[Concurrency] Replace nonisolated with nonisolated(nonsending) when isolation is inferred

With `NonisolatedNonsendingByDefault` an explicit `nonisolated`
attribute in declaration context is inferred to mean `nonisolated(nonsending)`
and it should be printed as such in interface files and other places.

The inference logic that did didn't remove the original attribute
which meant that it would be printed twice i.e.
`nonisolated nonisolated(nonsending) func test() async` which is
incorrect and would fail swift interface validation.

Resolves: rdar://155847011
(cherry picked from commit b519c07)

Author: xedin

lib/Sema/TypeCheckConcurrency.cpp

@@ -6275,10 +6275,12 @@ static InferredActorIsolation computeActorIsolation(Evaluator &evaluator,
   if (isolationFromAttr && isolationFromAttr->getKind() ==
           ActorIsolation::CallerIsolationInheriting) {
     auto nonisolated = value->getAttrs().getAttribute<NonisolatedAttr>();
-    if (!nonisolated || !nonisolated->isNonSending())
-      value->getAttrs().add(new (ctx) NonisolatedAttr(
-          /*atLoc*/ {}, /*range=*/{}, NonIsolatedModifier::NonSending,
-          /*implicit=*/true));
+    // Replace `nonisolated` with `nonisolated(nonsending)`
+    if (!nonisolated || !nonisolated->isNonSending()) {
+      value->getAttrs().removeAttribute(nonisolated);
+      value->getAttrs().add(NonisolatedAttr::createImplicit(
+          ctx, NonIsolatedModifier::NonSending));
+    }
   }
 
   if (auto *fd = dyn_cast<FuncDecl>(value)) {

test/Concurrency/attr_execution/nonisolated_cross_module_with_flag_enabled.swift

@@ -0,0 +1,43 @@
+// RUN: %empty-directory(%t/src)
+// RUN: split-file %s %t/src
+
+// REQUIRES: swift_feature_NonisolatedNonsendingByDefault
+
+/// Build the library A
+// RUN: %target-swift-frontend -emit-module %t/src/A.swift \
+// RUN:   -module-name A -swift-version 6 -enable-library-evolution \
+// RUN:   -enable-upcoming-feature NonisolatedNonsendingByDefault \
+// RUN:   -emit-module-path %t/A.swiftmodule \
+// RUN:   -emit-module-interface-path %t/A.swiftinterface
+
+// RUN: %target-swift-typecheck-module-from-interface(%t/A.swiftinterface) -module-name A
+
+// Build the client using module
+// RUN: %target-swift-emit-sil -verify -module-name Client -I %t %t/src/Client.swift | %FileCheck %t/src/Client.swift
+
+// RUN: rm %t/A.swiftmodule
+
+// Re-build the client using interface
+// RUN: %target-swift-emit-sil -verify -module-name Client -I %t %t/src/Client.swift | %FileCheck %t/src/Client.swift
+
+//--- A.swift
+@MainActor
+
+public final class Test {
+  public nonisolated func test() async {}
+}
+
+//--- Client.swift
+import A
+
+// CHECK-LABEL: sil hidden @$s6Client4test1ty1A4TestC_tYaF : $@convention(thin) @async (@guaranteed Test) -> ()
+// CHECK: bb0([[SELF:%.*]] : $Test):
+// CHECK:  [[MAIN_ACTOR_EXISTENTIAL:%.*]] = init_existential_ref %4 : $MainActor : $MainActor, $any Actor
+// CHECK:  [[ANY_ACTOR:%.*]] = enum $Optional<any Actor>, #Optional.some!enumelt, [[MAIN_ACTOR_EXISTENTIAL]]
+// CHECK:  [[TEST_METHOD:%.*]] = function_ref @$s1A4TestC4testyyYaF : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed Test) -> ()
+// CHECK:  apply [[TEST_METHOD]]([[ANY_ACTOR]], [[SELF]])
+// CHECK: } // end sil function '$s6Client4test1ty1A4TestC_tYaF'
+@MainActor
+func test(t: Test) async {
+  await t.test() // Ok
+}