AST: Weak-link declarations in extensions of weak-linked types

include/swift/AST/DiagnosticsSema.def

@@ -4446,21 +4446,23 @@ NOTE(availability_protocol_requirement_here, none,
      "protocol requirement here", ())
 
 WARNING(public_decl_needs_availability, none,
-     "public declarations should have an availability attribute with -require-explicit-availability", ())
+        "public declarations should have an availability attribute when building "
+        "with -require-explicit-availability", ())
 
 // This doesn't display as an availability diagnostic, but it's
 // implemented there and fires when these subscripts are marked
 // unavailable, so it seems appropriate to put it here.
 ERROR(availabilty_string_subscript_migration, none,
-      "subscripts returning String were obsoleted in Swift 4; explicitly construct a String from subscripted result", ())
+      "subscripts returning String were obsoleted in Swift 4; explicitly "
+      "construct a String from subscripted result", ())
 
 //------------------------------------------------------------------------------
 // MARK: @discardableResult
 //------------------------------------------------------------------------------
 
 WARNING(discardable_result_on_void_never_function, none,
-        "@discardableResult declared on a function returning %select{Never|Void}0 is unnecessary",
-        (bool))
+        "@discardableResult declared on a function returning %select{Never|Void}0 "
+        "is unnecessary", (bool))
 
 //------------------------------------------------------------------------------
 // MARK: Resilience diagnostics

lib/AST/Decl.cpp

@@ -785,6 +785,10 @@ AvailabilityContext Decl::getAvailabilityForLinkage() const {
   if (auto *accessor = dyn_cast<AccessorDecl>(this))
     return accessor->getStorage()->getAvailabilityForLinkage();
 
+  if (auto *ext = dyn_cast<ExtensionDecl>(this))
+    if (auto *nominal = ext->getExtendedNominal())
+      return nominal->getAvailabilityForLinkage();
+
   auto *dc = getDeclContext();
   if (auto *ext = dyn_cast<ExtensionDecl>(dc))
     return ext->getAvailabilityForLinkage();
@@ -806,6 +810,10 @@ bool Decl::isAlwaysWeakImported() const {
   if (auto *accessor = dyn_cast<AccessorDecl>(this))
     return accessor->getStorage()->isAlwaysWeakImported();
 
+  if (auto *ext = dyn_cast<ExtensionDecl>(this))
+    if (auto *nominal = ext->getExtendedNominal())
+      return nominal->isAlwaysWeakImported();
+
   auto *dc = getDeclContext();
   if (auto *ext = dyn_cast<ExtensionDecl>(dc))
     return ext->isAlwaysWeakImported();

lib/Driver/ToolChains.cpp

@@ -192,6 +192,8 @@ static void addCommonFrontendArgs(const ToolChain &TC, const OutputInfo &OI,
   inputArgs.AddLastArg(arguments, options::OPT_typo_correction_limit);
   inputArgs.AddLastArg(arguments, options::OPT_enable_app_extension);
   inputArgs.AddLastArg(arguments, options::OPT_enable_library_evolution);
+  inputArgs.AddLastArg(arguments, options::OPT_require_explicit_availability);
+  inputArgs.AddLastArg(arguments, options::OPT_require_explicit_availability_target);
   inputArgs.AddLastArg(arguments, options::OPT_enable_testing);
   inputArgs.AddLastArg(arguments, options::OPT_enable_private_imports);
   inputArgs.AddLastArg(arguments, options::OPT_enable_cxx_interop);

test/IRGen/Inputs/weak_import_extension_helper.swift

@@ -0,0 +1,8 @@
+@available(macOS 10.60, *)
+public struct Foo {
+  public init() {}
+}
+
+extension Foo {
+  public func extensionMethod() {}
+}

test/IRGen/weak_import_extension.swift

@@ -0,0 +1,22 @@
+// RUN: %empty-directory(%t)
+//
+// RUN: %target-swift-frontend -enable-library-evolution -emit-module -target x86_64-apple-macosx10.60 -emit-module-path %t/weak_import_extension_helper.swiftmodule -parse-as-library %S/Inputs/weak_import_extension_helper.swift
+// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -target x86_64-apple-macosx10.50 | %FileCheck %s --check-prefix=CHECK-OLD
+// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -target x86_64-apple-macosx10.60 | %FileCheck %s --check-prefix=CHECK-NEW
+//
+// REQUIRES: OS=macosx
+
+import weak_import_extension_helper
+
+@available(macOS 10.60, *)
+public func callsExtensionMethod() {
+  Foo().extensionMethod()
+}
+
+// CHECK-OLD: declare extern_weak swiftcc %swift.metadata_response @"$s28weak_import_extension_helper3FooVMa"
+// CHECK-OLD: declare extern_weak swiftcc void @"$s28weak_import_extension_helper3FooVACycfC"
+// CHECK-OLD: declare extern_weak swiftcc void @"$s28weak_import_extension_helper3FooV0C6MethodyyF"
+
+// CHECK-NEW: declare swiftcc %swift.metadata_response @"$s28weak_import_extension_helper3FooVMa"
+// CHECK-NEW: declare swiftcc void @"$s28weak_import_extension_helper3FooVACycfC"
+// CHECK-NEW: declare swiftcc void @"$s28weak_import_extension_helper3FooV0C6MethodyyF"

test/attr/require_explicit_availability.swift

@@ -1,14 +1,14 @@
-// RUN: %swift -typecheck -parse-stdlib -target x86_64-apple-macosx10.10 -verify -require-explicit-availability -require-explicit-availability-target "macOS 10.10"  %s
-// RUN: %swift -typecheck -parse-stdlib -target x86_64-apple-macosx10.10 -warnings-as-errors %s
+// RUN: %swiftc_driver -typecheck -parse-stdlib -target x86_64-apple-macosx10.10 -Xfrontend -verify -require-explicit-availability -require-explicit-availability-target "macOS 10.10"  %s
+// RUN: %swiftc_driver -typecheck -parse-stdlib -target x86_64-apple-macosx10.10 -warnings-as-errors %s
 
-public struct S { // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}}
+public struct S { // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}}
   public func method() { }
 }
 
-public func foo() { bar() } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+public func foo() { bar() } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
 @usableFromInline
-func bar() { } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+func bar() { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
 @available(macOS 10.1, *)
 public func ok() { }
@@ -17,10 +17,10 @@ public func ok() { }
 public func unavailableOk() { }
 
 @available(macOS, deprecated: 10.10)
-public func missingIntro() { } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+public func missingIntro() { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
 @available(iOS 9.0, *)
-public func missingTargetPlatform() { } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+public func missingTargetPlatform() { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
 func privateFunc() { }
 
@@ -35,19 +35,19 @@ struct SOk {
 precedencegroup MediumPrecedence {}
 infix operator + : MediumPrecedence
 
-public func +(lhs: S, rhs: S) -> S { } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+public func +(lhs: S, rhs: S) -> S { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
-public enum E { } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+public enum E { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
-public class C { } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+public class C { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
-public protocol P { } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+public protocol P { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
-extension S { // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+extension S { // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
   func ok() { }
 }
 
-open class OpenClass { } // expected-warning {{public declarations should have an availability attribute with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
+open class OpenClass { } // expected-warning {{public declarations should have an availability attribute when building with -require-explicit-availability}} {{1-1=@available(macOS 10.10, *)\n}}
 
 private class PrivateClass { }