Remove support for Swift 3 @objc inference.

Obsolete the `-enable-swift3-objc-inference` option and related options by
removing support for inferring `@objc` attributes using Swift 3 rules.
Automated migration from Swift 3 has not been supported by the compiler for
many years.

Author: tshortli

include/swift/AST/Attr.h

@@ -118,17 +118,13 @@ class DeclAttribute : public AttributeBase {
       AddedByAccessNote : 1
     );
 
-    SWIFT_INLINE_BITFIELD(ObjCAttr, DeclAttribute, 1+1+1,
+    SWIFT_INLINE_BITFIELD(ObjCAttr, DeclAttribute, 1+1,
       /// Whether this attribute has location information that trails the main
       /// record, which contains the locations of the parentheses and any names.
       HasTrailingLocationInfo : 1,
 
       /// Whether the name is implicit, produced as the result of caching.
-      ImplicitName : 1,
-
-      /// Whether the @objc was inferred using Swift 3's deprecated inference
-      /// rules.
-      Swift3Inferred : 1
+      ImplicitName : 1
     );
 
     SWIFT_INLINE_BITFIELD(DynamicReplacementAttr, DeclAttribute, 1,
@@ -823,7 +819,6 @@ class ObjCAttr final : public DeclAttribute,
         NameData(nullptr) {
     Bits.ObjCAttr.HasTrailingLocationInfo = false;
     Bits.ObjCAttr.ImplicitName = implicitName;
-    Bits.ObjCAttr.Swift3Inferred = false;
 
     if (name) {
       NameData = name->getOpaqueValue();
@@ -933,18 +928,6 @@ class ObjCAttr final : public DeclAttribute,
     Bits.ObjCAttr.ImplicitName = implicit;
   }
 
-  /// Determine whether this attribute was inferred based on Swift 3's
-  /// deprecated @objc inference rules.
-  bool isSwift3Inferred() const {
-    return Bits.ObjCAttr.Swift3Inferred;
-  }
-
-  /// Set whether this attribute was inferred based on Swift 3's deprecated
-  /// @objc inference rules.
-  void setSwift3Inferred(bool inferred = true) {
-    Bits.ObjCAttr.Swift3Inferred = inferred;
-  }
-
   /// Retrieve the source locations for the names in a non-implicit
   /// nullary or selector attribute.
   ArrayRef<SourceLoc> getNameLocs() const;

include/swift/AST/DiagnosticsSema.def

@@ -644,10 +644,6 @@ ERROR(expression_unused_keypath_result,NoUsage,
 ERROR(expr_keypath_non_objc_property,none,
       "argument of '#keyPath' refers to non-'@objc' property %0",
       (Identifier))
-WARNING(expr_keypath_swift3_objc_inference,Deprecation,
-        "argument of '#keyPath' refers to property %0 in %1 that depends on "
-        "'@objc' inference deprecated in Swift 4",
-        (Identifier, Identifier))
 ERROR(expr_keypath_type_of_property,none,
       "cannot refer to type member %0 within instance of type %1",
       (DeclNameRef, Type))
@@ -755,10 +751,6 @@ ERROR(expr_selector_not_objc,none,
 NOTE(make_decl_objc,none,
      "add '@objc' to expose this %0 to Objective-C",
      (DescriptiveDeclKind))
-WARNING(expr_selector_swift3_objc_inference,Deprecation,
-        "argument of '#selector' refers to %kind0 in %1 that depends on "
-        "'@objc' inference deprecated in Swift 4",
-        (const ValueDecl *, const ValueDecl *))
 
 // Selectors-as-string-literals.
 WARNING(selector_literal_invalid,none,
@@ -2132,11 +2124,6 @@ ERROR(missing_unimplemented_init_runtime,none,
 ERROR(missing_undefined_runtime,none,
       "standard library error: missing _undefined", ())
 
