[PrintAsObjC] Emit Xcode-7-compatible class properties.

There's not yet a released version of Apple Clang that supports
Objective-C class properties, so make sure the generated header
guards any uses of them with a __has_feature check, and provides
declarations of the accessor methods as well.

https://bugs.swift.org/browse/SR-1442

Author: jrose-apple

lib/PrintAsObjC/PrintAsObjC.cpp

@@ -566,10 +566,15 @@ class ObjCPrinter : private DeclVisitor<ObjCPrinter>,
 
     printDocumentationComment(VD);
 
+    if (VD->isStatic()) {
+      // Older Clangs don't support class properties.
+      os << "SWIFT_CLASS_PROPERTY(";
+    }
+
     // For now, never promise atomicity.
     os << "@property (nonatomic";
 
-    if (!VD->isInstanceMember())
+    if (VD->isStatic())
       os << ", class";
 
     ASTContext &ctx = M.getASTContext();
@@ -670,7 +675,17 @@ class ObjCPrinter : private DeclVisitor<ObjCPrinter>,
       print(ty, OTK_None, objCName);
     }
 
-    os << ";\n";
+    os << ";";
+    if (VD->isStatic()) {
+      os << ")\n";
+      // Older Clangs don't support class properties, so print the accessors as
+      // well. This is harmless.
+      printAbstractFunctionAsMethod(VD->getGetter(), true);
+      if (auto setter = VD->getSetter())
+        printAbstractFunctionAsMethod(setter, true);
+    } else {
+      os << "\n";
+    }
   }
 
   void visitSubscriptDecl(SubscriptDecl *SD) {
@@ -1751,6 +1766,13 @@ class ModuleWriter {
            "#if !defined(SWIFT_METATYPE)\n"
            "# define SWIFT_METATYPE(X) Class\n"
            "#endif\n"
+           "#if !defined(SWIFT_CLASS_PROPERTY)\n"
+           "# if __has_feature(objc_class_property)\n"
+           "#  define SWIFT_CLASS_PROPERTY(X) X\n"
+           "# else\n"
+           "#  define SWIFT_CLASS_PROPERTY(X)\n"
+           "# endif\n"
+           "#endif\n"
            "\n"
            "#if defined(__has_attribute) && "
              "__has_attribute(objc_runtime_name)\n"

test/PrintAsObjC/Inputs/comments-expected-output.h

@@ -22,7 +22,8 @@ SWIFT_CLASS("_TtC8comments21A010_AttachToEntities")
 /**
   Aaa.  v2.
 */
-@property (nonatomic, class, readonly) NSInteger v2;
+SWIFT_CLASS_PROPERTY(@property (nonatomic, class, readonly) NSInteger v2;)
++ (NSInteger)v2;
 @end
 
 

test/PrintAsObjC/classes.swift

@@ -369,8 +369,11 @@ public class NonObjCClass { }
 // CHECK-NEXT: @property (nonatomic, readonly, strong) Properties * _Nonnull mySelf;
 // CHECK-NEXT: @property (nonatomic, readonly) double pi;
 // CHECK-NEXT: @property (nonatomic) NSInteger computed;
-// CHECK-NEXT: @property (nonatomic, class, strong) Properties * _Nonnull shared;
-// CHECK-NEXT: @property (nonatomic, class, readonly, strong) Properties * _Nonnull sharedRO;
+// CHECK-NEXT: SWIFT_CLASS_PROPERTY(@property (nonatomic, class, strong) Properties * _Nonnull shared;)
+// CHECK-NEXT: + (Properties * _Nonnull)shared;
+// CHECK-NEXT: + (void)setShared:(Properties * _Nonnull)newValue;
+// CHECK-NEXT: SWIFT_CLASS_PROPERTY(@property (nonatomic, class, readonly, strong) Properties * _Nonnull sharedRO;)
+// CHECK-NEXT: + (Properties * _Nonnull)sharedRO;
 // CHECK-NEXT: @property (nonatomic, weak) Properties * _Nullable weakOther;
 // CHECK-NEXT: @property (nonatomic, assign) Properties * _Nonnull unownedOther;
 // CHECK-NEXT: @property (nonatomic, unsafe_unretained) Properties * _Nonnull unmanagedOther;
@@ -399,9 +402,13 @@ public class NonObjCClass { }
 // CHECK-NEXT: @property (nonatomic, copy) IBOutletCollection(CustomName) NSArray<CustomName *> *  _Nullable outletCollectionOptional;
 // CHECK-NEXT: @property (nonatomic, copy) IBOutletCollection(id) NSArray * _Nullable outletCollectionAnyObject;
 // CHECK-NEXT: @property (nonatomic, copy) IBOutletCollection(id) NSArray<id <NSObject>> * _Nullable outletCollectionProto;
-// CHECK-NEXT: @property (nonatomic, class, readonly) NSInteger staticInt;
-// CHECK-NEXT: @property (nonatomic, class, copy) NSString * _Nonnull staticString;
-// CHECK-NEXT: @property (nonatomic, class, readonly) double staticDouble;
+// CHECK-NEXT: SWIFT_CLASS_PROPERTY(@property (nonatomic, class, readonly) NSInteger staticInt;)
+// CHECK-NEXT: + (NSInteger)staticInt;
+// CHECK-NEXT: SWIFT_CLASS_PROPERTY(@property (nonatomic, class, copy) NSString * _Nonnull staticString;)
+// CHECK-NEXT: + (NSString * _Nonnull)staticString;
+// CHECK-NEXT: + (void)setStaticString:(NSString * _Nonnull)value;
+// CHECK-NEXT: SWIFT_CLASS_PROPERTY(@property (nonatomic, class, readonly) double staticDouble;)
+// CHECK-NEXT: + (double)staticDouble;
 // CHECK-NEXT: @property (nonatomic, strong) Properties * _Nullable wobble;
 // CHECK-NEXT: @property (nonatomic, getter=isEnabled, setter=setIsEnabled:) BOOL enabled;
 // CHECK-NEXT: @property (nonatomic, getter=isAnimated) BOOL animated;