Change objcImpl syntax to @objc @implementation

include/swift/AST/Attr.h

@@ -2422,6 +2422,9 @@ class DocumentationAttr: public DeclAttribute {
 
 class ObjCImplementationAttr final : public DeclAttribute {
 public:
+  /// Name of the category being implemented. This should only be used with
+  /// the early adopter \@\_objcImplementation syntax, but we support it there
+  /// for backwards compatibility.
   Identifier CategoryName;
 
   ObjCImplementationAttr(Identifier CategoryName, SourceLoc AtLoc,

include/swift/AST/Decl.h

@@ -1025,6 +1025,10 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl> {
   /// Returns the source range of the declaration including its attributes.
   SourceRange getSourceRangeIncludingAttrs() const;
 
+  /// Retrieve the location at which we should insert a new attribute or
+  /// modifier.
+  SourceLoc getAttributeInsertionLoc(bool forModifier) const;
+
   using ImportAccessLevel = std::optional<AttributedImport<ImportedModule>>;
 
   /// Returns the import that may restrict the access to this decl
@@ -1912,11 +1916,6 @@ class ExtensionDecl final : public GenericContext, public Decl,
   /// \endcode
   bool isWrittenWithConstraints() const;
 
-  /// Returns the name of the category specified by the \c \@_objcImplementation
-  /// attribute, or \c None if the name is invalid or
-  /// \c isObjCImplementation() is false.
-  std::optional<Identifier> getCategoryNameForObjCImplementation() const;
-
   /// If this extension represents an imported Objective-C category, returns the
   /// category's name. Otherwise returns the empty identifier.
   Identifier getObjCCategoryName() const;
@@ -3177,10 +3176,6 @@ class ValueDecl : public Decl {
   /// can't be "static" or are in a context where "static" doesn't make sense.
   bool isStatic() const;
 
-  /// Retrieve the location at which we should insert a new attribute or
-  /// modifier.
-  SourceLoc getAttributeInsertionLoc(bool forModifier) const;
-
   static bool classof(const Decl *D) {
     return D->getKind() >= DeclKind::First_ValueDecl &&
            D->getKind() <= DeclKind::Last_ValueDecl;
@@ -4204,6 +4199,12 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   /// Retrieve the set of extensions of this type.
   ExtensionRange getExtensions();
 
+  /// Retrieve the extension most recently added to this type. Helpful to
+  /// determine if an extension has been added.
+  ExtensionDecl *getLastExtension() const {
+    return LastExtension;
+  }
+
   /// Special-behaviour flags passed to lookupDirect()
   enum class LookupDirectFlags {
     /// Whether to include @_implements members.
@@ -5069,6 +5070,11 @@ class ClassDecl final : public NominalTypeDecl {
   llvm::TinyPtrVector<Decl *>
   getImportedObjCCategory(Identifier name) const;
 
+  /// Return a map of category names to extensions with that category name,
+  /// whether imported or otherwise. 
+  llvm::DenseMap<Identifier, llvm::TinyPtrVector<ExtensionDecl *>>
+  getObjCCategoryNameMap();
+
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) {
     return D->getKind() == DeclKind::Class;

include/swift/AST/DiagnosticsClangImporter.def

@@ -136,12 +136,10 @@ WARNING(api_pattern_attr_ignored, none,
         (StringRef, StringRef))
 
 ERROR(objc_implementation_two_impls, none,
-      "duplicate implementation of Objective-C %select{|category %0 on }0"
-      "%kind1",
-      (Identifier, Decl *))
-
+      "duplicate implementation of imported %kind0",
+      (Decl *))
 NOTE(previous_objc_implementation, none,
-     "previously implemented by extension here", ())
+     "previously implemented here", ())
 
 NOTE(macro_not_imported_unsupported_operator, none, "operator not supported in macro arithmetic", ())
 NOTE(macro_not_imported_unsupported_named_operator, none, "operator '%0' not supported in macro arithmetic", (StringRef))

include/swift/AST/DiagnosticsSema.def

@@ -763,6 +763,9 @@ ERROR(expr_selector_not_objc,none,
 NOTE(make_decl_objc,none,
      "add '@objc' to expose this %0 to Objective-C",
      (DescriptiveDeclKind))
+NOTE(make_decl_objc_for_implementation,none,
+     "add '@objc' to implement an Objective-C %0",
+     (DescriptiveDeclKind))
 
