Box URL into checked-dynamic unions beside fetch's Request and Response (#1459)

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

@@ -619,6 +619,20 @@ export function lowerFetchCall(lowerer: Lowerer, call: ts.CallExpression): IrExp
         : lowerer.lowerExpr(argument);
       stmts.push({ kind: "exprStmt", expr: discarded, loc: discarded.loc });
     }
+    // A union input holding a URL arm (`string | URL`) converts through the
+    // checked-dynamic input path, which reads the URL's href at the call
+    // like the bare-URL arm below; narrowing it to a string would throw on
+    // the URL arm.
+    const unionWithUrl =
+      input.type.kind === "union" &&
+      (lowerer.unions.get(input.type.unionId)?.arms.some((arm) => arm.kind === "url") ?? false) &&
+      lowerer.dynConvertible(input.type);
+    const dynInput: IrExpr | null =
+      input.type.kind === "dyn"
+        ? inputRef
+        : unionWithUrl
+          ? { kind: "dynFrom", value: inputRef, type: DYN, loc: locOf(inputNode) }
+          : null;
     const url: IrExpr =
       input.type.kind === "url"
         ? {
@@ -628,13 +642,13 @@ export function lowerFetchCall(lowerer: Lowerer, call: ts.CallExpression): IrExp
             type: STRING,
             loc: locOf(inputNode),
           }
-        : input.type.kind === "dyn"
-          ? inputRef
+        : dynInput !== null
+          ? dynInput
           : lowerer.coerceInto(inputNode, inputRef, STRING);
     const answer: IrExpr = {
       kind: "libCall",
-      fn: input.type.kind === "dyn" ? "fetch.input" : "fetch.start",
-      args: [input.type.kind === "dyn" ? inputRef : url, initRef],
+      fn: dynInput !== null ? "fetch.input" : "fetch.start",
+      args: [url, initRef],
       type: { kind: "promise", inner: DYN },
       loc,
     };

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

@@ -1360,8 +1360,9 @@ export function mapAsyncGeneratorAnnotation(type: ts.Type, ctx: TypeMapperCtx):
   if (
     !symbol ||
     !["AsyncIterator", "AsyncIterableIterator", "AsyncIterable"].includes(symbol.name) ||
-    !symbol.declarations
-      .some((d) => ts.isInterfaceDeclaration(d) && ctx.isStdlibFile(d.getSourceFile()))
+    !symbol.declarations.some(
+      (d) => ts.isInterfaceDeclaration(d) && ctx.isStdlibFile(d.getSourceFile()),
+    )
   )
     return null;
   const args = checker.getTypeArguments(type as ts.TypeReference);
@@ -2513,12 +2514,11 @@ function mapTypeInner(type: ts.Type, ctx: TypeMapperCtx): IrType | null {
   if (
     psym &&
     WEBCRYPTO_DYN_TYPES.has(psym.name) &&
-    psym.declarations
-      .some(
-        (d) =>
-          (ts.isClassDeclaration(d) || ts.isInterfaceDeclaration(d)) &&
-          ctx.isStdlibFile(d.getSourceFile()),
-      )
+    psym.declarations.some(
+      (d) =>
+        (ts.isClassDeclaration(d) || ts.isInterfaceDeclaration(d)) &&
+        ctx.isStdlibFile(d.getSourceFile()),
+    )
   ) {
     return DYN;
   }
@@ -4184,7 +4184,9 @@ function mapTypeInner(type: ts.Type, ctx: TypeMapperCtx): IrType | null {
       // semantics would DEGRADE under the collapse — class instances,
       // Maps/Sets, functions (closure identity, `x === String`
       // narrowing), promises, regexes, generators, handles — keep their
-      // existing union homes and fences below. A pending recursive
+      // existing union homes and fences below. URL is the
+      // exception: its handle boxes by reference and keeps every member,
+      // so it collapses too (dynSubsumableUnionArm). A pending recursive
       // placeholder cannot collapse (back-references already hold the
       // union id); the degenerate recursive spelling keeps its fence.
       if (
@@ -6285,6 +6287,13 @@ function dynSubsumableUnionArm(arm: IrType, ctx: TypeMapperCtx): boolean {
     case "undefinedT":
     case "nullT":
       return true;
+    // URL boxes BY REFERENCE (its checked-dynamic handle keeps identity,
+    // reads and writes its members through the native accessors, answers
+    // `instanceof URL`, and checks back out to the typed value), so it
+    // rides the collapse beside fetch's Request/Response handles:
+    // `string | URL | Request`, fetch's own input type under @types/node.
+    case "url":
+      return true;
     case "record":
     case "array":
       return canConvertToDyn(

