Auto merge of #118126 - Nilstrieb:rollup-5ogh896, r=Nilstrieb

Rollup of 7 pull requests

Successful merges:

 - #117790 (CFI: Add missing use core::ffi::c_int)
 - #118059 (Explicitly unset $CARGO for compiletest)
 - #118081 (`rustc_ty_utils` cleanups)
 - #118094 (feat: specialize `SpecFromElem` for `()`)
 - #118097 (Update books)
 - #118115 (Fix occurrences of old fn names in comment and tracing)
 - #118121 (`rustc_hir` cleanups)

r? `@ghost`
`@rustbot` modify labels: rollup

1 files changed, 19 insertions, 4 deletions

diff --git a/library/alloc/src/vec/spec_from_elem.rs b/library/alloc/src/vec/spec_from_elem.rs
index da43d17bf36..01a6db14474 100644
--- a/library/alloc/src/vec/spec_from_elem.rs
+++ b/library/alloc/src/vec/spec_from_elem.rs
@@ -36,12 +36,12 @@ impl SpecFromElem for i8 {
         if elem == 0 {
             return Vec { buf: RawVec::with_capacity_zeroed_in(n, alloc), len: n };
         }
+        let mut v = Vec::with_capacity_in(n, alloc);
         unsafe {
-            let mut v = Vec::with_capacity_in(n, alloc);
             ptr::write_bytes(v.as_mut_ptr(), elem as u8, n);
             v.set_len(n);
-            v
         }
+        v
     }
 }
 
@@ -51,11 +51,26 @@ impl SpecFromElem for u8 {
         if elem == 0 {
             return Vec { buf: RawVec::with_capacity_zeroed_in(n, alloc), len: n };
         }
+        let mut v = Vec::with_capacity_in(n, alloc);
         unsafe {
-            let mut v = Vec::with_capacity_in(n, alloc);
             ptr::write_bytes(v.as_mut_ptr(), elem, n);
             v.set_len(n);
-            v
         }
+        v
+    }
+}
+
+// A better way would be to implement this for all ZSTs which are `Copy` and have trivial `Clone`
+// but the latter cannot be detected currently
+impl SpecFromElem for () {
+    #[inline]
+    fn from_elem<A: Allocator>(_elem: (), n: usize, alloc: A) -> Vec<(), A> {
+        let mut v = Vec::with_capacity_in(n, alloc);
+        // SAFETY: the capacity has just been set to `n`
+        // and `()` is a ZST with trivial `Clone` implementation
+        unsafe {
+            v.set_len(n);
+        }
+        v
     }
 }