Half-Hidden tab getting close while not clicking on close button

[MikaelDesharnais-ST]

Bug Description:

When you are clicking at the right most part of a half-hidden tab, the tab in question gets closed (Zone highlighted in red) :

Steps to Reproduce:

1. Open many files
2. Scroll your tabs to have on tab half hidden to the right of the tabbar
3. click on the right most part of the tab

Additional Information

This error comes from PhosphorJS which is now abandonned as discussed in this thread :
#6501
In phosphorJS tabbar when the mousedown event is received, the tab that is clicked becomes the default one, so the tabbar gets centered on this tab.
In the mouse up event, there is a check if the click was made on the close icon. This check returns true because now the tabbar was recentered on the tab clicked and so the click calls the close tab.
I checked with VSCode and in this case, the tab only gets selected : not closed

• Operating System: Any
• Theia Version: Latest

[vince-fugnitto]

@MikaelDesharnais-ST it really depends on where the tab is clicked, as the closing of the tab does not occur reliably (for example, it never occurs when clicking the beginning of the tab which is the more natural place). In any case, I think its a minor bug (it will likely be much better when we drop phosphor).