Auto merge of #139598 - compiler-errors:no-bound-var-symbol, r=WaffleLapkin

Remove `Symbol` from `Named` variant of `BoundRegionKind`/`LateParamRegionKind`

The `Symbol` is redundant, since we already store a `DefId` in the region variant. Instead, load the name via `item_name` when needed (which is almost always on the diagnostic path).

This introduces a `BoundRegionKind::NamedAnon` which is used for giving anonymous bound regions names, but which should only be used during pretty printing and error reporting.

7 files changed, 34 insertions, 52 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index abbe497858b..87db80f2423 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -1239,7 +1239,7 @@ fn check_region_late_boundedness<'tcx>(
                 .unwrap_region_constraints()
                 .opportunistic_resolve_var(tcx, vid)
             && let ty::ReLateParam(ty::LateParamRegion {
-                kind: ty::LateParamRegionKind::Named(trait_param_def_id, _),
+                kind: ty::LateParamRegionKind::Named(trait_param_def_id),
                 ..
             }) = r.kind()
             && let ty::ReEarlyParam(ebr) = id_arg.expect_region().kind()
@@ -1264,7 +1264,7 @@ fn check_region_late_boundedness<'tcx>(
                 .unwrap_region_constraints()
                 .opportunistic_resolve_var(tcx, vid)
             && let ty::ReLateParam(ty::LateParamRegion {
-                kind: ty::LateParamRegionKind::Named(impl_param_def_id, _),
+                kind: ty::LateParamRegionKind::Named(impl_param_def_id),
                 ..
             }) = r.kind()
             && let ty::ReEarlyParam(ebr) = id_arg.expect_region().kind()
@@ -2468,7 +2468,7 @@ fn param_env_with_gat_bounds<'tcx>(
         let normalize_impl_ty_args = ty::GenericArgs::identity_for_item(tcx, container_id)
             .extend_to(tcx, impl_ty.def_id, |param, _| match param.kind {
                 GenericParamDefKind::Type { .. } => {
-                    let kind = ty::BoundTyKind::Param(param.def_id, param.name);
+                    let kind = ty::BoundTyKind::Param(param.def_id);
                     let bound_var = ty::BoundVariableKind::Ty(kind);
                     bound_vars.push(bound_var);
                     Ty::new_bound(
@@ -2479,7 +2479,7 @@ fn param_env_with_gat_bounds<'tcx>(
                     .into()
                 }
                 GenericParamDefKind::Lifetime => {
-                    let kind = ty::BoundRegionKind::Named(param.def_id, param.name);
+                    let kind = ty::BoundRegionKind::Named(param.def_id);
                     let bound_var = ty::BoundVariableKind::Region(kind);
                     bound_vars.push(bound_var);
                     ty::Region::new_bound(
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 4934136bc7a..0a3e018b79a 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -2338,7 +2338,7 @@ fn lint_redundant_lifetimes<'tcx>(
             lifetimes.push(ty::Region::new_late_param(tcx, owner_id.to_def_id(), kind));
         }
     }
-    lifetimes.retain(|candidate| candidate.has_name());
+    lifetimes.retain(|candidate| candidate.is_named(tcx));
 
     // Keep track of lifetimes which have already been replaced with other lifetimes.
     // This makes sure that if `'a = 'b = 'c`, we don't say `'c` should be replaced by
diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index 65bc441a473..8356a0af63c 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
@@ -654,7 +654,7 @@ fn infringing_fields_error<'tcx>(
                                 .or_default()
                                 .push(origin.span());
                             if let ty::RegionKind::ReEarlyParam(ebr) = b.kind()
-                                && ebr.has_name()
+                                && ebr.is_named()
                             {
                                 bounds.push((b.to_string(), a.to_string(), None));
                             }
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 271104c20c6..25064c327d0 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -578,13 +578,7 @@ fn get_new_lifetime_name<'tcx>(
     let existing_lifetimes = tcx
         .collect_referenced_late_bound_regions(poly_trait_ref)
         .into_iter()
-        .filter_map(|lt| {
-            if let ty::BoundRegionKind::Named(_, name) = lt {
-                Some(name.as_str().to_string())
-            } else {
-                None
-            }
-        })
+        .filter_map(|lt| lt.get_name(tcx).map(|name| name.as_str().to_string()))
         .chain(generics.params.iter().filter_map(|param| {
             if let hir::GenericParamKind::Lifetime { .. } = &param.kind {
                 Some(param.name.ident().as_str().to_string())
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index 0e775d374ab..a0d1273eb85 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -279,19 +279,13 @@ fn resolve_bound_vars(tcx: TyCtxt<'_>, local_def_id: hir::OwnerId) -> ResolveBou
     rbv
 }
 
