Remove unnecessary const_fn feature gates

This flag opts out of the min-const-fn checks entirely, which is usually
not what we want. The few cases where the flag is still necessary have
been annotated.

Author: ecstatic-morse

src/libcore/lib.rs

@@ -70,7 +70,6 @@
 #![feature(bound_cloned)]
 #![feature(cfg_target_has_atomic)]
 #![feature(concat_idents)]
-#![feature(const_fn)]
 #![feature(const_if_match)]
 #![feature(const_panic)]
 #![feature(const_fn_union)]

src/libcore/tests/lib.rs

@@ -31,7 +31,6 @@
 #![feature(slice_internals)]
 #![feature(slice_partition_dedup)]
 #![feature(int_error_matching)]
-#![feature(const_fn)]
 #![feature(array_value_iter)]
 #![feature(iter_partition_in_place)]
 #![feature(iter_is_partitioned)]

src/libproc_macro/lib.rs

@@ -21,7 +21,6 @@
 #![feature(nll)]
 #![feature(staged_api)]
 #![feature(allow_internal_unstable)]
-#![feature(const_fn)]
 #![feature(decl_macro)]
 #![feature(extern_types)]
 #![feature(in_band_lifetimes)]

src/librustc/lib.rs

@@ -31,7 +31,6 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(const_transmute)]
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]

src/librustc_hir/lib.rs

@@ -3,7 +3,7 @@
 //! [rustc guide]: https://rust-lang.github.io/rustc-guide/hir.html
 
 #![feature(crate_visibility_modifier)]
-#![feature(const_fn)]
+#![feature(const_fn)] // For the unsizing cast on `&[]`
 #![feature(in_band_lifetimes)]
 #![feature(specialization)]
 #![recursion_limit = "256"]

src/librustc_mir/lib.rs

@@ -13,7 +13,6 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![feature(box_syntax)]
 #![feature(crate_visibility_modifier)]
 #![feature(core_intrinsics)]
-#![feature(const_fn)]
 #![feature(decl_macro)]
 #![feature(drain_filter)]
 #![feature(exhaustive_patterns)]

src/librustc_span/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/")]
-#![feature(const_fn)]
 #![feature(crate_visibility_modifier)]
 #![feature(nll)]
 #![feature(optin_builtin_traits)]

src/librustdoc/lib.rs

@@ -12,7 +12,6 @@
 #![feature(test)]
 #![feature(ptr_offset_from)]
 #![feature(crate_visibility_modifier)]
-#![feature(const_fn)]
 #![feature(drain_filter)]
 #![feature(never_type)]
 #![feature(unicode_internals)]

src/libsyntax/lib.rs

@@ -7,7 +7,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/", test(attr(deny(warnings))))]
 #![feature(bool_to_option)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
+#![feature(const_fn)] // For the `transmute` in `P::new`
 #![feature(const_transmute)]
 #![feature(crate_visibility_modifier)]
 #![feature(label_break_value)]

src/test/ui/consts/const-mut-refs/const_mut_refs.rs

@@ -1,7 +1,6 @@
 // run-pass
 
 #![feature(const_mut_refs)]
-#![feature(const_fn)]
 
 struct Foo {
     x: usize