hermes-webui/tests/test_issue4856_android_scroll_regression.py

"""Regression tests for #4856: Android scroll-to-top on every interaction."""

from pathlib import Path

REPO = Path(__file__).parent.parent
UI_JS = (REPO / "static" / "ui.js").read_text(encoding="utf-8")
MESSAGES_JS = (REPO / "static" / "messages.js").read_text(encoding="utf-8")

_FUNC_MARKER = "window._fixMobileScrollJank=function _fixMobileScrollJank(){"
_RAF_MARKER = "requestAnimationFrame(()=>{"


def _extract_fix_mobile_scroll_jank(src: str) -> str:
    idx = src.find(_FUNC_MARKER)
    assert idx != -1, "_fixMobileScrollJank not found in ui.js"
    depth = 0
    for i, ch in enumerate(src[idx:], idx):
        if ch == "{":
            depth += 1
        elif ch == "}":
            depth -= 1
            if depth == 0:
                return src[idx : i + 1]
    raise AssertionError("Could not extract _fixMobileScrollJank")


def _extract_raf_body(fn_src: str) -> str:
    idx = fn_src.find(_RAF_MARKER)
    assert idx != -1, "requestAnimationFrame callback not found in function"
    depth = 0
    for i, ch in enumerate(fn_src[idx:], idx):
        if ch == "{":
            depth += 1
        elif ch == "}":
            depth -= 1
            if depth == 0:
                return fn_src[idx : i + 1]
    raise AssertionError("Could not extract rAF body")


def test_fix_sets_none_not_auto():
    # Base-fails/head-passes: function must set 'none' to suppress Chromium
    # scroll-anchor re-selection; 'auto' is already the CSS default so setting
    # it is a no-op and leaves the anchor engine active during the DOM wipe.
    fn = _extract_fix_mobile_scroll_jank(UI_JS)
    assert "overflowAnchor='none'" in fn, (
        "_fixMobileScrollJank() must set overflowAnchor='none' to suppress "
        "Chromium scroll-anchor re-selection during the DOM wipe (#4856)."
    )
    assert "overflowAnchor='auto'" not in fn, (
        "_fixMobileScrollJank() must not set overflowAnchor='auto'; that is "
        "already the CSS resting value on mobile and is a no-op."
    )


def test_raf_cleanup_checks_none():
    # The rAF guard must check for 'none' so it only clears the inline style
    # it set; checking 'auto' was always false and left the inline style on.
    fn = _extract_fix_mobile_scroll_jank(UI_JS)
    raf = _extract_raf_body(fn)
    assert "overflowAnchor==='none'" in raf, (
        "The rAF cleanup in _fixMobileScrollJank() must check for 'none' so it "
        "clears the inline style after the synchronous scrollTop write lands."
    )
    assert "overflowAnchor==='auto'" not in raf, (
        "The rAF cleanup must not check for 'auto'; that check was always false."
    )


def test_rebuild_path_calls_fix_before_wipe():
    # renderMessages() must call _fixMobileScrollJank() before innerHTML='' so
    # anchor suppression is active during the full wipe-and-rebuild window.
    fix_idx = UI_JS.find("window._fixMobileScrollJank()")
    assert fix_idx != -1, (
        "renderMessages() must call window._fixMobileScrollJank() before innerHTML=''."
    )
    wipe_idx = UI_JS.find("innerHTML=''", fix_idx)
    assert wipe_idx != -1, (
        "innerHTML='' not found after _fixMobileScrollJank() call site."
    )
    assert fix_idx < wipe_idx, (
        "_fixMobileScrollJank() must be called before innerHTML='' in renderMessages()."
    )


def test_rebuild_path_marks_dom_wipe_scroll_as_programmatic():
    # During innerHTML='' the scroller can transiently collapse to clientHeight
    # and clamp scrollTop to 0. That browser event must be suppressed as
    # programmatic; otherwise the scroll listener treats it as user upward
    # intent and disables live auto-follow.
    fix_idx = UI_JS.find("window._fixMobileScrollJank()")
    assert fix_idx != -1, "renderMessages() guard call not found"
    wipe_idx = UI_JS.find("innerHTML=''", fix_idx)
    assert wipe_idx != -1, "innerHTML='' not found after _fixMobileScrollJank()"
    window = UI_JS[fix_idx:wipe_idx]
    assert "_programmaticScroll=true" in window, (
        "renderMessages() must mark the DOM wipe/rebuild scroll event as "
        "programmatic before innerHTML='' can clamp scrollTop."
    )
    assert "_programmaticScrollSetAt=performance.now()" in window
    assert UI_JS.find("_deferClearProgrammaticScroll(160)", wipe_idx) != -1, (
        "renderMessages() must clear the programmatic-scroll suppression after "
        "the rebuild/post-render paint window."
    )


