Make all internal-or-more @_objcImpl members impls

Author: beccadax

docs/ReferenceGuides/UnderscoredAttributes.md

@@ -698,7 +698,7 @@ you replace a native Objective-C `@implementation Foo (Bar)` with a Swift
 
 You create a class with this feature very differently from normal ObjC interop:
 
-1. Hand-write headers that declare the classes' Objective-C interface, just as
+1. Hand-write headers that declare the class's Objective-C interface, just as
    you would for a native Objective-C class. Since you're handwriting these
    headers, you can write them just as you would for an Objective-C class:
    splitting them across multiple files, grouping related declarations together,
@@ -720,28 +720,35 @@ You create a class with this feature very differently from normal ObjC interop:
    * To implement a category in Swift, use
      `@_objcImplementation(CategoryName) extension ClassName`.
 
-   * We should think about Objective-C generics.
-
-4. Every member of an `@_objcImplementation` extension should be either `@objc`
-   or `final`. The `final` members can be made `public` if you want to expose
-   them to Swift clients. The `@objc` members are implicitly `dynamic`.
+The members of an `@_objcImplementation` extension should fall into one of
+three categories:
 
-   * Eventually, we'd like to allow members which are not explicitly marked
-     `@objc`. The compiler will check that they match something declared in the
-     header, and if they do, it will automatically apply appropriate attributes.
-     If not, it will reject them. Members with an explicit `@objc` will not be
-     checked, so you can define helpers that are callable by selector but not in
-     any header.
+* **Swift-only members** include any member marked `final`. These are not
+  `@objc` or `dynamic` and are only callable from Swift. Use these for
+  Swift-only APIs, random helper methods, etc. 
+    
+* **ObjC helper members** include any non-`final` member marked `fileprivate`
+  or `private`. These are implicitly `@objc dynamic`. Use these for action
+  methods, selector-based callbacks, and other situations where you need a
+  helper method to be accessible from an Objective-C message.
 
-   * Eventually, we want the main `@_objcImplementation` extension to be able to
-     declare stored properties that aren't in the interface. We also want
-     `final` stored properties to be allowed to be resilent Swift types, but
-     it's not clear how to achieve that without boxing them in `__SwiftValue`
-     (which we might do as a stopgap).
+* **Member implementations** include any other non-`final` member. These are
+  implicitly `@objc dynamic` and must match a member declared in the
+  Objective-C header. Use these to implement the APIs declared in your
+  headers. Swift will emit an error if these don't match your headers.
+
+Notes:
+
+* We don't currently plan to support ObjC generics.
+
+* Eventually, we want the main `@_objcImplementation` extension to be able to
+  declare stored properties that aren't in the interface. We also want
+  `final` stored properties to be allowed to be resilent Swift types, but
+  it's not clear how to achieve that without boxing them in `__SwiftValue`
+  (which we might do as a stopgap).
 
-   * We should think about ObjC `direct` members.
-      
-   * Access control design for ObjC methods TBD.
+* We should think about ObjC "direct" members, but that would probably
+  require a way to spell this in Swift. 
 
 ## `@_objc_non_lazy_realization`
 

lib/AST/Decl.cpp

@@ -3742,6 +3742,21 @@ static bool checkAccessUsingAccessScopes(const DeclContext *useDC,
          VD->getDeclContext()->getParentModule() == useDC->getParentModule();
 }
 
+/// Checks if \p VD is an ObjC member implementation:
+///
+/// \li It's in an \c \@_objcImplementation extension
+/// \li It's \c \@objc
+/// \li Its access level is not \c private or \c fileprivate
+static bool
+isObjCMemberImplementation(const ValueDecl *VD,
+                           llvm::function_ref<AccessLevel()> getAccessLevel) {
+  if (auto ED = dyn_cast<ExtensionDecl>(VD->getDeclContext()))
+    if (ED->isObjCImplementation())
+      return VD->isObjC() && getAccessLevel() >= AccessLevel::Internal;
+
+  return false;
+}
+
 /// Checks if \p VD may be used from \p useDC, taking \@testable and \@_spi
 /// imports into account.
 ///
@@ -3756,6 +3771,12 @@ static bool checkAccess(const DeclContext *useDC, const ValueDecl *VD,
                         bool forConformance,
                         bool includeInlineable,
                         llvm::function_ref<AccessLevel()> getAccessLevel) {
+  // If this is an @_objcImplementation member implementation, unconditionally
+  // forbid access. Name lookups will instead find and use the matching
+  // interface decl.
+  if (isObjCMemberImplementation(VD, getAccessLevel))
+    return false;
+
   if (VD->getASTContext().isAccessControlDisabled())
     return true;
 
@@ -9552,4 +9573,4 @@ bool ActorIsolation::isDistributedActor() const {
 BuiltinTupleDecl::BuiltinTupleDecl(Identifier Name,
                                    DeclContext *Parent)
   : NominalTypeDecl(DeclKind::BuiltinTuple, Parent, Name, SourceLoc(),
-                    ArrayRef<InheritedEntry>(), nullptr) {}
+                    ArrayRef<InheritedEntry>(), nullptr) {}

test/decl/ext/objc_implementation.swift

@@ -14,7 +14,7 @@
     // FIXME: Should complain about the wrong category
   }
 
-  @objc func methodNot(fromHeader1: CInt) {
+  @objc fileprivate func methodNot(fromHeader1: CInt) {
     // OK, declares a new @objc dynamic method.
   }
 
@@ -38,7 +38,7 @@
     // OK, provides an implementation for the header's method.
   }
 
-  @objc func categoryMethodNot(fromHeader1: CInt) {
+  @objc fileprivate func categoryMethodNot(fromHeader1: CInt) {
     // OK, declares a new @objc dynamic method.
   }