feat: Added virtualization component

[rkaraivanov]

Description

Added virtualization component

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that causes existing functionality to change)
• Documentation update
• Refactoring (code improvements without functional changes)

Checklist

• My code follows the project's coding standards
• I have tested my changes locally
• I have updated documentation if needed
• Breaking changes are documented in the description

[Copilot]

Pull request overview

Introduces a new igc-virtual-scroll component to provide in-house list virtualization and wires it into the Combo component to replace the previous @lit-labs/virtualizer-based implementation.

Changes:

• Added a new virtualization engine + igc-virtual-scroll component, along with Storybook stories and unit tests.
• Updated Combo to use igc-virtual-scroll for its dropdown list (types, navigation behavior, styles, and tests updated accordingly).
• Improved test stability/logging by centralizing ResizeObserver-loop suppression and filtering benign null browser logs in web-test-runner output.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
web-test-runner.config.mjs	Adds a custom reporter to filter benign null browser logs before the default reporter runs.
stories/virtual-scroll.stories.ts	New Storybook stories demonstrating vertical/horizontal, variable size, and remote-data virtualization scenarios.
src/index.ts	Exports the new virtual scroll component and its public types/events.
src/components/virtualization/virtualization.ts	New igc-virtual-scroll Lit component integrating the engine, measurements, scrolling API, and events.
src/components/virtualization/virtualization.spec.ts	New tests for accessibility, events, public API, engine integration, and RTL behavior.
src/components/virtualization/types.ts	Defines public types: item context, state snapshot, and data request payload.
src/components/virtualization/engine.ts	New virtualization math engine (Fenwick tree/BIT-based sizing + visible-range computations).
src/components/common/utils.spec.ts	Adds shared suppressResizeObserverLoopError() helper for tests.
src/components/combo/types.ts	Switches Combo render-function typing to use the new virtual scroll item template type.
src/components/combo/themes/combo.base.scss	Adjusts list sizing styles to work with the new virtual scroll list element.
src/components/combo/controllers/navigation.ts	Updates scrolling behavior to use scrollToIndex() instead of scrollIntoView().
src/components/combo/combo.ts	Replaces igc-combo-list with igc-virtual-scroll and adapts rendering/theming integration.
src/components/combo/combo.spec.ts	Updates Combo tests to await virtual scroll layoutComplete and query the new list element.
src/components/combo/combo-list.ts	Removes the old LitVirtualizer-based igc-combo-list component.
src/components/chat/chat.spec.ts	Uses the shared ResizeObserver-loop suppression helper.

[ChronosSF]

@rkaraivanov , I am noticing a potentially faulty behavior. So I added a virtualization combo story (with opus, we can remove it later) in the storybook with some controls. When navigating by index, the item, while in the rendered frame is actually not in the view frame.

You can reproduce it by either scrolling to the middle with the button or by searching for a specific item.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (2)

src/components/virtualization/virtualization.ts:309

• aria-hidden="true" on the track element hides all rendered items from the accessibility tree (including when the host is used as a role="listbox" in combo), which can make options undiscoverable to screen readers.

      <div part="igc-vs-track" style=${styleMap(trackStyle)} aria-hidden="true">

src/components/virtualization/virtualization.ts:473

• scrollToIndex() accepts ScrollIntoViewOptions, but it forwards those options into Element.scrollTo(), which expects ScrollToOptions. This is already causing callers to pass block: 'center', which has no effect and is misleading.

  /** Programmatically scrolls to the specified item index. */
  public scrollToIndex(index: number, options?: ScrollIntoViewOptions): void {
    const offset = this._engine.getScrollOffsetForIndex(index);

[rkaraivanov]

@ChronosSF
This should be fixed with the latest commit.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 5 comments.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 19 out of 20 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 19 out of 20 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/components/virtualization/virtualization.ts:261

• When orientation changes, _scrollPosition keeps the previous axis value until the next scroll event fires. This can render the wrong range immediately after switching orientation (e.g. a scrolled vertical list switched to horizontal still uses the old scrollTop value as if it were scrollLeft). Consider syncing _scrollPosition to the current axis right after updating the listener.

    if (changed.has('orientation')) {
      this._measureViewport();
      this._setupScrollListener();
    }

[Copilot]

Pull request overview

Copilot reviewed 19 out of 20 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (3)

web-test-runner.config.mjs:15

• The comment claims this reporter filters only the benign ResizeObserver-loop noise “without hiding other, legitimate console.* output”, but the filter condition removes any single-argument null log entry — including an intentional console.log(null) from a test. Either narrow the filter further (if possible with the available log metadata) or adjust the comment to reflect the trade-off.

 * but web-test-runner's browser log collection picks the (error-less)
 * exception up independently of that, printing it as a bare `null` line.
 * This reporter strips those specific single-`null`-argument log entries
 * before the default reporter prints anything, without hiding other,
 * legitimate `console.*` output from tests.

src/components/virtualization/virtualization.ts:425

• _scrollAndWaitForEnd() attaches a scrollend listener but if the timeout wins the Promise.race, the listener is never removed. In browsers/environments where scrollend doesn't fire (unsupported, disconnected mid-scroll, etc.), repeated calls can leak listeners and later resolve stale promises unexpectedly. Consider removing the listener in a finally block (or using an AbortController signal) so the timeout path always cleans up.

    const settled = new Promise<void>((resolve) => {
      this.addEventListener('scrollend', () => resolve(), { once: true });
    });

    this._applyScroll(offset, behavior);

    return Promise.race([settled, this._timeout(SCROLL_END_TIMEOUT_MS)]);

src/components/combo/combo.ts:249

• aria-activedescendant can become stale when the active index is reset to -1: _activeDescendant is never cleared, so the listbox can keep pointing to an element ID that no longer exists in the DOM. Clear _activeDescendant when deactivating to avoid invalid ARIA references.

  @state()
  private set _activeIndex(index: number) {
    this._navigation.active = index;
    this._listRef.value?.requestUpdate();
  }

[Copilot]

Pull request overview

Copilot reviewed 19 out of 20 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/components/combo/controllers/navigation.ts:220

• _scrollToActive() now calls scrollToIndex(this.active, ...) unconditionally. When active is -1 (the initial value), scrollToIndex() clamps it to 0, so pressing ArrowUp as the first navigation key can unexpectedly scroll the list to the top even though no item became active (previously element(-1) was undefined so no scroll occurred). Guard against negative active before scrolling.

  private _scrollToActive(behavior?: ScrollBehavior): void {
    this._list?.scrollToIndex(this.active, {
      block: 'center',
      behavior: behavior ?? 'auto',
    });