Store AbortController and AbortSignal handles in class fields

A class field typed AbortController or AbortSignal (plain, optional,
nullable, or in an array) maps to checked-dynamic storage, and the
class-field rule refused it (SC1090) although the same handles already
live in locals, Map values, and closures. They now take the checked-dynamic
slot, like the fetch Headers, Request, and Response handles.

controller?.abort() on a nullable controller was refused as a method call
(also for locals): the static abort lowering ran only without an optional
chain. It now runs again once the chain has narrowed the receiver.

Found by pi's TUI Editor (autocompleteAbort: AbortController | undefined).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/compiler/src/frontend/lowering/lower-stdlib.ts

@@ -1630,16 +1630,22 @@ export function lowerStaticAbortControllerCall(
   call: ts.CallExpression,
 ): IrExpr | null {
   const access = call.expression;
+  // An optional chain (`controller?.abort()`) lowers the call again once it
+  // has narrowed the receiver (Lowerer.chainHandled).
   if (
-    call.questionDotToken ||
+    (call.questionDotToken && !lowerer.chainHandled.has(call)) ||
     call.arguments.nodes.some((argument) => ts.isSpreadElement(argument)) ||
     (!ts.isPropertyAccessExpression(access) && !ts.isElementAccessExpression(access)) ||
-    access.questionDotToken ||
+    (access.questionDotToken && !lowerer.chainHandled.has(access)) ||
     staticResponseMemberName(lowerer, access) !== "abort"
   ) {
     return null;
   }
-  const receiverTs = lowerer.checker.getBaseTypeOfLiteralType(lowerer.typeOf(access.expression));
+  const receiverTs = lowerer.checker.getBaseTypeOfLiteralType(
+    access.questionDotToken
+      ? lowerer.checker.getNonNullableType(lowerer.typeOf(access.expression))
+      : lowerer.typeOf(access.expression),
+  );
   const symbol = receiverTs.getAliasSymbol() ?? receiverTs.getSymbol();
   if (
     symbol === undefined ||

packages/compiler/src/frontend/lowering/lowerer.ts

@@ -3910,7 +3910,8 @@ export class Lowerer {
   /** Declared class fields may store a DYN value only when its static type
    * is `unknown` or `object` (also with `null` or `undefined`, or an array
    * of those), names checked protocol identity, is an owned runtime
-   * handle (a Worker or MessagePort, a fetch Headers/Request/Response, or
+   * handle (a Worker or MessagePort, a fetch Headers/Request/Response or
+   * AbortController/AbortSignal, or
    * a node:crypto ECDH, DiffieHellman or DiffieHellmanGroup), or is a
    * WeakMap/WeakSet (native weak collections live in checked-dynamic
    * storage, as locals of those types do); `any` fields stay refused. */

packages/compiler/src/frontend/type-mapper.ts

@@ -1747,9 +1747,17 @@ export function mapAsyncGeneratorAnnotation(type: ts.Type, ctx: TypeMapperCtx):
   return { kind: "generator", async: true, ...channels };
 }
 
-/** The native fetch handles (Headers, Request, Response), optionally in
- * arrays or with null/undefined: checked-dynamic handles wherever they are
- * stored, like the worker handles above. */
+const FETCH_HANDLE_NAMES: ReadonlySet<string> = new Set([
+  "Headers",
+  "Request",
+  "Response",
+  "AbortController",
+  "AbortSignal",
+]);
+
+/** The native fetch handles (Headers, Request, Response, AbortController,
+ * AbortSignal), optionally in arrays or with null/undefined: checked-dynamic
+ * handles wherever they are stored, like the worker handles above. */
 export function isFetchHandleType(
   type: ts.Type,
   ctx: Pick<TypeMapperCtx, "checker" | "isStdlibFile">,
@@ -1765,9 +1773,7 @@ export function isFetchHandleType(
       const symbol = member.getSymbol();
       if (
         !symbol ||
-        (ts.symbolName(symbol) !== "Headers" &&
-          ts.symbolName(symbol) !== "Request" &&
-          ts.symbolName(symbol) !== "Response") ||
+        !FETCH_HANDLE_NAMES.has(ts.symbolName(symbol)) ||
         !symbol.declarations.some(
           (d) =>
             (ts.isInterfaceDeclaration(d) || ts.isClassDeclaration(d)) &&

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/class-abort-controller-fields.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/class-abort-controller-fields.ts"
+ ],
+ "diags": []
+}

tests/corpus/class-abort-controller-fields.ts

@@ -0,0 +1,52 @@
+// Class fields typed AbortController and AbortSignal (plain, optional,
+// `| undefined`, `| null`, in arrays) hold the live handles: aborting
+// through the field is seen through every other reference, and optional
+// calls on a nullable field skip an empty slot.
+class Editor {
+  private abort: AbortController | undefined;
+  private signal: AbortSignal | null = null;
+  private readonly lifetime = new AbortController();
+  history: AbortController[] = [];
+  last?: AbortSignal;
+  start(): AbortSignal {
+    this.abort?.abort();
+    this.abort = new AbortController();
+    this.history.push(this.abort);
+    this.signal = this.abort.signal;
+    this.last = this.signal;
+    return this.signal;
+  }
+  cancel(reason?: string): boolean {
+    this.abort?.abort(reason);
+    return this.signal?.aborted ?? false;
+  }
+  reason(): unknown {
+    return this.signal?.reason;
+  }
+  dispose(): boolean {
+    this.lifetime.abort();
+    return this.lifetime.signal.aborted;
+  }
+}
+
+const idle = new Editor();
+console.log(idle.cancel(), idle.reason());
+
+const e = new Editor();
+const first = e.start();
+let events = 0;
+first.addEventListener("abort", () => {
+  events++;
+});
+const second = e.start();
+console.log(first.aborted, second.aborted, events, e.history.length);
+console.log(e.cancel("stop"), e.reason(), second.aborted, second.reason);
+console.log(e.history[0]!.signal === first, e.last === second, e.dispose());
+
+// A nullable local takes the same optional call.
+let maybe: AbortController | undefined = e.history.length > 5 ? new AbortController() : undefined;
+maybe?.abort();
+console.log(maybe?.signal.aborted);
+maybe = new AbortController();
+maybe?.abort("late");
+console.log(maybe?.signal.aborted, maybe?.signal.reason);

tests/harness/corpus-costs/class-abort-controller-fields.ts.json

@@ -0,0 +1 @@
+{ "plain": 4302 }