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, 4 insertions, 0 deletions

diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index b4b794d4e09..04ebe22a9eb 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -700,6 +700,10 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         "#[rustc_pass_by_value] is used to mark types that must be passed by value instead of reference."
     ),
     rustc_attr!(
+        rustc_never_returns_null_ptr, Normal, template!(Word), ErrorFollowing,
+        "#[rustc_never_returns_null_ptr] is used to mark functions returning non-null pointers."
+    ),
+    rustc_attr!(
         rustc_coherence_is_core, AttributeType::CrateLevel, template!(Word), ErrorFollowing, @only_local: true,
         "#![rustc_coherence_is_core] allows inherent methods on builtin types, only intended to be used in `core`."
     ),