Record in HIR whether lifetime elision was succesful.

compiler/rustc_ast_lowering/src/expr.rs

@@ -603,6 +603,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             output,
             c_variadic: false,
             implicit_self: hir::ImplicitSelfKind::None,
+            lifetime_elision_allowed: false,
         });
 
         // Lower the argument pattern/ident. The ident is used again in the `.await` lowering.
@@ -907,7 +908,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
         // Lower outside new scope to preserve `is_in_loop_condition`.
-        let fn_decl = self.lower_fn_decl(decl, None, fn_decl_span, FnDeclKind::Closure, None);
+        let fn_decl = self.lower_fn_decl(decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
 
         let c = self.arena.alloc(hir::Closure {
             def_id: self.local_def_id(closure_id),
@@ -1017,7 +1018,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // have to conserve the state of being inside a loop condition for the
         // closure argument types.
         let fn_decl =
-            self.lower_fn_decl(&outer_decl, None, fn_decl_span, FnDeclKind::Closure, None);
+            self.lower_fn_decl(&outer_decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
 
         let c = self.arena.alloc(hir::Closure {
             def_id: self.local_def_id(closure_id),

compiler/rustc_ast_lowering/src/item.rs

@@ -274,7 +274,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     let mut itctx = ImplTraitContext::Universal;
                     let (generics, decl) = this.lower_generics(generics, id, &mut itctx, |this| {
                         let ret_id = asyncness.opt_return_id();
-                        this.lower_fn_decl(&decl, Some(id), *fn_sig_span, FnDeclKind::Fn, ret_id)
+                        this.lower_fn_decl(&decl, id, *fn_sig_span, FnDeclKind::Fn, ret_id)
                     });
                     let sig = hir::FnSig {
                         decl,
@@ -659,7 +659,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                                 // Disallow `impl Trait` in foreign items.
                                 this.lower_fn_decl(
                                     fdec,
-                                    None,
+                                    i.id,
                                     sig.span,
                                     FnDeclKind::ExternFn,
                                     None,
@@ -1247,7 +1247,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let header = self.lower_fn_header(sig.header);
         let mut itctx = ImplTraitContext::Universal;
         let (generics, decl) = self.lower_generics(generics, id, &mut itctx, |this| {
-            this.lower_fn_decl(&sig.decl, Some(id), sig.span, kind, is_async)
+            this.lower_fn_decl(&sig.decl, id, sig.span, kind, is_async)
         });
         (generics, hir::FnSig { header, decl, span: self.lower_span(sig.span) })
     }

compiler/rustc_ast_lowering/src/lib.rs

@@ -327,7 +327,14 @@ enum FnDeclKind {
 }
 
 impl FnDeclKind {
-    fn impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
+    fn param_impl_trait_allowed(&self) -> bool {
+        match self {
+            FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait => true,
+            _ => false,
+        }
+    }
+
+    fn return_impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
         match self {
             FnDeclKind::Fn | FnDeclKind::Inherent => true,
             FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
@@ -1267,7 +1274,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     generic_params,
                     unsafety: self.lower_unsafety(f.unsafety),
                     abi: self.lower_extern(f.ext),
-                    decl: self.lower_fn_decl(&f.decl, None, t.span, FnDeclKind::Pointer, None),
+                    decl: self.lower_fn_decl(&f.decl, t.id, t.span, FnDeclKind::Pointer, None),
                     param_names: self.lower_fn_params_to_names(&f.decl),
                 }))
             }
@@ -1671,7 +1678,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_fn_decl(
         &mut self,
         decl: &FnDecl,
-        fn_node_id: Option<NodeId>,
+        fn_node_id: NodeId,
         fn_span: Span,
         kind: FnDeclKind,
         make_ret_async: Option<(NodeId, Span)>,
@@ -1686,23 +1693,21 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             inputs = &inputs[..inputs.len() - 1];
         }
         let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
-            if fn_node_id.is_some() {
+            let itctx = if kind.param_impl_trait_allowed() {
-                self.lower_ty_direct(&param.ty, &ImplTraitContext::Universal)
+                ImplTraitContext::Universal
             } else {
-                self.lower_ty_direct(
+                ImplTraitContext::Disallowed(match kind {
-                    &param.ty,
+                    FnDeclKind::Fn | FnDeclKind::Inherent => {
-                    &ImplTraitContext::Disallowed(match kind {
+                        unreachable!("fn should allow APIT")
-                        FnDeclKind::Fn | FnDeclKind::Inherent => {
+                    }
-                            unreachable!("fn should allow in-band lifetimes")
+                    FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
-                        }
+                    FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
-                        FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
+                    FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
-                        FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
+                    FnDeclKind::Trait => ImplTraitPosition::TraitParam,
-                        FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
+                    FnDeclKind::Impl => ImplTraitPosition::ImplParam,
-                        FnDeclKind::Trait => ImplTraitPosition::TraitParam,
+                })
-                        FnDeclKind::Impl => ImplTraitPosition::ImplParam,
+            };
-                    }),
+            self.lower_ty_direct(&param.ty, &itctx)
-                )
-            }
         }));
 
