[clang-tools-extra] [clang-tidy] ignore `[[clang::lifetimebound]]` param in return-const-ref-from-parameter (PR #118315)

[Julian Schmidt via cfe-commits]

================
@@ -38,3 +29,21 @@ Example
 
   const S& s = fn(S{1});
   s.v; // use after free
+
+
+This issue can be resolved by declaring an overload of the problematic function
+where the ``const &`` parameter is instead declared as ``&&``. The developer has
+to ensure that the implementation of that function does not produce a
+use-after-free, the exact error that this check is warning against.
+Marking such an ``&&`` overload as ``deleted``, will silence the warning as 
+well. In the case of different ``const &`` parameters being returned depending
+on the control flow of the function, an overload where all problematic
+``const &`` parameters have been declared as ``&&`` will resolve the issue.
+
+This issue can also be resolved by adding ``[[clang::lifetimebound]]`` and
+enabling ``-Wdangling`` in clang. See `lifetimebound attribute<https://clang.llvm.org/docs/AttributeReference.html#id11>`_
+for details.
+
+.. code-block:: c++
+  const int &f(const int &a [[clang::lifetimebound]]) { return a; }
+  const int &v = f(1); // warning: temporary bound to local reference 'v' will be destroyed at the end of the full-expression [-Wdangling]
----------------
5chmidti wrote:

It would be good to add a comment behind the `f` function, stating that there is no warning by the check in that case.

https://github.com/llvm/llvm-project/pull/118315