 // Selectors-as-string-literals.
 WARNING(selector_literal_invalid,none,
@@ -1760,10 +1763,6 @@ WARNING(objc_implementation_early_spelling_deprecated,none,
 ERROR(attr_objc_implementation_must_be_unconditional,none,
       "only unconditional extensions can implement an Objective-C '@interface'",
       ())
-ERROR(attr_objc_implementation_must_extend_class,none,
-      "cannot mark extension of %kind0 with '@_objcImplementation'; it is not "
-      "an imported Objective-C class",
-      (ValueDecl *))
 ERROR(attr_objc_implementation_must_be_imported,none,
       "'@_objcImplementation' cannot be used to extend %kind0 because it was "
       "defined by a Swift 'class' declaration, not an imported Objective-C "
@@ -1800,6 +1799,14 @@ ERROR(attr_objc_implementation_raise_minimum_deployment_target,none,
       "'@implementation' of an Objective-C class requires a minimum deployment "
       "target of at least %0 %1",
       (StringRef, llvm::VersionTuple))
+ERROR(attr_implementation_requires_language,none,
+      "'@implementation' used without specifying the language being "
+      "implemented",
+      ())
+ERROR(attr_implementation_category_goes_on_objc_attr,none,
+      "Objective-C category should be specified on '@objc', not "
+      "'@implementation'",
+      ())
 
 ERROR(member_of_objc_implementation_not_objc_or_final,none,
       "%kind0 does not match any %kindonly0 declared in the headers for %1; "
@@ -6295,7 +6302,7 @@ ERROR(objc_extension_not_class,none,
       "'@objc' can only be applied to an extension of a class", ())
 
 // If you change this, also change enum ObjCReason
-#define OBJC_ATTR_SELECT "select{marked @_cdecl|marked dynamic|marked @objc|marked @objcMembers|marked @IBOutlet|marked @IBAction|marked @IBSegueAction|marked @NSManaged|a member of an @objc protocol|implicitly @objc|an @objc override|an implementation of an @objc requirement|marked @IBInspectable|marked @GKInspectable|in an @objc extension of a class (without @nonobjc)|in an @_objcImplementation extension of a class (without final or @nonobjc)|marked @objc by an access note}"
+#define OBJC_ATTR_SELECT "select{marked @_cdecl|marked dynamic|marked @objc|marked @objcMembers|marked @IBOutlet|marked @IBAction|marked @IBSegueAction|marked @NSManaged|a member of an @objc protocol|implicitly @objc|an @objc override|an implementation of an @objc requirement|marked @IBInspectable|marked @GKInspectable|in an @objc extension of a class (without @nonobjc)|in an @objc @implementation extension of a class (without final or @nonobjc)|marked @objc by an access note}"
 
 ERROR(objc_invalid_on_var,none,
       "property cannot be %" OBJC_ATTR_SELECT "0 "
@@ -6450,6 +6457,12 @@ ERROR(objc_redecl_same,none,
       "previous declaration with the same Objective-C selector",
       (unsigned, DeclName, unsigned, DeclName, ObjCSelector))
 
+ERROR(objc_redecl_category_name,none,
+      "%select{|imported }0extension with Objective-C category name %2 "
+      "conflicts with previous %select{|imported }1extension with the same "
+      "category name",
+      (bool, bool, Identifier))
+
 ERROR(objc_override_other,none,
       OBJC_DIAG_SELECT " with Objective-C selector %4 conflicts with "
       OBJC_DIAG_SELECT_2 " from superclass %5 with the same Objective-C "

include/swift/AST/NameLookupRequests.h

@@ -970,6 +970,39 @@ class LookupIntrinsicRequest
   bool isCached() const { return true; }
 };
 
+using ObjCCategoryNameMap =
+  llvm::DenseMap<Identifier, llvm::TinyPtrVector<ExtensionDecl *>>;
+
+/// Generate a map of all known extensions of the given class that have an
+/// explicit category name. This request does not force clang categories that
+/// haven't been imported already, but it will generate a new map if new
+/// categories have been imported since the cached value was generated.
+///
+/// \seeAlso ClassDecl::getObjCCategoryNameMap()
+class ObjCCategoryNameMapRequest
+    : public SimpleRequest<ObjCCategoryNameMapRequest,
+                           ObjCCategoryNameMap(ClassDecl *, ExtensionDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+  // Convenience to automatically extract `lastExtension`.
+  ObjCCategoryNameMapRequest(ClassDecl *classDecl)
+    : ObjCCategoryNameMapRequest(classDecl, classDecl->getLastExtension())
+  {}
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  ObjCCategoryNameMap evaluate(Evaluator &evaluator,
+                               ClassDecl *classDecl,
+                               ExtensionDecl *lastExtension) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
 #define SWIFT_TYPEID_ZONE NameLookup
 #define SWIFT_TYPEID_HEADER "swift/AST/NameLookupTypeIDZone.def"
 #include "swift/Basic/DefineTypeIDZone.h"