def test_recent_render_scroll_artifact_window_suppresses_upward_unpin():
    # Some browsers emit a follow-up scroll event shortly after renderMessages()
    # finishes (for example while late layout settles after a send). With no
    # wheel/touch intent, that post-render upward delta is still a render
    # artifact and must not disable live follow.
    assert "let _lastMessageRenderAt=-Infinity" in UI_JS
    assert "_lastMessageRenderAt=performance.now()" in UI_JS
    assert "function _recentMessageRenderArtifactWindow" in UI_JS
    listener_idx = UI_JS.find("el.addEventListener('scroll'")
    assert listener_idx != -1, "messages scroll listener not found"
    listener = UI_JS[listener_idx: listener_idx + 4000]
    assert "_recentMessageRenderArtifactWindow(1400)" in listener
    assert "!_recentMessageTouchScrollIntent()" in listener
    assert "!_recentNonMessageScrollIntent()" in listener
    assert "!_recentMessageWheelIntent()" in listener, (
        "#4970: the post-render artifact suppression must also require no recent "
        "low-delta message-pane wheel intent so a gentle trackpad scroll-up is "
        "not swallowed."
    )
    assert listener.find("return;") < listener.find("if(movedUp){"), (
        "recent render artifact scrolls must return before the movedUp branch "
        "can mark the reader unpinned."
    )


# ── #4970 low-delta wheel intent: behavioral node-harness ────────────────────
import json  # noqa: E402
import shutil  # noqa: E402
import subprocess  # noqa: E402

import pytest  # noqa: E402

NODE = shutil.which("node")


def _balanced_block(src: str, brace_start: int) -> str:
    depth = 0
    for i in range(brace_start, len(src)):
        ch = src[i]
        if ch == "{":
            depth += 1
        elif ch == "}":
            depth -= 1
            if depth == 0:
                return src[brace_start + 1 : i]
    raise AssertionError("balanced block not found")


def _scroll_listener_raf_body() -> str:
    listener_start = UI_JS.index("el.addEventListener('scroll'")
    raf_start = UI_JS.index("requestAnimationFrame(()=>", listener_start)
    brace_start = UI_JS.index("{", raf_start)
    return _balanced_block(UI_JS, brace_start)


def _run_listener_with_wheel_intent(
    samples, *, render_artifact, wheel_intent, scrollbar_drag=False, key_scroll=False
):
    """Run the extracted scroll-listener body in node with controllable stubs.

    Mirrors the #4295 harness shape but injects the #4970 helpers so we can
    exercise the production suppression path: artifact window active AND a
    recent gentle wheel intent must still unpin (return _messageUserUnpinned).
    """
    payload = {
        "body": _scroll_listener_raf_body(),
        "samples": samples,
        "renderArtifact": bool(render_artifact),
        "wheelIntent": bool(wheel_intent),
        "scrollbarDrag": bool(scrollbar_drag),
        "keyScroll": bool(key_scroll),
    }
    script = (
        "const payload = " + json.dumps(payload) + ";\n"
        + r"""
const step = new Function(
  'el',
  '_lastScrollTop',
  '_lastMessageClientHeight',
  '_nearBottomCount',
  '_scrollPinned',
  '_messageUserUnpinned',
  '_newMessageCueVisible',
  '_programmaticScroll',
  '_cancelBottomSettle',
  '_clearNewMessageScrollCue',
  '_syncScrollToBottomCue',
  '_updateSessionStartJumpButton',
  '_isSessionEndlessScrollEnabled',
  '_messagesTruncated',
  '_loadOlderMessages',
  '_recentMessageRenderArtifactWindow',
  '_recentMessageTouchScrollIntent',
  '_recentNonMessageScrollIntent',
  '_recentMessageWheelIntent',
  '_scrollbarDragActive',
  '_recentMessageKeyScrollIntent',
  // The extracted listener body uses bare `return;` in the suppression branch.
  // Wrap it in an inner arrow IIFE so that early return exits the IIFE (not the
  // outer Function), then read the mutated locals afterward. Without this the
  // suppression path would return undefined before the state snapshot.
  '(()=>{' + payload.body + `})();
return {
  _lastScrollTop,
  _lastMessageClientHeight,
  _nearBottomCount,
  _scrollPinned,
  _messageUserUnpinned,
};
`
);

let state = {
  _lastScrollTop: 800,
  _lastMessageClientHeight: null,
  _nearBottomCount: 0,
  _scrollPinned: true,
  _messageUserUnpinned: false,
};

const noop = () => {};
const renderArtifact = () => payload.renderArtifact;
const noTouch = () => false;
const noNonMessage = () => false;
const wheelIntent = () => payload.wheelIntent;
const keyScroll = () => payload.keyScroll;

for (const sample of payload.samples) {
  state = step(
    sample,
    state._lastScrollTop,
    state._lastMessageClientHeight,
    state._nearBottomCount,
    state._scrollPinned,
    state._messageUserUnpinned,
    false,
    false,
    noop,
    noop,
    noop,
    noop,
    () => false,
    false,
    noop,
    renderArtifact,
    noTouch,
    noNonMessage,
    wheelIntent,
    payload.scrollbarDrag,
    keyScroll
  );
}

console.log(JSON.stringify(state));
"""
    )
    result = subprocess.run(
        [NODE, "-e", script],
        check=True,
        capture_output=True,
        text=True,
        timeout=30,
    )
    return json.loads(result.stdout.strip())


