implement (unused) matching solver

nikomatsakis · nikomatsakis · commit c5ed318b22c4 · 2022-06-15T11:47:04.000-04:00
diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
@@ -299,7 +299,7 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
 
     // Solve the region constraints.
     let (closure_region_requirements, nll_errors) =
-        regioncx.solve(infcx, &body, polonius_output.clone());
+        regioncx.solve(infcx, param_env, &body, polonius_output.clone());
 
     if !nll_errors.is_empty() {
         // Suppress unhelpful extra errors in `infer_opaque_types`.
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -10,14 +10,16 @@ use rustc_hir::def_id::{DefId, CRATE_DEF_ID};
 use rustc_hir::CRATE_HIR_ID;
 use rustc_index::vec::IndexVec;
 use rustc_infer::infer::canonical::QueryOutlivesConstraint;
-use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound};
+use rustc_infer::infer::outlives::test_type_match;
+use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound, VerifyIfEq};
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin};
 use rustc_middle::mir::{
     Body, ClosureOutlivesRequirement, ClosureOutlivesSubject, ClosureRegionRequirements,
     ConstraintCategory, Local, Location, ReturnConstraint,
 };
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::traits::ObligationCauseCode;
+use rustc_middle::ty::Region;
 use rustc_middle::ty::{self, subst::SubstsRef, RegionVid, Ty, TyCtxt, TypeFoldable};
 use rustc_span::Span;
 
@@ -46,6 +48,7 @@ pub mod values;
 
 pub struct RegionInferenceContext<'tcx> {
     pub var_infos: VarInfos,
+
     /// Contains the definition for every region variable. Region
     /// variables are identified by their index (`RegionVid`). The
     /// definition contains information about where the region came
@@ -559,6 +562,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     pub(super) fn solve(
         &mut self,
         infcx: &InferCtxt<'_, 'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
         body: &Body<'tcx>,
         polonius_output: Option<Rc<PoloniusOutput>>,
     ) -> (Option<ClosureRegionRequirements<'tcx>>, RegionErrors<'tcx>) {
@@ -574,7 +578,13 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // eagerly.
         let mut outlives_requirements = infcx.tcx.is_typeck_child(mir_def_id).then(Vec::new);
 
-        self.check_type_tests(infcx, body, outlives_requirements.as_mut(), &mut errors_buffer);
+        self.check_type_tests(
+            infcx,
+            param_env,
+            body,
+            outlives_requirements.as_mut(),
+            &mut errors_buffer,
+        );
 
         // In Polonius mode, the errors about missing universal region relations are in the output
         // and need to be emitted or propagated. Otherwise, we need to check whether the
@@ -823,6 +833,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     fn check_type_tests(
         &self,
         infcx: &InferCtxt<'_, 'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
         body: &Body<'tcx>,
         mut propagated_outlives_requirements: Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
         errors_buffer: &mut RegionErrors<'tcx>,
@@ -839,7 +850,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
             let generic_ty = type_test.generic_kind.to_ty(tcx);
             if self.eval_verify_bound(
-                tcx,
+                infcx,
+                param_env,
                 body,
                 generic_ty,
                 type_test.lower_bound,
@@ -851,6 +863,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             if let Some(propagated_outlives_requirements) = &mut propagated_outlives_requirements {
                 if self.try_promote_type_test(
                     infcx,
+                    param_env,
                     body,
                     type_test,
                     propagated_outlives_requirements,
@@ -907,6 +920,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     fn try_promote_type_test(
         &self,
         infcx: &InferCtxt<'_, 'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
         body: &Body<'tcx>,
         type_test: &TypeTest<'tcx>,
         propagated_outlives_requirements: &mut Vec<ClosureOutlivesRequirement<'tcx>>,
@@ -938,7 +952,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             // where `ur` is a local bound -- we are sometimes in a
             // position to prove things that our caller cannot.  See
             // #53570 for an example.
-            if self.eval_verify_bound(tcx, body, generic_ty, ur, &type_test.verify_bound) {
+            if self.eval_verify_bound(
+                infcx,
+                param_env,
+                body,
+                generic_ty,
+                ur,
+                &type_test.verify_bound,
+            ) {
                 continue;
             }
 