include/swift/AST/NameLookupTypeIDZone.def

@@ -116,3 +116,5 @@ SWIFT_REQUEST(NameLookup, ImplementsAttrProtocolRequest,
               ProtocolDecl *(const ImplementsAttr *, DeclContext *), Cached, NoLocationInfo)
 SWIFT_REQUEST(NameLookup, LookupIntrinsicRequest,
               FuncDecl *(ModuleDecl *, Identifier), Cached, NoLocationInfo)
+SWIFT_REQUEST(NameLookup, ObjCCategoryNameMapRequest,
+              ObjCCategoryNameMap(ClassDecl *, ExtensionDecl *), Cached, NoLocationInfo)

include/swift/AST/SourceFile.h

@@ -359,6 +359,10 @@ class SourceFile final : public FileUnit {
   /// List of Objective-C member conflicts we have found during type checking.
   llvm::SetVector<ObjCMethodConflict> ObjCMethodConflicts;
 
+  /// Categories (extensions with explicit @objc names) declared in this
+  /// source file. They need to be checked for conflicts after type checking.
+  llvm::TinyPtrVector<ExtensionDecl *> ObjCCategories;
+
   /// List of attributes added by access notes, used to emit remarks for valid
   /// ones.
   llvm::DenseMap<ValueDecl *, std::vector<DeclAttribute *>>

include/swift/ClangImporter/ClangImporterRequests.h

@@ -256,7 +256,7 @@ struct ObjCInterfaceAndImplementation final {
   ObjCInterfaceAndImplementation()
       : interfaceDecls(), implementationDecl(nullptr) {}
 
-  operator bool() const {
+  bool empty() const {
     return interfaceDecls.empty();
   }
 

lib/AST/Decl.cpp

@@ -1891,16 +1891,6 @@ bool Decl::isObjCImplementation() const {
   return getAttrs().hasAttribute<ObjCImplementationAttr>(/*AllowInvalid=*/true);
 }
 
-std::optional<Identifier>
-ExtensionDecl::getCategoryNameForObjCImplementation() const {
-  auto attr = getAttrs()
-                  .getAttribute<ObjCImplementationAttr>(/*AllowInvalid=*/true);
-  if (!attr || attr->isCategoryNameInvalid())
-    return std::nullopt;
-
-  return attr->CategoryName;
-}
-
 PatternBindingDecl::PatternBindingDecl(SourceLoc StaticLoc,
                                        StaticSpellingKind StaticSpelling,
                                        SourceLoc VarLoc,
@@ -3717,6 +3707,20 @@ void ValueDecl::setIsObjC(bool value) {
   LazySemanticInfo.isObjC = value;
 }
 
+Identifier ExtensionDecl::getObjCCategoryName() const {
+  // If there's an @objc attribute, it's authoritative. (ClangImporter
+  // attaches one automatically.)
+  if (auto objcAttr = getAttrs().getAttribute<ObjCAttr>(/*AllowInvalid*/true)) {
+    if (objcAttr->hasName() && objcAttr->getName()->getNumArgs() == 0)
+      return objcAttr->getName()->getSimpleName();
+
+    return Identifier();
+  }
+
+  // Not a category, evidently.
+  return Identifier();
+}
+
 bool ValueDecl::isSemanticallyFinal() const {
   // Actor types are semantically final.
   if (auto classDecl = dyn_cast<ClassDecl>(this)) {
@@ -4011,25 +4015,86 @@ bool ValueDecl::canInferObjCFromRequirement(ValueDecl *requirement) {
   return false;
 }
 
-SourceLoc ValueDecl::getAttributeInsertionLoc(bool forModifier) const {
-  if (isImplicit())
+SourceLoc Decl::getAttributeInsertionLoc(bool forModifier) const {
+  // Some decls have a parent/child split where the introducer keyword is on the
+  // parent, but the attributes are on the children. If this is a child in such
+  // a pair, `introDecl` will be changed to point to the parent. (The parent
+  // decl should delegate to one of its children.)
+  const Decl *introDecl = this;
+
+  switch (getKind()) {
+  case DeclKind::Module:
+  case DeclKind::TopLevelCode:
+  case DeclKind::IfConfig:
+  case DeclKind::PoundDiagnostic:
+  case DeclKind::Missing:
+  case DeclKind::MissingMember:
+  case DeclKind::MacroExpansion:
+  case DeclKind::BuiltinTuple:
+    // These don't take attributes.
     return SourceLoc();
 
