[Concurrency] Emit a better note when an isolated stored property initializer

cannot be used in an init with mismatching isolation.

Author: hborla

include/swift/AST/DiagnosticsSIL.def

@@ -237,6 +237,9 @@ ERROR(use_of_self_before_fully_init,none,
 
 NOTE(stored_property_not_initialized,none,
      "'%0' not initialized", (StringRef))
+NOTE(isolated_property_initializer,none,
+     "%1 default value of '%0' cannot be used in a %2 initalizer",
+     (StringRef, ActorIsolation, ActorIsolation))
 
 ERROR(selfinit_multiple_times,none,
       "'%select{super|self}0.init' called multiple times in initializer",

lib/SILOptimizer/Mandatory/DefiniteInitialization.cpp

@@ -725,8 +725,13 @@ void LifetimeChecker::noteUninitializedMembers(const DIMemoryUse &Use) {
     std::string Name;
     auto *Decl = TheMemory.getPathStringToElement(i, Name);
     SILLocation Loc = Use.Inst->getLoc();
+    auto propertyInitIsolation = ActorIsolation::forUnspecified();
 
     if (Decl) {
+      if (auto *var = dyn_cast<VarDecl>(Decl)) {
+        propertyInitIsolation = var->getInitializerIsolation();
+      }
+
       // If we found a non-implicit declaration, use its source location.
       if (!Decl->isImplicit())
         Loc = SILLocation(Decl);
@@ -741,8 +746,17 @@ void LifetimeChecker::noteUninitializedMembers(const DIMemoryUse &Use) {
       }
     }
 
-    diagnose(Module, Loc, diag::stored_property_not_initialized,
-             StringRef(Name));
+    if (propertyInitIsolation.isGlobalActor()) {
+      auto *init =
+          dyn_cast<ConstructorDecl>(F.getDeclContext()->getAsDecl());
+      diagnose(Module, Loc, diag::isolated_property_initializer,
+               StringRef(Name), propertyInitIsolation,
+               getActorIsolation(init));
+    } else {
+      diagnose(Module, Loc, diag::stored_property_not_initialized,
+               StringRef(Name));
+    }
+
     emittedNote = true;
   }
 

test/Concurrency/isolated_default_property_inits.swift

@@ -20,9 +20,11 @@ func requiresMainActor() -> Int { 0 }
 func requiresSomeGlobalActor() -> Int { 0 }
 
 class C1 {
-  // expected-note@+1 2 {{'self.x' not initialized}}
+  // expected-note@+2 {{main actor-isolated default value of 'self.x' cannot be used in a nonisolated initalizer}}
+  // expected-note@+1 {{main actor-isolated default value of 'self.x' cannot be used in a global actor 'SomeGlobalActor'-isolated initalizer}}
   @MainActor var x = requiresMainActor()
-  // expected-note@+1 2 {{'self.y' not initialized}}
+  // expected-note@+2 {{global actor 'SomeGlobalActor'-isolated default value of 'self.y' cannot be used in a nonisolated initalizer}}
+  // expected-note@+1 {{global actor 'SomeGlobalActor'-isolated default value of 'self.y' cannot be used in a main actor-isolated initalizer}}
   @SomeGlobalActor var y = requiresSomeGlobalActor()
   var z = 10