell<usize>,
+
+    /// Invocations of `sum` will signal this stage on entry.
+    pub(crate) sum_signal_on_entry: Cell<usize>,
+
+    /// Invocations of `sum` will wait for this stage on entry.
+    pub(crate) sum_wait_for_on_entry: Cell<usize>,
+
+    /// If true, invocations of `sum` will panic before they exit.
+    pub(crate) sum_should_panic: Cell<bool>,
+
+    /// If true, invocations of `sum` will wait for cancellation before
+    /// they exit.
+    pub(crate) sum_wait_for_cancellation: Cell<CancellationFlag>,
+
+    /// Invocations of `sum` will wait for this stage prior to exiting.
+    pub(crate) sum_wait_for_on_exit: Cell<usize>,
+
+    /// Invocations of `sum` will signal this stage prior to exiting.
+    pub(crate) sum_signal_on_exit: Cell<usize>,
+
+    /// Invocations of `sum3_drop_sum` will panic unconditionally
+    pub(crate) sum3_drop_sum_should_panic: Cell<bool>,
+}
+
+fn sum(db: &dyn ParDatabase, key: &'static str) -> usize {
+    let mut sum = 0;
+
+    db.signal(db.knobs().sum_signal_on_entry.get());
+
+    db.wait_for(db.knobs().sum_wait_for_on_entry.get());
+
+    if db.knobs().sum_should_panic.get() {
+        panic!("query set to panic before exit")
+    }
+
+    for ch in key.chars() {
+        sum += db.input(ch);
+    }
+
+    match db.knobs().sum_wait_for_cancellation.get() {
+        CancellationFlag::Down => (),
+        CancellationFlag::Panic => {
+            tracing::debug!("waiting for cancellation");
+            loop {
+                db.unwind_if_cancelled();
+                std::thread::yield_now();
+            }
+        }
+    }
+
+    db.wait_for(db.knobs().sum_wait_for_on_exit.get());
+
+    db.signal(db.knobs().sum_signal_on_exit.get());
+
+    sum
+}
+
+fn sum2(db: &dyn ParDatabase, key: &'static str) -> usize {
+    db.sum(key)
+}
+
+fn sum2_drop_sum(db: &dyn ParDatabase, key: &'static str) -> usize {
+    let _ = db.sum(key);
+    22
+}
+
+fn sum3(db: &dyn ParDatabase, key: &'static str) -> usize {
+    db.sum2(key)
+}
+
+fn sum3_drop_sum(db: &dyn ParDatabase, key: &'static str) -> usize {
+    if db.knobs().sum3_drop_sum_should_panic.get() {
+        panic!("sum3_drop_sum executed")
+    }
+    db.sum2_drop_sum(key)
+}
+
+#[salsa::database(
+    Par,
+    crate::parallel_cycle_all_recover::ParallelCycleAllRecover,
+    crate::parallel_cycle_none_recover::ParallelCycleNoneRecover,
+    crate::parallel_cycle_mid_recover::ParallelCycleMidRecovers,
+    crate::parallel_cycle_one_recovers::ParallelCycleOneRecovers
+)]
+#[derive(Default)]
+pub(crate) struct ParDatabaseImpl {
+    storage: salsa::Storage<Self>,
+    knobs: KnobsStruct,
+}
+
+impl Database for ParDatabaseImpl {
+    fn salsa_event(&self, event: salsa::Event) {
+        if let salsa::EventKind::WillBlockOn { .. } = event.kind {
+            self.signal(self.knobs().signal_on_will_block.get());
+        }
+    }
+}
+
+impl ParallelDatabase for ParDatabaseImpl {
+    fn snapshot(&self) -> Snapshot<Self> {
+        Snapshot::new(ParDatabaseImpl {
+            storage: self.storage.snapshot(),
+            knobs: self.knobs.clone(),
+        })
+    }
+}
+
+impl Knobs for ParDatabaseImpl {
+    fn knobs(&self) -> &KnobsStruct {
+        &self.knobs
+    }
+
+    fn signal(&self, stage: usize) {
+        self.knobs.signal.signal(stage);
+    }
+
+    fn wait_for(&self, stage: usize) {
+        self.knobs.signal.wait_for(stage);
+    }
+}

