From 91fdadba6103b6926ff0c886a6a5da002a80994a Mon Sep 17 00:00:00 2001
From: Ariel Ben-Yehuda <ariel.byd@gmail.com>
Date: Fri, 6 Oct 2017 17:12:24 +0300
Subject: [PATCH] fix logic error in #44269's `prune_cache_value_obligations`
We want to retain obligations that *contain* inference variables, not
obligations that *don't contain* them, in order to fix #43132. Because
of surrounding changes to inference, the ICE doesn't occur in its
original case, but I believe it could still be made to occur on master.
Maybe I should try to write a new test case? Certainly not right now
(I'm mainly trying to get us a beta that we can ship) but maybe before
we land this PR on nightly?
This seems to cause a 10% performance regression in my imprecise
attempt to benchmark item-body checking for #43613, but it's better to
be slow and right than fast and wrong. If we want to recover that, I
think we can change the constrained-type-parameter code to actually
give a list of projections that are important for resolving inference
variables and filter everything else out.
---
src/librustc/traits/project.rs | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/librustc/traits/project.rs b/src/librustc/traits/project.rs
index 54e31aed272a3..b5449f5176926 100644
--- a/src/librustc/traits/project.rs
+++ b/src/librustc/traits/project.rs
@@ -639,7 +639,7 @@ fn prune_cache_value_obligations<'a, 'gcx, 'tcx>(infcx: &'a InferCtxt<'a, 'gcx,
// but we have `T: Foo<X = ?1>` and `?1: Bar<X =
// ?0>`).
ty::Predicate::Projection(ref data) =>
- !infcx.any_unresolved_type_vars(&data.ty()),
+ infcx.any_unresolved_type_vars(&data.ty()),
// We are only interested in `T: Foo<X = U>` predicates, whre
// `U` references one of `unresolved_type_vars`. =)