Auto merge of #98584 - lcnr:region-stuff-more-beans, r=oli-obk

continue nll transition by removing stuff

r? `@jackh726` for now

building on #98641

6 files changed, 48 insertions, 136 deletions

diff --git a/compiler/rustc_infer/src/infer/canonical/query_response.rs b/compiler/rustc_infer/src/infer/canonical/query_response.rs
index 8938ed78a94..7120d5ad934 100644
--- a/compiler/rustc_infer/src/infer/canonical/query_response.rs
+++ b/compiler/rustc_infer/src/infer/canonical/query_response.rs
@@ -128,7 +128,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         let region_constraints = self.with_region_constraints(|region_constraints| {
             make_query_region_constraints(
                 tcx,
-                region_obligations.iter().map(|(_, r_o)| (r_o.sup_type, r_o.sub_region)),
+                region_obligations.iter().map(|r_o| (r_o.sup_type, r_o.sub_region)),
                 region_constraints,
             )
         });
diff --git a/compiler/rustc_infer/src/infer/free_regions.rs b/compiler/rustc_infer/src/infer/free_regions.rs
index 082eb1bf111..fad949a3bc6 100644
--- a/compiler/rustc_infer/src/infer/free_regions.rs
+++ b/compiler/rustc_infer/src/infer/free_regions.rs
@@ -4,7 +4,6 @@
 //! and use that to decide when one free region outlives another, and so forth.
 
 use rustc_data_structures::transitive_relation::TransitiveRelation;
-use rustc_hir::def_id::DefId;
 use rustc_middle::ty::{self, Lift, Region, TyCtxt};
 
 /// Combines a `FreeRegionMap` and a `TyCtxt`.
@@ -14,16 +13,13 @@ use rustc_middle::ty::{self, Lift, Region, TyCtxt};
 pub(crate) struct RegionRelations<'a, 'tcx> {
     pub tcx: TyCtxt<'tcx>,
 
-    /// The context used for debug messages
-    pub context: DefId,
-
     /// Free-region relationships.
     pub free_regions: &'a FreeRegionMap<'tcx>,
 }
 
 impl<'a, 'tcx> RegionRelations<'a, 'tcx> {
-    pub fn new(tcx: TyCtxt<'tcx>, context: DefId, free_regions: &'a FreeRegionMap<'tcx>) -> Self {
-        Self { tcx, context, free_regions }
+    pub fn new(tcx: TyCtxt<'tcx>, free_regions: &'a FreeRegionMap<'tcx>) -> Self {
+        Self { tcx, free_regions }
     }
 
     pub fn lub_free_regions(&self, r_a: Region<'tcx>, r_b: Region<'tcx>) -> Region<'tcx> {
diff --git a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
index 68c709a2e24..87fa22b3835 100644
--- a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
+++ b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
@@ -120,13 +120,9 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
     ) -> LexicalRegionResolutions<'tcx> {
         let mut var_data = self.construct_var_data(self.tcx());
 
-        // Dorky hack to cause `dump_constraints` to only get called
-        // if debug mode is enabled:
-        debug!(
-            "----() End constraint listing (context={:?}) {:?}---",
-            self.region_rels.context,
-            self.dump_constraints(self.region_rels)
-        );
+        if cfg!(debug_assertions) {
+            self.dump_constraints();
+        }
 
         let graph = self.construct_graph();
         self.expand_givens(&graph);
@@ -156,8 +152,8 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         }
     }
 
-    fn dump_constraints(&self, free_regions: &RegionRelations<'_, 'tcx>) {
-        debug!("----() Start constraint listing (context={:?}) ()----", free_regions.context);
+    #[instrument(level = "debug", skip(self))]
+    fn dump_constraints(&self) {
         for (idx, (constraint, _)) in self.data.constraints.iter().enumerate() {
             debug!("Constraint {} => {:?}", idx, constraint);
         }
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 6f88b83a473..c73302c7e41 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -15,7 +15,6 @@ use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::undo_log::Rollback;
 use rustc_data_structures::unify as ut;
 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed};
-use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
@@ -147,7 +146,7 @@ pub struct InferCtxtInner<'tcx> {
     /// for each body-id in this map, which will process the
     /// obligations within. This is expected to be done 'late enough'
     /// that all type inference variables have been bound and so forth.
-    region_obligations: Vec<(hir::HirId, RegionObligation<'tcx>)>,
+    region_obligations: Vec<RegionObligation<'tcx>>,
 
     undo_log: InferCtxtUndoLogs<'tcx>,
 
@@ -171,7 +170,7 @@ impl<'tcx> InferCtxtInner<'tcx> {
     }
 
     #[inline]
-    pub fn region_obligations(&self) -> &[(hir::HirId, RegionObligation<'tcx>)] {
+    pub fn region_obligations(&self) -> &[RegionObligation<'tcx>] {
         &self.region_obligations
     }
 
