Auto merge of #125468 - BoxyUwU:remove_defid_from_regionparam, r=compiler-errors

Remove `DefId` from `EarlyParamRegion`

Currently we represent usages of `Region` parameters via the `ReEarlyParam` or `ReLateParam` variants. The `ReEarlyParam` is effectively equivalent to `TyKind::Param` and `ConstKind::Param` (i.e. it stores a `Symbol` and a `u32` index) however it also stores a `DefId` for the definition of the lifetime parameter.

This was used in roughly two places:
- Borrowck diagnostics instead of threading the appropriate `body_id` down to relevant locations. Interestingly there were already some places that had to pass down a `DefId` manually.
- Some opaque type checking logic was using the `DefId` field to track captured lifetimes

I've split this PR up into a commit for generate rote changes to diagnostics code to pass around a `DefId` manually everywhere, and another commit for the opaque type related changes which likely require more careful review as they might change the semantics of lints/errors.

Instead of manually passing the `DefId` around everywhere I previously tried to bundle it in with `TypeErrCtxt` but ran into issues with some call sites of `infcx.err_ctxt` being unable to provide a `DefId`, particularly places involved with trait solving and normalization. It might be worth investigating adding some new wrapper type to pass this around everywhere but I think this might be acceptable for now.

This pr also has the effect of reducing the size of `EarlyParamRegion` from 16 bytes -> 8 bytes. I wouldn't expect this to have any direct performance improvement however, other variants of `RegionKind` over `8` bytes are all because they contain a `BoundRegionKind` which is, as far as I know, mostly there for diagnostics. If we're ever able to remove this it would shrink the `RegionKind` type from `24` bytes to `12` (and with clever bit packing we might be able to get it to `8` bytes). I am curious what the performance impact would be of removing interning of `Region`'s if we ever manage to shrink `RegionKind` that much.

Sidenote: by removing the `DefId` the `Debug` output for `Region` has gotten significantly nicer. As an example see this opaque type debug print before vs after this PR:
`Opaque(DefId(0:13 ~ impl_trait_captures[aeb9]::foo::{opaque#0}), [DefId(0:9 ~ impl_trait_captures[aeb9]::foo::'a)_'a/#0, T, DefId(0:9 ~ impl_trait_captures[aeb9]::foo::'a)_'a/#0])`
`Opaque(DefId(0:13 ~ impl_trait_captures[aeb9]::foo::{opaque#0}), ['a/#0, T, 'a/#0])`

r? `@compiler-errors` (I would like someone who understands the opaque type setup to atleast review the type system commit, but the rest is likely reviewable by anyone)

Author: bors

Diff for: compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs

@@ -1,4 +1,5 @@
 use rustc_errors::Diag;
+use rustc_hir::def_id::LocalDefId;
 use rustc_infer::infer::canonical::Canonical;
 use rustc_infer::infer::error_reporting::nice_region_error::NiceRegionError;
 use rustc_infer::infer::region_constraints::Constraint;
@@ -241,7 +242,7 @@ impl<'tcx> TypeOpInfo<'tcx> for PredicateQuery<'tcx> {
             mbcx.infcx.tcx.infer_ctxt().build_with_canonical(cause.span, &self.canonical_query);
         let ocx = ObligationCtxt::new(&infcx);
         type_op_prove_predicate_with_cause(&ocx, key, cause);
-        try_extract_error_from_fulfill_cx(&ocx, placeholder_region, error_region)
+        try_extract_error_from_fulfill_cx(&ocx, mbcx.mir_def_id(), placeholder_region, error_region)
     }
 }
 
@@ -287,7 +288,7 @@ where
         let (param_env, value) = key.into_parts();
         let _ = ocx.normalize(&cause, param_env, value.value);
 
-        try_extract_error_from_fulfill_cx(&ocx, placeholder_region, error_region)
+        try_extract_error_from_fulfill_cx(&ocx, mbcx.mir_def_id(), placeholder_region, error_region)
     }
 }
 
