[concurrency] Inherit caller isolation inheriting when inferring isolation from a nominal type context for a method on the nominal type.

lib/Sema/TypeCheckConcurrency.cpp

@@ -5950,10 +5950,19 @@ InferredActorIsolation ActorIsolationRequest::evaluate(
     if (auto selfTypeDecl = value->getDeclContext()->getSelfNominalTypeDecl()) {
       auto selfTypeIsolation = getInferredActorIsolation(selfTypeDecl);
       if (selfTypeIsolation.isolation) {
-        return {
-          inferredIsolation(selfTypeIsolation.isolation, onlyGlobal),
-          selfTypeIsolation.source
-        };
+        auto isolation = selfTypeIsolation.isolation;
+
+        if (auto *func = dyn_cast<AbstractFunctionDecl>(value);
+            ctx.LangOpts.hasFeature(
+                Feature::NonIsolatedAsyncInheritsIsolationFromContext) &&
+            func && func->hasAsync() &&
+            func->getModuleContext() == ctx.MainModule &&
+            isolation.isNonisolated()) {
+          isolation = ActorIsolation::forCallerIsolationInheriting();
+        }
+
+        return {inferredIsolation(isolation, onlyGlobal),
+                selfTypeIsolation.source};
       }
     }
   }

test/Concurrency/nonisolated_inherits_isolation.swift

@@ -16,6 +16,11 @@
 
 class NonSendableKlass {}
 
+nonisolated class NonIsolatedNonSendableKlass {
+  func unspecifiedMethod() async {}
+  nonisolated func nonisolatedMethod() async {}
+}
+
 func unspecifiedSyncUse<T>(_ t: T) {}
 func unspecifiedAsyncUse<T>(_ t: T) async {}
 nonisolated func nonisolatedSyncUse<T>(_ t: T) {}
@@ -148,3 +153,17 @@ class MainActorKlass {
     // expected-enabled-note @-1 {{sending main actor-isolated 'x4' to global actor 'CustomActor'-isolated global function 'sendToCustom' risks causing data races between global actor 'CustomActor'-isolated and main actor-isolated uses}}
   }
 }
+
+// We should not error on either of these since c is in the main actor's region
+// and our nonisolated/unspecified methods are inheriting the main actor
+// isolation which is safe since they are type checked as something that cannot
+// access any state that is outside of the current actor that c is reachable from.
+@MainActor
+func validateNonisolatedOnClassMeansCallerIsolationInheritingOnFuncDecl(
+  c: NonIsolatedNonSendableKlass
+) async {
+  await c.unspecifiedMethod() // expected-disabled-error {{sending 'c' risks causing data races}}
+  // expected-disabled-note @-1 {{sending main actor-isolated 'c' to nonisolated instance method 'unspecifiedMethod()' risks causing data races between nonisolated and main actor-isolated uses}}
+  await c.nonisolatedMethod() // expected-disabled-error {{sending 'c' risks causing data races}}
+  // expected-disabled-note @-1 {{sending main actor-isolated 'c' to nonisolated instance method 'nonisolatedMethod()' risks causing data races between nonisolated and main actor-isolated uses}}
+}