crates/salsa/tests/parallel/signal.rs

@@ -0,0 +1,40 @@
+use parking_lot::{Condvar, Mutex};
+
+#[derive(Default)]
+pub(crate) struct Signal {
+    value: Mutex<usize>,
+    cond_var: Condvar,
+}
+
+impl Signal {
+    pub(crate) fn signal(&self, stage: usize) {
+        tracing::debug!("signal({})", stage);
+
+        // This check avoids acquiring the lock for things that will
+        // clearly be a no-op. Not *necessary* but helps to ensure we
+        // are more likely to encounter weird race conditions;
+        // otherwise calls to `sum` will tend to be unnecessarily
+        // synchronous.
+        if stage > 0 {
+            let mut v = self.value.lock();
+            if stage > *v {
+                *v = stage;
+                self.cond_var.notify_all();
+            }
+        }
+    }
+
+    /// Waits until the given condition is true; the fn is invoked
+    /// with the current stage.
+    pub(crate) fn wait_for(&self, stage: usize) {
+        tracing::debug!("wait_for({})", stage);
+
+        // As above, avoid lock if clearly a no-op.
+        if stage > 0 {
+            let mut v = self.value.lock();
+            while *v < stage {
+                self.cond_var.wait(&mut v);
+            }
+        }
+    }
+}

crates/salsa/tests/parallel/stress.rs

@@ -0,0 +1,168 @@
+use rand::seq::SliceRandom;
+use rand::Rng;
+
+use salsa::ParallelDatabase;
+use salsa::Snapshot;
+use salsa::{Cancelled, Database};
+
+// Number of operations a reader performs
+const N_MUTATOR_OPS: usize = 100;
+const N_READER_OPS: usize = 100;
+
+#[salsa::query_group(Stress)]
+trait StressDatabase: salsa::Database {
+    #[salsa::input]
+    fn a(&self, key: usize) -> usize;
+
+    fn b(&self, key: usize) -> usize;
+
+    fn c(&self, key: usize) -> usize;
+}
+
+fn b(db: &dyn StressDatabase, key: usize) -> usize {
+    db.unwind_if_cancelled();
+    db.a(key)
+}
+
+fn c(db: &dyn StressDatabase, key: usize) -> usize {
+    db.b(key)
+}
+
+#[salsa::database(Stress)]
+#[derive(Default)]
+struct StressDatabaseImpl {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for StressDatabaseImpl {}
+
+impl salsa::ParallelDatabase for StressDatabaseImpl {
+    fn snapshot(&self) -> Snapshot<StressDatabaseImpl> {
+        Snapshot::new(StressDatabaseImpl { storage: self.storage.snapshot() })
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+enum Query {
+    A,
+    B,
+    C,
+}
+
+enum MutatorOp {
+    WriteOp(WriteOp),
+    LaunchReader { ops: Vec<ReadOp>, check_cancellation: bool },
+}
+
+#[derive(Debug)]
+enum WriteOp {
+    SetA(usize, usize),
+}
+
+#[derive(Debug)]
+enum ReadOp {
+    Get(Query, usize),
+}
+
+impl rand::distributions::Distribution<Query> for rand::distributions::Standard {
+    fn sample<R: rand::Rng + ?Sized>(&self, rng: &mut R) -> Query {
+        *[Query::A, Query::B, Query::C].choose(rng).unwrap()
+    }
+}
