Add a function for querying the isolation of an Initializer.

include/swift/AST/ActorIsolation.h

@@ -28,6 +28,7 @@ class raw_ostream;
 
 namespace swift {
 class DeclContext;
+class Initializer;
 class ModuleDecl;
 class VarDecl;
 class NominalTypeDecl;
@@ -434,6 +435,10 @@ InferredActorIsolation getInferredActorIsolation(ValueDecl *value);
 ActorIsolation
 __AbstractClosureExpr_getActorIsolation(AbstractClosureExpr *CE);
 
+/// Determine how the given initialization context is isolated.
+ActorIsolation getActorIsolation(Initializer *init,
+                                 bool ignoreDefaultArguments = false);
+
 /// Determine how the given declaration context is isolated.
 /// \p getClosureActorIsolation allows the specification of actor isolation for
 /// closures that haven't been saved been saved to the AST yet. This is useful

lib/AST/Decl.cpp

@@ -12008,7 +12008,6 @@ ActorIsolation swift::getActorIsolationOfContext(
     DeclContext *dc,
     llvm::function_ref<ActorIsolation(AbstractClosureExpr *)>
         getClosureActorIsolation) {
-  auto &ctx = dc->getASTContext();
   auto dcToUse = dc;
 
   // Defer bodies share the actor isolation of their enclosing context.
@@ -12023,44 +12022,79 @@ ActorIsolation swift::getActorIsolationOfContext(
   if (auto *vd = dyn_cast_or_null<ValueDecl>(dcToUse->getAsDecl()))
     return getActorIsolation(vd);
 
-  // In the context of the initializing or default-value expression of a
-  // stored property:
-  //   - For a static stored property, the isolation matches the VarDecl.
-  //     Static properties are initialized upon first use, so the isolation
-  //     of the initializer must match the isolation required to access the
-  //     property.
-  //   - For a field of a nominal type, the expression can require the same
-  //     actor isolation as the field itself. That default expression may only
-  //     be used from inits that meet the required isolation.
-  if (auto *var = dcToUse->getNonLocalVarDecl()) {
-    // If IsolatedDefaultValues are enabled, treat this context as having
-    // unspecified isolation. We'll compute the required isolation for
-    // the initializer and validate that it matches the isolation of the
-    // var itself in the DefaultInitializerIsolation request.
-    if (ctx.LangOpts.hasFeature(Feature::IsolatedDefaultValues))
-      return ActorIsolation::forUnspecified();
-
-    return getActorIsolation(var);
-  }
-
   if (auto *closure = dyn_cast<AbstractClosureExpr>(dcToUse)) {
     return getClosureActorIsolation(closure);
   }
 
+  if (auto *init = dyn_cast<Initializer>(dcToUse)) {
+    // FIXME: force default argument initializers to report a meaningless
+    // isolation in order to break a bunch of cycles with the way that
+    // isolation is computed for them.
+    return getActorIsolation(init, /*ignoreDefaultArguments*/ true);
+  }
+
   if (isa<TopLevelCodeDecl>(dcToUse)) {
+    auto &ctx = dc->getASTContext();
     if (dcToUse->isAsyncContext() ||
-        dcToUse->getASTContext().LangOpts.StrictConcurrencyLevel >=
-            StrictConcurrency::Complete) {
-      if (Type mainActor = dcToUse->getASTContext().getMainActorType())
+        ctx.LangOpts.StrictConcurrencyLevel >= StrictConcurrency::Complete) {
+      if (Type mainActor = ctx.getMainActorType())
         return ActorIsolation::forGlobalActor(mainActor)
-            .withPreconcurrency(
-                !dcToUse->getASTContext().isSwiftVersionAtLeast(6));
+            .withPreconcurrency(!ctx.isSwiftVersionAtLeast(6));
     }
   }
 
   return ActorIsolation::forUnspecified();
 }
 
+ActorIsolation swift::getActorIsolation(Initializer *init,
+                                        bool ignoreDefaultArguments) {
+  switch (init->getInitializerKind()) {
+  case InitializerKind::PatternBinding:
+    // In the context of the initializing or default-value expression of a
+    // stored property:
+    //   - For a static stored property, the isolation matches the VarDecl.
+    //     Static properties are initialized upon first use, so the isolation
+    //     of the initializer must match the isolation required to access the
+    //     property.
+    //   - For a field of a nominal type, the expression can require the same
+    //     actor isolation as the field itself. That default expression may only
+    //     be used from inits that meet the required isolation.
+    if (auto *var = init->getNonLocalVarDecl()) {
+      auto &ctx = var->getASTContext();
+
+      // If IsolatedDefaultValues are enabled, treat this context as having
+      // unspecified isolation. We'll compute the required isolation for
+      // the initializer and validate that it matches the isolation of the
+      // var itself in the DefaultInitializerIsolation request.
+      if (ctx.LangOpts.hasFeature(Feature::IsolatedDefaultValues))
+        return ActorIsolation::forUnspecified();
+
+      return getActorIsolation(var);
+    }
+
+    return ActorIsolation::forUnspecified();
+
+  case InitializerKind::DefaultArgument: {
+    auto defArgInit = cast<DefaultArgumentInitializer>(init);
+
+    // A hack when used from getActorIsolationOfContext to maintain the
+    // current behavior and avoid request cycles.
+    if (ignoreDefaultArguments)
+      return ActorIsolation::forUnspecified();
+
+    auto fn = cast<ValueDecl>(defArgInit->getParent()->getAsDecl());
+    auto param = getParameterAt(fn, defArgInit->getIndex());
+    assert(param);
+    return param->getInitializerIsolation();
+  }
+
+  case InitializerKind::PropertyWrapper:
+  case InitializerKind::CustomAttribute:
+    return ActorIsolation::forUnspecified();
+  }
+  llvm_unreachable("bad initializer kind");
+}
+
 bool swift::isSameActorIsolated(ValueDecl *value, DeclContext *dc) {
     auto valueIsolation = getActorIsolation(value);
     auto dcIsolation = getActorIsolationOfContext(dc);