-WARNING(expr_dynamic_lookup_swift3_objc_inference,Deprecation,
-        "reference to %kind0 of %1 depends on '@objc' inference "
-        "deprecated in Swift 4",
-        (const ValueDecl *, Identifier))
-
 ERROR(inherited_default_value_not_in_designated_constructor,none,
       "default value inheritance via 'super' is only valid on the parameters of "
       "designated initializers", ())
@@ -3450,11 +3437,6 @@ WARNING(implicitly_final_cannot_be_open_swift4,none,
         "static declarations}0 are implicitly 'final'; use 'public' instead of "
         "'open'", (unsigned))
 
-WARNING(override_swift3_objc_inference,Deprecation,
-        "override of %kind0 from extension of %1 depends on deprecated "
-        "inference of '@objc'",
-        (const ValueDecl *, Identifier))
-
 // Inheritance
 ERROR(duplicate_inheritance,none,
   "duplicate inheritance from %0", (Type))
@@ -6126,18 +6108,6 @@ ERROR(objc_operator, none,
       "operator methods cannot be declared @objc", ())
 ERROR(objc_operator_proto, none,
       "@objc protocols must not have operator requirements", ())
-WARNING(objc_inference_swift3_dynamic,Deprecation,
-        "inference of '@objc' for 'dynamic' members is deprecated", ())
-WARNING(objc_inference_swift3_objc_derived,Deprecation,
-        "inference of '@objc' for members of Objective-C-derived classes is "
-        "deprecated", ())
-
-NOTE(objc_inference_swift3_addobjc,none,
-     "add '@objc' to continue exposing an Objective-C entry point (Swift 3 "
-     "behavior)", ())
-NOTE(objc_inference_swift3_addnonobjc,none,
-     "add '@nonobjc' to suppress the Objective-C entry point (Swift 4 "
-     "behavior)", ())
 
 ERROR(objc_for_generic_class,none,
       "generic subclasses of '@objc' classes cannot have an explicit '@objc' "
@@ -6153,10 +6123,6 @@ ERROR(objc_setter_for_nonobjc_property,none,
       "'@objc' setter for non-'@objc' property", ())
 ERROR(objc_setter_for_nonobjc_subscript,none,
       "'@objc' setter for non-'@objc' subscript", ())
-WARNING(accessor_swift3_objc_inference,Deprecation,
-        "%kind0 with '@objc' %select{getter|setter}1 depends on "
-        "deprecated inference of '@objc'",
-        (const AbstractStorageDecl *, bool))
 
 ERROR(objc_enum_generic,none,
       "'@objc' enum cannot be generic", ())
@@ -6187,10 +6153,6 @@ ERROR(objc_extension_not_class,none,
 // 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}"
 
-WARNING(attribute_meaningless_when_nonobjc,none,
-        "'@%0' attribute is meaningless on a property that cannot be "
-        "represented in Objective-C", (StringRef))
-
 ERROR(objc_invalid_on_var,none,
       "property cannot be %" OBJC_ATTR_SELECT "0 "
       "because its type cannot be represented in Objective-C", (unsigned))
@@ -6249,10 +6211,6 @@ NOTE(objc_overriding_objc_decl,none,
 NOTE(objc_witness_objc_requirement,none,
      "satisfying requirement for %kind0 in protocol %1",
      (const ValueDecl *, const ProtocolDecl *))
-WARNING(witness_swift3_objc_inference,Deprecation,
-        "use of %kind0 to satisfy a requirement of protocol %1 depends on "
-        "'@objc' inference deprecated in Swift 4",
-        (const ValueDecl *, Type))
 
 ERROR(no_opaque_return_type_of,none,
       "unable to resolve type for _opaqueReturnTypeOf attribute", ())

include/swift/Basic/LangOptions.h

@@ -51,19 +51,6 @@ namespace swift {
 #include "swift/AST/PlatformConditionKinds.def"
   };
 
