Rollup merge of #85850 - bjorn3:less_feature_gates, r=jyn514

Remove unused feature gates

The first commit removes a usage of a feature gate, but I don't expect it to be controversial as the feature gate was only used to workaround a limitation of rust in the past. (closures never being `Clone`)

The second commit uses `#[allow_internal_unstable]` to avoid leaking the `trusted_step` feature gate usage from inside the index newtype macro. It didn't work for the `min_specialization` feature gate though.

The third commit removes (almost) all feature gates from the compiler that weren't used anyway.

24 files changed, 2 insertions, 69 deletions

diff --git a/compiler/rustc_ast/src/lib.rs b/compiler/rustc_ast/src/lib.rs
index 14ecf27813d..7c79b4aab3c 100644
--- a/compiler/rustc_ast/src/lib.rs
+++ b/compiler/rustc_ast/src/lib.rs
@@ -12,13 +12,11 @@
 #![feature(box_patterns)]
 #![cfg_attr(bootstrap, feature(const_fn_unsize))]
 #![feature(const_fn_transmute)]
-#![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(iter_zip)]
 #![feature(label_break_value)]
 #![feature(nll)]
 #![feature(min_specialization)]
-#![feature(trusted_step)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_ast_passes/src/lib.rs b/compiler/rustc_ast_passes/src/lib.rs
index c9e2d202da9..26da18b571c 100644
--- a/compiler/rustc_ast_passes/src/lib.rs
+++ b/compiler/rustc_ast_passes/src/lib.rs
@@ -6,7 +6,6 @@
 
 #![feature(bindings_after_at)]
 #![feature(iter_is_partitioned)]
-#![feature(box_syntax)]
 #![feature(box_patterns)]
 #![recursion_limit = "256"]
 
diff --git a/compiler/rustc_codegen_ssa/src/lib.rs b/compiler/rustc_codegen_ssa/src/lib.rs
index 6c4bb021cb3..12da3d9e155 100644
--- a/compiler/rustc_codegen_ssa/src/lib.rs
+++ b/compiler/rustc_codegen_ssa/src/lib.rs
@@ -1,15 +1,11 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
-#![feature(assert_matches)]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
-#![feature(drain_filter)]
 #![feature(try_blocks)]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
 #![feature(associated_type_bounds)]
-#![feature(iter_zip)]
 #![recursion_limit = "256"]
-#![feature(box_syntax)]
 
 //! This crate contains codegen code that is used by all codegen backends (LLVM and others).
 //! The backend-agnostic functions of this crate use functions defined in various traits that
diff --git a/compiler/rustc_data_structures/src/lib.rs b/compiler/rustc_data_structures/src/lib.rs
index adbb98fa750..a8b9f479f1e 100644
--- a/compiler/rustc_data_structures/src/lib.rs
+++ b/compiler/rustc_data_structures/src/lib.rs
@@ -10,15 +10,12 @@
 #![feature(array_windows)]
 #![feature(control_flow_enum)]
 #![feature(in_band_lifetimes)]
-#![feature(unboxed_closures)]
 #![feature(generator_trait)]
-#![feature(fn_traits)]
 #![feature(min_specialization)]
 #![feature(auto_traits)]
 #![feature(nll)]
 #![feature(allow_internal_unstable)]
 #![feature(hash_raw_entry)]
-#![feature(stmt_expr_attributes)]
 #![feature(core_intrinsics)]
 #![feature(test)]
 #![feature(associated_type_bounds)]
diff --git a/compiler/rustc_data_structures/src/obligation_forest/mod.rs b/compiler/rustc_data_structures/src/obligation_forest/mod.rs
index 29d685ab530..3aabe94bfc6 100644
--- a/compiler/rustc_data_structures/src/obligation_forest/mod.rs
+++ b/compiler/rustc_data_structures/src/obligation_forest/mod.rs
@@ -597,7 +597,7 @@ impl<O: ForestObligation> ObligationForest<O> {
                 Some(rpos) => {
                     // Cycle detected.
                     processor.process_backedge(
-                        stack[rpos..].iter().map(GetObligation(&self.nodes)),
+                        stack[rpos..].iter().map(|&i| &self.nodes[i].obligation),
                         PhantomData,
                     );
                 }
@@ -705,20 +705,3 @@ impl<O: ForestObligation> ObligationForest<O> {
         });
     }
 }
-
-// I need a Clone closure.
-#[derive(Clone)]
-struct GetObligation<'a, O>(&'a [Node<O>]);
-
-impl<'a, 'b, O> FnOnce<(&'b usize,)> for GetObligation<'a, O> {
-    type Output = &'a O;
-    extern "rust-call" fn call_once(self, args: (&'b usize,)) -> &'a O {
-        &self.0[*args.0].obligation
-    }
-}
-
-impl<'a, 'b, O> FnMut<(&'b usize,)> for GetObligation<'a, O> {
-    extern "rust-call" fn call_mut(&mut self, args: (&'b usize,)) -> &'a O {
-        &self.0[*args.0].obligation
-    }
-}
diff --git a/compiler/rustc_expand/src/lib.rs b/compiler/rustc_expand/src/lib.rs
index 16510b3eb07..f77eac2b068 100644
--- a/compiler/rustc_expand/src/lib.rs
+++ b/compiler/rustc_expand/src/lib.rs
@@ -1,4 +1,3 @@
-#![feature(bool_to_option)]
 #![feature(crate_visibility_modifier)]
 #![feature(decl_macro)]
 #![feature(destructuring_assignment)]
diff --git a/compiler/rustc_hir/src/lib.rs b/compiler/rustc_hir/src/lib.rs
index 7f3c410b1ec..ad2ecae9233 100644
--- a/compiler/rustc_hir/src/lib.rs
+++ b/compiler/rustc_hir/src/lib.rs
@@ -3,12 +3,10 @@
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/hir.html
 
