[Sema] Diagnose clash between inferred global actor isolation and @execution(concurrent)

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -8220,7 +8220,7 @@ ERROR(attr_execution_concurrent_only_on_async,none,
 
 ERROR(attr_execution_concurrent_incompatible_with_global_actor,none,
       "cannot use '@execution(concurrent)' on %kind0 isolated to global actor %1",
-      (ValueDecl *, ValueDecl *))
+      (ValueDecl *, Type))
 
 ERROR(attr_execution_concurrent_incompatible_isolated_parameter,none,
       "cannot use '@execution(concurrent)' on %kind0 because it has "

lib/Sema/TypeCheckAttr.cpp

@@ -264,9 +264,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
       return;
     }
 
-    // Checks based on explicit attributes, inferred ones would
-    // have to be handled during actor isolation inference.
-
     switch (attr->getBehavior()) {
     case ExecutionKind::Concurrent: {
       // 'concurrent' doesn't work with explicit `nonisolated`
@@ -277,14 +274,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
               diag::attr_execution_concurrent_incompatible_with_nonisolated, F);
           return;
         }
-
-        if (auto globalActor = F->getGlobalActorAttr()) {
-          diagnoseAndRemoveAttr(
-              attr,
-              diag::attr_execution_concurrent_incompatible_with_global_actor, F,
-              globalActor->second);
-          return;
-        }
       }
 
       auto parameters = F->getParameters();
@@ -317,6 +306,18 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
         }
       }
 
+      // We need isolation check here because global actor isolation
+      // could be inferred.
+
+      auto isolation = getActorIsolation(F);
+      if (isolation.isGlobalActor()) {
+        diagnoseAndRemoveAttr(
+            attr,
+            diag::attr_execution_concurrent_incompatible_with_global_actor, F,
+            isolation.getGlobalActor());
+        return;
+      }
+
       break;
     }
 

test/attr/attr_execution.swift

@@ -55,3 +55,19 @@ struct TestAttributeCollisions {
 
   @execution(concurrent) @Sendable func test(_: @Sendable () -> Void, _: sending Int) async {} // Ok
 }
+
+@MainActor
+protocol P {
+  func test() async
+}
+
+struct InfersMainActor : P {
+  @execution(concurrent) func test() async {}
+  // expected-error@-1 {{cannot use '@execution(concurrent)' on instance method 'test()' isolated to global actor 'MainActor'}}
+}
+
+@MainActor
+struct IsolatedType {
+  @execution(concurrent) func test() async {}
+  // expected-error@-1 {{cannot use '@execution(concurrent)' on instance method 'test()' isolated to global actor 'MainActor'}}
+}