@@ -318,7 +319,7 @@ impl<'tcx> TypeOpInfo<'tcx> for AscribeUserTypeQuery<'tcx> {
             mbcx.infcx.tcx.infer_ctxt().build_with_canonical(cause.span, &self.canonical_query);
         let ocx = ObligationCtxt::new(&infcx);
         type_op_ascribe_user_type_with_span(&ocx, key, Some(cause.span)).ok()?;
-        try_extract_error_from_fulfill_cx(&ocx, placeholder_region, error_region)
+        try_extract_error_from_fulfill_cx(&ocx, mbcx.mir_def_id(), placeholder_region, error_region)
     }
 }
 
@@ -342,6 +343,7 @@ impl<'tcx> TypeOpInfo<'tcx> for crate::type_check::InstantiateOpaqueType<'tcx> {
     ) -> Option<Diag<'tcx>> {
         try_extract_error_from_region_constraints(
             mbcx.infcx,
+            mbcx.mir_def_id(),
             placeholder_region,
             error_region,
             self.region_constraints.as_ref().unwrap(),
@@ -358,6 +360,7 @@ impl<'tcx> TypeOpInfo<'tcx> for crate::type_check::InstantiateOpaqueType<'tcx> {
 #[instrument(skip(ocx), level = "debug")]
 fn try_extract_error_from_fulfill_cx<'tcx>(
     ocx: &ObligationCtxt<'_, 'tcx>,
+    generic_param_scope: LocalDefId,
     placeholder_region: ty::Region<'tcx>,
     error_region: Option<ty::Region<'tcx>>,
 ) -> Option<Diag<'tcx>> {
@@ -368,6 +371,7 @@ fn try_extract_error_from_fulfill_cx<'tcx>(
     let region_constraints = ocx.infcx.with_region_constraints(|r| r.clone());
     try_extract_error_from_region_constraints(
         ocx.infcx,
+        generic_param_scope,
         placeholder_region,
         error_region,
         &region_constraints,
@@ -379,6 +383,7 @@ fn try_extract_error_from_fulfill_cx<'tcx>(
 #[instrument(level = "debug", skip(infcx, region_var_origin, universe_of_region))]
 fn try_extract_error_from_region_constraints<'tcx>(
     infcx: &InferCtxt<'tcx>,
+    generic_param_scope: LocalDefId,
     placeholder_region: ty::Region<'tcx>,
     error_region: Option<ty::Region<'tcx>>,
     region_constraints: &RegionConstraintData<'tcx>,
@@ -452,15 +457,18 @@ fn try_extract_error_from_region_constraints<'tcx>(
             RegionResolutionError::ConcreteFailure(cause.clone(), sub_region, placeholder_region)
         }
     };
-    NiceRegionError::new(&infcx.err_ctxt(), error).try_report_from_nll().or_else(|| {
-        if let SubregionOrigin::Subtype(trace) = cause {
-            Some(
-                infcx
-                    .err_ctxt()
-                    .report_and_explain_type_error(*trace, TypeError::RegionsPlaceholderMismatch),
-            )
-        } else {
-            None
-        }
-    })
+    NiceRegionError::new(&infcx.err_ctxt(), generic_param_scope, error)
+        .try_report_from_nll()
+        .or_else(|| {
+            if let SubregionOrigin::Subtype(trace) = cause {
+                Some(
+                    infcx.err_ctxt().report_and_explain_type_error(
+                        *trace,
+                        TypeError::RegionsPlaceholderMismatch,
+                    ),
+                )
+            } else {
+                None
+            }
+        })
 }

Diff for: compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -361,6 +361,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     let named_region = self.regioncx.name_regions(self.infcx.tcx, member_region);
                     let diag = unexpected_hidden_region_diagnostic(
                         self.infcx.tcx,
+                        self.mir_def_id(),
                         span,
                         named_ty,
                         named_region,
@@ -453,7 +454,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         // Check if we can use one of the "nice region errors".
         if let (Some(f), Some(o)) = (self.to_error_region(fr), self.to_error_region(outlived_fr)) {
             let infer_err = self.infcx.err_ctxt();
-            let nice = NiceRegionError::new_from_span(&infer_err, cause.span, o, f);
+            let nice =
+                NiceRegionError::new_from_span(&infer_err, self.mir_def_id(), cause.span, o, f);
             if let Some(diag) = nice.try_report_from_nll() {
                 self.buffer_error(diag);
                 return;
@@ -843,14 +845,16 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             if *outlived_f != ty::ReStatic {
                 return;
             }
-            let suitable_region = self.infcx.tcx.is_suitable_region(f);
+            let suitable_region = self.infcx.tcx.is_suitable_region(self.mir_def_id(), f);
             let Some(suitable_region) = suitable_region else {
                 return;
             };
 
             let fn_returns = self.infcx.tcx.return_type_impl_or_dyn_traits(suitable_region.def_id);
 
