Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -7032,6 +7032,37 @@
   return dyn_cast<NamedDecl>(OrigCtx);
 }
 
+namespace {
+
+struct AttributeInsertion {
+  StringRef Prefix;
+  SourceLocation Loc;
+  StringRef Suffix;
+
+  static AttributeInsertion createInsertionAfter(const NamedDecl *D) {
+    return {" ", D->getLocEnd(), ""};
+  }
+  static AttributeInsertion createInsertionBefore(const NamedDecl *D) {
+    return {"", D->getLocStart(), "\n"};
+  }
+};
+
+} // end anonymous namespace
+
+/// Returns a source location in which it's appropriate to insert a new
+/// attribute for the given declaration \D.
+static Optional<AttributeInsertion>
+createAttributeInsertion(const NamedDecl *D) {
+  if (isa<ObjCPropertyDecl>(D))
+    return AttributeInsertion::createInsertionAfter(D);
+  if (const auto *MD = dyn_cast<ObjCMethodDecl>(D)) {
+    if (MD->hasBody())
+      return None;
+    return AttributeInsertion::createInsertionAfter(D);
+  }
+  return AttributeInsertion::createInsertionBefore(D);
+}
+
 /// Actually emit an availability diagnostic for a reference to an unavailable
 /// decl.
 ///
@@ -7221,8 +7252,30 @@
               << /*Anonymous*/1 << TD->getKindName();
           return;
         }
-      S.Diag(Enclosing->getLocation(), diag::note_partial_availability_silence)
-          << /*Named*/0 << Enclosing;
+      auto FixitNoteDiag = S.Diag(Enclosing->getLocation(),
+                                  diag::note_partial_availability_silence)
+                           << /*Named*/ 0 << Enclosing;
+      // Don't offer a fixit for declarations with availability attributes.
+      if (Enclosing->hasAttr<AvailabilityAttr>())
+        return;
+      if (!S.getPreprocessor().getMacroDefinition(
+              &S.getASTContext().Idents.get("API_AVAILABLE")))
+        return;
+      Optional<AttributeInsertion> Insertion =
+          createAttributeInsertion(Enclosing);
+      if (!Insertion)
+        return;
+      std::string PlatformName =
+          AvailabilityAttr::getPlatformNameSourceSpelling(
+              S.getASTContext().getTargetInfo().getPlatformName())
+              .lower();
+      std::string Introduced =
+          OffendingDecl->getVersionIntroduced().getAsString();
+      FixitNoteDiag << FixItHint::CreateInsertion(
+          Insertion->Loc,
+          (llvm::Twine(Insertion->Prefix) + "API_AVAILABLE(" + PlatformName +
+           "(" + Introduced + "))" + Insertion->Suffix)
+              .str());
     }
 }
 
Index: test/FixIt/fixit-availability.c
===================================================================
--- test/FixIt/fixit-availability.c
+++ test/FixIt/fixit-availability.c
@@ -8,3 +8,11 @@
 // CHECK: fix-it:{{.*}}:{[[@LINE-1]]:3-[[@LINE-1]]:3}:"if (__builtin_available(macOS 10.12, *)) {\n      "
 // CHECK-NEXT: fix-it:{{.*}}:{[[@LINE-2]]:14-[[@LINE-2]]:14}:"\n  } else {\n      // Fallback on earlier versions\n  }"
 }
+
+__attribute__((availability(macos, introduced=10.12)))
+struct New { };
+
+struct NoFixit {
+  struct New field;
+};
+// CHECK-NOT: API_AVAILABLE
Index: test/FixIt/fixit-availability.mm
===================================================================
--- test/FixIt/fixit-availability.mm
+++ test/FixIt/fixit-availability.mm
@@ -109,3 +109,28 @@
   anotherFunction(y);
   anotherFunction(x);
 }
+
+#define API_AVAILABLE(X) __attribute__((availability(macos, introduced=10.12))) // dummy macro
+
+API_AVAILABLE(macos(10.12))
+@interface NewClass
+@end
+
+@interface OldButOfferFixit
+@property(copy) NewClass *prop;
+// CHECK: fix-it:{{.*}}:{[[@LINE-2]]:1-[[@LINE-2]]:1}:"API_AVAILABLE(macos(10.12))\n"
+
+- (NewClass *)fixitMe;
+// CHECK: fix-it:{{.*}}:{[[@LINE-1]]:22-[[@LINE-1]]:22}:" API_AVAILABLE(macos(10.12))"
+@end
+
+void oldButOfferFixitFn(NewClass *) {
+// CHECK: fix-it:{{.*}}:{[[@LINE-1]]:1-[[@LINE-1]]:1}:"API_AVAILABLE(macos(10.12))\n"
+}
+
+// Avoid a fixit for declarations that already have an attribute:
+__attribute__((availability(macos, introduced=10.11)))
+@interface WithoutFixit
+@property(copy) NewClass *prop;
+// CHECK-NOT: API_AVAILABLE
+@end