+
+impl rand::distributions::Distribution<MutatorOp> for rand::distributions::Standard {
+    fn sample<R: rand::Rng + ?Sized>(&self, rng: &mut R) -> MutatorOp {
+        if rng.gen_bool(0.5) {
+            MutatorOp::WriteOp(rng.gen())
+        } else {
+            MutatorOp::LaunchReader {
+                ops: (0..N_READER_OPS).map(|_| rng.gen()).collect(),
+                check_cancellation: rng.gen(),
+            }
+        }
+    }
+}
+
+impl rand::distributions::Distribution<WriteOp> for rand::distributions::Standard {
+    fn sample<R: rand::Rng + ?Sized>(&self, rng: &mut R) -> WriteOp {
+        let key = rng.gen::<usize>() % 10;
+        let value = rng.gen::<usize>() % 10;
+        WriteOp::SetA(key, value)
+    }
+}
+
+impl rand::distributions::Distribution<ReadOp> for rand::distributions::Standard {
+    fn sample<R: rand::Rng + ?Sized>(&self, rng: &mut R) -> ReadOp {
+        let query = rng.gen::<Query>();
+        let key = rng.gen::<usize>() % 10;
+        ReadOp::Get(query, key)
+    }
+}
+
+fn db_reader_thread(db: &StressDatabaseImpl, ops: Vec<ReadOp>, check_cancellation: bool) {
+    for op in ops {
+        if check_cancellation {
+            db.unwind_if_cancelled();
+        }
+        op.execute(db);
+    }
+}
+
+impl WriteOp {
+    fn execute(self, db: &mut StressDatabaseImpl) {
+        match self {
+            WriteOp::SetA(key, value) => {
+                db.set_a(key, value);
+            }
+        }
+    }
+}
+
+impl ReadOp {
+    fn execute(self, db: &StressDatabaseImpl) {
+        match self {
+            ReadOp::Get(query, key) => match query {
+                Query::A => {
+                    db.a(key);
+                }
+                Query::B => {
+                    let _ = db.b(key);
+                }
+                Query::C => {
+                    let _ = db.c(key);
+                }
+            },
+        }
+    }
+}
+
+#[test]
+fn stress_test() {
+    let mut db = StressDatabaseImpl::default();
+    for i in 0..10 {
+        db.set_a(i, i);
+    }
+
+    let mut rng = rand::thread_rng();
+
+    // generate the ops that the mutator thread will perform
+    let write_ops: Vec<MutatorOp> = (0..N_MUTATOR_OPS).map(|_| rng.gen()).collect();
+
+    // execute the "main thread", which sometimes snapshots off other threads
+    let mut all_threads = vec![];
+    for op in write_ops {
+        match op {
+            MutatorOp::WriteOp(w) => w.execute(&mut db),
+            MutatorOp::LaunchReader { ops, check_cancellation } => {
+                all_threads.push(std::thread::spawn({
+                    let db = db.snapshot();
+                    move || Cancelled::catch(|| db_reader_thread(&db, ops, check_cancellation))
+                }))
+            }
+        }
+    }
+
+    for thread in all_threads {
+        thread.join().unwrap().ok();
+    }
+}