 #![feature(crate_visibility_modifier)]
-#![feature(const_panic)]
 #![cfg_attr(bootstrap, feature(extended_key_value_attributes))]
 #![feature(in_band_lifetimes)]
 #![feature(once_cell)]
 #![feature(min_specialization)]
-#![feature(trusted_step)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_index/src/lib.rs b/compiler/rustc_index/src/lib.rs
index 04d62391c02..0093fa5e562 100644
--- a/compiler/rustc_index/src/lib.rs
+++ b/compiler/rustc_index/src/lib.rs
@@ -1,12 +1,10 @@
 #![feature(allow_internal_unstable)]
 #![feature(bench_black_box)]
-#![feature(const_panic)]
 #![feature(extend_one)]
 #![feature(iter_zip)]
 #![feature(unboxed_closures)]
 #![feature(test)]
 #![feature(fn_traits)]
-#![feature(trusted_step)]
 
 pub mod bit_set;
 pub mod vec;
diff --git a/compiler/rustc_index/src/vec.rs b/compiler/rustc_index/src/vec.rs
index 3f759f4023b..246fa28d986 100644
--- a/compiler/rustc_index/src/vec.rs
+++ b/compiler/rustc_index/src/vec.rs
@@ -65,7 +65,7 @@ impl Idx for u32 {
 /// `u32::MAX`. You can also customize things like the `Debug` impl,
 /// what traits are derived, and so forth via the macro.
 #[macro_export]
-#[allow_internal_unstable(step_trait, rustc_attrs)]
+#[allow_internal_unstable(step_trait, rustc_attrs, trusted_step)]
 macro_rules! newtype_index {
     // ---- public rules ----
 
diff --git a/compiler/rustc_infer/src/lib.rs b/compiler/rustc_infer/src/lib.rs
index 6b452bca8e7..ee358c52c2f 100644
--- a/compiler/rustc_infer/src/lib.rs
+++ b/compiler/rustc_infer/src/lib.rs
@@ -16,14 +16,12 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_panic)]
 #![feature(extend_one)]
 #![feature(iter_zip)]
 #![feature(never_type)]
 #![feature(in_band_lifetimes)]
 #![feature(control_flow_enum)]
 #![feature(min_specialization)]
-#![feature(trusted_step)]
 #![recursion_limit = "512"] // For rustdoc
 