@@ -1267,7 +1266,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// `resolve_vars_if_possible` as well as `fully_resolve`.
     pub fn resolve_regions(
         &self,
-        region_context: DefId,
         outlives_env: &OutlivesEnvironment<'tcx>,
     ) -> Vec<RegionResolutionError<'tcx>> {
         let (var_infos, data) = {
@@ -1286,8 +1284,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 .into_infos_and_data()
         };
 
-        let region_rels =
-            &RegionRelations::new(self.tcx, region_context, outlives_env.free_region_map());
+        let region_rels = &RegionRelations::new(self.tcx, outlives_env.free_region_map());
 
         let (lexical_region_resolutions, errors) =
             lexical_region_resolve::resolve(outlives_env.param_env, region_rels, var_infos, data);
@@ -1302,12 +1299,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use
     /// `resolve_vars_if_possible` as well as `fully_resolve`.
-    pub fn resolve_regions_and_report_errors(
-        &self,
-        region_context: DefId,
-        outlives_env: &OutlivesEnvironment<'tcx>,
-    ) {
-        let errors = self.resolve_regions(region_context, outlives_env);
+    pub fn resolve_regions_and_report_errors(&self, outlives_env: &OutlivesEnvironment<'tcx>) {
+        let errors = self.resolve_regions(outlives_env);
 
         if !self.is_tainted_by_errors() {
             // As a heuristic, just skip reporting region errors
diff --git a/compiler/rustc_infer/src/infer/outlives/env.rs b/compiler/rustc_infer/src/infer/outlives/env.rs
index 9ddda7b92eb..b897de7315a 100644
--- a/compiler/rustc_infer/src/infer/outlives/env.rs
+++ b/compiler/rustc_infer/src/infer/outlives/env.rs
@@ -1,8 +1,6 @@
 use crate::infer::free_regions::FreeRegionMap;
 use crate::infer::{GenericKind, InferCtxt};
 use crate::traits::query::OutlivesBound;
-use rustc_data_structures::fx::FxHashMap;
-use rustc_hir as hir;
 use rustc_middle::ty::{self, ReEarlyBound, ReFree, ReVar, Region};
 
 use super::explicit_outlives_bounds;
@@ -31,9 +29,7 @@ pub struct OutlivesEnvironment<'tcx> {
     pub param_env: ty::ParamEnv<'tcx>,
     free_region_map: FreeRegionMap<'tcx>,
 
-    // Contains, for each body B that we are checking (that is, the fn
-    // item, but also any nested closures), the set of implied region
-    // bounds that are in scope in that particular body.
+    // Contains the implied region bounds in scope for our current body.
     //
     // Example:
     //
@@ -43,24 +39,15 @@ pub struct OutlivesEnvironment<'tcx> {
     // } // body B0
     // ```
     //
-    // Here, for body B0, the list would be `[T: 'a]`, because we
+    // Here, when checking the body B0, the list would be `[T: 'a]`, because we
     // infer that `T` must outlive `'a` from the implied bounds on the
     // fn declaration.
     //
-    // For the body B1, the list would be `[T: 'a, T: 'b]`, because we
+    // For the body B1 however, the list would be `[T: 'a, T: 'b]`, because we
     // also can see that -- within the closure body! -- `T` must
     // outlive `'b`. This is not necessarily true outside the closure
     // body, since the closure may never be called.
-    //
-    // We collect this map as we descend the tree. We then use the
-    // results when proving outlives obligations like `T: 'x` later
-    // (e.g., if `T: 'x` must be proven within the body B1, then we
-    // know it is true if either `'a: 'x` or `'b: 'x`).
-    region_bound_pairs_map: FxHashMap<hir::HirId, RegionBoundPairs<'tcx>>,
-
-    // Used to compute `region_bound_pairs_map`: contains the set of
-    // in-scope region-bound pairs thus far.
-    region_bound_pairs_accum: RegionBoundPairs<'tcx>,
+    region_bound_pairs: RegionBoundPairs<'tcx>,
 }
 
