Auto merge of #54778 - scottmcm:stabilize-ihle, r=pnkfelix

Stabilize impl_header_lifetime_elision in 2015

~~This is currently blocked on https://github.com/rust-lang/rust/issues/54902; it should be good after that~~

It's already stable in 2018; this finishes the stabilization.

FCP completed (https://github.com/rust-lang/rust/issues/15872#issuecomment-417953153), proposal (https://github.com/rust-lang/rust/issues/15872#issuecomment-412759783).

Tracking issue: https://github.com/rust-lang/rust/issues/15872
Usage examples (from libcore): https://github.com/rust-lang/rust/pull/54687

src/libcore/lib.rs

@@ -87,7 +87,7 @@
 #![feature(doc_spotlight)]
 #![feature(extern_types)]
 #![feature(fundamental)]
-#![feature(impl_header_lifetime_elision)]
+#![cfg_attr(stage0, feature(impl_header_lifetime_elision))]
 #![feature(intrinsics)]
 #![feature(lang_items)]
 #![feature(link_llvm_intrinsics)]

src/libcore/tests/lib.rs

@@ -19,7 +19,7 @@
 #![feature(flt2dec)]
 #![feature(fmt_internals)]
 #![feature(hashmap_internals)]
-#![feature(impl_header_lifetime_elision)]
+#![cfg_attr(stage0, feature(impl_header_lifetime_elision))]
 #![feature(pattern)]
 #![feature(range_is_empty)]
 #![feature(raw)]

src/librustc/hir/lowering.rs

@@ -125,9 +125,8 @@ pub struct LoweringContext<'a> {
 
     // Whether or not in-band lifetimes are being collected. This is used to
     // indicate whether or not we're in a place where new lifetimes will result
-    // in in-band lifetime definitions, such a function or an impl header.
-    // This will always be false unless the `in_band_lifetimes` or
-    // `impl_header_lifetime_elision` feature is enabled.
+    // in in-band lifetime definitions, such a function or an impl header,
+    // including implicit lifetimes from `impl_header_lifetime_elision`.
     is_collecting_in_band_lifetimes: bool,
 
     // Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
@@ -709,12 +708,8 @@ impl<'a> LoweringContext<'a> {
         assert!(self.lifetimes_to_define.is_empty());
         let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
 
-        if self.sess.features_untracked().impl_header_lifetime_elision {
-            self.anonymous_lifetime_mode = anonymous_lifetime_mode;
-            self.is_collecting_in_band_lifetimes = true;
-        } else if self.sess.features_untracked().in_band_lifetimes {
-            self.is_collecting_in_band_lifetimes = true;
-        }
+        self.anonymous_lifetime_mode = anonymous_lifetime_mode;
+        self.is_collecting_in_band_lifetimes = true;
 
         let (in_band_ty_params, res) = f(self);
 

src/librustc/lib.rs

@@ -67,7 +67,7 @@
 #![feature(step_trait)]
 #![feature(integer_atomics)]
 #![feature(test)]
-#![feature(impl_header_lifetime_elision)]
+#![cfg_attr(stage0, feature(impl_header_lifetime_elision))]
 #![feature(in_band_lifetimes)]
 #![feature(macro_at_most_once_rep)]
 #![feature(crate_visibility_modifier)]

src/librustc_data_structures/lib.rs

@@ -21,7 +21,7 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 
 #![feature(in_band_lifetimes)]
-#![feature(impl_header_lifetime_elision)]
+#![cfg_attr(stage0, feature(impl_header_lifetime_elision))]
 #![feature(unboxed_closures)]
 #![feature(fn_traits)]
 #![feature(unsize)]

src/librustc_mir/lib.rs

@@ -16,7 +16,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 
 #![feature(nll)]
 #![feature(in_band_lifetimes)]
-#![feature(impl_header_lifetime_elision)]
+#![cfg_attr(stage0, feature(impl_header_lifetime_elision))]
 #![feature(slice_patterns)]
 #![feature(slice_sort_by_cached_key)]
 #![feature(box_patterns)]

src/libsyntax/diagnostic_list.rs

@@ -375,15 +375,15 @@ and likely to change in the future.
 
