Allow '@usableFromInline' on 'dynamic' decls

It actually /does/ make sense to enforce the usable-from-inline rules
on dynamic declarations, but that would break source compatibility at
this point. Just allow '@usableFromInline' to be written on 'dynamic'
declarations, so that it'll be compatible with Swift 5.

Author: jrose-apple

include/swift/AST/DiagnosticsSema.def

@@ -4031,9 +4031,6 @@ WARNING(inlinable_implies_usable_from_inline,none,
 ERROR(usable_from_inline_attr_in_protocol,none,
       "'@usableFromInline' attribute cannot be used in protocols", ())
 
-ERROR(usable_from_inline_dynamic_not_supported,none,
-      "'@usableFromInline' attribute cannot be applied to 'dynamic' declarations", ())
-
 #define FRAGILE_FUNC_KIND \
   "%select{a '@_transparent' function|" \
   "an '@inline(__always)' function|" \

lib/Sema/TypeCheckAttr.cpp

@@ -1844,16 +1844,6 @@ void AttributeChecker::visitUsableFromInlineAttr(UsableFromInlineAttr *attr) {
     return;
   }
 
-  // Symbols of dynamically-dispatched declarations are never referenced
-  // directly, so marking them as @usableFromInline does not make sense.
-  if (VD->isDynamic()) {
-    if (attr->isImplicit())
-      attr->setInvalid();
-    else
-      diagnoseAndRemoveAttr(attr, diag::usable_from_inline_dynamic_not_supported);
-    return;
-  }
-
   // On internal declarations, @inlinable implies @usableFromInline.
   if (VD->getAttrs().hasAttribute<InlinableAttr>()) {
     if (TC.Context.isSwiftVersionAtLeast(4,2))

test/Compatibility/attr_usableFromInline_swift4.swift

@@ -1,5 +1,5 @@
-// RUN: %target-typecheck-verify-swift -swift-version 4
-// RUN: %target-typecheck-verify-swift -enable-testing -swift-version 4
+// RUN: %target-typecheck-verify-swift -swift-version 4 -disable-objc-attr-requires-foundation-module -enable-objc-interop
+// RUN: %target-typecheck-verify-swift -enable-testing -swift-version 4 -disable-objc-attr-requires-foundation-module -enable-objc-interop
 
 @usableFromInline private func privateVersioned() {}
 // expected-error@-1 {{'@usableFromInline' attribute can only be applied to internal declarations, but 'privateVersioned()' is private}}
@@ -121,3 +121,9 @@ enum BadEnum {
 
 @usableFromInline
 class BadClass : InternalClass {}
+
+public class DynamicMembers {
+  @usableFromInline @objc dynamic init() {}
+  @usableFromInline @objc dynamic func foo() {}
+  @usableFromInline @objc dynamic var bar: Int = 0
+}

test/Compatibility/attr_usableFromInline_swift42.swift

@@ -1,5 +1,5 @@
-// RUN: %target-typecheck-verify-swift -swift-version 4.2
-// RUN: %target-typecheck-verify-swift -enable-testing -swift-version 4.2
+// RUN: %target-typecheck-verify-swift -swift-version 4.2 -disable-objc-attr-requires-foundation-module -enable-objc-interop
+// RUN: %target-typecheck-verify-swift -enable-testing -swift-version 4.2 -disable-objc-attr-requires-foundation-module -enable-objc-interop
 
 @usableFromInline private func privateVersioned() {}
 // expected-error@-1 {{'@usableFromInline' attribute can only be applied to internal declarations, but 'privateVersioned()' is private}}
@@ -141,3 +141,9 @@ enum BadEnum {
 @usableFromInline
 class BadClass : InternalClass {}
 // expected-warning@-1 {{type referenced from the superclass of a '@usableFromInline' class should be '@usableFromInline' or public}}
+
+public class DynamicMembers {
+  @usableFromInline @objc dynamic init() {}
+  @usableFromInline @objc dynamic func foo() {}
+  @usableFromInline @objc dynamic var bar: Int = 0
+}

test/attr/attr_objc.swift

@@ -2291,13 +2291,10 @@ class User: NSObject {
   }
 }
 
-// 'dynamic' methods cannot be @inlinable or @usableFromInline
+// 'dynamic' methods cannot be @inlinable.
 class BadClass {
   @inlinable @objc dynamic func badMethod1() {}
   // expected-error@-1 {{'@inlinable' attribute cannot be applied to 'dynamic' declarations}}
-
-  @usableFromInline @objc dynamic func badMethod2() {}
-  // expected-error@-1 {{'@usableFromInline' attribute cannot be applied to 'dynamic' declarations}}
 }
 
 @objc

test/attr/attr_usableFromInline.swift

@@ -1,5 +1,5 @@
-// RUN: %target-typecheck-verify-swift -swift-version 5
-// RUN: %target-typecheck-verify-swift -enable-testing -swift-version 5
+// RUN: %target-typecheck-verify-swift -swift-version 5 -disable-objc-attr-requires-foundation-module -enable-objc-interop
+// RUN: %target-typecheck-verify-swift -swift-version 5 -disable-objc-attr-requires-foundation-module -enable-objc-interop -enable-testing
 
 @usableFromInline private func privateVersioned() {}
 // expected-error@-1 {{'@usableFromInline' attribute can only be applied to internal declarations, but 'privateVersioned()' is private}}
@@ -68,6 +68,12 @@ public func usesEqEnum() -> Bool {
   _ = RawEnum(rawValue: 0)
 }
 
+public class DynamicMembers {
+  @usableFromInline @objc dynamic init() {}
+  @usableFromInline @objc dynamic func foo() {}
+  @usableFromInline @objc dynamic var bar: Int = 0
+}
+
 internal struct InternalStruct {}
 // expected-note@-1 9{{type declared here}}