Auto merge of #54767 - pietroalbini:rollup, r=pietroalbini

Rollup of 10 pull requests

Successful merges:

 - #54269 (#53840: Consolidate pattern check errors)
 - #54458 (Allow both explicit and elided lifetimes in the same impl header)
 - #54603 (Add `crate::` to trait suggestions in Rust 2018.)
 - #54648 (Update Cargo's submodule)
 - #54680 (make run-pass tests with empty main just compile-pass tests)
 - #54687 (Use impl_header_lifetime_elision in libcore)
 - #54699 (Re-export `getopts` so custom drivers can reference it.)
 - #54702 (do not promote comparing function pointers)
 - #54728 (Renumber `proc_macro` tracking issues)
 - #54745 (make `CStr::from_bytes_with_nul_unchecked()` a const fn)

Failed merges:

r? @ghost

2 files changed, 13 insertions, 1 deletions

diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index 63dd12f782f..dfec13cd2ec 100644
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -1040,7 +1040,8 @@ impl CStr {
     /// ```
     #[inline]
     #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
-    pub unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
+    #[rustc_const_unstable(feature = "const_cstr_unchecked")]
+    pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
         &*(bytes as *const [u8] as *const CStr)
     }
 
@@ -1471,4 +1472,13 @@ mod tests {
         assert_eq!(&*rc2, cstr);
         assert_eq!(&*arc2, cstr);
     }
+
+    #[test]
+    fn cstr_const_constructor() {
+        const CSTR: &'static CStr = unsafe {
+            CStr::from_bytes_with_nul_unchecked(b"Hello, world!\0")
+        };
+
+        assert_eq!(CSTR.to_str().unwrap(), "Hello, world!");
+    }
 }
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 7ae4f2de4c3..afe0b67e330 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -253,6 +253,8 @@
 #![feature(min_const_fn)]
 #![feature(const_int_ops)]
 #![feature(const_ip)]
+#![feature(const_raw_ptr_deref)]
+#![feature(const_cstr_unchecked)]
 #![feature(core_intrinsics)]
 #![feature(dropck_eyepatch)]
 #![feature(exact_size_is_empty)]