change HIR typeck unification handling approach

2 files changed, 27 insertions, 0 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 3bb8353f49e..3e66f7dcb2c 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -696,6 +696,22 @@ rustc_queries! {
         return_result_from_ensure_ok
     }
 
+    /// Used in case `mir_borrowck` fails to prove an obligation. We generally assume that
+    /// all goals we prove in MIR type check hold as we've already checked them in HIR typeck.
+    ///
+    /// However, we replace each free region in the MIR body with a unique region inference
+    /// variable. As we may rely on structural identity when proving goals this may cause a
+    /// goal to no longer hold. We store obligations for which this may happen during HIR
+    /// typeck in the `TypeckResults`. We then uniquify and reprove them in case MIR typeck
+    /// encounters an unexpected error. We expect this to result in an error when used and
+    /// delay a bug if it does not.
+    query check_potentially_region_dependent_goals(key: LocalDefId) -> Result<(), ErrorGuaranteed> {
+        desc {
+            |tcx| "reproving potentially region dependent HIR typeck goals for `{}",
+            tcx.def_path_str(key)
+        }
+    }
+
     /// MIR after our optimization passes have run. This is MIR that is ready
     /// for codegen. This is also the only query that can fetch non-local MIR, at present.
     query optimized_mir(key: DefId) -> &'tcx mir::Body<'tcx> {
diff --git a/compiler/rustc_middle/src/ty/typeck_results.rs b/compiler/rustc_middle/src/ty/typeck_results.rs
index 6b187c5325a..44b080fb0d0 100644
--- a/compiler/rustc_middle/src/ty/typeck_results.rs
+++ b/compiler/rustc_middle/src/ty/typeck_results.rs
@@ -206,6 +206,16 @@ pub struct TypeckResults<'tcx> {
     /// formatting modified file tests/ui/coroutine/retain-resume-ref.rs
     pub coroutine_stalled_predicates: FxIndexSet<(ty::Predicate<'tcx>, ObligationCause<'tcx>)>,
 
+    /// Goals proven during HIR typeck which may be potentially region dependent.
+    ///
+    /// Borrowck *uniquifies* regions which may cause these goal to be ambiguous in MIR
+    /// type check. We ICE if goals fail in borrowck to detect bugs during MIR building or
+    /// missed checks in HIR typeck. To avoid ICE due to region dependence we store all
+    /// goals which may be region dependent and reprove them in case borrowck encounters
+    /// an error.
+    pub potentially_region_dependent_goals:
+        FxIndexSet<(ty::Predicate<'tcx>, ObligationCause<'tcx>)>,
+
     /// Contains the data for evaluating the effect of feature `capture_disjoint_fields`
     /// on closure size.
     pub closure_size_eval: LocalDefIdMap<ClosureSizeProfileData<'tcx>>,
@@ -240,6 +250,7 @@ impl<'tcx> TypeckResults<'tcx> {
             closure_fake_reads: Default::default(),
             rvalue_scopes: Default::default(),
             coroutine_stalled_predicates: Default::default(),
+            potentially_region_dependent_goals: Default::default(),
             closure_size_eval: Default::default(),
             offset_of_data: Default::default(),
         }