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6252-fetch-input-url-unions.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6252-fetch-input-url-unions.ts"
+ ],
+ "diags": []
+}

packages/compiler/test/ts7/baselines/order-parity/tests/fixtures/node-types/fetch-input-unions.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/fixtures/node-types/fetch-input-unions.ts"
+ ],
+ "diags": []
+}

tests/corpus/6252-fetch-input-url-unions.ts

@@ -0,0 +1,48 @@
+// `typeof globalThis.fetch` under @types/node takes `string | URL | Request`:
+// unions holding URL handles beside fetch handles compile (URL boxes by
+// reference into the checked-dynamic representation), and a custom fetch
+// cast to that type through `unknown` keeps working, including an extra
+// init member written through a record view (the dispatcher pattern).
+import * as http from "node:http";
+type FetchImpl = typeof globalThis.fetch;
+interface DispatchingInit {
+  method?: string;
+  headers?: Record<string, string>;
+  dispatcher?: { name: string };
+}
+function customFetch(input: string | URL, init?: DispatchingInit): Promise<Response> {
+  console.log("custom fetch", typeof input === "string" ? "string" : "url", init?.dispatcher?.name ?? "none");
+  return fetch(input, { method: init?.method, headers: init?.headers });
+}
+const server = http.createServer((req, res) => res.end(`ok ${req.method} ${req.url}`));
+server.listen(0, "127.0.0.1", async () => {
+  const address = server.address();
+  const port = address !== null && typeof address === "object" ? address.port : 0;
+  const impl: FetchImpl = customFetch as unknown as FetchImpl;
+  const init: RequestInit = { method: "POST" };
+  (init as Record<string, unknown>).dispatcher = { name: "pinned" };
+  const res = await impl(`http://127.0.0.1:${port}/a`, init);
+  console.log(res.status, await res.text());
+  const viaUrl = await impl(new URL(`http://127.0.0.1:${port}/b`));
+  console.log(viaUrl.status, await viaUrl.text());
+  const direct = await fetch(new URL(`http://127.0.0.1:${port}/c`));
+  console.log(direct.status, await direct.text());
+  server.close();
+});
+
+function describeInput(input: string | Request | URL): string {
+  if (typeof input === "string") return `string ${input}`;
+  if (input instanceof URL) return `url ${input.href} ${input.hostname}`;
+  return `request ${input.method} ${input.url}`;
+}
+console.log(describeInput("http://a.test/x"));
+const u = new URL("http://b.test:8080/p?q=1");
+console.log(describeInput(u));
+console.log(describeInput(new Request("http://c.test/r", { method: "PUT" })));
+const items: (string | URL | Request)[] = [u, "s"];
+console.log(items.length, items[0] === u, String(items[0]));
+let slot: string | URL | Request = u;
+if (slot instanceof URL) { slot.pathname = "/changed"; }
+console.log(u.href);
+const params: string | Request | URL = new URL("http://d.test/?b=2");
+console.log(typeof params === "string" ? params : params instanceof URL ? params.searchParams.get("b") : "req");