-  /// Describes which Swift 3 Objective-C inference warnings should be
-  /// emitted.
-  enum class Swift3ObjCInferenceWarnings {
-    /// No warnings; this is the default.
-    None,
-    /// "Minimal" warnings driven by uses of declarations that make use of
-    /// the Objective-C entry point directly.
-    Minimal,
-    /// "Complete" warnings that add "@objc" for every entry point that
-    /// Swift 3 would have inferred as "@objc" but Swift 4 will not.
-    Complete,
-  };
-
   /// Describes how strict concurrency checking should be.
   enum class StrictConcurrency {
     /// Enforce Sendable constraints where it has been explicitly adopted and
@@ -439,21 +426,12 @@ namespace swift {
     /// will be used in editor. This usually leads to more aggressive fixit.
     bool DiagnosticsEditorMode = false;
 
-    /// Whether to enable Swift 3 @objc inference, e.g., for members of
-    /// Objective-C-derived classes and 'dynamic' members.
-    bool EnableSwift3ObjCInference = false;
-
     /// Access or distribution level of the whole module being parsed.
     LibraryLevel LibraryLevel = LibraryLevel::Other;
 
     /// The name of the package this module belongs to.
     std::string PackageName;
 
-    /// Warn about cases where Swift 3 would infer @objc but later versions
-    /// of Swift do not.
-    Swift3ObjCInferenceWarnings WarnSwift3ObjCInference =
-      Swift3ObjCInferenceWarnings::None;
-
     /// Diagnose implicit 'override'.
     bool WarnImplicitOverrides = false;
 

include/swift/Migrator/FixitFilter.h

@@ -80,13 +80,6 @@ struct FixitFilter {
     if (Info.ID == diag::could_not_find_enum_case.ID)
       return false;
 
-    // Sema suggests adding both `@objc` and `@nonobjc` as alternative fix-its
-    // for inferring Swift-3 style @objc visibility, but we don't want the
-    // migrator to suggest `@nonobjc`.
-    if (Info.ID == diag::objc_inference_swift3_addnonobjc.ID) {
-      return false;
-    }
-
     // With SE-110, the migrator may get a recommendation to add a Void
     // placeholder in the call to f in:
     // func foo(f: (Void) -> ()) {
@@ -132,10 +125,6 @@ struct FixitFilter {
         Info.ID == diag::deprecated_any_composition.ID ||
         Info.ID == diag::deprecated_operator_body.ID ||
         Info.ID == diag::unbound_generic_parameter_explicit_fix.ID ||
-        Info.ID == diag::objc_inference_swift3_addobjc.ID ||
-        Info.ID == diag::objc_inference_swift3_dynamic.ID ||
-        Info.ID == diag::override_swift3_objc_inference.ID ||
-        Info.ID == diag::objc_inference_swift3_objc_derived.ID ||
         Info.ID == diag::missing_several_cases.ID ||
         Info.ID == diag::missing_particular_case.ID ||
         Info.ID == diag::missing_unknown_case.ID ||

include/swift/Option/FrontendOptions.td

@@ -677,12 +677,12 @@ def report_errors_to_debugger : Flag<["-"], "report-errors-to-debugger">,
 
 def enable_swift3_objc_inference : Flag<["-"], "enable-swift3-objc-inference">,
   Flags<[FrontendOption, HelpHidden]>,
-HelpText<"Deprecated">;
+  HelpText<"Deprecated, has no effect">;
 
 def disable_swift3_objc_inference :
   Flag<["-"], "disable-swift3-objc-inference">,
   Flags<[FrontendOption, HelpHidden]>,
-  HelpText<"Deprecated">;
+  HelpText<"Deprecated, has no effect">;
 
 def enable_implicit_dynamic : Flag<["-"], "enable-implicit-dynamic">,
   Flags<[FrontendOption, NoInteractiveOption, HelpHidden]>,

