Auto merge of #114494 - est31:extend_useless_ptr_null_checks, r=jackh726

Make useless_ptr_null_checks smarter about some std functions

This teaches the `useless_ptr_null_checks` lint that some std functions can't ever return null pointers, because they need to point to valid data, get references as input, etc.

This is achieved by introducing an `#[rustc_never_returns_null_ptr]` attribute and adding it to these std functions (gated behind bootstrap `cfg_attr`).

Later on, the attribute could maybe be used to tell LLVM that the returned pointer is never null. I don't expect much impact of that though, as the functions are pretty shallow and usually the input data is already never null.

Follow-up of PR #113657

Fixes #114442

1 files changed, 2 insertions, 0 deletions

diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index d3b7558440c..c53e9a5dd7a 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -1454,6 +1454,7 @@ impl<T: ?Sized, A: Allocator> Arc<T, A> {
     /// ```
     #[must_use = "losing the pointer will leak memory"]
     #[stable(feature = "rc_raw", since = "1.17.0")]
+    #[cfg_attr(not(bootstrap), rustc_never_returns_null_ptr)]
     pub fn into_raw(this: Self) -> *const T {
         let ptr = Self::as_ptr(&this);
         mem::forget(this);
@@ -1478,6 +1479,7 @@ impl<T: ?Sized, A: Allocator> Arc<T, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rc_as_ptr", since = "1.45.0")]
+    #[cfg_attr(not(bootstrap), rustc_never_returns_null_ptr)]
     pub fn as_ptr(this: &Self) -> *const T {
         let ptr: *mut ArcInner<T> = NonNull::as_ptr(this.ptr);