Clean up HIR-based lifetime resolution

compiler/rustc_ast_lowering/src/lib.rs

@@ -1883,29 +1883,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 }
                 hir::LifetimeName::Param(param, ParamName::Fresh)
             }
-            LifetimeRes::Anonymous { binder, elided } => {
-                let mut l_name = None;
-                if let Some(mut captured_lifetimes) = self.captured_lifetimes.take() {
-                    if !captured_lifetimes.binders_to_ignore.contains(&binder) {
-                        let p_id = self.next_node_id();
-                        let p_def_id = self.create_def(
-                            captured_lifetimes.parent_def_id,
-                            p_id,
-                            DefPathData::LifetimeNs(kw::UnderscoreLifetime),
-                        );
-                        captured_lifetimes
-                            .captures
-                            .insert(p_def_id, (span, p_id, ParamName::Fresh, res));
-                        l_name = Some(hir::LifetimeName::Param(p_def_id, ParamName::Fresh));
-                    }
-                    self.captured_lifetimes = Some(captured_lifetimes);
-                };
-                l_name.unwrap_or(if elided {
-                    hir::LifetimeName::Implicit
-                } else {
-                    hir::LifetimeName::Underscore
-                })
-            }
+            LifetimeRes::Infer => hir::LifetimeName::Infer,
             LifetimeRes::Static => hir::LifetimeName::Static,
             LifetimeRes::Error => hir::LifetimeName::Error,
             res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -589,8 +589,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
 
             hir::LifetimeName::Param(_, hir::ParamName::Fresh)
             | hir::LifetimeName::ImplicitObjectLifetimeDefault
-            | hir::LifetimeName::Implicit
-            | hir::LifetimeName::Underscore => {
+            | hir::LifetimeName::Infer => {
                 // In this case, the user left off the lifetime; so
                 // they wrote something like:
                 //

compiler/rustc_hir/src/def.rs

@@ -738,13 +738,8 @@ pub enum LifetimeRes {
         binder: NodeId,
     },
     /// This variant is used for anonymous lifetimes that we did not resolve during
-    /// late resolution.  Shifting the work to the HIR lifetime resolver.
-    Anonymous {
-        /// Id of the introducing place. See `Param`.
-        binder: NodeId,
-        /// Whether this lifetime was spelled or elided.
-        elided: bool,
-    },
+    /// late resolution.  Those lifetimes will be inferred by typechecking.
+    Infer,
     /// Explicit `'static` lifetime.
     Static,
     /// Resolution failure.

compiler/rustc_hir/src/hir.rs

@@ -90,9 +90,6 @@ pub enum LifetimeName {
     /// User-given names or fresh (synthetic) names.
     Param(LocalDefId, ParamName),
 
-    /// User wrote nothing (e.g., the lifetime in `&u32`).
-    Implicit,
-
     /// Implicit lifetime in a context like `dyn Foo`. This is
     /// distinguished from implicit lifetimes elsewhere because the
     /// lifetime that they default to must appear elsewhere within the
@@ -110,8 +107,9 @@ pub enum LifetimeName {
     /// that was already reported.
     Error,
 
-    /// User wrote specifies `'_`.
-    Underscore,
+    /// User wrote an anonymous lifetime, either `'_` or nothing.
+    /// The semantics of this lifetime should be inferred by typechecking code.
+    Infer,
 
     /// User wrote `'static`.
     Static,
@@ -120,10 +118,8 @@ pub enum LifetimeName {
 impl LifetimeName {
     pub fn ident(&self) -> Ident {
         match *self {
-            LifetimeName::ImplicitObjectLifetimeDefault
-            | LifetimeName::Implicit
-            | LifetimeName::Error => Ident::empty(),
-            LifetimeName::Underscore => Ident::with_dummy_span(kw::UnderscoreLifetime),
+            LifetimeName::ImplicitObjectLifetimeDefault | LifetimeName::Error => Ident::empty(),
+            LifetimeName::Infer => Ident::with_dummy_span(kw::UnderscoreLifetime),
             LifetimeName::Static => Ident::with_dummy_span(kw::StaticLifetime),
             LifetimeName::Param(_, param_name) => param_name.ident(),
         }
@@ -132,8 +128,7 @@ impl LifetimeName {
     pub fn is_anonymous(&self) -> bool {
         match *self {
             LifetimeName::ImplicitObjectLifetimeDefault
-            | LifetimeName::Implicit
-            | LifetimeName::Underscore
+            | LifetimeName::Infer
             | LifetimeName::Param(_, ParamName::Fresh)
             | LifetimeName::Error => true,
             LifetimeName::Static | LifetimeName::Param(..) => false,
@@ -142,9 +137,7 @@ impl LifetimeName {
 
     pub fn is_elided(&self) -> bool {
         match self {
-            LifetimeName::ImplicitObjectLifetimeDefault
-            | LifetimeName::Implicit
-            | LifetimeName::Underscore => true,
+            LifetimeName::ImplicitObjectLifetimeDefault | LifetimeName::Infer => true,
 
