tab selected should be adjacent when closing last one. (#13912)

fixes #13886

contributed on behalf of STMicroelectronics

Signed-off-by: Remi Schnekenburger <rschnekenburger@eclipsesource.com>

CHANGELOG.md

@@ -7,6 +7,7 @@
 <!-- ## not yet released 
 
 - [core] introduce `FRONTEND_CONNECTION_TIMEOUT` environment variable to override application connexion settings. [#13936](https://github.com/eclipse-theia/theia/pull/13936) - Contributed on behalf of STMicroelectronics
+- [core] tab selected should be adjacent when closing last one [#13912](https://github.com/eclipse-theia/theia/pull/13912) - contributed on behalf of STMicroelectronics
 
 <a name="breaking_changes_not_yet_released">[Breaking Changes:](#breaking_changes_not_yet_released)</a> 
 

packages/core/src/browser/shell/application-shell.ts

@@ -1896,6 +1896,10 @@ export class ApplicationShell extends Widget {
  if (index < current.titles.length - 1) {
  return index + 1;
  }
+ // last item in tab bar. select the previous one.
+ if (index === current.titles.length - 1) {
+ return index - 1;
+ }
  return 0;
  }