@pytest.mark.skipif(NODE is None, reason="node not on PATH")
class TestPostRenderWheelIntentScope:
    # A small upward scrollTop delta (800 -> 760) is `movedUp`. We hold the
    # render artifact window OPEN for all cases so the only variable is whether
    # the reader had recent gentle wheel intent.
    _SAMPLES = [{"scrollTop": 760, "scrollHeight": 1200, "clientHeight": 200}]

    def test_gentle_wheel_inside_artifact_window_still_unpins(self):
        # #4970 MUST-FIX: with the artifact window active but a recent low-delta
        # wheel intent, a real upward scroll must NOT be swallowed — it must
        # unpin live-follow just like any genuine scroll-up.
        state = _run_listener_with_wheel_intent(
            self._SAMPLES, render_artifact=True, wheel_intent=True
        )
        assert state["_messageUserUnpinned"] is True, (
            "A genuine gentle (low-delta) wheel scroll-up inside the post-render "
            "artifact window must still unpin; the suppression must be scoped to "
            "the no-intent artifact case only."
        )
        assert state["_scrollPinned"] is False

    def test_no_intent_artifact_inside_window_is_suppressed(self):
        # Control: same upward delta, same open window, but NO wheel intent — a
        # true post-render artifact — stays pinned (the suppression still works).
        state = _run_listener_with_wheel_intent(
            self._SAMPLES, render_artifact=True, wheel_intent=False
        )
        assert state["_messageUserUnpinned"] is False, (
            "A no-intent upward delta inside the artifact window is a render "
            "artifact and must be suppressed (reader stays pinned)."
        )
        assert state["_scrollPinned"] is True

    def test_gentle_wheel_outside_window_unpins(self):
        # Outside the artifact window the suppression never applies, so the
        # upward delta unpins regardless of intent tracking.
        state = _run_listener_with_wheel_intent(
            self._SAMPLES, render_artifact=False, wheel_intent=False
        )
        assert state["_messageUserUnpinned"] is True
        assert state["_scrollPinned"] is False

    def test_scrollbar_drag_inside_window_still_unpins(self):
        # #4970 review SHOULD-FIX: a manual scrollbar-drag upward scroll inside
        # the post-render window is real user intent and must NOT be swallowed,
        # even with no wheel/touch intent recorded.
        state = _run_listener_with_wheel_intent(
            self._SAMPLES,
            render_artifact=True,
            wheel_intent=False,
            scrollbar_drag=True,
        )
        assert state["_messageUserUnpinned"] is True, (
            "A scrollbar-drag upward scroll inside the artifact window must "
            "unpin; the suppression must not swallow an active scrollbar drag."
        )
        assert state["_scrollPinned"] is False

    def test_keyboard_scroll_inside_window_still_unpins(self):
        # #4970 review (greptile P1): a keyboard scroll-up (PageUp/Arrow/etc.)
        # inside the post-render window is real intent and must NOT be swallowed,
        # even with no wheel/touch/scrollbar intent recorded.
        state = _run_listener_with_wheel_intent(
            self._SAMPLES,
            render_artifact=True,
            wheel_intent=False,
            key_scroll=True,
        )
        assert state["_messageUserUnpinned"] is True, (
            "A keyboard scroll-up inside the artifact window must unpin; the "
            "suppression must not swallow a recent keyboard scroll intent."
        )
        assert state["_scrollPinned"] is False


def test_low_delta_wheel_intent_is_tracked_separately():
    # The intent recorder must stamp _lastMessageWheelIntentMs for ANY upward
    # wheel (deltaY<0), not only the decisive deltaY<-30 sticky-unpin threshold.
    assert "let _lastMessageWheelIntentMs=-Infinity" in UI_JS
    assert "function _recentMessageWheelIntent" in UI_JS
    rec_idx = UI_JS.find("function _recordNonMessageScrollIntent")
    assert rec_idx != -1, "_recordNonMessageScrollIntent not found"
    rec = UI_JS[rec_idx: rec_idx + 1400]
    assert "e.deltaY<0) _lastMessageWheelIntentMs=performance.now()" in rec, (
        "#4970: _recordNonMessageScrollIntent must record low-delta upward wheel "
        "intent (deltaY<0) separately from the decisive deltaY<-30 unpin."
    )
    # The decisive sticky-unpin threshold must remain unchanged.
    assert "e.deltaY< -30" in rec, (
        "The existing deltaY<-30 direct sticky-unpin threshold must be preserved."
    )


