[Clang] [Sema] Handle placeholders in '.*' expressions

clang/docs/ReleaseNotes.rst

@@ -288,6 +288,8 @@ Bug Fixes to C++ Support
   templates when determining the primary template of an explicit specialization.
 - Fixed a crash in Microsoft compatibility mode where unqualified dependent base class
   lookup searches the bases of an incomplete class.
+- Fix a crash when an unresolved overload set is encountered on the RHS of a ``.*`` operator.
+  (`#53815 <https://github.com/llvm/llvm-project/issues/53815>`_)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaOverload.cpp

@@ -14571,6 +14571,23 @@ ExprResult Sema::CreateOverloadedBinOp(SourceLocation OpLoc,
                                        CurFPFeatureOverrides());
   }
 
+  // If this is the .* operator, which is not overloadable, just
+  // create a built-in binary operator.
+  if (Opc == BO_PtrMemD) {
+    auto CheckPlaceholder = [&](Expr *&Arg) {
+      ExprResult Res = CheckPlaceholderExpr(Arg);
+      if (Res.isUsable())
+        Arg = Res.get();
+      return !Res.isUsable();
+    };
+
+    // CreateBuiltinBinOp() doesn't like it if we tell it to create a '.*'
+    // expression that contains placeholders (in either the LHS or RHS).
+    if (CheckPlaceholder(Args[0]) || CheckPlaceholder(Args[1]))
+      return ExprError();
+    return CreateBuiltinBinOp(OpLoc, Opc, Args[0], Args[1]);
+  }
+
   // Always do placeholder-like conversions on the RHS.
   if (checkPlaceholderForOverload(*this, Args[1]))
     return ExprError();
@@ -14590,11 +14607,6 @@ ExprResult Sema::CreateOverloadedBinOp(SourceLocation OpLoc,
   if (Opc == BO_Assign && !Args[0]->getType()->isOverloadableType())
     return CreateBuiltinBinOp(OpLoc, Opc, Args[0], Args[1]);
 
-  // If this is the .* operator, which is not overloadable, just
-  // create a built-in binary operator.
-  if (Opc == BO_PtrMemD)
-    return CreateBuiltinBinOp(OpLoc, Opc, Args[0], Args[1]);
-
   // Build the overload set.
   OverloadCandidateSet CandidateSet(OpLoc, OverloadCandidateSet::CSK_Operator,
                                     OverloadCandidateSet::OperatorRewriteInfo(

clang/test/SemaCXX/gh53815.cpp

@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
+// expected-no-diagnostics
+
+// Check that we don't crash due to forgetting to check for placeholders
+// in the RHS of '.*'.
+
+template <typename Fn>
+static bool has_explicitly_named_overload() {
+  return requires { Fn().*&Fn::operator(); };
+}
+
+int main() {
+  has_explicitly_named_overload<decltype([](auto){})>();
+}
+
+template <typename Fn>
+constexpr bool has_explicitly_named_overload_2() {
+  return requires { Fn().*&Fn::operator(); };
+}
+
+static_assert(!has_explicitly_named_overload_2<decltype([](auto){})>());