[clang] [Clang] Diagnose down casting static_cast (PR #117914)

[Erich Keane via cfe-commits]

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@@ -593,6 +593,10 @@ Improvements to Clang's diagnostics
 - Clang now supports using alias templates in deduction guides, aligning with the C++ standard,
   which treats alias templates as synonyms for their underlying types (#GH54909).
 
+- Added ``-Wstatic-downcast`` to diagnose potentially dangerous uses of ``static_cast`` that perform a base-to-derived cast
+  on pointers and references of polymorphic types.
+
+
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erichkeane wrote:

Should this be just 1 newline?

https://github.com/llvm/llvm-project/pull/117914