AST: Fix nesting of unavailable AvailabilityContexts.

Author: tshortli

lib/AST/AvailabilityContext.cpp

@@ -39,15 +39,21 @@ bool AvailabilityContext::PlatformInfo::constrainUnavailability(
   if (!unavailablePlatform)
     return false;
 
-  // Check whether the decl's unavailability reason is the same.
-  if (IsUnavailable && UnavailablePlatform == *unavailablePlatform)
-    return false;
+  if (IsUnavailable) {
+    // Universal unavailability cannot be refined.
+    if (UnavailablePlatform == PlatformKind::none)
+      return false;
 
-  // Check whether the decl's unavailability reason is more specific.
-  if (*unavailablePlatform != PlatformKind::none &&
-      inheritsAvailabilityFromPlatform(*unavailablePlatform,
-                                       UnavailablePlatform))
-    return false;
+    // There's nothing to do if the platforms already match.
+    if (UnavailablePlatform == *unavailablePlatform)
+      return false;
+
+    // The new platform must be more restrictive.
+    if (*unavailablePlatform != PlatformKind::none &&
+        inheritsAvailabilityFromPlatform(*unavailablePlatform,
+                                         UnavailablePlatform))
+      return false;
+  }
 
   IsUnavailable = true;
   UnavailablePlatform = *unavailablePlatform;

test/Sema/availability_refinement_contexts.swift

@@ -319,23 +319,38 @@ func unavailableOnMacOS() {
   let x = 1
 }
 
-// CHECK-NEXT: {{^}}  (decl_implicit version=50 deprecated decl=deprecatedOnMacOS()
-// CHECK-NEXT: {{^}}    (decl_implicit version=50 deprecated decl=x
-
-@available(macOS, deprecated)
-func deprecatedOnMacOS() {
-  let x = 1
-}
-
 // CHECK-NEXT: {{^}}  (decl_implicit version=50 decl=extension.SomeEnum
 // CHECK-NEXT: {{^}}    (decl_implicit version=50 unavailable=macOS decl=extension.SomeEnum
-// CHECK-NEXT: {{^}}      (decl_implicit version=50 unavailable=macOS decl=propertyInUnavailableExtension
-// CHECK-NEXT: {{^}}        (decl version=52 unavailable=macOS decl=propertyInUnavailableExtension
+// CHECK-NEXT: {{^}}      (decl_implicit version=50 unavailable=macOS decl=availableMacOS_52
+// CHECK-NEXT: {{^}}        (decl version=52 unavailable=macOS decl=availableMacOS_52
+// CHECK-NEXT: {{^}}      (decl_implicit version=50 unavailable=* decl=neverAvailable()
 
 @available(macOS, unavailable)
 extension SomeEnum {
   @available(OSX 52, *)
-  var propertyInUnavailableExtension: Int { 1 }
+  var availableMacOS_52: Int { 1 }
+
+  @available(macOSApplicationExtension, unavailable)
+  func unavailableInAppExtensions() {}
+
+  @available(*, unavailable)
+  func neverAvailable() {}
+}
+
+// CHECK-NEXT: {{^}}  (decl_implicit version=50 unavailable=* decl=NeverAvailable
+
+@available(*, unavailable)
+struct NeverAvailable {
+  @available(macOS, unavailable)
+  func unavailableOnMacOS() {}
+}
+
+// CHECK-NEXT: {{^}}  (decl_implicit version=50 deprecated decl=deprecatedOnMacOS()
+// CHECK-NEXT: {{^}}    (decl_implicit version=50 deprecated decl=x
+
+@available(macOS, deprecated)
+func deprecatedOnMacOS() {
+  let x = 1
 }
 
 // CHECK-NEXT: {{^}}  (decl version=51 decl=FinalDecl