[Clang] Extend lifetime bound analysis to support assignments for the built-in pointer type (#96475)

The lifetime bound warning in Clang currently only considers
initializations. This patch extends the warning to include assignments.

- **Support for assignments of built-in pointer types**: this is done is
by reusing the existing statement-local implementation. Clang now warns
if the pointer is assigned to a temporary object that being destoryed at
the end of the full assignment expression.

With this patch, we will detect more cases under the on-by-default
diagnostic `-Wdangling`. I have added a new category for this specific
diagnostic so that people can temporarily disable it if their codebase
is not yet clean.

This is the first step to address #63310, focusing only on pointer
types. Support for C++ assignment operators will come in a follow-up
patch.

Fixes #54492

1 files changed, 4 insertions, 0 deletions

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f893d8a..90c2469 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -641,6 +641,10 @@ Improvements to Clang's diagnostics
   used rather than when they are needed for constant evaluation or when code is generated for them.
   The check is now stricter to prevent crashes for some unsupported declarations (Fixes #GH95495).
 
+- Clang now diagnoses dangling cases where a pointer is assigned to a temporary
+  that will be destroyed at the end of the full expression.
+  Fixes #GH54492.
+
 Improvements to Clang's time-trace
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