Under what conditions will the Visual Studio 2012 Difference Viewer allowing editing a source file

Question

Rather than continuing with Winmerge as my tool of choice, I've decided to commit to using the Difference Viewer built into Visual Studio 2012 Premium especially given it uses the edit window providing intellisense and resharper integration.

However, I've noticed that in one solution I compare a local file with latest and I'm allowed to edit the source file. However, in another solution which exists on the same TFS 2010 server but a different project and is checked out to a separate workspace, I'm not allowed to edit the local file.

According to the Visual Studio 2012 Help ("4. The Diff window appears. You can continue to make changes to the file in this window.") I should be able to edit the file if it is local. I will also need to be a member of the Contributors TFS group (I'm actually a member of the Project Administrators group too.)

I've tried running the compare from the command-line too something like "tf difference filename.cs" and compared two local files but they're all still read-only.

Can someone confirm what conditions I need to meet in order for the local file to be editable in the difference viewer?

UPDATE: I'm not sure how I missed this but it would appear that it's .aspx files that can't be edited in any of my solutions!

Answer 1

If you click the Merge button instead of Compare Files, you get a slightly different diff window that lets you edit the local file. Also see the edit in the answer about aspx files.