tests/fixtures/node-types/fetch-input-unions.ts

@@ -0,0 +1,48 @@
+// `typeof globalThis.fetch` under @types/node takes `string | URL | Request`:
+// unions holding URL handles beside fetch handles compile (URL boxes by
+// reference into the checked-dynamic representation), and a custom fetch
+// cast to that type through `unknown` keeps working, including an extra
+// init member written through a record view (the dispatcher pattern).
+import * as http from "node:http";
+type FetchImpl = typeof globalThis.fetch;
+interface DispatchingInit {
+  method?: string;
+  headers?: Record<string, string>;
+  dispatcher?: { name: string };
+}
+function customFetch(input: string | URL, init?: DispatchingInit): Promise<Response> {
+  console.log("custom fetch", typeof input === "string" ? "string" : "url", init?.dispatcher?.name ?? "none");
+  return fetch(input, { method: init?.method, headers: init?.headers });
+}
+const server = http.createServer((req, res) => res.end(`ok ${req.method} ${req.url}`));
+server.listen(0, "127.0.0.1", async () => {
+  const address = server.address();
+  const port = address !== null && typeof address === "object" ? address.port : 0;
+  const impl: FetchImpl = customFetch as unknown as FetchImpl;
+  const init: RequestInit = { method: "POST" };
+  (init as Record<string, unknown>).dispatcher = { name: "pinned" };
+  const res = await impl(`http://127.0.0.1:${port}/a`, init);
+  console.log(res.status, await res.text());
+  const viaUrl = await impl(new URL(`http://127.0.0.1:${port}/b`));
+  console.log(viaUrl.status, await viaUrl.text());
+  const direct = await fetch(new URL(`http://127.0.0.1:${port}/c`));
+  console.log(direct.status, await direct.text());
+  server.close();
+});
+
+function describeInput(input: string | Request | URL): string {
+  if (typeof input === "string") return `string ${input}`;
+  if (input instanceof URL) return `url ${input.href} ${input.hostname}`;
+  return `request ${input.method} ${input.url}`;
+}
+console.log(describeInput("http://a.test/x"));
+const u = new URL("http://b.test:8080/p?q=1");
+console.log(describeInput(u));
+console.log(describeInput(new Request("http://c.test/r", { method: "PUT" })));
+const items: (string | URL | Request)[] = [u, "s"];
+console.log(items.length, items[0] === u, String(items[0]));
+let slot: string | URL | Request = u;
+if (slot instanceof URL) { slot.pathname = "/changed"; }
+console.log(u.href);
+const params: string | Request | URL = new URL("http://d.test/?b=2");
+console.log(typeof params === "string" ? params : params instanceof URL ? params.searchParams.get("b") : "req");

tests/harness/project-config.test.ts

@@ -73,6 +73,27 @@ test("node-types: Headers, Request and Response members typed by undici-types ru
   expect(comparableStderr(native.stderr)).toBe(node.stderr);
 });
 
+test("node-types: fetch's string | URL | Request input and a custom fetch cast to typeof fetch", async () => {
+  const outDir = outDirFor("fetch-input-unions");
+  const entry = join(nodeTypesDir, "fetch-input-unions.ts");
+  const result = await compile(entry, {
+    outPath: join(
+      outDir,
+      process.platform === "win32" ? "fetch-input-unions.exe" : "fetch-input-unions",
+    ),
+    outDir,
+    sanitize,
+  });
+  expect(result.ok, !result.ok ? JSON.stringify(result.diagnostics, null, 2) : "").toBe(true);
+  if (!result.ok) return;
+  const [native, node] = await Promise.all([
+    execFileAsync(result.binaryPath),
+    execFileAsync(process.execPath, ["--disable-warning=MODULE_TYPELESS_PACKAGE_JSON", entry]),
+  ]);
+  expect(native.stdout).toBe(node.stdout);
+  expect(comparableStderr(native.stderr)).toBe(node.stderr);
+});
+
 test("node-types: http header arrays and server.address() follow @types/node's types", async () => {
   const outDir = outDirFor("http-headers-address");
   const entry = join(nodeTypesDir, "http-headers-address.ts");