 E0705: r##"
 A `#![feature]` attribute was declared for a feature that is stable in
-the current edition.
+the current edition, but not in all editions.
 
 Erroneous code example:
 
 ```ignore (limited to a warning during 2018 edition development)
 #![feature(rust_2018_preview)]
-#![feature(impl_header_lifetime_elision)] // error: the feature
-                                          // `impl_header_lifetime_elision` is
-                                          // included in the Rust 2018 edition
+#![feature(test_2018_feature)] // error: the feature
+                               // `test_2018_feature` is
+                               // included in the Rust 2018 edition
 ```
 
 "##,

src/libsyntax/feature_gate.rs

@@ -462,9 +462,8 @@ declare_features! (
 
     (active, abi_amdgpu_kernel, "1.29.0", Some(51575), None),
 
-    // impl<I:Iterator> Iterator for &mut Iterator
-    // impl Debug for Foo<'_>
-    (active, impl_header_lifetime_elision, "1.30.0", Some(15872), Some(Edition::Edition2018)),
+    // Perma-unstable; added for testing E0705
+    (active, test_2018_feature, "1.31.0", Some(0), Some(Edition::Edition2018)),
 
     // Support for arbitrary delimited token streams in non-macro attributes
     (active, unrestricted_attribute_tokens, "1.30.0", Some(44690), None),
@@ -684,6 +683,9 @@ declare_features! (
     (accepted, min_const_fn, "1.31.0", Some(53555), None),
     // Scoped lints
     (accepted, tool_lints, "1.31.0", Some(44690), None),
+    // impl<I:Iterator> Iterator for &mut Iterator
+    // impl Debug for Foo<'_>
+    (accepted, impl_header_lifetime_elision, "1.31.0", Some(15872), None),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must

src/test/ui/E0705.rs

@@ -10,8 +10,11 @@
 
 // compile-pass
 
-#![feature(impl_header_lifetime_elision)]
-//~^ WARN the feature `impl_header_lifetime_elision` is included in the Rust 2018 edition
+// This is a stub feature that doesn't control anything, so to make tidy happy,
+// gate-test-test_2018_feature
+
+#![feature(test_2018_feature)]
+//~^ WARN the feature `test_2018_feature` is included in the Rust 2018 edition
 #![feature(rust_2018_preview)]
 
 fn main() {}

src/test/ui/E0705.stderr

@@ -1,6 +1,6 @@
-warning[E0705]: the feature `impl_header_lifetime_elision` is included in the Rust 2018 edition
-  --> $DIR/E0705.rs:13:12
+warning[E0705]: the feature `test_2018_feature` is included in the Rust 2018 edition
+  --> $DIR/E0705.rs:16:12
    |
-LL | #![feature(impl_header_lifetime_elision)]
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #![feature(test_2018_feature)]
+   |            ^^^^^^^^^^^^^^^^^
 

src/test/ui/feature-gates/feature-gate-impl_header_lifetime_elision-with-in_band.stderr

@@ -1,15 +0,0 @@
-error[E0106]: missing lifetime specifier
-  --> $DIR/feature-gate-impl_header_lifetime_elision-with-in_band.rs:18:22
-   |
-LL | impl MyTrait<'a> for &u32 { }
-   |                      ^ expected lifetime parameter
-
-error[E0106]: missing lifetime specifier
-  --> $DIR/feature-gate-impl_header_lifetime_elision-with-in_band.rs:24:23
-   |
-LL | impl MarkerTrait for &'_ MyStruct { }
-   |                       ^^ expected lifetime parameter
-
-error: aborting due to 2 previous errors
-
-For more information about this error, try `rustc --explain E0106`.

