[Sema] @preconcurrency conformances have no effect for protocols that adopted concurrency

Don't treat isolated or explicitly `nonisolated` requirements as
preconcurrency because in that case we consider protocol as
concurrency adopter.

Author: xedin

lib/Sema/TypeCheckProtocol.cpp

@@ -3094,6 +3094,14 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
       getDeclRefInContext(witness), witness->getLoc(), DC, llvm::None,
       llvm::None, llvm::None, requirementIsolation);
   bool sameConcurrencyDomain = false;
+  // If the requirement is isolated (explicitly or implicitly) or
+  // explicitly marked as `nonisolated` it means that the protocol
+  // has adopted concurrency and `@preconcurrency` doesn't apply.
+  bool isPreconcurrency =
+      Conformance->isPreconcurrency() &&
+      !(requirementIsolation.isActorIsolated() ||
+        requirement->getAttrs().hasAttribute<NonisolatedAttr>());
+
   switch (refResult) {
   case ActorReferenceResult::SameConcurrencyDomain:
     // If the witness has distributed-actor isolation, we have extra
@@ -3184,7 +3192,7 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
 
   // If we aren't missing anything or this is a witness to a `@preconcurrency`
   // conformance, do a Sendable check and move on.
-  if (!missingOptions || Conformance->isPreconcurrency()) {
+  if (!missingOptions || isPreconcurrency) {
     // FIXME: Disable Sendable checking when the witness is an initializer
     // that is explicitly marked nonisolated.
     if (isa<ConstructorDecl>(witness) &&
@@ -3216,7 +3224,7 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
         return refResult.isolation;
 
       // Always treat `@preconcurrency` witnesses as isolated.
-      if (Conformance->isPreconcurrency() &&
+      if (isPreconcurrency &&
           missingOptions.contains(MissingFlags::RequirementAsync))
         return refResult.isolation;
     }

test/Concurrency/preconcurrency_conformances.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -disable-availability-checking %s -emit-sil -o /dev/null -verify -enable-experimental-feature PreconcurrencyConformances -strict-concurrency=complete -verify-additional-prefix complete-tns-
+// RUN: %target-swift-frontend -swift-version 5 -disable-availability-checking %s -emit-sil -o /dev/null -verify -enable-experimental-feature PreconcurrencyConformances -strict-concurrency=complete -verify-additional-prefix complete-tns-
 
 // REQUIRES: concurrency
 // REQUIRES: asserts
@@ -104,3 +104,52 @@ struct TestConditional<T> {}
 extension TestConditional : @preconcurrency WithAssoc where T == Int {
   @MainActor func test() -> T { 42 } // Ok
 }
+
+@globalActor
+struct GlobalActor {
+  static var shared: MyActor = MyActor()
+}
+
+protocol WithIndividuallyIsolatedRequirements {
+  @MainActor var a: Int { get set }
+  @GlobalActor var b: Int { get set }
+  // expected-note@-1 {{'b' declared here}}
+
+  @GlobalActor func test()
+  // expected-note@-1 {{mark the protocol requirement 'test()' 'async' to allow actor-isolated conformances}}
+}
+
+do {
+  @MainActor
+  struct TestExplicitGlobalActorAttrs : @preconcurrency WithIndividuallyIsolatedRequirements {
+    var a: Int = 42
+
+    @MainActor var b: Int {
+      // expected-warning@-1 {{main actor-isolated property 'b' cannot be used to satisfy global actor 'GlobalActor'-isolated protocol requirement}}
+      get { 0 }
+      set {}
+    }
+
+    @MainActor func test() {
+      // expected-warning@-1 {{main actor-isolated instance method 'test()' cannot be used to satisfy global actor 'GlobalActor'-isolated protocol requirement}}
+    }
+  }
+}
+
+@MainActor
+protocol WithNonIsolated {
+  var prop: Int { get set }
+  // expected-note@-1 {{'prop' declared here}}
+  nonisolated func test()
+  // expected-note@-1 {{mark the protocol requirement 'test()' 'async' to allow actor-isolated conformances}}
+}
+
+do {
+  class TestExplicitOtherIsolation : @preconcurrency WithNonIsolated {
+    @GlobalActor var prop: Int = 42
+    // expected-warning@-1 {{global actor 'GlobalActor'-isolated property 'prop' cannot be used to satisfy main actor-isolated protocol requirement}}
+
+    @MainActor func test() {}
+    // expected-warning@-1 {{main actor-isolated instance method 'test()' cannot be used to satisfy nonisolated protocol requirement}}
+  }
+}