crates/salsa/tests/parallel/true_parallel.rs

@@ -0,0 +1,125 @@
+use crate::setup::{Knobs, ParDatabase, ParDatabaseImpl, WithValue};
+use salsa::ParallelDatabase;
+use std::panic::{self, AssertUnwindSafe};
+
+/// Test where two threads are executing sum. We show that they can
+/// both be executing sum in parallel by having thread1 wait for
+/// thread2 to send a signal before it leaves (similarly, thread2
+/// waits for thread1 to send a signal before it enters).
+#[test]
+fn true_parallel_different_keys() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 100);
+    db.set_input('b', 10);
+    db.set_input('c', 1);
+
+    // Thread 1 will signal stage 1 when it enters and wait for stage 2.
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            let v = db
+                .knobs()
+                .sum_signal_on_entry
+                .with_value(1, || db.knobs().sum_wait_for_on_exit.with_value(2, || db.sum("a")));
+            v
+        }
+    });
+
+    // Thread 2 will wait_for stage 1 when it enters and signal stage 2
+    // when it leaves.
+    let thread2 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            let v = db
+                .knobs()
+                .sum_wait_for_on_entry
+                .with_value(1, || db.knobs().sum_signal_on_exit.with_value(2, || db.sum("b")));
+            v
+        }
+    });
+
+    assert_eq!(thread1.join().unwrap(), 100);
+    assert_eq!(thread2.join().unwrap(), 10);
+}
+
+/// Add a test that tries to trigger a conflict, where we fetch
+/// `sum("abc")` from two threads simultaneously, and of them
+/// therefore has to block.
+#[test]
+fn true_parallel_same_keys() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 100);
+    db.set_input('b', 10);
+    db.set_input('c', 1);
+
+    // Thread 1 will wait_for a barrier in the start of `sum`
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            let v = db
+                .knobs()
+                .sum_signal_on_entry
+                .with_value(1, || db.knobs().sum_wait_for_on_entry.with_value(2, || db.sum("abc")));
+            v
+        }
+    });
+
+    // Thread 2 will wait until Thread 1 has entered sum and then --
+    // once it has set itself to block -- signal Thread 1 to
+    // continue. This way, we test out the mechanism of one thread
+    // blocking on another.
+    let thread2 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            db.knobs().signal.wait_for(1);
+            db.knobs().signal_on_will_block.set(2);
+            db.sum("abc")
+        }
+    });
+
+    assert_eq!(thread1.join().unwrap(), 111);
+    assert_eq!(thread2.join().unwrap(), 111);
+}
+
+/// Add a test that tries to trigger a conflict, where we fetch `sum("a")`
+/// from two threads simultaneously. After `thread2` begins blocking,
+/// we force `thread1` to panic and should see that propagate to `thread2`.
+#[test]
+fn true_parallel_propagate_panic() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 1);
+
+    // `thread1` will wait_for a barrier in the start of `sum`. Once it can
+    // continue, it will panic.
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            let v = db.knobs().sum_signal_on_entry.with_value(1, || {
+                db.knobs()
+                    .sum_wait_for_on_entry
+                    .with_value(2, || db.knobs().sum_should_panic.with_value(true, || db.sum("a")))
+            });
+            v
+        }
+    });
+
+    // `thread2` will wait until `thread1` has entered sum and then -- once it
+    // has set itself to block -- signal `thread1` to continue.
+    let thread2 = std::thread::spawn({
+        let db = db.snapshot();
+        move || {
+            db.knobs().signal.wait_for(1);
+            db.knobs().signal_on_will_block.set(2);
+            db.sum("a")
+        }
+    });
+
+    let result1 = panic::catch_unwind(AssertUnwindSafe(|| thread1.join().unwrap()));
+    let result2 = panic::catch_unwind(AssertUnwindSafe(|| thread2.join().unwrap()));
+
+    assert!(result1.is_err());
+    assert!(result2.is_err());
+}

crates/salsa/tests/storage_varieties/implementation.rs

@@ -0,0 +1,19 @@
+use crate::queries;
+use std::cell::Cell;
+
+#[salsa::database(queries::GroupStruct)]
+#[derive(Default)]
+pub(crate) struct DatabaseImpl {
+    storage: salsa::Storage<Self>,
+    counter: Cell<usize>,
+}
+
+impl queries::Counter for DatabaseImpl {
+    fn increment(&self) -> usize {
+        let v = self.counter.get();
+        self.counter.set(v + 1);
+        v
+    }
+}
+
+impl salsa::Database for DatabaseImpl {}

crates/salsa/tests/storage_varieties/main.rs

@@ -0,0 +1,5 @@
+mod implementation;
+mod queries;
+mod tests;
+
+fn main() {}

crates/salsa/tests/storage_varieties/queries.rs

@@ -0,0 +1,22 @@
+pub(crate) trait Counter: salsa::Database {
+    fn increment(&self) -> usize;
+}
+
+#[salsa::query_group(GroupStruct)]
+pub(crate) trait Database: Counter {
+    fn memoized(&self) -> usize;
+    fn volatile(&self) -> usize;
+}
+
+/// Because this query is memoized, we only increment the counter
+/// the first time it is invoked.
+fn memoized(db: &dyn Database) -> usize {
+    db.volatile()
+}
+
+/// Because this query is volatile, each time it is invoked,
+/// we will increment the counter.
+fn volatile(db: &dyn Database) -> usize {
+    db.salsa_runtime().report_untracked_read();
+    db.increment()
+}

