[cxx-interop] Allow old spelling of AppKit constants

AppKit defines certain constants in Objective-C, and then renames them into different constants in Swift, e.g. `NSUpArrowFunctionKey` is renamed into `NSEvent.SpecialKey.upArrow.rawValue`.

In addition to that, AppKit also re-defines these constants in pure-Swift, which isn't the intended mechanism for renaming such constants.

Prior to llvm/llvm-project#145947, Clang was silently dropping the `SwiftName` API Notes attributes on these constants due to a bug in the name validation mechanism. Clients of AppKit relied on that behavior and continued to use the old spelling in Swift. To preserve source compatibility and avoid a deprecation error, let's continue dropping the `SwiftName` attribute on select constants from AppKit.

rdar://157485334

Author: egorzhdan

lib/ClangImporter/ImportDecl.cpp

@@ -8680,6 +8680,26 @@ bool importer::isSpecialUIKitStructZeroProperty(const clang::NamedDecl *decl) {
   return ident->isStr("UIEdgeInsetsZero") || ident->isStr("UIOffsetZero");
 }
 
+bool importer::isSpecialAppKitFunctionKeyProperty(
+    const clang::NamedDecl *decl) {
+  auto constant = dyn_cast<clang::EnumConstantDecl>(decl);
+  if (!constant)
+    return false;
+
+  auto module = constant->getOwningModule();
+  if (!module || module->getTopLevelModuleName() != "AppKit")
+    return false;
+
+  clang::DeclarationName name = constant->getDeclName();
+  const clang::IdentifierInfo *ident = name.getAsIdentifierInfo();
+  if (!ident)
+    return false;
+  auto rawName = ident->getName();
+
+  return rawName.starts_with("NS") &&
+         (rawName.ends_with("FunctionKey") || rawName.ends_with("Character"));
+}
+
 bool importer::hasSameUnderlyingType(const clang::Type *a,
                                      const clang::TemplateTypeParmDecl *b) {
   while (a->isPointerType() || a->isReferenceType())

lib/ClangImporter/ImportName.cpp

@@ -646,9 +646,12 @@ findSwiftNameAttr(const clang::Decl *decl, ImportNameVersion version) {
   if (version > ImportNameVersion::swift2()) {
     // FIXME: Until Apple gets a chance to update UIKit's API notes, always use
     // the new name for certain properties.
-    if (auto *namedDecl = dyn_cast<clang::NamedDecl>(decl))
+    if (auto *namedDecl = dyn_cast<clang::NamedDecl>(decl)) {
       if (importer::isSpecialUIKitStructZeroProperty(namedDecl))
         version = ImportNameVersion::swift4_2();
+      if (importer::isSpecialAppKitFunctionKeyProperty(namedDecl))
+        return std::nullopt;
+    }
 
     // Dig out the attribute that specifies the Swift name.
     std::optional<AnySwiftNameAttr> activeAttr;

lib/ClangImporter/ImporterImpl.h

@@ -1976,6 +1976,12 @@ bool shouldSuppressDeclImport(const clang::Decl *decl);
 /// but are now renamed using the swift_name attribute.
 bool isSpecialUIKitStructZeroProperty(const clang::NamedDecl *decl);
 
+/// Identifies certain AppKit constants that have overlay equivalents but are
+/// also annotated with SwiftName API Notes attributes at the same time. Older
+/// Clang versions were silently dropping the API Notes attribute on those
+/// constants.
+bool isSpecialAppKitFunctionKeyProperty(const clang::NamedDecl *decl);
+
 /// \returns true if \p a has the same underlying type as \p b after removing
 /// any pointer/reference specifiers. Note that this does not currently look through
 /// nested types other than pointers or references.

test/Interop/Cxx/objc-correctness/appkit-uikit.swift

@@ -11,6 +11,9 @@ import AppKit
 var _: AttributeScopes.AppKitAttributes.UnderlineStyleAttribute! = nil
 
 var _ = NSEvent.SpecialKey.upArrow.rawValue
+var _ = NSEvent.SpecialKey.enter.rawValue
+var _ = NSUpArrowFunctionKey
+var _ = NSEnterCharacter
 
 #elseif canImport(UIKit)
 import UIKit