-            let param = if let Some(param) = find_param_with_region(self.infcx.tcx, f, outlived_f) {
+            let param = if let Some(param) =
+                find_param_with_region(self.infcx.tcx, self.mir_def_id(), f, outlived_f)
+            {
                 param
             } else {
                 return;
@@ -959,7 +963,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             return;
         };
 
-        let param = match find_param_with_region(tcx, f, o) {
+        let param = match find_param_with_region(tcx, self.mir_def_id(), f, o) {
             Some(param) => param,
             None => return,
         };
@@ -1022,25 +1026,30 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             return;
         };
 
-        let Some((ty_sub, _)) = self
-            .infcx
-            .tcx
-            .is_suitable_region(sub)
-            .and_then(|anon_reg| find_anon_type(self.infcx.tcx, sub, &anon_reg.bound_region))
+        let Some((ty_sub, _)) =
+            self.infcx.tcx.is_suitable_region(self.mir_def_id(), sub).and_then(|anon_reg| {
+                find_anon_type(self.infcx.tcx, self.mir_def_id(), sub, &anon_reg.bound_region)
+            })
         else {
             return;
         };
 
-        let Some((ty_sup, _)) = self
-            .infcx
-            .tcx
-            .is_suitable_region(sup)
-            .and_then(|anon_reg| find_anon_type(self.infcx.tcx, sup, &anon_reg.bound_region))
+        let Some((ty_sup, _)) =
+            self.infcx.tcx.is_suitable_region(self.mir_def_id(), sup).and_then(|anon_reg| {
+                find_anon_type(self.infcx.tcx, self.mir_def_id(), sup, &anon_reg.bound_region)
+            })
         else {
             return;
         };
 
-        suggest_adding_lifetime_params(self.infcx.tcx, sub, ty_sup, ty_sub, diag);
+        suggest_adding_lifetime_params(
+            self.infcx.tcx,
+            diag,
+            self.mir_def_id(),
+            sub,
+            ty_sup,
+            ty_sub,
+        );
     }
 
     #[allow(rustc::diagnostic_outside_of_impl)]

Diff for: compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -289,7 +289,8 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         debug!("give_region_a_name: error_region = {:?}", error_region);
         match *error_region {
             ty::ReEarlyParam(ebr) => ebr.has_name().then(|| {
-                let span = tcx.hir().span_if_local(ebr.def_id).unwrap_or(DUMMY_SP);
+                let def_id = tcx.generics_of(self.mir_def_id()).region_param(ebr, tcx).def_id;
+                let span = tcx.hir().span_if_local(def_id).unwrap_or(DUMMY_SP);
                 RegionName { name: ebr.name, source: RegionNameSource::NamedEarlyParamRegion(span) }
             }),
 
@@ -912,7 +913,8 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         };
 
         let tcx = self.infcx.tcx;
-        let region_parent = tcx.parent(region.def_id);
+        let region_def = tcx.generics_of(self.mir_def_id()).region_param(region, tcx).def_id;
+        let region_parent = tcx.parent(region_def);
         let DefKind::Impl { .. } = tcx.def_kind(region_parent) else {
             return None;
         };
@@ -925,7 +927,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         Some(RegionName {
             name: self.synthesize_region_name(),
             source: RegionNameSource::AnonRegionFromImplSignature(
-                tcx.def_span(region.def_id),
+                tcx.def_span(region_def),
                 // FIXME(compiler-errors): Does this ever actually show up
                 // anywhere other than the self type? I couldn't create an
                 // example of a `'_` in the impl's trait being referenceable.