src/test/ui/feature-gates/feature-gate-impl_header_lifetime_elision.stderr

@@ -1,15 +0,0 @@
-error[E0106]: missing lifetime specifier
-  --> $DIR/feature-gate-impl_header_lifetime_elision.rs:15:26
-   |
-LL | impl<'a> MyTrait<'a> for &u32 { }
-   |                          ^ expected lifetime parameter
-
-error[E0106]: missing lifetime specifier
-  --> $DIR/feature-gate-impl_header_lifetime_elision.rs:18:18
-   |
-LL | impl<'a> MyTrait<'_> for &'a f32 { }
-   |                  ^^ expected lifetime parameter
-
-error: aborting due to 2 previous errors
-
-For more information about this error, try `rustc --explain E0106`.

src/test/ui/feature-gates/feature-gate-in_band_lifetimes.rs

@@ -10,9 +10,6 @@
 
 #![allow(warnings)]
 
-// Make sure this related feature didn't accidentally enable this
-#![feature(impl_header_lifetime_elision)]
-
 fn foo(x: &'x u8) -> &'x u8 { x }
 //~^ ERROR use of undeclared lifetime name
 //~^^ ERROR use of undeclared lifetime name

src/test/ui/feature-gates/feature-gate-in_band_lifetimes.stderr

@@ -1,101 +1,101 @@
 error[E0261]: use of undeclared lifetime name `'x`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:16:12
+  --> $DIR/feature-gate-in_band_lifetimes.rs:13:12
    |
 LL | fn foo(x: &'x u8) -> &'x u8 { x }
    |            ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'x`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:16:23
+  --> $DIR/feature-gate-in_band_lifetimes.rs:13:23
    |
 LL | fn foo(x: &'x u8) -> &'x u8 { x }
    |                       ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:28:12
+  --> $DIR/feature-gate-in_band_lifetimes.rs:25:12
    |
 LL | impl<'a> X<'b> {
    |            ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:30:27
+  --> $DIR/feature-gate-in_band_lifetimes.rs:27:27
    |
 LL |     fn inner_2(&self) -> &'b u8 {
    |                           ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:36:8
+  --> $DIR/feature-gate-in_band_lifetimes.rs:33:8
    |
 LL | impl X<'b> {
    |        ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:38:27
+  --> $DIR/feature-gate-in_band_lifetimes.rs:35:27
    |
 LL |     fn inner_3(&self) -> &'b u8 {
    |                           ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:46:9
+  --> $DIR/feature-gate-in_band_lifetimes.rs:43:9
    |
 LL | impl Y<&'a u8> {
    |         ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:48:25
+  --> $DIR/feature-gate-in_band_lifetimes.rs:45:25
    |
 LL |     fn inner(&self) -> &'a u8 {
    |                         ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:56:27
+  --> $DIR/feature-gate-in_band_lifetimes.rs:53:27
    |
 LL |     fn any_lifetime() -> &'b u8;
    |                           ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:58:27
+  --> $DIR/feature-gate-in_band_lifetimes.rs:55:27
    |
 LL |     fn borrowed_lifetime(&'b self) -> &'b u8;
    |                           ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:58:40
+  --> $DIR/feature-gate-in_band_lifetimes.rs:55:40
    |
 LL |     fn borrowed_lifetime(&'b self) -> &'b u8;
    |                                        ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:63:14
+  --> $DIR/feature-gate-in_band_lifetimes.rs:60:14
    |
 LL | impl MyTrait<'a> for Y<&'a u8> {
    |              ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:63:25
+  --> $DIR/feature-gate-in_band_lifetimes.rs:60:25
    |
 LL | impl MyTrait<'a> for Y<&'a u8> {
    |                         ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:66:31
+  --> $DIR/feature-gate-in_band_lifetimes.rs:63:31
    |
 LL |     fn my_lifetime(&self) -> &'a u8 { self.0 }
    |                               ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:68:27
+  --> $DIR/feature-gate-in_band_lifetimes.rs:65:27
    |
 LL |     fn any_lifetime() -> &'b u8 { &0 }
    |                           ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:70:27
+  --> $DIR/feature-gate-in_band_lifetimes.rs:67:27
    |
 LL |     fn borrowed_lifetime(&'b self) -> &'b u8 { &*self.0 }
    |                           ^^ undeclared lifetime
 