@@ -1161,7 +1182,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// `point`.
     fn eval_verify_bound(
         &self,
-        tcx: TyCtxt<'tcx>,
+        infcx: &InferCtxt<'_, 'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
         body: &Body<'tcx>,
         generic_ty: Ty<'tcx>,
         lower_bound: RegionVid,
@@ -1170,14 +1192,13 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         debug!("eval_verify_bound(lower_bound={:?}, verify_bound={:?})", lower_bound, verify_bound);
 
         match verify_bound {
-            VerifyBound::IfEq(test_ty, verify_bound1) => self.eval_if_eq(
-                tcx,
-                body,
-                generic_ty,
-                lower_bound,
-                *test_ty,
-                &VerifyBound::OutlivedBy(*verify_bound1),
-            ),
+            VerifyBound::IfEq(test_ty, verify_bound1) => {
+                self.eval_if_eq(infcx, generic_ty, lower_bound, *test_ty, *verify_bound1)
+            }
+
+            VerifyBound::IfEqBound(verify_if_eq_b) => {
+                self.eval_if_eq_bound(infcx, param_env, generic_ty, lower_bound, *verify_if_eq_b)
+            }
 
             VerifyBound::IsEmpty => {
                 let lower_bound_scc = self.constraint_sccs.scc(lower_bound);
@@ -1190,33 +1211,71 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             }
 
             VerifyBound::AnyBound(verify_bounds) => verify_bounds.iter().any(|verify_bound| {
-                self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound)
+                self.eval_verify_bound(
+                    infcx,
+                    param_env,
+                    body,
+                    generic_ty,
+                    lower_bound,
+                    verify_bound,
+                )
             }),
 
             VerifyBound::AllBounds(verify_bounds) => verify_bounds.iter().all(|verify_bound| {
-                self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound)
+                self.eval_verify_bound(
+                    infcx,
+                    param_env,
+                    body,
+                    generic_ty,
+                    lower_bound,
+                    verify_bound,
+                )
             }),
         }
     }
 
     fn eval_if_eq(
         &self,
-        tcx: TyCtxt<'tcx>,
-        body: &Body<'tcx>,
+        infcx: &InferCtxt<'_, 'tcx>,
         generic_ty: Ty<'tcx>,
         lower_bound: RegionVid,
         test_ty: Ty<'tcx>,
-        verify_bound: &VerifyBound<'tcx>,
+        verify_bound: Region<'tcx>,
     ) -> bool {
-        let generic_ty_normalized = self.normalize_to_scc_representatives(tcx, generic_ty);
-        let test_ty_normalized = self.normalize_to_scc_representatives(tcx, test_ty);
+        let generic_ty_normalized = self.normalize_to_scc_representatives(infcx.tcx, generic_ty);
+        let test_ty_normalized = self.normalize_to_scc_representatives(infcx.tcx, test_ty);
         if generic_ty_normalized == test_ty_normalized {
-            self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound)
+            let verify_bound_vid = self.to_region_vid(verify_bound);
+            self.eval_outlives(verify_bound_vid, lower_bound)
         } else {
             false
         }
     }
 
