[clang-tools-extra] [clang-tidy] Add `bugprone-pointer-arithmetic-on-polymorphic-object` check (PR #91951)

[Piotr Zegar via cfe-commits]

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@@ -0,0 +1,78 @@
+//===--- PointerArithmeticOnPolymorphicObjectCheck.cpp - clang-tidy--------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "PointerArithmeticOnPolymorphicObjectCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+namespace {
+AST_MATCHER(CXXRecordDecl, isAbstract) { return Node.isAbstract(); }
+} // namespace
+
+PointerArithmeticOnPolymorphicObjectCheck::
+    PointerArithmeticOnPolymorphicObjectCheck(StringRef Name,
+                                              ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      MatchInheritedVirtualFunctions(
+          Options.get("MatchInheritedVirtualFunctions", false)) {}
+
+void PointerArithmeticOnPolymorphicObjectCheck::storeOptions(
+    ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "MatchInheritedVirtualFunctions", true);
+}
+
+void PointerArithmeticOnPolymorphicObjectCheck::registerMatchers(
+    MatchFinder *Finder) {
+  const auto PolymorphicPointerExpr =
+      expr(hasType(hasCanonicalType(
+               pointerType(pointee(hasCanonicalType(hasDeclaration(
+                   cxxRecordDecl(unless(isFinal()),
+                                 cxxRecordDecl(hasMethod(isVirtual()))))))))))
+          .bind("pointer");
+
+  const auto PointerExprWithVirtualMethod =
+      expr(hasType(hasCanonicalType(pointerType(
+               pointee(hasCanonicalType(hasDeclaration(cxxRecordDecl(
+                   unless(isFinal()),
+                   anyOf(hasMethod(isVirtualAsWritten()), isAbstract())))))))))
+          .bind("pointer");
----------------
PiotrZSL wrote:

This doesn't make sense, simply IF type is derived with added new methods, then there will be no issues, as vtable will handle everything correctly, and even if operation would be done on base class everything will be fine.

Actually only issue will be if size of classes does not match, but that can happen whatever this is polymorphic object of not.

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