[clang-tools-extra] [clang-tidy] Add `bugprone-virtual-arithmetic` check (PR #91951)

[Julian Schmidt via cfe-commits]

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+.. title:: clang-tidy - bugprone-virtual-arithmetic
+
+bugprone-virtual-arithmetic
+===========================
+
+Warn if pointer arithmetic is performed on a class that declares a
+virtual function.
+
+Pointer arithmetic on polymorphic objects where the pointer's static type is 
+different from its dynamic type is undefined behavior.
+Finding pointers where the static type contains a virtual member function is a
+good heuristic, as the pointer is likely to point to a different, derived class.
+
+This check corresponds to the SEI Cert rule `CTR56-CPP: Do not use pointer arithmetic on polymorphic objects <https://wiki.sei.cmu.edu/confluence/display/cplusplus/CTR56-CPP.+Do+not+use+pointer+arithmetic+on+polymorphic+objects>`_.
+
+Example:
+
+.. code-block:: c++
+
+  struct Base {
+    virtual void ~Base();
+  };
+
+  struct Derived : public Base {};
+
+  void foo() {
+    Base *b = new Derived[10];
+
+    b += 1;
+    // warning: pointer arithmetic on class that declares a virtual function, undefined behavior if the pointee is a different class
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5chmidti wrote:

Please reflow this comment to fit into 80 columns.

https://github.com/llvm/llvm-project/pull/91951