Reported by users and repro'd in beta labs
Log in and edit any page with VE at http://en.wikipedia.beta.wmflabs.org/
From the hamburger list select "Switch to source editing"
Nothing happens. In the javascript console find the error
Uncaught Error: OO.ui.Tool.onSelect not implemented in this subclass:function VeUiMWEditModeSourceTool(toolGroup,config){ve.ui.MWEditModeTool.call(this,toolGroup,config);}
Version: unspecified
Severity: normal
Change 123806 had a related patch set uploaded by Alex Monk:
Revert edit mode tool's onSelect method
Change 123806 had a related patch set uploaded by Alex Monk:
Revert edit mode tool's onSelect method
Change 123825 had a related patch set uploaded by Jforrester:
Revert edit mode tool's onSelect method
Verified the fix on Betalabs: http://en.wikipedia.beta.wmflabs.org/wiki/Regression3rdaprilchrome
Verified the fix in production:
https://en.wikipedia.org/wiki/User:RYasmeen_(WMF)/sandbox