[clang] [RFC] Initial implementation of P2719 (PR #113510)

[Oliver Hunt via cfe-commits]

================
@@ -1098,12 +1098,39 @@ static TypeSourceInfo *getTypeSourceInfoForStdAlignValT(Sema &S,
   return S.Context.getTrivialTypeSourceInfo(StdAlignValDecl);
 }
 
+// When searching for custom allocators on the PromiseType we want to
+// warn that we will ignore type aware allocators.
+static bool DiagnoseTypeAwareAllocators(Sema &S, SourceLocation Loc,
+                                        unsigned DiagnosticID,
+                                        DeclarationName Name,
+                                        QualType PromiseType) {
+  assert(PromiseType->isRecordType());
+
+  LookupResult R(S, Name, Loc, Sema::LookupOrdinaryName);
+  S.LookupQualifiedName(R, PromiseType->getAsCXXRecordDecl());
+  bool HaveIssuedWarning = false;
+  for (auto Decl : R) {
+    if (!Decl->getAsFunction()->isTypeAwareOperatorNewOrDelete())
+      continue;
+    if (!HaveIssuedWarning) {
+      S.Diag(Loc, DiagnosticID) << Name;
+      HaveIssuedWarning = true;
+    }
+    S.Diag(Decl->getLocation(), diag::note_type_aware_operator_declared)
+        << /* isTypeAware */ 1 << Decl << Decl->getDeclContext();
----------------
ojhunt wrote:

Mercifully for P2719 the semantically relevant location is the declaration scope is the scope of the original function declaration and there's now a test that:
```cpp
struct A { operator new ...; operator delete ...; }
struct B { operator new ...; operator delete ...; }
struct C : A, B {
   using A::operator new;
   using B::operator delete;
};
```
is detected as invalid due to new and delete coming from different scopes.

https://github.com/llvm/llvm-project/pull/113510