def _extract_fn_body(name: str) -> str:
    idx = UI_JS.find("function " + name + "(")
    assert idx != -1, name + " not found in ui.js"
    brace = UI_JS.index("{", idx)
    depth = 0
    for i in range(brace, len(UI_JS)):
        ch = UI_JS[i]
        if ch == "{":
            depth += 1
        elif ch == "}":
            depth -= 1
            if depth == 0:
                return UI_JS[idx : i + 1]
    raise AssertionError("unbalanced body for " + name)


def test_session_switch_reset_clears_wheel_intent():
    # #4970 review MUST-FIX 1: _resetScrollDirectionTracker() must clear the
    # low-delta wheel intent stamp so a gentle wheel in the previous chat does
    # not leak into the new chat's first post-render artifact window.
    body = _extract_fn_body("_resetScrollDirectionTracker")
    assert "_lastMessageWheelIntentMs=-Infinity" in body, (
        "_resetScrollDirectionTracker() must reset _lastMessageWheelIntentMs so "
        "stale wheel intent cannot cross a session switch."
    )


def test_stream_start_reset_clears_wheel_intent():
    # #4970 review MUST-FIX 2: _resetStreamScrollFollow() must clear the wheel
    # intent stamp so a gentle wheel just before a fresh stream cannot
    # under-suppress a no-intent artifact and silently disable live follow.
    body = _extract_fn_body("_resetStreamScrollFollow")
    assert "_lastMessageWheelIntentMs=-Infinity" in body, (
        "_resetStreamScrollFollow() must reset _lastMessageWheelIntentMs so "
        "stale wheel intent cannot cross a fresh stream start."
    )


def test_suppression_gates_on_scrollbar_drag():
    # #4970 review SHOULD-FIX 3: the post-render suppression must not fire while
    # a scrollbar drag is active — that upward scroll is real user intent.
    assert "let _scrollbarDragActive=false" in UI_JS
    listener_idx = UI_JS.find("el.addEventListener('scroll'")
    assert listener_idx != -1, "messages scroll listener not found"
    listener = UI_JS[listener_idx: listener_idx + 4000]
    assert "!_scrollbarDragActive" in listener, (
        "#4970 review: the suppression branch must reference !_scrollbarDragActive "
        "so a scrollbar-drag upward scroll inside the window is not swallowed."
    )


def test_keyboard_scroll_intent_tracked_and_gated():
    # #4970 review (greptile P1): keyboard message-pane scrolling must be recorded
    # as user intent and excluded from the post-render suppression branch.
    assert "let _lastMessageKeyScrollIntentMs=-Infinity" in UI_JS
    assert "function _recentMessageKeyScrollIntent" in UI_JS
    # A keydown listener must stamp the intent for the pane scroll keys.
    assert "_lastMessageKeyScrollIntentMs=performance.now()" in UI_JS, (
        "a keydown handler must stamp _lastMessageKeyScrollIntentMs when the "
        "reader uses the keyboard to scroll the message pane."
    )
    assert "'PageUp'" in UI_JS and "'PageDown'" in UI_JS
    # The suppression branch must consult it.
    listener_idx = UI_JS.find("el.addEventListener('scroll'")
    listener = UI_JS[listener_idx: listener_idx + 4000]
    assert "!_recentMessageKeyScrollIntent()" in listener, (
        "#4970 review: the suppression branch must reference "
        "!_recentMessageKeyScrollIntent() so a keyboard scroll-up unpins."
    )
    # Both resets must clear the keyboard stamp (stale-state hygiene).
    assert "_lastMessageKeyScrollIntentMs=-Infinity" in _extract_fn_body(
        "_resetScrollDirectionTracker"
    )
    assert "_lastMessageKeyScrollIntentMs=-Infinity" in _extract_fn_body(
        "_resetStreamScrollFollow"
    )


def test_streaming_tick_calls_fix_before_dom_writes():
    # The streaming render tick in messages.js must call _fixMobileScrollJank()
    # before _lastRenderMs=performance.now() so anchor suppression covers every
    # incremental DOM update during streaming.
    guard_idx = MESSAGES_JS.find("window._fixMobileScrollJank")
    assert guard_idx != -1, (
        "The streaming tick must call window._fixMobileScrollJank() before DOM writes."
    )
    render_idx = MESSAGES_JS.find("_lastRenderMs=performance.now()")
    assert render_idx != -1, "streaming render timestamp not found in messages.js"
    assert guard_idx < render_idx, (
        "The mobile scroll-jank guard must run before streaming DOM work begins."
    )