Allow @nonobjc inits in objcImpl extensions

Initializers can’t be made final, but they *can* be made @nonobjc. (This isn’t always enough to ensure they’re actually valid, but I’ll get to that in a follow-up commit.)

Author: beccadax

Diff for: lib/AST/Decl.cpp

@@ -4300,6 +4300,7 @@ isObjCMemberImplementation(const ValueDecl *VD,
                     ? cast<AccessorDecl>(VD)->getStorage()
                     : VD;
       return !attrDecl->isFinal()
+                  && !attrDecl->getAttrs().hasAttribute<NonObjCAttr>()
                   && !attrDecl->getAttrs().hasAttribute<OverrideAttr>()
                   && getAccessLevel() >= AccessLevel::Internal;
     }

Diff for: lib/Sema/TypeCheckDeclObjC.cpp

@@ -3553,9 +3553,15 @@ class ObjCImplementationChecker {
                                  "private ");
       }
 
-      diagnose(cand, diag::fixit_add_final_for_objc_implementation,
-               cand->getDescriptiveKind())
-          .fixItInsert(cand->getAttributeInsertionLoc(true), "final ");
+      // Initializers can't be 'final', but they can be '@nonobjc'
+      if (isa<ConstructorDecl>(cand))
+        diagnose(cand, diag::fixit_add_nonobjc_for_objc_implementation,
+                 cand->getDescriptiveKind())
+            .fixItInsert(cand->getAttributeInsertionLoc(false), "@nonobjc ");
+      else
+        diagnose(cand, diag::fixit_add_final_for_objc_implementation,
+                 cand->getDescriptiveKind())
+            .fixItInsert(cand->getAttributeInsertionLoc(true), "final ");
     }
   }
 };

Diff for: test/decl/ext/objc_implementation.swift

@@ -183,6 +183,36 @@ protocol EmptySwiftProto {}
   class func instanceMethod2(_: CInt) {
     // expected-warning@-1 {{class method 'instanceMethod2' does not match instance method declared in header; this will become an error before '@_objcImplementation' is stabilized}} {{3-9=}}
   }
+
+  public init(notFromHeader1: CInt) {
+    // expected-warning@-1 {{initializer 'init(notFromHeader1:)' does not match any initializer declared in the headers for 'ObjCClass'; did you use the initializer's Swift name?}}
+    // expected-note@-2 {{add 'private' or 'fileprivate' to define an Objective-C-compatible initializer not declared in the header}} {{3-9=private}}
+    // expected-note@-3 {{add '@nonobjc' to define a Swift-only initializer}} {{3-3=@nonobjc }}
+  }
+
+  public required init(notFromHeader2: CInt) {
+    // expected-warning@-1 {{initializer 'init(notFromHeader2:)' does not match any initializer declared in the headers for 'ObjCClass'; did you use the initializer's Swift name?}}
+    // expected-note@-2 {{add 'private' or 'fileprivate' to define an Objective-C-compatible initializer not declared in the header}} {{3-9=private}}
+    // expected-note@-3 {{add '@nonobjc' to define a Swift-only initializer}} {{3-3=@nonobjc }}
+  }
+
+  public convenience init(notFromHeader3: CInt) {
+    // expected-warning@-1 {{initializer 'init(notFromHeader3:)' does not match any initializer declared in the headers for 'ObjCClass'; did you use the initializer's Swift name?}}
+    // expected-note@-2 {{add 'private' or 'fileprivate' to define an Objective-C-compatible initializer not declared in the header}} {{3-9=private}}
+    // expected-note@-3 {{add '@nonobjc' to define a Swift-only initializer}} {{3-3=@nonobjc }}
+  }
+
+  @nonobjc public init(notFromHeader4: CInt) {
+    // FIXME: Should be an error; requires a vtable entry
+  }
+
+  @nonobjc public required init(notFromHeader5: CInt) {
+    // FIXME: Should be an error; requires a vtable entry
+  }
+
+  @nonobjc public convenience init(notFromHeader6: CInt) {
+    // OK
+  }
 }
 
 @_objcImplementation(PresentAdditions) extension ObjCClass {