Auto merge of #98109 - nikomatsakis:issue-98095, r=jackh726

fix universes in the NLL type tests

In the NLL code, we were not accommodating universes in the
`type_test` logic.

Fixes #98095.

r? `@compiler-errors`

This breaks some tests, however, so the purpose of this branch is more explanatory and perhaps to do a crater run.

Author: bors

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`.

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -10,7 +10,8 @@ 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,
@@ -46,6 +47,7 @@ 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 +561,7 @@ 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 +577,13 @@ 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 +832,7 @@ 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 +849,8 @@ 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 +862,7 @@ 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 +919,7 @@ 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 +951,14 @@ 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 +1181,8 @@ 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,
@@ -1170,8 +1191,8 @@ 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, verify_bound1)
+            VerifyBound::IfEq(verify_if_eq_b) => {
+                self.eval_if_eq(infcx, param_env, generic_ty, lower_bound, *verify_if_eq_b)
             }
 
             VerifyBound::IsEmpty => {
@@ -1185,30 +1206,50 @@ 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>,
+        param_env: ty::ParamEnv<'tcx>,
         generic_ty: Ty<'tcx>,
         lower_bound: RegionVid,
-        test_ty: Ty<'tcx>,
-        verify_bound: &VerifyBound<'tcx>,
+        verify_if_eq_b: ty::Binder<'tcx, VerifyIfEq<'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);
-        if generic_ty_normalized == test_ty_normalized {
-            self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound)
-        } else {
-            false
+        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(
+            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,
         }
     }
 
@@ -1278,6 +1319,18 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let sub_region_scc = self.constraint_sccs.scc(sub_region);
         let sup_region_scc = self.constraint_sccs.scc(sup_region);
 
+        // If we are checking that `'sup: 'sub`, and `'sub` contains
+        // some placeholder that `'sup` cannot name, then this is only
+        // true if `'sup` outlives static.
+        if !self.universe_compatible(sub_region_scc, sup_region_scc) {
+            debug!(
+                "eval_outlives: sub universe `{sub_region_scc:?}` is not nameable \
+                by super `{sup_region_scc:?}`, promoting to static",
+            );
+
+            return self.eval_outlives(sup_region, self.universal_regions.fr_static);
+        }
+
         // Both the `sub_region` and `sup_region` consist of the union
         // of some number of universal regions (along with the union
         // of various points in the CFG; ignore those points for
@@ -1292,6 +1345,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             });
 
         if !universal_outlives {
+            debug!(
+                "eval_outlives: returning false because sub region contains a universal region not present in super"
+            );
             return false;
         }
 
@@ -1300,10 +1356,15 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
         if self.universal_regions.is_universal_region(sup_region) {
             // Micro-opt: universal regions contain all points.
+            debug!(
+                "eval_outlives: returning true because super is universal and hence contains all points"
+            );
             return true;
         }
 
-        self.scc_values.contains_points(sup_region_scc, sub_region_scc)
+        let result = self.scc_values.contains_points(sup_region_scc, sub_region_scc);
+        debug!("returning {} because of comparison between points in sup/sub", result);
+        result
     }
 
     /// Once regions have been propagated, this method is used to see

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>,
@@ -818,9 +822,20 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         min: ty::Region<'tcx>,
     ) -> bool {
         match bound {
-            VerifyBound::IfEq(k, b) => {
-                (var_values.normalize(self.region_rels.tcx, *k) == generic_ty)
-                    && self.bound_is_met(b, var_values, generic_ty, min)
+            VerifyBound::IfEq(verify_if_eq_b) => {
+                let verify_if_eq_b = var_values.normalize(self.region_rels.tcx, *verify_if_eq_b);
+                match test_type_match::extract_verify_if_eq(
+                    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) => {

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());

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;

compiler/rustc_infer/src/infer/outlives/obligations.rs

@@ -318,17 +318,13 @@ where
         self.delegate.push_verify(origin, generic, region, verify_bound);
     }
 
+    #[tracing::instrument(level = "debug", skip(self))]
     fn projection_must_outlive(
         &mut self,
         origin: infer::SubregionOrigin<'tcx>,
         region: ty::Region<'tcx>,
         projection_ty: ty::ProjectionTy<'tcx>,
     ) {
-        debug!(
-            "projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})",
-            region, projection_ty, origin
-        );
-
         // This case is thorny for inference. The fundamental problem is
         // that there are many cases where we have choice, and inference
         // doesn't like choice (the current region inference in
@@ -363,13 +359,21 @@ where
         // #55756) in cases where you have e.g., `<T as Foo<'a>>::Item:
         // 'a` in the environment but `trait Foo<'b> { type Item: 'b
         // }` in the trait definition.
-        approx_env_bounds.retain(|bound| match *bound.0.kind() {
-            ty::Projection(projection_ty) => self
-                .verify_bound
-                .projection_declared_bounds_from_trait(projection_ty)
-                .all(|r| r != bound.1),
-
-            _ => panic!("expected only projection types from env, not {:?}", bound.0),
+        approx_env_bounds.retain(|bound_outlives| {
+            // OK to skip binder because we only manipulate and compare against other
+            // values from the same binder. e.g. if we have (e.g.) `for<'a> <T as Trait<'a>>::Item: 'a`
+            // in `bound`, the `'a` will be a `^1` (bound, debruijn index == innermost) region.
+            // If the declaration is `trait Trait<'b> { type Item: 'b; }`, then `projection_declared_bounds_from_trait`
+            // will be invoked with `['b => ^1]` and so we will get `^1` returned.
+            let bound = bound_outlives.skip_binder();
+            match *bound.0.kind() {
+                ty::Projection(projection_ty) => self
+                    .verify_bound
+                    .projection_declared_bounds_from_trait(projection_ty)
+                    .all(|r| r != bound.1),
+
+                _ => panic!("expected only projection types from env, not {:?}", bound.0),
+            }
         });
 
         // If declared bounds list is empty, the only applicable rule is
@@ -420,8 +424,16 @@ where
         if !trait_bounds.is_empty()
             && trait_bounds[1..]
                 .iter()
-                .chain(approx_env_bounds.iter().map(|b| &b.1))
-                .all(|b| *b == trait_bounds[0])
+                .map(|r| Some(*r))
+                .chain(
+                    // NB: The environment may contain `for<'a> T: 'a` style bounds.
+                    // In that case, we don't know if they are equal to the trait bound
+                    // or not (since we don't *know* whether the environment bound even applies),
+                    // so just map to `None` here if there are bound vars, ensuring that
+                    // the call to `all` will fail below.
+                    approx_env_bounds.iter().map(|b| b.map_bound(|b| b.1).no_bound_vars()),
+                )
+                .all(|b| b == Some(trait_bounds[0]))
         {
             let unique_bound = trait_bounds[0];
             debug!("projection_must_outlive: unique trait bound = {:?}", unique_bound);
@@ -437,6 +449,7 @@ where
         // even though a satisfactory solution exists.
         let generic = GenericKind::Projection(projection_ty);
         let verify_bound = self.verify_bound.generic_bound(generic);
+        debug!("projection_must_outlive: pushing {:?}", verify_bound);
         self.delegate.push_verify(origin, generic, region, verify_bound);
     }
 }