-fn late_arg_as_bound_arg<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    param: &GenericParam<'tcx>,
-) -> ty::BoundVariableKind {
+fn late_arg_as_bound_arg<'tcx>(param: &GenericParam<'tcx>) -> ty::BoundVariableKind {
     let def_id = param.def_id.to_def_id();
-    let name = tcx.item_name(def_id);
     match param.kind {
         GenericParamKind::Lifetime { .. } => {
-            ty::BoundVariableKind::Region(ty::BoundRegionKind::Named(def_id, name))
-        }
-        GenericParamKind::Type { .. } => {
-            ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(def_id, name))
+            ty::BoundVariableKind::Region(ty::BoundRegionKind::Named(def_id))
         }
+        GenericParamKind::Type { .. } => ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(def_id)),
         GenericParamKind::Const { .. } => ty::BoundVariableKind::Const,
     }
 }
@@ -302,10 +296,10 @@ fn late_arg_as_bound_arg<'tcx>(
 fn generic_param_def_as_bound_arg(param: &ty::GenericParamDef) -> ty::BoundVariableKind {
     match param.kind {
         ty::GenericParamDefKind::Lifetime => {
-            ty::BoundVariableKind::Region(ty::BoundRegionKind::Named(param.def_id, param.name))
+            ty::BoundVariableKind::Region(ty::BoundRegionKind::Named(param.def_id))
         }
         ty::GenericParamDefKind::Type { .. } => {
-            ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(param.def_id, param.name))
+            ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(param.def_id))
         }
         ty::GenericParamDefKind::Const { .. } => ty::BoundVariableKind::Const,
     }
@@ -386,7 +380,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
             trait_ref.bound_generic_params.iter().enumerate().map(|(late_bound_idx, param)| {
                 let arg = ResolvedArg::late(initial_bound_vars + late_bound_idx as u32, param);
                 bound_vars.insert(param.def_id, arg);
-                late_arg_as_bound_arg(self.tcx, param)
+                late_arg_as_bound_arg(param)
             });
         binders.extend(binders_iter);
 
@@ -485,7 +479,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                     .map(|(late_bound_idx, param)| {
                         (
                             (param.def_id, ResolvedArg::late(late_bound_idx as u32, param)),
-                            late_arg_as_bound_arg(self.tcx, param),
+                            late_arg_as_bound_arg(param),
                         )
                     })
                     .unzip();
@@ -718,7 +712,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                     .map(|(late_bound_idx, param)| {
                         (
                             (param.def_id, ResolvedArg::late(late_bound_idx as u32, param)),
-                            late_arg_as_bound_arg(self.tcx, param),
+                            late_arg_as_bound_arg(param),
                         )
                     })
                     .unzip();
@@ -748,7 +742,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                         .map(|(late_bound_idx, param)| {
                             (
                                 (param.def_id, ResolvedArg::late(late_bound_idx as u32, param)),
-                                late_arg_as_bound_arg(self.tcx, param),
+                                late_arg_as_bound_arg(param),
                             )
                         })
                         .unzip();
@@ -957,7 +951,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                         .map(|(late_bound_idx, param)| {
                             (
                                 (param.def_id, ResolvedArg::late(late_bound_idx as u32, param)),
-                                late_arg_as_bound_arg(self.tcx, param),
+                                late_arg_as_bound_arg(param),
                             )
                         })
                         .unzip();
@@ -1171,7 +1165,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                 matches!(param.kind, GenericParamKind::Lifetime { .. })
                     && self.tcx.is_late_bound(param.hir_id)
             })
-            .map(|param| late_arg_as_bound_arg(self.tcx, param))
+            .map(|param| late_arg_as_bound_arg(param))
             .collect();
         self.record_late_bound_vars(hir_id, binders);
         let scope = Scope::Binder {
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
index d17986d45d2..4784cfb5235 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
@@ -12,7 +12,7 @@ use rustc_middle::ty::{
     self as ty, IsSuggestable, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt,
     TypeVisitor, Upcast,
 };
-use rustc_span::{ErrorGuaranteed, Ident, Span, Symbol, kw, sym};
+use rustc_span::{ErrorGuaranteed, Ident, Span, kw, sym};
 use rustc_trait_selection::traits;
 use smallvec::SmallVec;
 use tracing::{debug, instrument};
@@ -888,7 +888,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     ty::INNERMOST,
                     ty::BoundRegion {
                         var: ty::BoundVar::from_usize(num_bound_vars),
-                        kind: ty::BoundRegionKind::Named(param.def_id, param.name),
+                        kind: ty::BoundRegionKind::Named(param.def_id),
                     },
                 )
                 .into(),
@@ -1006,12 +1006,12 @@ fn check_assoc_const_binding_type<'tcx>(
             ty_note,
         }));
     }
-    for (var_def_id, var_name) in collector.vars {
+    for var_def_id in collector.vars {
         guar.get_or_insert(cx.dcx().emit_err(
             crate::errors::EscapingBoundVarInTyOfAssocConstBinding {
                 span: assoc_const.span,
                 assoc_const,
-                var_name,
+                var_name: cx.tcx().item_name(var_def_id),
                 var_def_kind: tcx.def_descr(var_def_id),
                 var_defined_here_label: tcx.def_ident_span(var_def_id).unwrap(),
                 ty_note,
@@ -1026,7 +1026,7 @@ fn check_assoc_const_binding_type<'tcx>(
 struct GenericParamAndBoundVarCollector<'a, 'tcx> {
     cx: &'a dyn HirTyLowerer<'tcx>,
     params: FxIndexSet<u32>,
-    vars: FxIndexSet<(DefId, Symbol)>,
+    vars: FxIndexSet<DefId>,
     depth: ty::DebruijnIndex,
 }
 
