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

Stabilize impl_header_lifetime_elision in 2015

~~This is currently blocked on #54902; it should be good after that~~

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

FCP completed (#15872 (comment)), proposal (#15872 (comment)).

Tracking issue: #15872
Usage examples (from libcore): #54687

Author: bors

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)]
+   |            ^^^^^^^^^^^^^^^^^