diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs index 848d0646d009f..1f4fa5aac102a 100644 --- a/compiler/rustc_trait_selection/src/solve/fulfill.rs +++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs @@ -163,15 +163,15 @@ where fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec { assert_eq!(self.usable_in_snapshot, infcx.num_open_snapshots()); let mut errors = Vec::new(); - for i in 0.. { - if !infcx.tcx.recursion_limit().value_within_limit(i) { - self.obligations.on_fulfillment_overflow(infcx); - // Only return true errors that we have accumulated while processing. - return errors; - } - + loop { let mut has_changed = false; - for obligation in self.obligations.drain_pending(|_| true) { + for mut obligation in self.obligations.drain_pending(|_| true) { + if !infcx.tcx.recursion_limit().value_within_limit(obligation.recursion_depth) { + self.obligations.on_fulfillment_overflow(infcx); + // Only return true errors that we have accumulated while processing. + return errors; + } + let goal = obligation.as_goal(); let result = <&SolverDelegate<'tcx>>::from(infcx) .evaluate_root_goal(goal, GenerateProofTree::No, obligation.cause.span) @@ -189,6 +189,13 @@ where }; if changed == HasChanged::Yes { + // We increment the recursion depth here to track the number of times + // this goal has resulted in inference progress. This doesn't precisely + // model the way that we track recursion depth in the old solver due + // to the fact that we only process root obligations, but it is a good + // approximation and should only result in fulfillment overflow in + // pathological cases. + obligation.recursion_depth += 1; has_changed = true; } diff --git a/tests/ui/traits/next-solver/coerce-depth.rs b/tests/ui/traits/next-solver/coerce-depth.rs new file mode 100644 index 0000000000000..c8fc3fcab59d8 --- /dev/null +++ b/tests/ui/traits/next-solver/coerce-depth.rs @@ -0,0 +1,31 @@ +//@ check-pass +//@ compile-flags: -Znext-solver + +// Ensure that a stack of coerce predicates doesn't end up overflowing when they get procesed +// in *reverse* order, which may require O(N) iterations of the fulfillment loop. + +#![recursion_limit = "16"] + +fn main() { + match 0 { + 0 => None, + 1 => None, + 2 => None, + 3 => None, + 4 => None, + 5 => None, + 6 => None, + 7 => None, + 8 => None, + 9 => None, + 10 => None, + 11 => None, + 12 => None, + 13 => None, + 14 => None, + 15 => None, + 16 => None, + 17 => None, + _ => Some(1u32), + }; +}