bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Rollup merge of #108033 - lcnr:coinductive-attr, r=compiler-errors

Browse source 
add an unstable `#[rustc_coinductive]` attribute

useful to test coinduction, especially in the new solver.

as this attribute should remain permanently unstable I don't think this needs any official approval. cc ``@rust-lang/types``

had to weaken the check for stable query results in the solver to prevent an ICE if there's a coinductive cycle with constraints.

r? ``@compiler-errors``
This commit is contained in:
Matthias Krüger 2023-02-14 18:24:42 +01:00 • committed by GitHub
commit edcdab08a4
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
10 changed files with 130 additions and 37 deletions
Download patch file Download diff file Expand all files Collapse all files

10
compiler/rustc_trait_selection/src/solve/mod.rs
View file

@ -265,12 +265,18 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
// call `exists<U> <T as Trait>::Assoc == U` to enable better caching. This goal
// could constrain `U` to `u32` which would cause this check to result in a
// solver cycle.
if cfg!(debug_assertions) && has_changed && !self.in_projection_eq_hack {
if cfg!(debug_assertions)
&& has_changed
&& !self.in_projection_eq_hack
&& !self.search_graph.in_cycle()
{
let mut orig_values = OriginalQueryValues::default();
let canonical_goal = self.infcx.canonicalize_query(goal, &mut orig_values);
let canonical_response =
EvalCtxt::evaluate_canonical_goal(self.tcx(), self.search_graph, canonical_goal)?;
assert!(canonical_response.value.var_values.is_identity());
if !canonical_response.value.var_values.is_identity() {
bug!("unstable result: {goal:?} {canonical_goal:?} {canonical_response:?}");
}
assert_eq!(certainty, canonical_response.value.certainty);
}

18
compiler/rustc_trait_selection/src/solve/search_graph/mod.rs
View file

@ -42,6 +42,24 @@ impl<'tcx> SearchGraph<'tcx> {
&& !self.overflow_data.did_overflow()
}
/// Whether we're currently in a cycle. This should only be used
/// for debug assertions.
pub(super) fn in_cycle(&self) -> bool {
if let Some(stack_depth) = self.stack.last() {
// Either the current goal on the stack is the root of a cycle...
if self.stack[stack_depth].has_been_used {
return true;
}
// ...or it depends on a goal with a lower depth.
let current_goal = self.stack[stack_depth].goal;
let entry_index = self.provisional_cache.lookup_table[&current_goal];
self.provisional_cache.entries[entry_index].depth != stack_depth
} else {
false
}
}
/// Tries putting the new goal on the stack, returning an error if it is already cached.
///
/// This correctly updates the provisional cache if there is a cycle.