[Concurrency] memberAccessHasSpecialPermissionInSwift5 should treat init accessors as stored properties

Init accessor properties cannot escape self and are only allowed
to initialized and access a set of properties declared in their
`@storageRestrictions(...)` attribute.

Resolves: #70550

Author: xedin

lib/Sema/TypeCheckConcurrency.cpp

@@ -1763,10 +1763,20 @@ static bool memberAccessHasSpecialPermissionInSwift5(
 
     // If the context in which we consider the access matches between the
     // old (escaping-use restriction) and new (flow-isolation) contexts,
-    // and it is a stored property, then permit it here without any warning.
+    // and it is a stored or init accessor property, then permit it here
+    // without any warning.
     // Later, flow-isolation pass will check and emit a warning if needed.
-    if (refCxt == oldFn && isStoredProperty(member))
-      return true;
+    if (refCxt == oldFn) {
+      if (isStoredProperty(member))
+        return true;
+
+      if (auto *var = dyn_cast<VarDecl>(member)) {
+        // Init accessor properties are permitted to access only stored
+        // properties.
+        if (var->hasInitAccessor())
+          return true;
+      }
+    }
 
     // Otherwise, it's definitely going to be illegal, so warn and permit.
     auto &diags = refCxt->getASTContext().Diags;

test/Concurrency/flow_isolation.swift

@@ -734,3 +734,28 @@ actor CheckDeinitFromActor {
     ns = nil // expected-warning {{cannot access property 'ns' with a non-sendable type 'NonSendableType?' from non-isolated deinit; this is an error in Swift 6}}
   }
 }
+
+// https://github.com/apple/swift/issues/70550
+func testActorWithInitAccessorInit() {
+  @available(SwiftStdlib 5.1, *)
+  actor Angle {
+    var degrees: Double
+    var radians: Double = 0 {
+      @storageRestrictions(initializes: degrees)
+      init(initialValue)  {
+        degrees = initialValue * 180 / .pi
+      }
+
+      get { degrees * .pi / 180 }
+      set { degrees = newValue * 180 / .pi }
+    }
+
+    init(degrees: Double) {
+      self.degrees = degrees // Ok
+    }
+
+    init(radians: Double) {
+      self.radians = radians // Ok
+    }
+  }
+}