[clang] [AST] Use explicit type erasure in TypeSourceInfo constructor (PR #68435)

[via cfe-commits]

https://github.com/bonktree created https://github.com/llvm/llvm-project/pull/68435

When this file is included in a project compiled with GCC 13 `-Werror`, compilation fails with the following diagnostic:
<pre>
/usr/lib/llvm-17.0/include/clang/AST/TypeLoc.h: In constructor 'clang::TypeSourceInfo::TypeSourceInfo(clang::QualType, size_t)':
/usr/lib/llvm-17.0/include/clang/AST/TypeLoc.h:245:9: error: 'void* memset(void*, int, size_t)' clearing an object of non-trivial type 'class clang::TypeSourceInfo'; use assignment instead [-Werror=class-memaccess]
  245 |   memset(this + 1, 0, DataSize);
      |   ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

</pre>
To avoid this, we add an explicit type cast. The cast to void makes sense, since other member functions of `TypeSourceInfo` also treat the buffer `(this + 1)` of length `DataSize` as opaque memory, and was likely left out by mistake.

Fixes: 4498663f3de0 ("[AST] Initialized data after TypeSourceInfo")

I also suggest to apply this to release/17.x if possible.

>From 753c2e0ad0c15d0af14368c574b3fa53d70416f9 Mon Sep 17 00:00:00 2001
From: Arseny Maslennikov <arseny at altlinux.org>
Date: Thu, 5 Oct 2023 10:05:14 +0300
Subject: [PATCH] [AST] Use explicit type erasure in TypeSourceInfo constructor

When this file is included in a project compiled with GCC 13 -Werror,
compilation fails with the following diagnostic:
  /usr/lib/llvm-17.0/include/clang/AST/TypeLoc.h: In constructor 'clang::TypeSourceInfo::TypeSourceInfo(clang::QualType, size_t)':
  /usr/lib/llvm-17.0/include/clang/AST/TypeLoc.h:245:9: error: 'void* memset(void*, int, size_t)' clearing an object of non-trivial type 'class clang::TypeSourceInfo'; use assignment instead
  +[-Werror=class-memaccess]
    245 |   memset(this + 1, 0, DataSize);
        |   ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

To avoid this, we add an explicit type cast. The cast to void makes
sense, since other member functions of TypeSourceInfo also treat the
buffer `(this + 1)` of length `DataSize` as opaque memory, and was
likely left out by mistake.

Fixes: 4498663f3de0 ("[AST] Initialized data after TypeSourceInfo")
---
 clang/include/clang/AST/TypeLoc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/include/clang/AST/TypeLoc.h b/clang/include/clang/AST/TypeLoc.h
index 98427a8dcbfe660..e38895099c9e30c 100644
--- a/clang/include/clang/AST/TypeLoc.h
+++ b/clang/include/clang/AST/TypeLoc.h
@@ -243,7 +243,7 @@ class TypeLoc {
 
 inline TypeSourceInfo::TypeSourceInfo(QualType ty, size_t DataSize) : Ty(ty) {
   // Init data attached to the object. See getTypeLoc.
-  memset(this + 1, 0, DataSize);
+  memset(const_cast<void*>(static_cast<const void*>(this + 1)), 0, DataSize);
 }
 
 /// Return the TypeLoc for a type source info.