 #[macro_use]
diff --git a/compiler/rustc_interface/src/lib.rs b/compiler/rustc_interface/src/lib.rs
index f2b69da3f86..b5af2bfca35 100644
--- a/compiler/rustc_interface/src/lib.rs
+++ b/compiler/rustc_interface/src/lib.rs
@@ -1,6 +1,5 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
-#![feature(box_syntax)]
 #![feature(internal_output_capture)]
 #![feature(nll)]
 #![feature(generator_trait)]
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 45ed6872f18..4f59460aa82 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -36,8 +36,6 @@
 #![feature(iter_zip)]
 #![feature(never_type)]
 #![feature(nll)]
-#![feature(half_open_range_patterns)]
-#![feature(exclusive_range_pattern)]
 #![feature(control_flow_enum)]
 #![recursion_limit = "256"]
 
diff --git a/compiler/rustc_metadata/src/lib.rs b/compiler/rustc_metadata/src/lib.rs
index 15c9eda9902..27842ac7796 100644
--- a/compiler/rustc_metadata/src/lib.rs
+++ b/compiler/rustc_metadata/src/lib.rs
@@ -1,5 +1,4 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
-#![feature(core_intrinsics)]
 #![feature(crate_visibility_modifier)]
 #![feature(drain_filter)]
 #![feature(in_band_lifetimes)]
@@ -7,7 +6,6 @@
 #![feature(once_cell)]
 #![feature(proc_macro_internals)]
 #![feature(min_specialization)]
-#![feature(stmt_expr_attributes)]
 #![feature(try_blocks)]
 #![feature(never_type)]
 #![recursion_limit = "256"]
diff --git a/compiler/rustc_middle/src/lib.rs b/compiler/rustc_middle/src/lib.rs
index 6f97716e2e0..e1d7bc4be53 100644
--- a/compiler/rustc_middle/src/lib.rs
+++ b/compiler/rustc_middle/src/lib.rs
@@ -29,7 +29,6 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_panic)]
 #![feature(core_intrinsics)]
 #![feature(discriminant_kind)]
 #![feature(never_type)]
@@ -50,7 +49,6 @@
 #![feature(associated_type_defaults)]
 #![feature(iter_zip)]
 #![feature(thread_local_const_init)]
-#![feature(trusted_step)]
 #![recursion_limit = "512"]
 
