Fix bug which stopped us scrolling down after we scrolled up

src/components/structures/TimelinePanel.js

@@ -241,11 +241,25 @@ var TimelinePanel = React.createClass({
             if (this.unmounted) { return; }
 
             debuglog("TimelinePanel: paginate complete backwards:"+backwards+"; success:"+r);
-            this.setState({
+
+            var newState = {
                 [paginatingKey]: false,
                 [canPaginateKey]: r,
                 events: this._getEvents(),
-            });
+            };
+
+            // moving the window in this direction may mean that we can now
+            // paginate in the other where we previously could not.
+            var otherDirection = backwards ? EventTimeline.FORWARDS : EventTimeline.BACKWARDS;
+            var canPaginateOtherWayKey = backwards ? 'canForwardPaginate' : 'canBackPaginate';
+            if (!this.state[canPaginateOtherWayKey] &&
+                    this._timelineWindow.canPaginate(otherDirection)) {
+                debuglog('TimelinePanel: can now', otherDirection, 'paginate again');
+                newState[canPaginateOtherWayKey] = true;
+            }
+
+            this.setState(newState);
+
             return r;
         });
     },

test/components/structures/TimelinePanel-test.js

@@ -204,4 +204,72 @@ describe('TimelinePanel', function() {
             }, 0);
         }, 0);
     });
+
+    it("should let you scroll down again after you've scrolled up", function(done) {
+        var N_EVENTS = 600;
+
+        // sadly, loading all those events takes a while
+        this.timeout(N_EVENTS * 20);
+
+        // client.getRoom is called a /lot/ in this test, so replace
+        // sinon's spy with a fast noop.
+        client.getRoom = function(id) { return null; };
+
+        // fill the timeline with lots of events
+        for (var i = 0; i < N_EVENTS; i++) {
+            timeline.addEvent(mkMessage());
+        }
+
+        var scrollDefer;
+        var panel = ReactDOM.render(
+            <TimelinePanel room={room} onScroll={()=>{scrollDefer.resolve()}} />,
+            parentDiv
+        );
+
+        var messagePanel = ReactTestUtils.findRenderedComponentWithType(
+            panel, sdk.getComponent('structures.MessagePanel'));
+        var scrollingDiv = ReactTestUtils.findRenderedDOMComponentWithClass(
+            panel, "gm-scroll-view");
+
+        // helper function which will return a promise which resolves when
+        // the TimelinePanel fires a scroll event
+        var awaitScroll = function() {
+            scrollDefer = q.defer();
+            return scrollDefer.promise;
+        };
+
+        function backPaginate() {
+            scrollingDiv.scrollTop = 0;
+            return awaitScroll().then(() => {
+                if(scrollingDiv.scrollTop > 0) {
+                    // need to go further
+                    return backPaginate();
+                }
+
+                // hopefully, we got to the start of the timeline
+                expect(messagePanel.props.backPaginating).toBe(false);
+            });
+        }
+
+        // let the first round of pagination finish off
+        awaitScroll().then(() => {
+            // we should now have loaded the first few events
+            expect(messagePanel.props.backPaginating).toBe(false);
+            expect(messagePanel.props.suppressFirstDateSeparator).toBe(true);
+
+            // back-paginate until we hit the start
+            return backPaginate();
+        }).then(() => {
+            expect(messagePanel.props.suppressFirstDateSeparator).toBe(false);
+            var events = scryEventTiles(panel);
+            expect(events[0].props.mxEvent).toBe(timeline.getEvents()[0])
+
+            // we should now be able to scroll down, and paginate in the other
+            // direction.
+            scrollingDiv.scrollTop = scrollingDiv.scrollHeight;
+            return awaitScroll();
+        }).then(() => {
+            console.log("done");
+        }).done(done, done);
+    });
 });

test/test-utils.js

@@ -42,16 +42,18 @@ module.exports.stubClient = function() {
         sendReadReceipt: sinon.stub().returns(q()),
     };
 
-    // create the peg
-
+    // stub out the methods in MatrixClientPeg
+    //
     // 'sandbox.restore()' doesn't work correctly on inherited methods,
     // so we do this for each method
     var methods = ['get', 'unset', 'replaceUsingUrls',
                    'replaceUsingAccessToken'];
     for (var i = 0; i < methods.length; i++) {
         sandbox.stub(peg, methods[i]);
     }
-    peg.get.returns(client);
+    // MatrixClientPeg.get() is called a /lot/, so implement it with our own
+    // fast stub function rather than a sinon stub
+    peg.get = function() { return client; };
     return sandbox;
 }