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)

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,

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,
             },

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;
             };
 

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),
                                             })

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((

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)) => {