[clang-tools-extra] [clang-tidy] Create bugprone-bit-cast-pointers check (PR #108083)

[Julian Schmidt via cfe-commits]

================
@@ -0,0 +1,32 @@
+//===--- BitCastPointersCheck.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 "BitCastPointersCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+void BitCastPointersCheck::registerMatchers(MatchFinder *Finder) {
+  auto IsPointerType = refersToType(qualType(isAnyPointer()));
+  Finder->addMatcher(callExpr(callee(functionDecl(allOf(
+                                  hasName("::std::bit_cast"),
+                                  hasTemplateArgument(0, IsPointerType),
+                                  hasTemplateArgument(1, IsPointerType)))))
+                         .bind("x"),
+                     this);
----------------
5chmidti wrote:

Note that this check will currently not detect when the source and target types are structs that contain pointer types:

```c++
struct A {
  uint64_t* ptr;
};
struct B {
  double* ptr;
};

A a{};
std::bit_cast<B>(a);
```

As was pointed out in `r0 -> r1` of the paper:

> The pointer-forbidding logic was removed. It was initially there to help developers when a better tool is available, but it’s easily worked around (e.g. with a struct containing a pointer).

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0476r2.html

https://github.com/llvm/llvm-project/pull/108083