Diff for: compiler/rustc_hir_analysis/src/check/check.rs

@@ -538,11 +538,9 @@ fn check_opaque_precise_captures<'tcx>(tcx: TyCtxt<'tcx>, opaque_def_id: LocalDe
                 // the cases that were stabilized with the `impl_trait_projection`
                 // feature -- see <https://github.com/rust-lang/rust/pull/115659>.
                 if let DefKind::LifetimeParam = tcx.def_kind(def_id)
-                    && let ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. })
-                    | ty::ReLateParam(ty::LateParamRegion {
-                        bound_region: ty::BoundRegionKind::BrNamed(def_id, _),
-                        ..
-                    }) = *tcx.map_opaque_lifetime_to_parent_lifetime(def_id.expect_local())
+                    && let Some(def_id) = tcx
+                        .map_opaque_lifetime_to_parent_lifetime(def_id.expect_local())
+                        .opt_param_def_id(tcx, tcx.parent(opaque_def_id.to_def_id()))
                 {
                     shadowed_captures.insert(def_id);
                 }
@@ -585,12 +583,9 @@ fn check_opaque_precise_captures<'tcx>(tcx: TyCtxt<'tcx>, opaque_def_id: LocalDe
                     // Check if the lifetime param was captured but isn't named in the precise captures list.
                     if variances[param.index as usize] == ty::Invariant {
                         if let DefKind::OpaqueTy = tcx.def_kind(tcx.parent(param.def_id))
-                            && let ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. })
-                            | ty::ReLateParam(ty::LateParamRegion {
-                                bound_region: ty::BoundRegionKind::BrNamed(def_id, _),
-                                ..
-                            }) = *tcx
+                            && let Some(def_id) = tcx
                                 .map_opaque_lifetime_to_parent_lifetime(param.def_id.expect_local())
+                                .opt_param_def_id(tcx, tcx.parent(opaque_def_id.to_def_id()))
                         {
                             tcx.dcx().emit_err(errors::LifetimeNotCaptured {
                                 opaque_span,

Diff for: compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -876,7 +876,8 @@ impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
             ty::ReLateParam(_) => {}
             // Remap early-bound regions as long as they don't come from the `impl` itself,
             // in which case we don't really need to renumber them.
-            ty::ReEarlyParam(ebr) if self.tcx.parent(ebr.def_id) != self.impl_def_id => {}
+            ty::ReEarlyParam(ebr)
+                if ebr.index >= self.tcx.generics_of(self.impl_def_id).count() as u32 => {}
             _ => return Ok(region),
         }
 
@@ -889,12 +890,8 @@ impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
                 );
             }
         } else {
-            let guar = match region.kind() {
-                ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. })
-                | ty::ReLateParam(ty::LateParamRegion {
-                    bound_region: ty::BoundRegionKind::BrNamed(def_id, _),
-                    ..
-                }) => {
+            let guar = match region.opt_param_def_id(self.tcx, self.tcx.parent(self.def_id)) {
+                Some(def_id) => {
                     let return_span = if let ty::Alias(ty::Opaque, opaque_ty) = self.ty.kind() {
                         self.tcx.def_span(opaque_ty.def_id)
                     } else {
@@ -914,7 +911,7 @@ impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
                         .with_note(format!("hidden type inferred to be `{}`", self.ty))
                         .emit()
                 }
-                _ => {
+                None => {
                     // This code path is not reached in any tests, but may be
                     // reachable. If this is triggered, it should be converted
                     // to `delayed_bug` and the triggering case turned into a
@@ -928,7 +925,6 @@ impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
         Ok(ty::Region::new_early_param(
             self.tcx,
             ty::EarlyParamRegion {
-                def_id: e.def_id,
                 name: e.name,
                 index: (e.index as usize - self.num_trait_args + self.num_impl_args) as u32,
             },

Diff for: compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -675,11 +675,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
                 let region_param = gat_generics.param_at(*region_a_idx, tcx);
                 let region_param = ty::Region::new_early_param(
                     tcx,
-                    ty::EarlyParamRegion {
-                        def_id: region_param.def_id,
-                        index: region_param.index,
-                        name: region_param.name,
-                    },
+                    ty::EarlyParamRegion { index: region_param.index, name: region_param.name },
                 );
                 // The predicate we expect to see. (In our example,
                 // `Self: 'me`.)
@@ -708,21 +704,13 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
                 let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
                 let region_a_param = ty::Region::new_early_param(
                     tcx,
-                    ty::EarlyParamRegion {
-                        def_id: region_a_param.def_id,
-                        index: region_a_param.index,
-                        name: region_a_param.name,
-                    },
+                    ty::EarlyParamRegion { index: region_a_param.index, name: region_a_param.name },
                 );
                 // Same for the region.
                 let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
                 let region_b_param = ty::Region::new_early_param(
                     tcx,
-                    ty::EarlyParamRegion {
-                        def_id: region_b_param.def_id,
-                        index: region_b_param.index,
-                        name: region_b_param.name,
-                    },
+                    ty::EarlyParamRegion { index: region_b_param.index, name: region_b_param.name },
                 );
                 // The predicate we expect to see.
                 bounds.insert(
@@ -2101,16 +2089,14 @@ fn lint_redundant_lifetimes<'tcx>(
         }
 
