reset anonymous-lifetime-mode as we enter () scopes

src/librustc/hir/lowering.rs

@@ -594,6 +594,18 @@ impl<'a> LoweringContext<'a> {
         span.with_ctxt(SyntaxContext::empty().apply_mark(mark))
     }
 
+    fn with_anonymous_lifetime_mode<R>(
+        &mut self,
+        anonymous_lifetime_mode: AnonymousLifetimeMode,
+        op: impl FnOnce(&mut Self) -> R,
+    ) -> R {
+        let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
+        self.anonymous_lifetime_mode = anonymous_lifetime_mode;
+        let result = op(self);
+        self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
+        result
+    }
+
     /// Creates a new hir::GenericParam for every new lifetime and
     /// type parameter encountered while evaluating `f`. Definitions
     /// are created with the parent provided. If no `parent_id` is
@@ -1021,17 +1033,22 @@ impl<'a> LoweringContext<'a> {
                     _ => None,
                 }),
                 |this| {
-                    hir::TyBareFn(P(hir::BareFnTy {
-                        generic_params: this.lower_generic_params(
-                            &f.generic_params,
-                            &NodeMap(),
-                            ImplTraitContext::Disallowed,
-                        ),
-                        unsafety: this.lower_unsafety(f.unsafety),
-                        abi: f.abi,
-                        decl: this.lower_fn_decl(&f.decl, None, false),
-                        arg_names: this.lower_fn_args_to_names(&f.decl),
-                    }))
+                    this.with_anonymous_lifetime_mode(
+                        AnonymousLifetimeMode::PassThrough,
+                        |this| {
+                            hir::TyBareFn(P(hir::BareFnTy {
+                                generic_params: this.lower_generic_params(
+                                    &f.generic_params,
+                                    &NodeMap(),
+                                    ImplTraitContext::Disallowed,
+                                ),
+                                unsafety: this.lower_unsafety(f.unsafety),
+                                abi: f.abi,
+                                decl: this.lower_fn_decl(&f.decl, None, false),
+                                arg_names: this.lower_fn_args_to_names(&f.decl),
+                            }))
+                        },
+                    )
                 },
             ),
             TyKind::Never => hir::TyNever,
@@ -1620,44 +1637,54 @@ impl<'a> LoweringContext<'a> {
         &mut self,
         data: &ParenthesizedParameterData,
     ) -> (hir::PathParameters, bool) {
-        const DISALLOWED: ImplTraitContext = ImplTraitContext::Disallowed;
-        let &ParenthesizedParameterData {
-            ref inputs,
-            ref output,
-            span,
-        } = data;
-        let inputs = inputs
-            .iter()
-            .map(|ty| self.lower_ty(ty, DISALLOWED))
-            .collect();
-        let mk_tup = |this: &mut Self, tys, span| {
-            let LoweredNodeId { node_id, hir_id } = this.next_id();
-            P(hir::Ty {
-                node: hir::TyTup(tys),
-                id: node_id,
-                hir_id,
-                span,
-            })
-        };
+        // Switch to `PassThrough` mode for anonymous lifetimes: this
+        // means that we permit things like `&Ref<T>`, where `Ref` has
+        // a hidden lifetime parameter. This is needed for backwards
+        // compatibility, even in contexts like an impl header where
+        // we generally don't permit such things (see #51008).
+        self.with_anonymous_lifetime_mode(
+            AnonymousLifetimeMode::PassThrough,
+            |this| {
+                const DISALLOWED: ImplTraitContext = ImplTraitContext::Disallowed;
+                let &ParenthesizedParameterData {
+                    ref inputs,
+                    ref output,
+                    span,
+                } = data;
+                let inputs = inputs
+                    .iter()
+                    .map(|ty| this.lower_ty(ty, DISALLOWED))
+                    .collect();
+                let mk_tup = |this: &mut Self, tys, span| {
+                    let LoweredNodeId { node_id, hir_id } = this.next_id();
+                    P(hir::Ty {
+                        node: hir::TyTup(tys),
+                        id: node_id,
+                        hir_id,
+                        span,
+                    })
+                };
 
-        (
-            hir::PathParameters {
-                lifetimes: hir::HirVec::new(),
-                types: hir_vec![mk_tup(self, inputs, span)],
-                bindings: hir_vec![
-                    hir::TypeBinding {
-                        id: self.next_id().node_id,
-                        name: Symbol::intern(FN_OUTPUT_NAME),
-                        ty: output
-                            .as_ref()
-                            .map(|ty| self.lower_ty(&ty, DISALLOWED))
-                            .unwrap_or_else(|| mk_tup(self, hir::HirVec::new(), span)),
-                        span: output.as_ref().map_or(span, |ty| ty.span),
-                    }
-                ],
-                parenthesized: true,
-            },
-            false,
+                (
+                    hir::PathParameters {
+                        lifetimes: hir::HirVec::new(),
+                        types: hir_vec![mk_tup(this, inputs, span)],
+                        bindings: hir_vec![
+                            hir::TypeBinding {
+                                id: this.next_id().node_id,
+                                name: Symbol::intern(FN_OUTPUT_NAME),
+                                ty: output
+                                    .as_ref()
+                                    .map(|ty| this.lower_ty(&ty, DISALLOWED))
+                                    .unwrap_or_else(|| mk_tup(this, hir::HirVec::new(), span)),
+                                span: output.as_ref().map_or(span, |ty| ty.span),
+                            }
+                        ],
+                        parenthesized: true,
+                    },
+                    false,
+                )
+            }
         )
     }
 

src/librustc/middle/resolve_lifetime.rs

@@ -101,6 +101,13 @@ impl Region {
         let depth = ty::DebruijnIndex::INNERMOST;
         let def_id = hir_map.local_def_id(def.lifetime.id);
         let origin = LifetimeDefOrigin::from_is_in_band(def.in_band);
+        debug!(
+            "Region::late: def={:?} depth={:?} def_id={:?} origin={:?}",
+            def,
+            depth,
+            def_id,
+            origin,
+        );
         (def.lifetime.name, Region::LateBound(depth, def_id, origin))
     }
 

src/test/ui/rust-2018/issue-51008-1.rs

@@ -0,0 +1,25 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for #51008 -- the anonymous lifetime in `&i32` was
+// being incorrectly considered part of the "elided lifetimes" from
+// the impl.
+//
+// run-pass
+
+#![feature(rust_2018_preview)]
+
+trait A {
+
+}
+
+impl<F> A for F where F: PartialEq<fn(&i32)> { }
+
+fn main() {}

src/test/ui/rust-2018/issue-51008.rs

@@ -0,0 +1,25 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for #51008 -- the anonymous lifetime in `&i32` was
+// being incorrectly considered part of the "elided lifetimes" from
+// the impl.
+//
+// run-pass
+
+#![feature(rust_2018_preview)]
+
+trait A {
+
+}
+
+impl<F> A for F where F: FnOnce(&i32) {}
+
+fn main() {}