include/swift/Option/Options.td

@@ -788,12 +788,12 @@ def continue_building_after_errors : Flag<["-"], "continue-building-after-errors
 def warn_swift3_objc_inference_complete :
   Flag<["-"], "warn-swift3-objc-inference-complete">,
   Flags<[FrontendOption, HelpHidden, DoesNotAffectIncrementalBuild]>,
-  HelpText<"Deprecated">;
+  HelpText<"Deprecated, has no effect">;
 
 def warn_swift3_objc_inference_minimal :
   Flag<["-"], "warn-swift3-objc-inference-minimal">,
   Flags<[FrontendOption, HelpHidden, DoesNotAffectIncrementalBuild]>,
-  HelpText<"Deprecated">;
+  HelpText<"Deprecated, has no effect">;
 
 def enable_actor_data_race_checks :
   Flag<["-"], "enable-actor-data-race-checks">,

lib/AST/Attr.cpp

@@ -1775,7 +1775,6 @@ ObjCAttr::ObjCAttr(SourceLoc atLoc, SourceRange baseRange,
   }
 
   Bits.ObjCAttr.ImplicitName = false;
-  Bits.ObjCAttr.Swift3Inferred = false;
 }
 
 ObjCAttr *ObjCAttr::create(ASTContext &Ctx, llvm::Optional<ObjCSelector> name,
@@ -1853,7 +1852,6 @@ SourceLoc ObjCAttr::getRParenLoc() const {
 
 ObjCAttr *ObjCAttr::clone(ASTContext &context) const {
   auto attr = new (context) ObjCAttr(getName(), isNameImplicit());
-  attr->setSwift3Inferred(isSwift3Inferred());
   attr->setAddedByAccessNote(getAddedByAccessNote());
   return attr;
 }

lib/Frontend/CompilerInvocation.cpp

@@ -917,10 +917,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
   Opts.EnableAppExtensionRestrictions |= Opts.EnableAppExtensionLibraryRestrictions;
 
-  Opts.EnableSwift3ObjCInference =
-    Args.hasFlag(OPT_enable_swift3_objc_inference,
-                 OPT_disable_swift3_objc_inference, false);
-
   if (Args.hasArg(OPT_enable_swift3_objc_inference))
     Diags.diagnose(SourceLoc(), diag::warn_flag_deprecated,
                    "-enable-swift3-objc-inference");
@@ -981,17 +977,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
 
   Opts.EnableSPIOnlyImports = Args.hasArg(OPT_experimental_spi_only_imports);
 
-  if (Opts.EnableSwift3ObjCInference) {
-    if (const Arg *A = Args.getLastArg(
-                                   OPT_warn_swift3_objc_inference_minimal,
-                                   OPT_warn_swift3_objc_inference_complete)) {
-      if (A->getOption().getID() == OPT_warn_swift3_objc_inference_minimal)
-        Opts.WarnSwift3ObjCInference = Swift3ObjCInferenceWarnings::Minimal;
-      else
-        Opts.WarnSwift3ObjCInference = Swift3ObjCInferenceWarnings::Complete;
-    }
-  }
-
   if (Args.hasArg(OPT_warn_swift3_objc_inference_minimal))
     Diags.diagnose(SourceLoc(), diag::warn_flag_deprecated,
                    "-warn-swift3-objc-inference-minimal");

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -1328,12 +1328,6 @@ class DeclAndTypePrinter::Implementation
       printAvailability(AFD);
     }
 
-    if (auto accessor = dyn_cast<AccessorDecl>(AFD)) {
-      printSwift3ObjCDeprecatedInference(accessor->getStorage());
-    } else {
-      printSwift3ObjCDeprecatedInference(AFD);
-    }
-
     os << ";\n";
 
     if (makeNewUnavailable) {
@@ -1775,36 +1769,6 @@ class DeclAndTypePrinter::Implementation
     }
   }
 
