fix feature use in rustc libs

compiler/rustc_ast/src/lib.rs

@@ -10,7 +10,8 @@
 )]
 #![feature(box_syntax)]
 #![feature(box_patterns)]
-#![feature(const_fn)] // For the `transmute` in `P::new`
+#![cfg_attr(bootstrap, feature(const_fn))] // For the `transmute` in `P::new`
+#![cfg_attr(not(bootstrap), feature(const_fn_unsize))] // For the `transmute` in `P::new`
 #![feature(const_fn_transmute)]
 #![feature(const_panic)]
 #![feature(crate_visibility_modifier)]

compiler/rustc_hir/src/lib.rs

@@ -3,7 +3,6 @@
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/hir.html
 
 #![feature(crate_visibility_modifier)]
-#![feature(const_fn)] // For the unsizing cast on `&[]`
 #![feature(const_panic)]
 #![feature(extended_key_value_attributes)]
 #![feature(in_band_lifetimes)]

compiler/rustc_index/src/lib.rs

@@ -1,5 +1,4 @@
 #![feature(allow_internal_unstable)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(extend_one)]
 #![feature(iter_zip)]

compiler/rustc_infer/src/lib.rs

@@ -16,7 +16,6 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(extend_one)]
 #![feature(iter_zip)]

compiler/rustc_middle/src/lib.rs

@@ -29,7 +29,6 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(core_intrinsics)]
 #![feature(discriminant_kind)]

compiler/rustc_mir/src/lib.rs

@@ -12,7 +12,6 @@ Rust MIR: a lowered representation of Rust.
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(decl_macro)]

compiler/rustc_mir_build/src/lib.rs

@@ -4,7 +4,6 @@
 #![feature(array_windows)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(control_flow_enum)]
 #![feature(crate_visibility_modifier)]

compiler/rustc_passes/src/lib.rs

@@ -5,7 +5,6 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(in_band_lifetimes)]

compiler/rustc_query_system/src/lib.rs

@@ -1,5 +1,4 @@
 #![feature(bool_to_option)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]

compiler/rustc_span/src/lib.rs

@@ -16,7 +16,6 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(array_windows)]
 #![feature(crate_visibility_modifier)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(negative_impls)]
 #![feature(nll)]

compiler/rustc_target/src/lib.rs

@@ -9,7 +9,6 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(bool_to_option)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(nll)]
 #![feature(never_type)]