 error[E0261]: use of undeclared lifetime name `'b`
-  --> $DIR/feature-gate-in_band_lifetimes.rs:70:40
+  --> $DIR/feature-gate-in_band_lifetimes.rs:67:40
    |
 LL |     fn borrowed_lifetime(&'b self) -> &'b u8 { &*self.0 }
    |                                        ^^ undeclared lifetime

src/test/ui/impl-header-lifetime-elision/assoc-type.rs

@@ -13,8 +13,6 @@
 
 #![allow(warnings)]
 
-#![feature(impl_header_lifetime_elision)]
-
 trait MyTrait {
     type Output;
 }

src/test/ui/impl-header-lifetime-elision/assoc-type.stderr

@@ -1,11 +1,11 @@
 error[E0106]: missing lifetime specifier
-  --> $DIR/assoc-type.rs:23:19
+  --> $DIR/assoc-type.rs:21:19
    |
 LL |     type Output = &i32;
    |                   ^ expected lifetime parameter
 
 error[E0106]: missing lifetime specifier
-  --> $DIR/assoc-type.rs:28:20
+  --> $DIR/assoc-type.rs:26:20
    |
 LL |     type Output = &'_ i32;
    |                    ^^ expected lifetime parameter

src/test/ui/impl-header-lifetime-elision/dyn-trait.rs

@@ -13,8 +13,6 @@
 
 #![allow(warnings)]
 
-#![feature(impl_header_lifetime_elision)]
-
 use std::fmt::Debug;
 
 // Equivalent to `Box<dyn Debug + 'static>`:

src/test/ui/impl-header-lifetime-elision/dyn-trait.stderr

@@ -1,11 +1,11 @@
 error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
-  --> $DIR/dyn-trait.rs:32:16
+  --> $DIR/dyn-trait.rs:30:16
    |
 LL |     static_val(x); //~ ERROR cannot infer
    |                ^
    |
-note: first, the lifetime cannot outlive the lifetime 'a as defined on the function body at 31:26...
-  --> $DIR/dyn-trait.rs:31:26
+note: first, the lifetime cannot outlive the lifetime 'a as defined on the function body at 29:26...
+  --> $DIR/dyn-trait.rs:29:26
    |
 LL | fn with_dyn_debug_static<'a>(x: Box<dyn Debug + 'a>) {
    |                          ^^

src/test/ui/impl-header-lifetime-elision/explicit-and-elided-same-header.rs

@@ -12,8 +12,6 @@
 
 #![allow(warnings)]
 
-#![feature(impl_header_lifetime_elision)]
-
 // This works for functions...
 fn foo<'a>(x: &str, y: &'a str) {}
 

src/test/ui/impl-header-lifetime-elision/inherent-impl.rs

@@ -8,14 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![allow(warnings)]
+// compile-pass
 
-trait MyTrait<'a> { }
+struct Foo<'a>(&'a u8);
 
-impl<'a> MyTrait<'a> for &u32 { }
-//~^ ERROR missing lifetime specifier
-
-impl<'a> MyTrait<'_> for &'a f32 { }
-//~^ ERROR missing lifetime specifier
+impl Foo<'_> {
+    fn x() {}
+}
 
 fn main() {}

src/test/ui/impl-header-lifetime-elision/path-elided.rs

@@ -9,8 +9,6 @@
 // except according to those terms.
 #![allow(warnings)]
 
