Auto merge of rust-lang#49255 - cramertj:stable-impl-trait, r=nikomatsakis

Stabilize impl Trait

Blocked on:

- [x] rust-lang#49041 and
- [ ] completion of FCP in rust-lang#34511 (comment) (3 days from now).

I have not yet done any docs work for this-- I probably won't get to it until this weekend (might be a project for the flight to the all-hands).

Author: bors

src/Cargo.lock

@@ -27,7 +27,7 @@
 #![cfg_attr(stage0, feature(inclusive_range_syntax))]
 #![feature(iterator_try_fold)]
 #![feature(iterator_flatten)]
-#![feature(conservative_impl_trait)]
+#![cfg_attr(stage0, feature(conservative_impl_trait))]
 #![feature(iter_rfind)]
 #![feature(iter_rfold)]
 #![feature(iterator_repeat_with)]

src/doc/unstable-book/src/language-features/conservative-impl-trait.md

@@ -1789,8 +1789,6 @@ allowed as function return types.
 Erroneous code example:
 
 ```compile_fail,E0562
-#![feature(conservative_impl_trait)]
-
 fn main() {
     let count_to_ten: impl Iterator<Item=usize> = 0..10;
     // error: `impl Trait` not allowed outside of function and inherent method
@@ -1804,8 +1802,6 @@ fn main() {
 Make sure `impl Trait` only appears in return-type position.
 
 ```
-#![feature(conservative_impl_trait)]
-
 fn count_to_n(n: usize) -> impl Iterator<Item=usize> {
     0..n
 }
@@ -2081,8 +2077,6 @@ appear within the `impl Trait` itself.
 Erroneous code example:
 
 ```compile-fail,E0909
-#![feature(conservative_impl_trait)]
-
 use std::cell::Cell;
 
 trait Trait<'a> { }
@@ -2109,8 +2103,6 @@ type. For example, changing the return type to `impl Trait<'y> + 'x`
 would work:
 
 ```
-#![feature(conservative_impl_trait)]
-
 use std::cell::Cell;
 
 trait Trait<'a> { }

src/doc/unstable-book/src/language-features/universal-impl-trait.md

@@ -1108,20 +1108,9 @@ impl<'a> LoweringContext<'a> {
                 hir::TyTraitObject(bounds, lifetime_bound)
             }
             TyKind::ImplTrait(ref bounds) => {
-                use syntax::feature_gate::{emit_feature_err, GateIssue};
                 let span = t.span;
                 match itctx {
                     ImplTraitContext::Existential => {
-                        let has_feature = self.sess.features_untracked().conservative_impl_trait;
-                        if !t.span.allows_unstable() && !has_feature {
-                            emit_feature_err(
-                                &self.sess.parse_sess,
-                                "conservative_impl_trait",
-                                t.span,
-                                GateIssue::Language,
-                                "`impl Trait` in return position is experimental",
-                            );
-                        }
                         let def_index = self.resolver.definitions().opt_def_index(t.id).unwrap();
                         let hir_bounds = self.lower_bounds(bounds, itctx);
                         let (lifetimes, lifetime_defs) =
@@ -1143,17 +1132,6 @@ impl<'a> LoweringContext<'a> {
                         )
                     }
                     ImplTraitContext::Universal(def_id) => {
-                        let has_feature = self.sess.features_untracked().universal_impl_trait;
-                        if !t.span.allows_unstable() && !has_feature {
-                            emit_feature_err(
-                                &self.sess.parse_sess,
-                                "universal_impl_trait",
-                                t.span,
-                                GateIssue::Language,
-                                "`impl Trait` in argument position is experimental",
-                            );
-                        }
-
                         let def_node_id = self.next_id().node_id;
 
                         // Add a definition for the in-band TyParam

src/libcore/tests/lib.rs

@@ -43,7 +43,7 @@
 
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(conservative_impl_trait)]
+#![cfg_attr(stage0, feature(conservative_impl_trait))]
 #![feature(const_fn)]
 #![cfg_attr(stage0, feature(copy_closures, clone_closures))]
 #![feature(core_intrinsics)]
@@ -70,7 +70,7 @@
 #![feature(specialization)]
 #![feature(unboxed_closures)]
 #![feature(underscore_lifetimes)]
-#![feature(universal_impl_trait)]
+#![cfg_attr(stage0, feature(universal_impl_trait))]
 #![feature(trace_macros)]
 #![feature(trusted_len)]
 #![feature(catch_expr)]

src/librustc/diagnostics.rs

@@ -28,13 +28,13 @@
 #![feature(unsize)]
 #![feature(i128_type)]
 #![feature(i128)]
-#![feature(conservative_impl_trait)]
+#![cfg_attr(stage0, feature(conservative_impl_trait))]
 #![feature(specialization)]
 #![feature(optin_builtin_traits)]
 #![feature(underscore_lifetimes)]
 #![feature(macro_vis_matcher)]
 #![feature(allow_internal_unstable)]
-#![feature(universal_impl_trait)]
+#![cfg_attr(stage0, feature(universal_impl_trait))]
 
 #![cfg_attr(unix, feature(libc))]
 #![cfg_attr(test, feature(test))]

src/librustc/hir/lowering.rs

@@ -17,7 +17,7 @@
 #![allow(unused_attributes)]
 #![feature(range_contains)]
 #![cfg_attr(unix, feature(libc))]
-#![feature(conservative_impl_trait)]
+#![cfg_attr(stage0, feature(conservative_impl_trait))]
 #![feature(i128_type)]
 #![feature(optin_builtin_traits)]
 

src/librustc/lib.rs

@@ -15,7 +15,7 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![deny(warnings)]
 
-#![feature(conservative_impl_trait)]
+#![cfg_attr(stage0, feature(conservative_impl_trait))]
 #![feature(fs_read_write)]
 #![feature(i128_type)]
 #![cfg_attr(stage0, feature(inclusive_range_syntax))]