         for &victim in &lifetimes[(idx + 1)..] {
-            // We should only have late-bound lifetimes of the `BrNamed` variety,
-            // since we get these signatures straight from `hir_lowering`. And any
-            // other regions (ReError/ReStatic/etc.) shouldn't matter, since we
+            // All region parameters should have a `DefId` available as:
+            // - Late-bound parameters should be of the`BrNamed` variety,
+            // since we get these signatures straight from `hir_lowering`.
+            // - Early-bound parameters unconditionally have a `DefId` available.
+            //
+            // Any other regions (ReError/ReStatic/etc.) shouldn't matter, since we
             // can't really suggest to remove them.
-            let (ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. })
-            | ty::ReLateParam(ty::LateParamRegion {
-                bound_region: ty::BoundRegionKind::BrNamed(def_id, _),
-                ..
-            })) = victim.kind()
-            else {
+            let Some(def_id) = victim.opt_param_def_id(tcx, owner_id.to_def_id()) else {
                 continue;
             };
 

Diff for: compiler/rustc_hir_analysis/src/collect.rs

@@ -453,7 +453,6 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
                                         poly_trait_ref,
                                         |_| {
                                             ty::Region::new_early_param(self.tcx, ty::EarlyParamRegion {
-                                                def_id: item_def_id,
                                                 index: 0,
                                                 name: Symbol::intern(&lt_name),
                                             })

Diff for: compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -323,7 +323,7 @@ fn compute_bidirectional_outlives_predicates<'tcx>(
         if let ty::ReEarlyParam(..) = *orig_lifetime {
             let dup_lifetime = ty::Region::new_early_param(
                 tcx,
-                ty::EarlyParamRegion { def_id: param.def_id, index: param.index, name: param.name },
+                ty::EarlyParamRegion { index: param.index, name: param.name },
             );
             let span = tcx.def_span(param.def_id);
             predicates.push((

Diff for: compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -280,7 +280,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 let item_def_id = tcx.hir().ty_param_owner(def_id.expect_local());
                 let generics = tcx.generics_of(item_def_id);
                 let index = generics.param_def_id_to_index[&def_id];
-                ty::Region::new_early_param(tcx, ty::EarlyParamRegion { def_id, index, name })
+                ty::Region::new_early_param(tcx, ty::EarlyParamRegion { index, name })
             }
 
             Some(rbv::ResolvedArg::Free(scope, id)) => {

Diff for: compiler/rustc_infer/src/errors/mod.rs

@@ -5,6 +5,7 @@ use rustc_errors::{
     MultiSpan, SubdiagMessageOp, Subdiagnostic,
 };
 use rustc_hir as hir;
+use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::{walk_ty, Visitor};
 use rustc_hir::FnRetTy;
 use rustc_macros::{Diagnostic, Subdiagnostic};
@@ -344,6 +345,7 @@ impl Subdiagnostic for LifetimeMismatchLabels {
 
 pub struct AddLifetimeParamsSuggestion<'a> {
     pub tcx: TyCtxt<'a>,
+    pub generic_param_scope: LocalDefId,
     pub sub: Region<'a>,
     pub ty_sup: &'a hir::Ty<'a>,
     pub ty_sub: &'a hir::Ty<'a>,
@@ -357,7 +359,8 @@ impl Subdiagnostic for AddLifetimeParamsSuggestion<'_> {
         _f: &F,
     ) {
         let mut mk_suggestion = || {
-            let Some(anon_reg) = self.tcx.is_suitable_region(self.sub) else {
+            let Some(anon_reg) = self.tcx.is_suitable_region(self.generic_param_scope, self.sub)
+            else {
                 return false;
             };