-  void printSwift3ObjCDeprecatedInference(ValueDecl *VD) {
-    const LangOptions &langOpts = getASTContext().LangOpts;
-    if (!langOpts.EnableSwift3ObjCInference ||
-        langOpts.WarnSwift3ObjCInference == Swift3ObjCInferenceWarnings::None) {
-      return;
-    }
-    auto attr = VD->getAttrs().getAttribute<ObjCAttr>();
-    if (!attr || !attr->isSwift3Inferred())
-      return;
-
-    os << " SWIFT_DEPRECATED_OBJC(\"Swift ";
-    if (isa<VarDecl>(VD))
-      os << "property";
-    else if (isa<SubscriptDecl>(VD))
-      os << "subscript";
-    else if (isa<ConstructorDecl>(VD))
-      os << "initializer";
-    else
-      os << "method";
-    os << " '";
-    auto nominal = VD->getDeclContext()->getSelfNominalTypeDecl();
-    printEncodedString(os, nominal->getName().str(), /*includeQuotes=*/false);
-    os << ".";
-    SmallString<32> scratch;
-    printEncodedString(os, VD->getName().getString(scratch),
-                       /*includeQuotes=*/false);
-    os << "' uses '@objc' inference deprecated in Swift 4; add '@objc' to "
-       <<   "provide an Objective-C entrypoint\")";
-  }
-
   void visitFuncDecl(FuncDecl *FD) {
     if (outputLang == OutputLanguageMode::Cxx) {
       if (FD->getDeclContext()->isTypeContext())
@@ -2041,8 +2005,6 @@ class DeclAndTypePrinter::Implementation
       print(objTy, kind, objCName.str().str());
     }
 
-    printSwift3ObjCDeprecatedInference(VD);
-
     printAvailability(VD);
 
     auto *getter = VD->getOpaqueAccessor(AccessorKind::Get);

lib/SILGen/SILGenBridging.cpp

@@ -1624,44 +1624,6 @@ void SILGenFunction::emitNativeToForeignThunk(SILDeclRef thunk) {
     }
   }
 
-  // If the '@objc' was inferred due to deprecated rules,
-  // emit a Builtin.swift3ImplicitObjCEntrypoint().
-  //
-  // However, don't do so for 'dynamic' members, which must use Objective-C
-  // dispatch and therefore create many false positives.
-  if (thunk.hasDecl()) {
-    auto decl = thunk.getDecl();
-
-    // For an accessor, look at the storage declaration's attributes.
-    if (auto accessor = dyn_cast<AccessorDecl>(decl)) {
-      decl = accessor->getStorage();
-    }
-
-    if (auto attr = decl->getAttrs().getAttribute<ObjCAttr>()) {
-      // If @objc was inferred based on the Swift 3 @objc inference rules, emit
-      // a call to Builtin.swift3ImplicitObjCEntrypoint() to enable runtime
-      // logging of the uses of such entrypoints.
-      if (attr->isSwift3Inferred() && !decl->shouldUseObjCDispatch()) {
-        // Get the starting source location of the declaration so we can say
-        // exactly where to stick '@objc'.
-        SourceLoc objcInsertionLoc =
-          decl->getAttributeInsertionLoc(/*modifier*/ false);
-
-        auto objcInsertionLocArgs
-          = emitSourceLocationArgs(objcInsertionLoc, loc);
-        
-        B.createBuiltin(loc,
-          getASTContext().getIdentifier("swift3ImplicitObjCEntrypoint"),
-          getModule().Types.getEmptyTupleType(), { }, {
-            objcInsertionLocArgs.filenameStartPointer.forward(*this),
-            objcInsertionLocArgs.filenameLength.forward(*this),
-            objcInsertionLocArgs.line.forward(*this),
-            objcInsertionLocArgs.column.forward(*this)
-          });
-      }
-    }
-  }
-
   // Now, enter a cleanup used for bridging the arguments. Note that if we
   // have an indirect result, it must be outside of this scope, otherwise
   // we will deallocate it too early.