             // It might seem surprising that `Fresh` counts as
             // *not* elided -- but this is because, as far as the code

compiler/rustc_hir/src/intravisit.rs

@@ -496,9 +496,8 @@ pub fn walk_lifetime<'v, V: Visitor<'v>>(visitor: &mut V, lifetime: &'v Lifetime
         | LifetimeName::Param(_, ParamName::Error)
         | LifetimeName::Static
         | LifetimeName::Error
-        | LifetimeName::Implicit
         | LifetimeName::ImplicitObjectLifetimeDefault
-        | LifetimeName::Underscore => {}
+        | LifetimeName::Infer => {}
     }
 }
 

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/find_anon_type.rs

@@ -100,23 +100,6 @@ impl<'tcx> Visitor<'tcx> for FindNestedTypeVisitor<'tcx> {
                 // the lifetime of the TyRptr
                 let hir_id = lifetime.hir_id;
                 match (self.tcx.named_region(hir_id), self.bound_region) {
-                    // Find the index of the anonymous region that was part of the
-                    // error. We will then search the function parameters for a bound
-                    // region at the right depth with the same index
-                    (
-                        Some(rl::Region::LateBoundAnon(debruijn_index, _, anon_index)),
-                        ty::BrAnon(br_index),
-                    ) => {
-                        debug!(
-                            "LateBoundAnon depth = {:?} anon_index = {:?} br_index={:?}",
-                            debruijn_index, anon_index, br_index
-                        );
-                        if debruijn_index == self.current_index && anon_index == br_index {
-                            self.found_type = Some(arg);
-                            return; // we can stop visiting now
-                        }
-                    }
-
                     // Find the index of the named region that was part of the
                     // error. We will then search the function parameters for a bound
                     // region at the right depth with the same index
@@ -151,8 +134,7 @@ impl<'tcx> Visitor<'tcx> for FindNestedTypeVisitor<'tcx> {
                             rl::Region::Static
                             | rl::Region::Free(_, _)
                             | rl::Region::EarlyBound(_, _)
-                            | rl::Region::LateBound(_, _, _)
-                            | rl::Region::LateBoundAnon(_, _, _),
+                            | rl::Region::LateBound(_, _, _),
                         )
                         | None,
                         _,
@@ -206,16 +188,6 @@ impl<'tcx> Visitor<'tcx> for TyPathVisitor<'tcx> {
     fn visit_lifetime(&mut self, lifetime: &hir::Lifetime) {
         match (self.tcx.named_region(lifetime.hir_id), self.bound_region) {
             // the lifetime of the TyPath!
-            (
-                Some(rl::Region::LateBoundAnon(debruijn_index, _, anon_index)),
-                ty::BrAnon(br_index),
-            ) => {
-                if debruijn_index == self.current_index && anon_index == br_index {
-                    self.found_it = true;
-                    return;
-                }
-            }
-
             (Some(rl::Region::EarlyBound(_, id)), ty::BrNamed(def_id, _)) => {
                 debug!("EarlyBound id={:?} def_id={:?}", id, def_id);
                 if id == def_id {
@@ -239,7 +211,6 @@ impl<'tcx> Visitor<'tcx> for TyPathVisitor<'tcx> {
                     rl::Region::Static
                     | rl::Region::EarlyBound(_, _)
                     | rl::Region::LateBound(_, _, _)
-                    | rl::Region::LateBoundAnon(_, _, _)
                     | rl::Region::Free(_, _),
                 )
                 | None,

compiler/rustc_middle/src/middle/resolve_lifetime.rs

@@ -12,7 +12,6 @@ pub enum Region {
     Static,
     EarlyBound(/* index */ u32, /* lifetime decl */ DefId),
     LateBound(ty::DebruijnIndex, /* late-bound index */ u32, /* lifetime decl */ DefId),
-    LateBoundAnon(ty::DebruijnIndex, /* late-bound index */ u32, /* anon index */ u32),
     Free(DefId, /* lifetime decl */ DefId),
 }