         let output = if let Some((ret_id, span)) = make_ret_async {
@@ -1725,22 +1730,21 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
             self.lower_async_fn_ret_ty(
                 &decl.output,
-                fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
+                fn_node_id,
                 ret_id,
                 matches!(kind, FnDeclKind::Trait),
             )
         } else {
             match &decl.output {
                 FnRetTy::Ty(ty) => {
-                    let mut context = match fn_node_id {
+                    let mut context = if kind.return_impl_trait_allowed(self.tcx) {
-                        Some(fn_node_id) if kind.impl_trait_allowed(self.tcx) => {
+                        let fn_def_id = self.local_def_id(fn_node_id);
-                            let fn_def_id = self.local_def_id(fn_node_id);
+                        ImplTraitContext::ReturnPositionOpaqueTy {
-                            ImplTraitContext::ReturnPositionOpaqueTy {
+                            origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
-                                origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
+                            in_trait: matches!(kind, FnDeclKind::Trait),
-                                in_trait: matches!(kind, FnDeclKind::Trait),
-                            }
                         }
-                        _ => ImplTraitContext::Disallowed(match kind {
+                    } else {
+                        ImplTraitContext::Disallowed(match kind {
                             FnDeclKind::Fn | FnDeclKind::Inherent => {
                                 unreachable!("fn should allow in-band lifetimes")
                             }
@@ -1749,7 +1753,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
                             FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
                             FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
-                        }),
+                        })
                     };
                     hir::FnRetTy::Return(self.lower_ty(ty, &mut context))
                 }
@@ -1761,6 +1765,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             inputs,
             output,
             c_variadic,
+            lifetime_elision_allowed: self.resolver.lifetime_elision_allowed.contains(&fn_node_id),
             implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
                 let is_mutable_pat = matches!(
                     arg.pat.kind,

compiler/rustc_hir/src/hir.rs

@@ -2670,6 +2670,8 @@ pub struct FnDecl<'hir> {
     pub c_variadic: bool,
     /// Does the function have an implicit self?
     pub implicit_self: ImplicitSelfKind,
+    /// Is lifetime elision allowed.
+    pub lifetime_elision_allowed: bool,
 }
 
 /// Represents what type of implicit self a function has, if any.

compiler/rustc_middle/src/ty/mod.rs

@@ -207,6 +207,8 @@ pub struct ResolverAstLowering {
     /// A small map keeping true kinds of built-in macros that appear to be fn-like on
     /// the surface (`macro` items in libcore), but are actually attributes or derives.
     pub builtin_macro_kinds: FxHashMap<LocalDefId, MacroKind>,
+    /// List functions and methods for which lifetime elision was successful.
+    pub lifetime_elision_allowed: FxHashSet<ast::NodeId>,
 }
 
 #[derive(Clone, Copy, Debug)]

compiler/rustc_resolve/src/late.rs

@@ -1838,6 +1838,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
 
         let outer_failures = take(&mut self.diagnostic_metadata.current_elision_failures);
         let output_rib = if let Ok(res) = elision_lifetime.as_ref() {
+            self.r.lifetime_elision_allowed.insert(fn_id);
             LifetimeRibKind::Elided(*res)
         } else {
             LifetimeRibKind::ElisionFailure

compiler/rustc_resolve/src/lib.rs

@@ -1036,6 +1036,8 @@ pub struct Resolver<'a> {
     /// they are declared in the static array generated by proc_macro_harness.
     proc_macros: Vec<NodeId>,
     confused_type_with_std_module: FxHashMap<Span, Span>,
+    /// Whether lifetime elision was successful.
+    lifetime_elision_allowed: FxHashSet<NodeId>,
 
     effective_visibilities: EffectiveVisibilities,
 }
@@ -1354,6 +1356,7 @@ impl<'a> Resolver<'a> {
             trait_impls: Default::default(),
             proc_macros: Default::default(),
             confused_type_with_std_module: Default::default(),
+            lifetime_elision_allowed: Default::default(),
             effective_visibilities: Default::default(),
         };
 
@@ -1448,6 +1451,7 @@ impl<'a> Resolver<'a> {
             def_id_to_node_id: self.def_id_to_node_id,
             trait_map: self.trait_map,
             builtin_macro_kinds: self.builtin_macro_kinds,
+            lifetime_elision_allowed: self.lifetime_elision_allowed,
         };
         ResolverOutputs { definitions, global_ctxt, ast_lowering }
     }
@@ -1491,6 +1495,7 @@ impl<'a> Resolver<'a> {
             def_id_to_node_id: self.def_id_to_node_id.clone(),
             trait_map: self.trait_map.clone(),
             builtin_macro_kinds: self.builtin_macro_kinds.clone(),
+            lifetime_elision_allowed: self.lifetime_elision_allowed.clone(),
         };
         ResolverOutputs { definitions, global_ctxt, ast_lowering }
     }