+    fn eval_if_eq_bound(
+        &self,
+        infcx: &InferCtxt<'_, 'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        generic_ty: Ty<'tcx>,
+        lower_bound: RegionVid,
+        verify_if_eq_b: ty::Binder<'tcx, VerifyIfEq<'tcx>>,
+    ) -> bool {
+        let generic_ty = self.normalize_to_scc_representatives(infcx.tcx, generic_ty);
+        let verify_if_eq_b = self.normalize_to_scc_representatives(infcx.tcx, verify_if_eq_b);
+        match test_type_match::extract_verify_if_eq_bound(
+            infcx.tcx,
+            param_env,
+            &verify_if_eq_b,
+            generic_ty,
+        ) {
+            Some(r) => {
+                let r_vid = self.to_region_vid(r);
+                self.eval_outlives(r_vid, lower_bound)
+            }
+            None => false,
+        }
+    }
+
     /// This is a conservative normalization procedure. It takes every
     /// free region in `value` and replaces it with the
     /// "representative" of its SCC (see `scc_representatives` field).
diff --git a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
@@ -22,19 +22,22 @@ use rustc_middle::ty::{Region, RegionVid};
 use rustc_span::Span;
 use std::fmt;
 
+use super::outlives::test_type_match;
+
 /// This function performs lexical region resolution given a complete
 /// set of constraints and variable origins. It performs a fixed-point
 /// iteration to find region values which satisfy all constraints,
 /// assuming such values can be found. It returns the final values of
 /// all the variables as well as a set of errors that must be reported.
 #[instrument(level = "debug", skip(region_rels, var_infos, data))]
 pub(crate) fn resolve<'tcx>(
+    param_env: ty::ParamEnv<'tcx>,
     region_rels: &RegionRelations<'_, 'tcx>,
     var_infos: VarInfos,
     data: RegionConstraintData<'tcx>,
 ) -> (LexicalRegionResolutions<'tcx>, Vec<RegionResolutionError<'tcx>>) {
     let mut errors = vec![];
-    let mut resolver = LexicalResolver { region_rels, var_infos, data };
+    let mut resolver = LexicalResolver { param_env, region_rels, var_infos, data };
     let values = resolver.infer_variable_values(&mut errors);
     (values, errors)
 }
@@ -100,6 +103,7 @@ struct RegionAndOrigin<'tcx> {
 type RegionGraph<'tcx> = Graph<(), Constraint<'tcx>>;
 
 struct LexicalResolver<'cx, 'tcx> {
+    param_env: ty::ParamEnv<'tcx>,
     region_rels: &'cx RegionRelations<'cx, 'tcx>,
     var_infos: VarInfos,
     data: RegionConstraintData<'tcx>,
@@ -823,6 +827,21 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                     && self.bound_is_met(&VerifyBound::OutlivedBy(*r), var_values, generic_ty, min)
             }
 
+            VerifyBound::IfEqBound(verify_if_eq_b) => {
+                match test_type_match::extract_verify_if_eq_bound(
+                    self.tcx(),
+                    self.param_env,
+                    verify_if_eq_b,
+                    generic_ty,
+                ) {
+                    Some(r) => {
+                        self.bound_is_met(&VerifyBound::OutlivedBy(r), var_values, generic_ty, min)
+                    }
+
+                    None => false,
+                }
+            }
+
             VerifyBound::OutlivedBy(r) => {
                 self.sub_concrete_regions(min, var_values.normalize(self.tcx(), *r))
             }
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
@@ -1290,7 +1290,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             &RegionRelations::new(self.tcx, region_context, outlives_env.free_region_map());
 
         let (lexical_region_resolutions, errors) =
-            lexical_region_resolve::resolve(region_rels, var_infos, data);
+            lexical_region_resolve::resolve(outlives_env.param_env, region_rels, var_infos, data);
 
         let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
         assert!(old_value.is_none());
diff --git a/compiler/rustc_infer/src/infer/outlives/mod.rs b/compiler/rustc_infer/src/infer/outlives/mod.rs
@@ -3,6 +3,7 @@
 pub mod components;
 pub mod env;
 pub mod obligations;
+pub mod test_type_match;
 pub mod verify;
 
 use rustc_middle::traits::query::OutlivesBound;
diff --git a/compiler/rustc_infer/src/infer/outlives/test_type_match.rs b/compiler/rustc_infer/src/infer/outlives/test_type_match.rs
diff --git a/compiler/rustc_infer/src/infer/region_constraints/mod.rs b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