-#![feature(impl_header_lifetime_elision)]
-
 trait MyTrait { }
 
 struct Foo<'a> { x: &'a u32 }

src/test/ui/impl-header-lifetime-elision/path-elided.stderr

@@ -1,5 +1,5 @@
 error[E0106]: missing lifetime specifier
-  --> $DIR/path-elided.rs:18:18
+  --> $DIR/path-elided.rs:16:18
    |
 LL | impl MyTrait for Foo {
    |                  ^^^ expected lifetime parameter

src/test/ui/impl-header-lifetime-elision/path-underscore.rs

@@ -14,8 +14,6 @@
 
 #![allow(warnings)]
 
-#![feature(impl_header_lifetime_elision)]
-
 trait MyTrait { }
 
 struct Foo<'a> { x: &'a u32 }

src/test/ui/impl-header-lifetime-elision/ref-underscore.rs

@@ -14,8 +14,6 @@
 
 #![allow(warnings)]
 
-#![feature(impl_header_lifetime_elision)]
-
 trait MyTrait { }
 
 impl MyTrait for &i32 {

src/test/ui/impl-header-lifetime-elision/trait-elided.rs

@@ -9,8 +9,6 @@
 // except according to those terms.
 #![allow(warnings)]
 
-#![feature(impl_header_lifetime_elision)]
-
 trait MyTrait<'a> { }
 
 impl MyTrait for u32 {

src/test/ui/impl-header-lifetime-elision/trait-elided.stderr

@@ -1,5 +1,5 @@
 error[E0106]: missing lifetime specifier
-  --> $DIR/trait-elided.rs:16:6
+  --> $DIR/trait-elided.rs:14:6
    |
 LL | impl MyTrait for u32 {
    |      ^^^^^^^ expected lifetime parameter

src/test/ui/impl-header-lifetime-elision/trait-underscore.rs

@@ -15,8 +15,6 @@
 
 #![allow(warnings)]
 
-#![feature(impl_header_lifetime_elision)]
-
 trait MyTrait<'a> { }
 
 // This is equivalent to `MyTrait<'a> for &'b i32`, which is proven by

src/test/ui/issues/issue-17905-2.rs

@@ -1,4 +1,4 @@
-// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -8,20 +8,19 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![allow(warnings)]
+#[derive(Debug)]
+struct Pair<T, V> (T, V);
 
-// Make sure this related feature didn't accidentally enable this
-#![feature(in_band_lifetimes)]
+impl Pair<
+    &str,
+    isize
+> {
+    fn say(self: &Pair<&str, isize>) {
+        println!("{:?}", self);
+    }
+}
 
-trait MyTrait<'a> { }
-
-impl MyTrait<'a> for &u32 { }
-//~^ ERROR missing lifetime specifier
-
-struct MyStruct;
-trait MarkerTrait {}
-
-impl MarkerTrait for &'_ MyStruct { }
-//~^ ERROR missing lifetime specifier
-
-fn main() {}
+fn main() {
+    let result = &Pair("shane", 1);
+    result.say();
+}

