cache chalk queries

This gives a significant speedup, because chalk will call these
functions several times even withing a single revision. The only
significant one here is `impl_data`, but I figured it might be good to
cache others just for consistency.

The results I get are:

Before:

from scratch:   16.081457952s
no change:      15.846493ms
trivial change: 352.95592ms
comment change: 361.998408ms
const change:   457.629212ms

After:

from scratch:   14.910610278s
no change:      14.934647ms
trivial change: 85.633023ms
comment change: 96.433023ms
const change:   171.543296ms

Seems like a nice win!

1 files changed, 1 insertions, 1 deletions

diff --git a/crates/ra_hir/src/ty/traits.rs b/crates/ra_hir/src/ty/traits.rs
index 9a6349d4b..69c03a36c 100644
--- a/crates/ra_hir/src/ty/traits.rs
+++ b/crates/ra_hir/src/ty/traits.rs
@@ -12,7 +12,7 @@ use super::{TraitRef, Ty, Canonical, ProjectionTy};
 
 use self::chalk::{ToChalk, from_chalk};
 
-mod chalk;
+pub(crate) mod chalk;
 
 pub(crate) type Solver = chalk_solve::Solver;