@@ -1050,7 +1050,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for GenericParamAndBoundVarCollector<'_, 't
             }
             ty::Bound(db, bt) if *db >= self.depth => {
                 self.vars.insert(match bt.kind {
-                    ty::BoundTyKind::Param(def_id, name) => (def_id, name),
+                    ty::BoundTyKind::Param(def_id) => def_id,
                     ty::BoundTyKind::Anon => {
                         let reported = self
                             .cx
@@ -1073,7 +1073,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for GenericParamAndBoundVarCollector<'_, 't
             }
             ty::ReBound(db, br) if db >= self.depth => {
                 self.vars.insert(match br.kind {
-                    ty::BoundRegionKind::Named(def_id, name) => (def_id, name),
+                    ty::BoundRegionKind::Named(def_id) => def_id,
                     ty::BoundRegionKind::Anon | ty::BoundRegionKind::ClosureEnv => {
                         let guar = self
                             .cx
@@ -1081,6 +1081,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for GenericParamAndBoundVarCollector<'_, 't
                             .delayed_bug(format!("unexpected bound region kind: {:?}", br.kind));
                         return ControlFlow::Break(guar);
                     }
+                    ty::BoundRegionKind::NamedAnon(_) => bug!("only used for pretty printing"),
                 });
             }
             _ => {}
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index e13daabeb50..434375060df 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -392,16 +392,14 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     #[instrument(level = "debug", skip(self), ret)]
     pub fn lower_resolved_lifetime(&self, resolved: rbv::ResolvedArg) -> ty::Region<'tcx> {
         let tcx = self.tcx();
-        let lifetime_name = |def_id| tcx.hir_name(tcx.local_def_id_to_hir_id(def_id));
 
         match resolved {
             rbv::ResolvedArg::StaticLifetime => tcx.lifetimes.re_static,
 
             rbv::ResolvedArg::LateBound(debruijn, index, def_id) => {
-                let name = lifetime_name(def_id);
                 let br = ty::BoundRegion {
                     var: ty::BoundVar::from_u32(index),
-                    kind: ty::BoundRegionKind::Named(def_id.to_def_id(), name),
+                    kind: ty::BoundRegionKind::Named(def_id.to_def_id()),
                 };
                 ty::Region::new_bound(tcx, debruijn, br)
             }
@@ -415,11 +413,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             }
 
             rbv::ResolvedArg::Free(scope, id) => {
-                let name = lifetime_name(id);
                 ty::Region::new_late_param(
                     tcx,
                     scope.to_def_id(),
-                    ty::LateParamRegionKind::Named(id.to_def_id(), name),
+                    ty::LateParamRegionKind::Named(id.to_def_id()),
                 )
 
                 // (*) -- not late-bound, won't change
@@ -2070,10 +2067,9 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let tcx = self.tcx();
         match tcx.named_bound_var(hir_id) {
             Some(rbv::ResolvedArg::LateBound(debruijn, index, def_id)) => {
-                let name = tcx.item_name(def_id.to_def_id());
                 let br = ty::BoundTy {
                     var: ty::BoundVar::from_u32(index),
-                    kind: ty::BoundTyKind::Param(def_id.to_def_id(), name),
+                    kind: ty::BoundTyKind::Param(def_id.to_def_id()),
                 };
                 Ty::new_bound(tcx, debruijn, br)
             }
@@ -2749,18 +2745,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         generate_err: impl Fn(&str) -> Diag<'cx>,
     ) {
         for br in referenced_regions.difference(&constrained_regions) {
-            let br_name = match *br {
-                ty::BoundRegionKind::Named(_, kw::UnderscoreLifetime)
-                | ty::BoundRegionKind::Anon
-                | ty::BoundRegionKind::ClosureEnv => "an anonymous lifetime".to_string(),
-                ty::BoundRegionKind::Named(_, name) => format!("lifetime `{name}`"),
+            let br_name = if let Some(name) = br.get_name(self.tcx()) {
+                format!("lifetime `{name}`")
+            } else {
+                "an anonymous lifetime".to_string()
             };
 
             let mut err = generate_err(&br_name);
 
-            if let ty::BoundRegionKind::Named(_, kw::UnderscoreLifetime)
-            | ty::BoundRegionKind::Anon = *br
-            {
+            if !br.is_named(self.tcx()) {
                 // The only way for an anonymous lifetime to wind up
                 // in the return type but **also** be unconstrained is
                 // if it only appears in "associated types" in the