 #[macro_use]
diff --git a/compiler/rustc_mir/src/lib.rs b/compiler/rustc_mir/src/lib.rs
index 647c368d2bb..12a36976f1d 100644
--- a/compiler/rustc_mir/src/lib.rs
+++ b/compiler/rustc_mir/src/lib.rs
@@ -12,16 +12,13 @@ Rust MIR: a lowered representation of Rust.
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(decl_macro)]
 #![feature(exact_size_is_empty)]
-#![feature(exhaustive_patterns)]
 #![feature(iter_zip)]
 #![feature(never_type)]
 #![feature(map_try_insert)]
 #![feature(min_specialization)]
-#![feature(slice_ptr_len)]
 #![feature(slice_ptr_get)]
 #![feature(trusted_len)]
 #![feature(try_blocks)]
@@ -31,7 +28,6 @@ Rust MIR: a lowered representation of Rust.
 #![feature(option_get_or_insert_default)]
 #![feature(once_cell)]
 #![feature(control_flow_enum)]
-#![feature(trusted_step)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_mir_build/src/lib.rs b/compiler/rustc_mir_build/src/lib.rs
index 99b854ff066..d2992f0bf18 100644
--- a/compiler/rustc_mir_build/src/lib.rs
+++ b/compiler/rustc_mir_build/src/lib.rs
@@ -1,17 +1,14 @@
 //! Construction of MIR from HIR.
 //!
 //! This crate also contains the match exhaustiveness and usefulness checking.
-#![feature(array_windows)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_panic)]
 #![feature(control_flow_enum)]
 #![feature(crate_visibility_modifier)]
 #![feature(bool_to_option)]
 #![feature(iter_zip)]
 #![feature(once_cell)]
 #![feature(min_specialization)]
-#![feature(trusted_step)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_parse/src/lib.rs b/compiler/rustc_parse/src/lib.rs
index da642bb2d28..51df06bd989 100644
--- a/compiler/rustc_parse/src/lib.rs
+++ b/compiler/rustc_parse/src/lib.rs
@@ -3,7 +3,6 @@
 #![feature(array_windows)]
 #![feature(crate_visibility_modifier)]
 #![feature(bindings_after_at)]
-#![feature(iter_order_by)]
 #![feature(box_syntax)]
 #![feature(box_patterns)]
 #![recursion_limit = "256"]
diff --git a/compiler/rustc_passes/src/lib.rs b/compiler/rustc_passes/src/lib.rs
index 4803148eba9..28633faa205 100644
--- a/compiler/rustc_passes/src/lib.rs
+++ b/compiler/rustc_passes/src/lib.rs
@@ -5,13 +5,11 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
-#![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(in_band_lifetimes)]
 #![feature(iter_zip)]
 #![feature(nll)]
 #![feature(min_specialization)]
-#![feature(trusted_step)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_query_impl/src/lib.rs b/compiler/rustc_query_impl/src/lib.rs
index ac81c0261e2..4175fb6925a 100644
--- a/compiler/rustc_query_impl/src/lib.rs
+++ b/compiler/rustc_query_impl/src/lib.rs
@@ -2,13 +2,9 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(in_band_lifetimes)]
-#![feature(exhaustive_patterns)]
 #![feature(nll)]
 #![feature(min_specialization)]
-#![feature(crate_visibility_modifier)]
-#![feature(once_cell)]
 #![feature(rustc_attrs)]
-#![feature(never_type)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_query_system/src/lib.rs b/compiler/rustc_query_system/src/lib.rs
index 7df3804c986..0d4fb34265c 100644
--- a/compiler/rustc_query_system/src/lib.rs
+++ b/compiler/rustc_query_system/src/lib.rs
@@ -1,12 +1,8 @@
 #![feature(bool_to_option)]
-#![feature(const_panic)]
 #![feature(core_intrinsics)]
-#![feature(drain_filter)]
 #![feature(hash_raw_entry)]
 #![feature(iter_zip)]
 #![feature(min_specialization)]
-#![feature(stmt_expr_attributes)]
-#![feature(trusted_step)]
 
 #[macro_use]
 extern crate tracing;
diff --git a/compiler/rustc_serialize/src/lib.rs b/compiler/rustc_serialize/src/lib.rs
index cf5a9118275..c79786a839f 100644
--- a/compiler/rustc_serialize/src/lib.rs
+++ b/compiler/rustc_serialize/src/lib.rs
@@ -14,10 +14,7 @@ Core encoding and decoding interfaces.
 #![feature(nll)]
 #![feature(associated_type_bounds)]
 #![feature(min_specialization)]
-#![feature(vec_spare_capacity)]
 #![feature(core_intrinsics)]
-#![feature(maybe_uninit_array_assume_init)]
-#![feature(maybe_uninit_uninit_array)]
 #![feature(maybe_uninit_slice)]
 #![feature(new_uninit)]
 #![cfg_attr(test, feature(test))]
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index dc15c531d1e..51a53918f07 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -16,12 +16,10 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(array_windows)]
 #![feature(crate_visibility_modifier)]
-#![feature(const_panic)]
 #![feature(negative_impls)]
 #![feature(nll)]
 #![feature(min_specialization)]
 #![feature(thread_local_const_init)]
-#![feature(trusted_step)]
 
 #[macro_use]
 extern crate rustc_macros;
diff --git a/compiler/rustc_target/src/lib.rs b/compiler/rustc_target/src/lib.rs
index a40de5ef18e..cb8f6b9656c 100644
--- a/compiler/rustc_target/src/lib.rs
+++ b/compiler/rustc_target/src/lib.rs
@@ -9,13 +9,11 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(bool_to_option)]
-#![feature(const_panic)]
 #![feature(nll)]
 #![feature(never_type)]
 #![feature(associated_type_bounds)]
 #![feature(exhaustive_patterns)]
 #![feature(min_specialization)]
-#![feature(trusted_step)]
 
 use std::path::{Path, PathBuf};
 
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index 3f4c8a72f1d..2d102127dd9 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -1,5 +1,4 @@
 #![feature(min_specialization)]
-#![feature(trusted_step)]
 
 #[macro_use]
 extern crate bitflags;