src/test/ui/issues/issue-17905-2.stderr

@@ -0,0 +1,45 @@
+error[E0308]: mismatched method receiver
+  --> $DIR/issue-17905-2.rs:18:18
+   |
+LL |     fn say(self: &Pair<&str, isize>) {
+   |                  ^^^^^^^^^^^^^^^^^^ lifetime mismatch
+   |
+   = note: expected type `Pair<&'_ str, _>`
+              found type `Pair<&str, _>`
+note: the anonymous lifetime #2 defined on the method body at 18:5...
+  --> $DIR/issue-17905-2.rs:18:5
+   |
+LL | /     fn say(self: &Pair<&str, isize>) {
+LL | |         println!("{:?}", self);
+LL | |     }
+   | |_____^
+note: ...does not necessarily outlive the lifetime '_ as defined on the impl at 15:5
+  --> $DIR/issue-17905-2.rs:15:5
+   |
+LL |     &str,
+   |     ^
+
+error[E0308]: mismatched method receiver
+  --> $DIR/issue-17905-2.rs:18:18
+   |
+LL |     fn say(self: &Pair<&str, isize>) {
+   |                  ^^^^^^^^^^^^^^^^^^ lifetime mismatch
+   |
+   = note: expected type `Pair<&'_ str, _>`
+              found type `Pair<&str, _>`
+note: the lifetime '_ as defined on the impl at 15:5...
+  --> $DIR/issue-17905-2.rs:15:5
+   |
+LL |     &str,
+   |     ^
+note: ...does not necessarily outlive the anonymous lifetime #2 defined on the method body at 18:5
+  --> $DIR/issue-17905-2.rs:18:5
+   |
+LL | /     fn say(self: &Pair<&str, isize>) {
+LL | |         println!("{:?}", self);
+LL | |     }
+   | |_____^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/issues/issue-17905.rs

@@ -8,15 +8,17 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// run-pass
+
 #[derive(Debug)]
 struct Pair<T, V> (T, V);
 
 impl Pair<
-    &str, //~ ERROR missing lifetime specifier
+    &str,
     isize
 > {
-    fn say(self: &Pair<&str, isize>) {
-        println!("{}", self);
+    fn say(&self) {
+        println!("{:?}", self);
     }
 }
 

src/test/ui/issues/issue-17905.stderr

@@ -1,9 +0,0 @@
-error[E0106]: missing lifetime specifier
-  --> $DIR/issue-17905.rs:15:5
-   |
-LL |     &str, //~ ERROR missing lifetime specifier
-   |     ^ expected lifetime parameter
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0106`.

src/test/ui/issues/issue-19982-2.rs

@@ -1,33 +0,0 @@
-// Copyright 2015 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.
-
-// compile-pass
-// pretty-expanded FIXME #23616
-
-#![feature(fn_traits, unboxed_closures)]
-
-#[allow(dead_code)]
-struct Foo;
-
-impl<'a> Fn<(&'a (),)> for Foo {
-    extern "rust-call" fn call(&self, (_,): (&(),)) {}
-}
-
-impl<'a> FnMut<(&'a (),)> for Foo {
-    extern "rust-call" fn call_mut(&mut self, (_,): (&(),)) {}
-}
-
-impl<'a> FnOnce<(&'a (),)> for Foo {
-    type Output = ();
-
-    extern "rust-call" fn call_once(self, (_,): (&(),)) {}
-}
-
-fn main() {}

src/test/ui/issues/issue-19982.rs

@@ -8,10 +8,25 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(unboxed_closures)]
+// compile-pass
 
+#![feature(fn_traits, unboxed_closures)]
+
+#[allow(dead_code)]
 struct Foo;
 
-impl Fn<(&(),)> for Foo { } //~ ERROR missing lifetime specifier
+impl Fn<(&(),)> for Foo {
+    extern "rust-call" fn call(&self, (_,): (&(),)) {}
+}
+
+impl FnMut<(&(),)> for Foo {
+    extern "rust-call" fn call_mut(&mut self, (_,): (&(),)) {}
+}
+
+impl FnOnce<(&(),)> for Foo {
+    type Output = ();
+
+    extern "rust-call" fn call_once(self, (_,): (&(),)) {}
+}
 
 fn main() {}

src/test/ui/issues/issue-19982.stderr

@@ -1,9 +0,0 @@
-error[E0106]: missing lifetime specifier
-  --> $DIR/issue-19982.rs:15:10
-   |
-LL | impl Fn<(&(),)> for Foo { } //~ ERROR missing lifetime specifier
-   |          ^ expected lifetime parameter
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0106`.

