Bug in editor/title when opening editors side by side

Bug Description:

There is a bug that when using an extension that adds a button in the editor/title and opening editors side by side. When opening editors side by side it will add the button also to the other editor that does not fulfil the condition to show the button. This bug happens for new extensions, and not for built in extensions. It happens in Theia.

I used a simple extension to reproduce the bug. I created an extension that adds a button on the editor/title when a file have .json extension. See example:

		"menus": {
			"editor/title": [
				{
					"**when": "resourceExtname == .json**",
					"command": "sbasbug.start",
					"group": "navigation"
				}
			]
		}

When having a side by side editors, the button appears (marked in yellow) in the 'test.json' file but also in the 'read.md' file, see in the example blow:

When pressing back on the 'read.md' file it disappears for both of them. See below:

The button should not appear on the read.md file (or any file without .json extension)

Steps to Reproduce:

I have a simple extension, that shows a button in the editor/title when the file is with a JSON extension. To reproduce it, please use the extension I supply and do the example with a readme (.md extension file) and a .json file. Because I debugged it and have some findings. The .md file is an example of a built in extension that shows a button and it works correctly (buttons on the .md files appears only on them), but it will be reproduced with other files that will be side by side with the .json file.

1. Clone https://github.com/avishaik/vscode-editor-btn-bug
2. Build it npm run package and add it as extension to theia
3. Open a file with .md extension and press on the 'Open preview to the side' button
4. To the right side panel open a file with a .json extension
5. When pressing on the JSON file tab, the button shows both in the JSON file and in the readme file (.md extension)
6. When pressing on the readme file tab, the button disappears from both the readme and the .json file

I debugged this code have some findings:

• In tab-bars.ts in function updateToolbar, for some reason if we press on one of the tabs (for example the .json tab) it will check the .md file twice if there is a need to add buttons.
• In monaco-context-key-service.ts in function match what happens is it get the context from this.contextKeyService.getContext(ctx) and in the value itself there is no resourceExtname , so it check if there is a resourceExtname in the _parent and it find it there, but the parent for some reason is the .json file! So when it check if the resourceExtname is .json it is actually true!

So I'm not sure if the issue is because it for some reason checks the editor twice in tab-bars.ts or because the parent in the context in monaco-context-key-service.ts is a different file from what it should be.

Adding item (button) on editor/title flow

It starts in tab-bars.ts in function updateToolbar, it will check to update 'read.md' file twice, 'test.json' once:

Then we enter visibleItems function in tab-bar-toolbar.ts that checks which item should appear on the widget (editor/title):

The issue happens in monaco-context-key-service.ts file in line 47, in what the keyContext now holds:

The value itself does not contain the resourceExtName but we can see it belongs to the read.md, because the editorLangId is markdown:

But when we go to the parent, we see values for the test.json file:

What happens is the contextMatchesRules function search for the resourceExtName in the value, when it does not find it there is searches in the _parent, and in the _parent it's the .json, so it concludes the condition to be true and shows the button on the read.md editor.

Additional Information

• Operating System: Windows 10
• Theia Version: latest