 /// "Region-bound pairs" tracks outlives relations that are known to
@@ -73,8 +60,7 @@ impl<'a, 'tcx> OutlivesEnvironment<'tcx> {
         let mut env = OutlivesEnvironment {
             param_env,
             free_region_map: Default::default(),
-            region_bound_pairs_map: Default::default(),
-            region_bound_pairs_accum: vec![],
+            region_bound_pairs: Default::default(),
         };
 
         env.add_outlives_bounds(None, explicit_outlives_bounds(param_env));
@@ -87,62 +73,9 @@ impl<'a, 'tcx> OutlivesEnvironment<'tcx> {
         &self.free_region_map
     }
 
-    /// Borrows current value of the `region_bound_pairs`.
-    pub fn region_bound_pairs_map(&self) -> &FxHashMap<hir::HirId, RegionBoundPairs<'tcx>> {
-        &self.region_bound_pairs_map
-    }
-
-    /// This is a hack to support the old-school regionck, which
-    /// processes region constraints from the main function and the
-    /// closure together. In that context, when we enter a closure, we
-    /// want to be able to "save" the state of the surrounding a
-    /// function. We can then add implied bounds and the like from the
-    /// closure arguments into the environment -- these should only
-    /// apply in the closure body, so once we exit, we invoke
-    /// `pop_snapshot_post_typeck_child` to remove them.
-    ///
-    /// Example:
-    ///
-    /// ```ignore (pseudo-rust)
-    /// fn foo<T>() {
-    ///    callback(for<'a> |x: &'a T| {
-    ///         // ^^^^^^^ not legal syntax, but probably should be
-    ///         // within this closure body, `T: 'a` holds
-    ///    })
-    /// }
-    /// ```
-    ///
-    /// This "containment" of closure's effects only works so well. In
-    /// particular, we (intentionally) leak relationships between free
-    /// regions that are created by the closure's bounds. The case
-    /// where this is useful is when you have (e.g.) a closure with a
-    /// signature like `for<'a, 'b> fn(x: &'a &'b u32)` -- in this
-    /// case, we want to keep the relationship `'b: 'a` in the
-    /// free-region-map, so that later if we have to take `LUB('b,
-    /// 'a)` we can get the result `'b`.
-    ///
-    /// I have opted to keep **all modifications** to the
-    /// free-region-map, however, and not just those that concern free
-    /// variables bound in the closure. The latter seems more correct,
-    /// but it is not the existing behavior, and I could not find a
-    /// case where the existing behavior went wrong. In any case, it
-    /// seems like it'd be readily fixed if we wanted. There are
-    /// similar leaks around givens that seem equally suspicious, to
-    /// be honest. --nmatsakis
-    pub fn push_snapshot_pre_typeck_child(&self) -> usize {
-        self.region_bound_pairs_accum.len()
-    }
-
-    /// See `push_snapshot_pre_typeck_child`.
-    pub fn pop_snapshot_post_typeck_child(&mut self, len: usize) {
-        self.region_bound_pairs_accum.truncate(len);
-    }
-
-    /// Save the current set of region-bound pairs under the given `body_id`.
-    pub fn save_implied_bounds(&mut self, body_id: hir::HirId) {
-        let old =
-            self.region_bound_pairs_map.insert(body_id, self.region_bound_pairs_accum.clone());
-        assert!(old.is_none());
+    /// Borrows current `region_bound_pairs`.
+    pub fn region_bound_pairs(&self) -> &RegionBoundPairs<'tcx> {
+        &self.region_bound_pairs
     }
 
     /// Processes outlives bounds that are known to hold, whether from implied or other sources.
@@ -164,11 +97,10 @@ impl<'a, 'tcx> OutlivesEnvironment<'tcx> {
             debug!("add_outlives_bounds: outlives_bound={:?}", outlives_bound);
             match outlives_bound {
                 OutlivesBound::RegionSubParam(r_a, param_b) => {
-                    self.region_bound_pairs_accum.push((r_a, GenericKind::Param(param_b)));
+                    self.region_bound_pairs.push((r_a, GenericKind::Param(param_b)));
                 }
                 OutlivesBound::RegionSubProjection(r_a, projection_b) => {
-                    self.region_bound_pairs_accum
-                        .push((r_a, GenericKind::Projection(projection_b)));
+                    self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b)));
                 }
                 OutlivesBound::RegionSubRegion(r_a, r_b) => {
                     if let (ReEarlyBound(_) | ReFree(_), ReVar(vid_b)) = (r_a.kind(), r_b.kind()) {
diff --git a/compiler/rustc_infer/src/infer/outlives/obligations.rs b/compiler/rustc_infer/src/infer/outlives/obligations.rs
index 1c1906f3375..b839566bec9 100644
--- a/compiler/rustc_infer/src/infer/outlives/obligations.rs
+++ b/compiler/rustc_infer/src/infer/outlives/obligations.rs
@@ -60,18 +60,16 @@
 //! imply that `'b: 'a`.
 
