Bug 1507952 - Part 5: stream.tee() should not try to call a .start() method. r=arai

This fix is not particularly clean, but at least it's possible to see why the
if statement is there, now that the comments explain how we (imperfectly)
implement the {start,pull,cancel}Algorithm arguments.

Differential Revision: https://phabricator.services.mozilla.com/D12459

--HG--
extra : moz-landing-system : lando

js/src/builtin/Stream.cpp

@@ -3135,10 +3135,14 @@ SetUpReadableStreamDefaultController(JSContext* cx,
     stream->setController(controller);
 
     // Step 9: Let startResult be the result of performing startAlgorithm.
+    // If this is a tee stream, the startAlgorithm does nothing and returns
+    // undefined.
     RootedValue startResult(cx);
-    RootedValue controllerVal(cx, ObjectValue(*controller));
-    if (!InvokeOrNoop(cx, underlyingSource, cx->names().start, controllerVal, &startResult)) {
-        return false;
+    if (!underlyingSource.isObject() || !underlyingSource.toObject().is<TeeState>()) {
+        RootedValue controllerVal(cx, ObjectValue(*controller));
+        if (!InvokeOrNoop(cx, underlyingSource, cx->names().start, controllerVal, &startResult)) {
+            return false;
+        }
     }
 
     // Step 10: Let startPromise be a promise resolved with startResult.

js/src/tests/non262/ReadableStream/tee-start.js

@@ -0,0 +1,11 @@
+// |reftest| skip-if(!this.ReadableStream||!this.drainJobQueue)
+// stream.tee() shouldn't try to call a .start() method.
+
+Object.prototype.start = function () { throw "FAIL"; };
+let source = Object.create(null);
+new ReadableStream(source).tee();
+
+drainJobQueue();
+
+if (typeof reportCompare == 'function')
+    reportCompare(0, 0);

testing/web-platform/meta/streams/readable-streams/patched-global.dedicatedworker.html.ini

@@ -1,4 +0,0 @@
-[patched-global.dedicatedworker.html]
-  [ReadableStream tee() should not touch Object.prototype properties]
-    expected: FAIL
-

testing/web-platform/meta/streams/readable-streams/patched-global.html.ini

@@ -1,4 +0,0 @@
-[patched-global.html]
-  [ReadableStream tee() should not touch Object.prototype properties]
-    expected: FAIL
-

testing/web-platform/meta/streams/readable-streams/patched-global.serviceworker.https.html.ini

@@ -1,4 +0,0 @@
-[patched-global.serviceworker.https.html]
-  [ReadableStream tee() should not touch Object.prototype properties]
-    expected: FAIL
-

testing/web-platform/meta/streams/readable-streams/patched-global.sharedworker.html.ini

@@ -1,4 +0,0 @@
-[patched-global.sharedworker.html]
-  [ReadableStream tee() should not touch Object.prototype properties]
-    expected: FAIL
-