crates/salsa/tests/storage_varieties/tests.rs

@@ -0,0 +1,49 @@
+#![cfg(test)]
+
+use crate::implementation::DatabaseImpl;
+use crate::queries::Database;
+use salsa::Database as _Database;
+use salsa::Durability;
+
+#[test]
+fn memoized_twice() {
+    let db = DatabaseImpl::default();
+    let v1 = db.memoized();
+    let v2 = db.memoized();
+    assert_eq!(v1, v2);
+}
+
+#[test]
+fn volatile_twice() {
+    let mut db = DatabaseImpl::default();
+    let v1 = db.volatile();
+    let v2 = db.volatile(); // volatiles are cached, so 2nd read returns the same
+    assert_eq!(v1, v2);
+
+    db.salsa_runtime_mut().synthetic_write(Durability::LOW); // clears volatile caches
+
+    let v3 = db.volatile(); // will re-increment the counter
+    let v4 = db.volatile(); // second call will be cached
+    assert_eq!(v1 + 1, v3);
+    assert_eq!(v3, v4);
+}
+
+#[test]
+fn intermingled() {
+    let mut db = DatabaseImpl::default();
+    let v1 = db.volatile();
+    let v2 = db.memoized();
+    let v3 = db.volatile(); // cached
+    let v4 = db.memoized(); // cached
+
+    assert_eq!(v1, v2);
+    assert_eq!(v1, v3);
+    assert_eq!(v2, v4);
+
+    db.salsa_runtime_mut().synthetic_write(Durability::LOW); // clears volatile caches
+
+    let v5 = db.memoized(); // re-executes volatile, caches new result
+    let v6 = db.memoized(); // re-use cached result
+    assert_eq!(v4 + 1, v5);
+    assert_eq!(v5, v6);
+}

crates/salsa/tests/transparent.rs

@@ -0,0 +1,39 @@
+//! Test that transparent (uncached) queries work
+
+#[salsa::query_group(QueryGroupStorage)]
+trait QueryGroup {
+    #[salsa::input]
+    fn input(&self, x: u32) -> u32;
+    #[salsa::transparent]
+    fn wrap(&self, x: u32) -> u32;
+    fn get(&self, x: u32) -> u32;
+}
+
+fn wrap(db: &dyn QueryGroup, x: u32) -> u32 {
+    db.input(x)
+}
+
+fn get(db: &dyn QueryGroup, x: u32) -> u32 {
+    db.wrap(x)
+}
+
+#[salsa::database(QueryGroupStorage)]
+#[derive(Default)]
+struct Database {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for Database {}
+
+#[test]
+fn transparent_queries_work() {
+    let mut db = Database::default();
+
+    db.set_input(1, 10);
+    assert_eq!(db.get(1), 10);
+    assert_eq!(db.get(1), 10);
+
+    db.set_input(1, 92);
+    assert_eq!(db.get(1), 92);
+    assert_eq!(db.get(1), 92);
+}

crates/salsa/tests/variadic.rs

@@ -0,0 +1,51 @@
+#[salsa::query_group(HelloWorld)]
+trait HelloWorldDatabase: salsa::Database {
+    #[salsa::input]
+    fn input(&self, a: u32, b: u32) -> u32;
+
+    fn none(&self) -> u32;
+
+    fn one(&self, k: u32) -> u32;
+
+    fn two(&self, a: u32, b: u32) -> u32;
+
+    fn trailing(&self, a: u32, b: u32) -> u32;
+}
+
+fn none(_db: &dyn HelloWorldDatabase) -> u32 {
+    22
+}
+
+fn one(_db: &dyn HelloWorldDatabase, k: u32) -> u32 {
+    k * 2
+}
+
+fn two(_db: &dyn HelloWorldDatabase, a: u32, b: u32) -> u32 {
+    a * b
+}
+
+fn trailing(_db: &dyn HelloWorldDatabase, a: u32, b: u32) -> u32 {
+    a - b
+}
+
+#[salsa::database(HelloWorld)]
+#[derive(Default)]
+struct DatabaseStruct {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for DatabaseStruct {}
+
+#[test]
+fn execute() {
+    let mut db = DatabaseStruct::default();
+
+    // test what happens with inputs:
+    db.set_input(1, 2, 3);
+    assert_eq!(db.input(1, 2), 3);
+
+    assert_eq!(db.none(), 22);
+    assert_eq!(db.one(11), 22);
+    assert_eq!(db.two(11, 2), 22);
+    assert_eq!(db.trailing(24, 2), 22);
+}