src/test/ui/nll/issue-52742.rs

@@ -10,7 +10,6 @@
 
 #![feature(nll)]
 #![feature(in_band_lifetimes)]
-#![feature(impl_header_lifetime_elision)]
 
 struct Foo<'a, 'b> {
     x: &'a u32,

src/test/ui/nll/issue-52742.stderr

@@ -1,5 +1,5 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/issue-52742.rs:26:9
+  --> $DIR/issue-52742.rs:25:9
    |
 LL |     fn take_bar(&mut self, b: Bar<'_>) {
    |                 ---------         -- let's call this `'1`

src/test/ui/underscore-lifetime/in-binder.Rust2015.stderr

@@ -1,46 +0,0 @@
-error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:12:6
-   |
-LL | impl<'_> IceCube<'_> {}
-   |      ^^ `'_` is a reserved lifetime name
-
-error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:17:15
-   |
-LL | struct Struct<'_> {
-   |               ^^ `'_` is a reserved lifetime name
-
-error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:23:11
-   |
-LL | enum Enum<'_> {
-   |           ^^ `'_` is a reserved lifetime name
-
-error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:29:13
-   |
-LL | union Union<'_> {
-   |             ^^ `'_` is a reserved lifetime name
-
-error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:35:13
-   |
-LL | trait Trait<'_> {
-   |             ^^ `'_` is a reserved lifetime name
-
-error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:40:8
-   |
-LL | fn foo<'_>() {
-   |        ^^ `'_` is a reserved lifetime name
-
-error[E0106]: missing lifetime specifier
-  --> $DIR/in-binder.rs:12:18
-   |
-LL | impl<'_> IceCube<'_> {}
-   |                  ^^ expected lifetime parameter
-
-error: aborting due to 7 previous errors
-
-Some errors occurred: E0106, E0637.
-For more information about an error, try `rustc --explain E0106`.

src/test/ui/underscore-lifetime/in-binder.rs

@@ -2,44 +2,34 @@
 //
 // Regression test for #52098.
 
-// revisions: Rust2015 Rust2018
-//[Rust2018] edition:2018
-
 struct IceCube<'a> {
     v: Vec<&'a char>
 }
 
 impl<'_> IceCube<'_> {}
-//[Rust2015]~^ ERROR `'_` cannot be used here
-//[Rust2015]~| ERROR missing lifetime specifier
-//[Rust2018]~^^^ ERROR `'_` cannot be used here
+//~^ ERROR `'_` cannot be used here
 
 struct Struct<'_> {
-//[Rust2015]~^ ERROR `'_` cannot be used here
-//[Rust2018]~^^ ERROR `'_` cannot be used here
+//~^ ERROR `'_` cannot be used here
     v: Vec<&'static char>
 }
 
 enum Enum<'_> {
-//[Rust2015]~^ ERROR `'_` cannot be used here
-//[Rust2018]~^^ ERROR `'_` cannot be used here
+//~^ ERROR `'_` cannot be used here
     Variant
 }
 
 union Union<'_> {
-//[Rust2015]~^ ERROR `'_` cannot be used here
-//[Rust2018]~^^ ERROR `'_` cannot be used here
+//~^ ERROR `'_` cannot be used here
     a: u32
 }
 
 trait Trait<'_> {
-//[Rust2015]~^ ERROR `'_` cannot be used here
-//[Rust2018]~^^ ERROR `'_` cannot be used here
+//~^ ERROR `'_` cannot be used here
 }
 
 fn foo<'_>() {
-    //[Rust2015]~^ ERROR `'_` cannot be used here
-    //[Rust2018]~^^ ERROR `'_` cannot be used here
+    //~^ ERROR `'_` cannot be used here
 }
 
 fn main() {}

src/test/ui/underscore-lifetime/in-binder.stderr

@@ -1,35 +1,35 @@
 error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:12:6
+  --> $DIR/in-binder.rs:9:6
    |
 LL | impl<'_> IceCube<'_> {}
    |      ^^ `'_` is a reserved lifetime name
 
