Hide twisties and indentation when tree nodes have flat hierarchy

[Copilot]

Fixes #259879

[dmitrivMS]

This is what it looks like:

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@TylerLeonhardt

Matched files:

• src/vs/platform/quickinput/browser/media/quickInput.css
• src/vs/platform/quickinput/browser/tree/quickInputTreeController.ts

[vs-code-engineering]

🤖 Copilot has tried out this change! Members of the team can view the recording here or download the Playwright trace here (run)

[vs-code-engineering]

🤖 Copilot has tried out this change! Members of the team can view the recording here or download the Playwright trace here (run)

[Copilot]

Pull Request Overview

This PR implements the hiding of twistie icons and indentation in tree views when there are no nested items, specifically for the QuickInputTree component. This saves horizontal space when all items are at the top level.

Key Changes

• Flat hierarchy detection: The setTreeData method now detects when items have no children by checking if item.children?.length exists during tree element creation
• Visual treatment: Applied CSS rules to hide twistie icons and indent containers when the quick-input-tree-flat class is present
• Bug fix: Corrected missing parentheses in Emitter constructor call

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/vs/platform/quickinput/browser/tree/quickInputTreeController.ts	Added flat hierarchy detection logic and constant, fixed Emitter syntax, and toggles CSS class based on nested items
src/vs/platform/quickinput/browser/media/quickInput.css	Added CSS rules to hide twistie and indent elements when flat hierarchy class is applied

[dmitrivMS]

@copilot change this:
if ((item.children?.length ?? 0) > 0) {
to
if (item.children && item.children.length > 0) {

[Copilot]

@copilot change this:
if ((item.children?.length ?? 0) > 0) {
to
...

Done in d7e8e78

[Copilot]

@dmitrivMS Unfortunately I hit an unexpected error while processing your comment. I've automatically reported this to GitHub.

You can ask me to try again later by mentioning me in a new comment.

If you want to contact GitHub about this error, please mention the following identifier so they can better serve you: f3260b50-3231-4aa9-af9d-4e7bfb6e10fe

Sorry for the inconvenience!