 use crate::infer::outlives::components::{push_outlives_components, Component};
+use crate::infer::outlives::env::OutlivesEnvironment;
 use crate::infer::outlives::env::RegionBoundPairs;
 use crate::infer::outlives::verify::VerifyBoundCx;
 use crate::infer::{
     self, GenericKind, InferCtxt, RegionObligation, SubregionOrigin, UndoLog, VerifyBound,
 };
 use crate::traits::{ObligationCause, ObligationCauseCode};
+use rustc_data_structures::undo_log::UndoLogs;
 use rustc_middle::ty::subst::GenericArgKind;
 use rustc_middle::ty::{self, Region, Ty, TyCtxt, TypeFoldable};
-
-use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::undo_log::UndoLogs;
-use rustc_hir as hir;
 use smallvec::smallvec;
 
 impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
@@ -80,16 +78,11 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     /// and later processed by regionck, when full type information is
     /// available (see `region_obligations` field for more
     /// information).
-    pub fn register_region_obligation(
-        &self,
-        body_id: hir::HirId,
-        obligation: RegionObligation<'tcx>,
-    ) {
-        debug!("register_region_obligation(body_id={:?}, obligation={:?})", body_id, obligation);
-
+    #[instrument(level = "debug", skip(self))]
+    pub fn register_region_obligation(&self, obligation: RegionObligation<'tcx>) {
         let mut inner = self.inner.borrow_mut();
         inner.undo_log.push(UndoLog::PushRegionObligation);
-        inner.region_obligations.push((body_id, obligation));
+        inner.region_obligations.push(obligation);
     }
 
     pub fn register_region_obligation_with_cause(
@@ -109,14 +102,11 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
             )
         });
 
-        self.register_region_obligation(
-            cause.body_id,
-            RegionObligation { sup_type, sub_region, origin },
-        );
+        self.register_region_obligation(RegionObligation { sup_type, sub_region, origin });
     }
 
     /// Trait queries just want to pass back type obligations "as is"
-    pub fn take_registered_region_obligations(&self) -> Vec<(hir::HirId, RegionObligation<'tcx>)> {
+    pub fn take_registered_region_obligations(&self) -> Vec<RegionObligation<'tcx>> {
         std::mem::take(&mut self.inner.borrow_mut().region_obligations)
     }
 
@@ -144,10 +134,10 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     /// - `param_env` is the parameter environment for the enclosing function.
     /// - `body_id` is the body-id whose region obligations are being
     ///   processed.
-    #[instrument(level = "debug", skip(self, region_bound_pairs_map))]
+    #[instrument(level = "debug", skip(self, region_bound_pairs))]
     pub fn process_registered_region_obligations(
         &self,
-        region_bound_pairs_map: &FxHashMap<hir::HirId, RegionBoundPairs<'tcx>>,
+        region_bound_pairs: &RegionBoundPairs<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) {
         assert!(
@@ -157,7 +147,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
 
         let my_region_obligations = self.take_registered_region_obligations();
 
-        for (body_id, RegionObligation { sup_type, sub_region, origin }) in my_region_obligations {
+        for RegionObligation { sup_type, sub_region, origin } in my_region_obligations {
             debug!(
                 "process_registered_region_obligations: sup_type={:?} sub_region={:?} origin={:?}",
                 sup_type, sub_region, origin
@@ -165,18 +155,23 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
 
             let sup_type = self.resolve_vars_if_possible(sup_type);
 
-            if let Some(region_bound_pairs) = region_bound_pairs_map.get(&body_id) {
-                let outlives =
-                    &mut TypeOutlives::new(self, self.tcx, &region_bound_pairs, None, param_env);
-                outlives.type_must_outlive(origin, sup_type, sub_region);
-            } else {
-                self.tcx.sess.delay_span_bug(
-                    origin.span(),
-                    &format!("no region-bound-pairs for {:?}", body_id),
-                );
-            }
+            let outlives =
+                &mut TypeOutlives::new(self, self.tcx, &region_bound_pairs, None, param_env);
+            outlives.type_must_outlive(origin, sup_type, sub_region);
         }
     }
+
+    pub fn check_region_obligations_and_report_errors(
+        &self,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+    ) {
+        self.process_registered_region_obligations(
+            outlives_env.region_bound_pairs(),
+            outlives_env.param_env,
+        );
+
+        self.resolve_regions_and_report_errors(outlives_env)
+    }
 }
 
 /// The `TypeOutlives` struct has the job of "lowering" a `T: 'a`