 error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:17:15
+  --> $DIR/in-binder.rs:12:15
    |
 LL | struct Struct<'_> {
    |               ^^ `'_` is a reserved lifetime name
 
 error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:23:11
+  --> $DIR/in-binder.rs:17:11
    |
 LL | enum Enum<'_> {
    |           ^^ `'_` is a reserved lifetime name
 
 error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:29:13
+  --> $DIR/in-binder.rs:22:13
    |
 LL | union Union<'_> {
    |             ^^ `'_` is a reserved lifetime name
 
 error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:35:13
+  --> $DIR/in-binder.rs:27:13
    |
 LL | trait Trait<'_> {
    |             ^^ `'_` is a reserved lifetime name
 
 error[E0637]: `'_` cannot be used here
-  --> $DIR/in-binder.rs:40:8
+  --> $DIR/in-binder.rs:31:8
    |
 LL | fn foo<'_>() {
    |        ^^ `'_` is a reserved lifetime name

src/test/ui/underscore-lifetime/underscore-lifetime-binders.rs

@@ -11,10 +11,6 @@
 struct Foo<'a>(&'a u8);
 struct Baz<'a>(&'_ &'a u8); //~ ERROR missing lifetime specifier
 
-impl Foo<'_> { //~ ERROR missing lifetime specifier
-    fn x() {}
-}
-
 fn foo<'_> //~ ERROR cannot be used here
 (_: Foo<'_>) {}
 

src/test/ui/underscore-lifetime/underscore-lifetime-binders.stderr

@@ -1,11 +1,11 @@
 error[E0637]: `'_` cannot be used here
-  --> $DIR/underscore-lifetime-binders.rs:18:8
+  --> $DIR/underscore-lifetime-binders.rs:14:8
    |
 LL | fn foo<'_> //~ ERROR cannot be used here
    |        ^^ `'_` is a reserved lifetime name
 
 error[E0637]: `'_` cannot be used here
-  --> $DIR/underscore-lifetime-binders.rs:24:21
+  --> $DIR/underscore-lifetime-binders.rs:20:21
    |
 LL | fn meh() -> Box<for<'_> Meh<'_>> //~ ERROR cannot be used here
    |                     ^^ `'_` is a reserved lifetime name
@@ -17,13 +17,7 @@ LL | struct Baz<'a>(&'_ &'a u8); //~ ERROR missing lifetime specifier
    |                 ^^ expected lifetime parameter
 
 error[E0106]: missing lifetime specifier
-  --> $DIR/underscore-lifetime-binders.rs:14:10
-   |
-LL | impl Foo<'_> { //~ ERROR missing lifetime specifier
-   |          ^^ expected lifetime parameter
-
-error[E0106]: missing lifetime specifier
-  --> $DIR/underscore-lifetime-binders.rs:24:29
+  --> $DIR/underscore-lifetime-binders.rs:20:29
    |
 LL | fn meh() -> Box<for<'_> Meh<'_>> //~ ERROR cannot be used here
    |                             ^^ expected lifetime parameter
@@ -32,14 +26,14 @@ LL | fn meh() -> Box<for<'_> Meh<'_>> //~ ERROR cannot be used here
    = help: consider giving it a 'static lifetime
 
 error[E0106]: missing lifetime specifier
-  --> $DIR/underscore-lifetime-binders.rs:30:35
+  --> $DIR/underscore-lifetime-binders.rs:26:35
    |
 LL | fn foo2(_: &'_ u8, y: &'_ u8) -> &'_ u8 { y } //~ ERROR missing lifetime specifier
    |                                   ^^ expected lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `_` or `y`
 
-error: aborting due to 6 previous errors
+error: aborting due to 5 previous errors
 
 Some errors occurred: E0106, E0637.
 For more information about an error, try `rustc --explain E0106`.