-  if (auto var = dyn_cast<VarDecl>(this)) {
-    // [attrs] var ...
-    // The attributes are part of the VarDecl, but the 'var' is part of the PBD.
-    SourceLoc resultLoc = var->getAttrs().getStartLoc(forModifier);
-    if (resultLoc.isValid()) {
-      return resultLoc;
-    } else if (auto pbd = var->getParentPatternBinding()) {
-      return pbd->getStartLoc();
-    } else {
-      return var->getStartLoc();
+  case DeclKind::EnumCase:
+    // An ECD's attributes are attached to its elements.
+    if (auto elem = cast<EnumCaseDecl>(this)->getFirstElement())
+      return elem->getAttributeInsertionLoc(forModifier);
+    break;
+
+  case DeclKind::EnumElement:
+    // An EED's introducer keyword is on its parent case.
+    if (auto parent = cast<EnumElementDecl>(this)->getParentCase())
+      introDecl = parent;
+    break;
+
+  case DeclKind::PatternBinding: {
+    // A PBD's attributes are attached to the vars in its patterns.
+    auto pbd = cast<PatternBindingDecl>(this);
+
+    for (unsigned i = 0; i < pbd->getNumPatternEntries(); i++) {
+      if (auto var = pbd->getAnchoringVarDecl(i)) {
+        return var->getAttributeInsertionLoc(forModifier);
+      }
     }
+
+    break;
   }
 
+  case DeclKind::Var:
+  case DeclKind::Param:
+    // A VarDecl's introducer keyword, if it has one, is on its pattern binding.
+    if (auto pbd = cast<VarDecl>(this)->getParentPatternBinding())
+      introDecl = pbd;
+    break;
+
+  case DeclKind::Enum:
+  case DeclKind::Struct:
+  case DeclKind::Class:
+  case DeclKind::Protocol:
+  case DeclKind::OpaqueType:
+  case DeclKind::TypeAlias:
+  case DeclKind::GenericTypeParam:
+  case DeclKind::AssociatedType:
+  case DeclKind::Subscript:
+  case DeclKind::Constructor:
+  case DeclKind::Destructor:
+  case DeclKind::Func:
+  case DeclKind::Accessor:
+  case DeclKind::Macro:
+  case DeclKind::Extension:
+  case DeclKind::Import:
+  case DeclKind::PrecedenceGroup:
+  case DeclKind::InfixOperator:
+  case DeclKind::PrefixOperator:
+  case DeclKind::PostfixOperator:
+    // Both the introducer keyword and the attributes are on `this`.
+    break;
+  }
+
+  if (isImplicit())
+    return SourceLoc();
+
   SourceLoc resultLoc = getAttrs().getStartLoc(forModifier);
-  return resultLoc.isValid() ? resultLoc : getStartLoc();
+  return resultLoc.isValid() ? resultLoc : introDecl->getStartLoc();
 }
 
 /// Returns true if \p VD needs to be treated as publicly-accessible
@@ -11278,7 +11343,7 @@ void swift::simple_display(llvm::raw_ostream &out, const Decl *decl) {
   }
 
   if (auto value = dyn_cast<ValueDecl>(decl)) {
-    simple_display(out, value);
+    return simple_display(out, value);
   } else if (auto ext = dyn_cast<ExtensionDecl>(decl)) {
     out << "extension of ";
     if (auto typeRepr = ext->getExtendedTypeRepr())
@@ -11288,13 +11353,13 @@ void swift::simple_display(llvm::raw_ostream &out, const Decl *decl) {
   } else if (auto med = dyn_cast<MacroExpansionDecl>(decl)) {
     out << '#' << med->getMacroName() << " in ";
     printContext(out, med->getDeclContext());
-    if (med->getLoc().isValid()) {
-      out << '@';
-      med->getLoc().print(out, med->getASTContext().SourceMgr);
-    }
   } else {
     out << "(unknown decl)";
   }
+  if (decl->getLoc().isValid()) {
+    out << '@';
+    decl->getLoc().print(out, decl->getASTContext().SourceMgr);
+  }
 }
 
 void swift::simple_display(llvm::raw_ostream &out,