Remove incorrect parallel_scope API (#797)

Rayon does not allow joining on the spawns, meaning we might end up with results in the tests before reading out the panics

tests/parallel/main.rs

@@ -7,5 +7,4 @@ mod cycle_panic;
 mod parallel_cancellation;
 mod parallel_join;
 mod parallel_map;
-mod parallel_scope;
 mod signal;

tests/parallel/parallel_scope.rs

@@ -1,114 +0,0 @@
-#![cfg(feature = "rayon")]
-// test for rayon-like scope interactions.
-
-use salsa::{Cancelled, Setter};
-
-use crate::setup::{Knobs, KnobsDatabase};
-
-#[salsa::input]
-struct ParallelInput {
-    a: u32,
-    b: u32,
-}
-
-#[salsa::tracked]
-fn tracked_fn(db: &dyn salsa::Database, input: ParallelInput) -> (u32, u32) {
-    let mut a = None;
-    let mut b = None;
-    salsa::scope(db, |scope| {
-        scope.spawn(|scope| a = Some(input.a(scope.db()) + 1));
-        scope.spawn(|scope| b = Some(input.b(scope.db()) + 1));
-    });
-    (a.unwrap(), b.unwrap())
-}
-
-#[salsa::tracked]
-fn a1(db: &dyn KnobsDatabase, input: ParallelInput) -> (u32, u32) {
-    db.signal(1);
-    let mut a = None;
-    let mut b = None;
-    salsa::scope(db, |scope| {
-        scope.spawn(|scope| {
-            scope.db().wait_for(2);
-            a = Some(input.a(scope.db()) + 1)
-        });
-        scope.spawn(|scope| {
-            scope.db().wait_for(2);
-            b = Some(input.b(scope.db()) + 1)
-        });
-    });
-    (a.unwrap(), b.unwrap())
-}
-
-#[salsa::tracked]
-fn dummy(_db: &dyn KnobsDatabase) -> u32 {
-    panic!("should never get here!")
-}
-
-#[test]
-#[cfg_attr(miri, ignore)]
-fn execute() {
-    let db = salsa::DatabaseImpl::new();
-
-    let input = ParallelInput::new(&db, 10, 20);
-
-    tracked_fn(&db, input);
-}
-
-// we expect this to panic, as `salsa::par_map` needs to be called from a query.
-#[test]
-#[cfg_attr(miri, ignore)]
-#[should_panic]
-fn direct_calls_panic() {
-    let db = salsa::DatabaseImpl::new();
-
-    let input = ParallelInput::new(&db, 10, 20);
-    salsa::scope(&db, |scope| {
-        scope.spawn(|scope| _ = input.a(scope.db()) + 1);
-        scope.spawn(|scope| _ = input.b(scope.db()) + 1);
-    });
-}
-
-// Cancellation signalling test
-//
-// The pattern is as follows.
-//
-// Thread A                   Thread B
-// --------                   --------
-// a1
-// |                          wait for stage 1
-// signal stage 1             set input, triggers cancellation
-// wait for stage 2 (blocks)  triggering cancellation sends stage 2
-// |
-// (unblocked)
-// dummy
-// panics
-
-#[test]
-#[cfg_attr(miri, ignore)]
-fn execute_cancellation() {
-    let mut db = Knobs::default();
-
-    let input = ParallelInput::new(&db, 10, 20);
-
-    let thread_a = std::thread::spawn({
-        let db = db.clone();
-        move || a1(&db, input)
-    });
-
-    db.signal_on_did_cancel(2);
-    input.set_a(&mut db).to(30);
-
-    // Assert thread A was cancelled
-    let cancelled = thread_a
-        .join()
-        .unwrap_err()
-        .downcast::<Cancelled>()
-        .unwrap();
-
-    // and inspect the output
-    expect_test::expect![[r#"
-        PendingWrite
-    "#]]
-    .assert_debug_eq(&cancelled);
-}