Use rustc attrs in dangling_pointers_from_temporaries lint

[Urgau]

If you want to do it in this PR (otherwise in a follow-up), we could add an rustc attribute to those as_ptr/as_mut_ptr methods.

You can follow afcb09b and 2a930d3 (from a PR of mine) with check_applied_to_fn_or_method instead, and something similar to this to check the attribute

rust/compiler/rustc_lint/src/ptr_nulls.rs

Lines 49 to 50 in e454c45

	&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
	&& cx.tcx.has_attr(def_id, sym::rustc_never_returns_null_ptr)

Originally posted by @Urgau in #128985 (comment)

[Urgau]

Steps

1. Create the attribute (symbol, register, and validation), let's say rustc_as_ptr_function (better name to be found)
2. Apply the newly created attribute to the relevant as_ptr/as_mut_ptr methods to the types listed
   

   rust/compiler/rustc_lint/src/dangling.rs

   Lines 202 to 219 in 2dece5b

   	// Array, Vec, String, CString, MaybeUninit, Cell, Box<[_]>, Box<str>, Box<CStr>,
   	// or any of the above in arbitrary many nested Box'es.
   	fn is_interesting(tcx: TyCtxt<'_>, ty: Ty<'_>) -> bool {
   	if ty.is_array() {
   	true
   	} else if let Some(inner) = ty.boxed_ty() {
   	inner.is_slice()
   	|| inner.is_str()
   	|| inner.ty_adt_def().is_some_and(|def| tcx.is_lang_item(def.did(), LangItem::CStr))
   	|| is_interesting(tcx, inner)
   	} else if let Some(def) = ty.ty_adt_def() {
   	for lang_item in [LangItem::String, LangItem::MaybeUninit] {
   	if tcx.is_lang_item(def.did(), lang_item) {
   	return true;
   	}
   	}
   	tcx.get_diagnostic_name(def.did())
   	.is_some_and(|name| matches!(name, sym::cstring_type | sym::Vec | sym::Cell))

3. Use the newly created attribute instead of is_interesting fn, with something similar to this
   

   rust/compiler/rustc_lint/src/ptr_nulls.rs

   Lines 49 to 50 in e454c45

   	&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
   	&& cx.tcx.has_attr(def_id, sym::rustc_never_returns_null_ptr)

More context in #128985 (comment)

[gavincrawford]

@rustbot claim
Oops

[gavincrawford]

@GrigorenkoPV sorry, didn't realize this your follow up issue. Apologies.
@rustbot release-assignment

[GrigorenkoPV]

@GrigorenkoPV sorry, didn't realize this your follow up issue. Apologies. @rustbot release-assignment

I, most likely, won't have a chance to work on it in the next few weeks, so you can claim it in the meantime if you want to.