[clang] [clang-tools-extra] [libcxx] [clang] fix diagnostic printing of expressions ignoring LangOpts (PR #134693)

[Matheus Izvekov via cfe-commits]

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@@ -7379,6 +7379,14 @@ class RecoveryExpr final : public Expr,
   friend class ASTStmtWriter;
 };
 
+/// Insertion operator for diagnostics.  This allows sending
+/// Expr into a diagnostic with <<.
+inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
+                                             const Expr *E) {
+  DB.AddTaggedVal(reinterpret_cast<uint64_t>(E), DiagnosticsEngine::ak_expr);
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mizvekov wrote:

If we care that uint64_t might not round trip a pointer in theory, even though it should always in practice, then do we care uintptr_t is not guaranteed to be provided in theory, even though it should always be in practice?

https://github.com/llvm/llvm-project/pull/134693