[cxx-interop] Allow instantiated operator methods to serve as protocol conformance witnesses

lib/ClangImporter/ClangImporter.cpp

@@ -4021,6 +4021,30 @@ SwiftLookupTable *ClangImporter::Implementation::findLookupTable(
   return known->second.get();
 }
 
+SwiftLookupTable *
+ClangImporter::Implementation::findLookupTable(const clang::Decl *decl) {
+  // Contents of a C++ namespace are added to the __ObjC module.
+  bool isWithinNamespace = false;
+  auto declContext = decl->getDeclContext();
+  while (!declContext->isTranslationUnit()) {
+    if (declContext->isNamespace()) {
+      isWithinNamespace = true;
+      break;
+    }
+    declContext = declContext->getParent();
+  }
+
+  clang::Module *owningModule = nullptr;
+  if (!isWithinNamespace) {
+    // Members of class template specializations don't have an owning module.
+    if (auto spec = dyn_cast<clang::ClassTemplateSpecializationDecl>(decl))
+      owningModule = spec->getSpecializedTemplate()->getOwningModule();
+    else
+      owningModule = decl->getOwningModule();
+  }
+  return findLookupTable(owningModule);
+}
+
 bool ClangImporter::Implementation::forEachLookupTable(
        llvm::function_ref<bool(SwiftLookupTable &table)> fn) {
   // Visit the bridging header's lookup table.

lib/ClangImporter/ImportDecl.cpp

@@ -2118,15 +2118,7 @@ namespace {
           if (friendDecl->getFriendDecl()) {
             m = friendDecl->getFriendDecl();
 
-            // Find the owning module of the class template. Members of class
-            // template specializations don't have an owning module.
-            clang::Module *owningModule = nullptr;
-            if (auto spec = dyn_cast<clang::ClassTemplateSpecializationDecl>(decl))
-              owningModule = spec->getSpecializedTemplate()->getOwningModule();
-            else
-              owningModule = decl->getOwningModule();
-
-            auto lookupTable = Impl.findLookupTable(owningModule);
+            auto lookupTable = Impl.findLookupTable(decl);
             addEntryToLookupTable(*lookupTable, friendDecl->getFriendDecl(),
                                   Impl.getNameImporter());
           }
@@ -2243,6 +2235,9 @@ namespace {
 
               // Make sure the synthesized decl can be found by lookupDirect.
               result->addMemberToLookupTable(opFuncDecl);
+
+              addEntryToLookupTable(*Impl.findLookupTable(decl), cxxMethod,
+                                    Impl.getNameImporter());
             }
           }
           methods.push_back(MD);

lib/ClangImporter/ImporterImpl.h

@@ -1644,6 +1644,9 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
   /// about the directly-parsed headers.
   SwiftLookupTable *findLookupTable(const clang::Module *clangModule);
 
+  /// Find the lookup table that should contain the given Clang declaration.
+  SwiftLookupTable *findLookupTable(const clang::Decl *decl);
+
   /// Visit each of the lookup tables in some deterministic order.
   ///
   /// \param fn Invoke the given visitor for each table. If the

test/Interop/Cxx/class/Inputs/protocol-conformance.h

@@ -55,4 +55,16 @@ struct HasOperatorEqualEqual {
   }
 };
 
+template <typename T>
+struct HasOperatorPlusEqual {
+  T value;
+
+  HasOperatorPlusEqual &operator+=(int x) {
+    value += x;
+    return *this;
+  }
+};
+
+using HasOperatorPlusEqualInt = HasOperatorPlusEqual<int>;
+
 #endif // TEST_INTEROP_CXX_CLASS_INPUTS_PROTOCOL_CONFORMANCE_H

test/Interop/Cxx/class/protocol-conformance-typechecker.swift

@@ -35,3 +35,10 @@ protocol Invertable {
 extension HasOperatorExclaim: Invertable {}
 
 extension HasOperatorEqualEqual: Equatable {}
+
+
+protocol HasOperatorPlusEqualProtocol {
+  static func +=(lhs: inout Self, x: Int32)
+}
+
+extension HasOperatorPlusEqualInt : HasOperatorPlusEqualProtocol {}