[C++20] Deleting destructors can be noexcept

Given a `noexcept` operator with an operand that calls `delete`, Clang
was not considering whether the selected `operator delete` function was
a destroying delete or not when inspecting whether the deleted object
type has a throwing destructor. Thus, the operator would return `false`
for a type with a potentially throwing destructor even though that
destructor would not be called due to the destroying delete. Clang now
takes the kind of delete operator into consideration.

Fixes #118660

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -654,6 +654,9 @@ Bug Fixes in This Version
 - Fixed a crash when GNU statement expression contains invalid statement (#GH113468).
 - Fixed a failed assertion when using ``__attribute__((noderef))`` on an
   ``_Atomic``-qualified type (#GH116124).
+- No longer return ``false`` for ``noexcept`` expressions involving a
+  ``delete`` which resolves to a destroying delete but the type of the object
+  being deleted as a potentially throwing destructor (#GH118660).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaExceptionSpec.cpp

@@ -1205,11 +1205,12 @@ CanThrowResult Sema::canThrow(const Stmt *S) {
     if (DTy.isNull() || DTy->isDependentType()) {
       CT = CT_Dependent;
     } else {
-      CT = canCalleeThrow(*this, DE, DE->getOperatorDelete());
+      const FunctionDecl *OperatorDelete = DE->getOperatorDelete();
+      CT = canCalleeThrow(*this, DE, OperatorDelete);
       if (const RecordType *RT = DTy->getAs<RecordType>()) {
         const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
         const CXXDestructorDecl *DD = RD->getDestructor();
-        if (DD)
+        if (DD && !OperatorDelete->isDestroyingOperatorDelete())
           CT = mergeCanThrow(CT, canCalleeThrow(*this, DE, DD));
       }
       if (CT == CT_Can)

clang/test/SemaCXX/noexcept-destroying-delete.cpp

@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -fcxx-exceptions -Wno-unevaluated-expression -std=c++20 %s
+// expected-no-diagnostics
+
+namespace std {
+  struct destroying_delete_t {
+    explicit destroying_delete_t() = default;
+  };
+
+  inline constexpr destroying_delete_t destroying_delete{};
+}
+
+struct Explicit {
+    ~Explicit() noexcept(false) {}
+
+    void operator delete(Explicit*, std::destroying_delete_t) noexcept {
+    }
+};
+
+Explicit *qn = nullptr;
+// This assertion used to fail, see GH118660
+static_assert(noexcept(delete(qn)));