From 0b83a5a8ae81f69dbfd1ed19566ab2d6eb588675 Mon Sep 17 00:00:00 2001
From: Eduard-Mihai Burtescu <edy.burt@gmail.com>
Date: Fri, 10 Apr 2020 05:13:20 +0300
Subject: [PATCH] ty/instance: use `ParamEnvAnd` in the `resolve_instance`
 query.

---
 src/librustc_middle/query/mod.rs     |  6 ++++--
 src/librustc_middle/ty/instance.rs   |  9 ++++++++-
 src/librustc_middle/ty/query/keys.rs | 11 -----------
 src/librustc_ty/instance.rs          |  6 ++++--
 4 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/src/librustc_middle/query/mod.rs b/src/librustc_middle/query/mod.rs
index 3ddb290fc8d..c974ab3190e 100644
--- a/src/librustc_middle/query/mod.rs
+++ b/src/librustc_middle/query/mod.rs
@@ -1258,8 +1258,10 @@ fn describe_as_module(def_id: DefId, tcx: TyCtxt<'_>) -> String {
             desc { "looking up enabled feature gates" }
         }
 
-        query resolve_instance(key: (ty::ParamEnv<'tcx>, DefId, SubstsRef<'tcx>)) -> Option<ty::Instance<'tcx>> {
-            desc { "resolving instance `{:?}` `{:?}` with {:?}", key.1, key.2, key.0 }
+        query resolve_instance(
+            key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>
+        ) -> Option<ty::Instance<'tcx>> {
+            desc { "resolving instance `{}`", ty::Instance::new(key.value.0, key.value.1) }
         }
     }
 }
diff --git a/src/librustc_middle/ty/instance.rs b/src/librustc_middle/ty/instance.rs
index ca76cfb1492..0366795a20e 100644
--- a/src/librustc_middle/ty/instance.rs
+++ b/src/librustc_middle/ty/instance.rs
@@ -290,7 +290,14 @@ pub fn resolve(
     ) -> Option<Instance<'tcx>> {
         // All regions in the result of this query are erased, so it's
         // fine to erase all of the input regions.
-        tcx.resolve_instance((tcx.erase_regions(&param_env), def_id, tcx.erase_regions(&substs)))
+
+        // HACK(eddyb) erase regions in `substs` first, so that `param_env.and(...)`
+        // below is more likely to ignore the bounds in scope (e.g. if the only
+        // generic parameters mentioned by `substs` were lifetime ones).
+        let substs = tcx.erase_regions(&substs);
+
+        // FIXME(eddyb) should this always use `param_env.with_reveal_all()`?
+        tcx.resolve_instance(tcx.erase_regions(&param_env.and((def_id, substs))))
     }
 
     pub fn resolve_for_fn_ptr(
diff --git a/src/librustc_middle/ty/query/keys.rs b/src/librustc_middle/ty/query/keys.rs
index 438e7ed4331..a261e484a85 100644
--- a/src/librustc_middle/ty/query/keys.rs
+++ b/src/librustc_middle/ty/query/keys.rs
@@ -296,14 +296,3 @@ fn default_span(&self, _tcx: TyCtxt<'_>) -> Span {
         DUMMY_SP
     }
 }
-
-impl<'tcx> Key for (ty::ParamEnv<'tcx>, DefId, SubstsRef<'tcx>) {
-    type CacheSelector = DefaultCacheSelector;
-
-    fn query_crate(&self) -> CrateNum {
-        self.1.krate
-    }
-    fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
-        tcx.def_span(self.1)
-    }
-}
diff --git a/src/librustc_ty/instance.rs b/src/librustc_ty/instance.rs
index 955e2e36159..d50e7f39d41 100644
--- a/src/librustc_ty/instance.rs
+++ b/src/librustc_ty/instance.rs
@@ -9,10 +9,12 @@
 
 use log::debug;
 
-pub fn resolve_instance<'tcx>(
+fn resolve_instance<'tcx>(
     tcx: TyCtxt<'tcx>,
-    (param_env, def_id, substs): (ty::ParamEnv<'tcx>, DefId, SubstsRef<'tcx>),
+    key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
 ) -> Option<Instance<'tcx>> {
+    let (param_env, (def_id, substs)) = key.into_parts();
+
     debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
     let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
-- 
2.44.0