Originally the question was "How do I configure WinMerge as the compare and merge tool for TFS". However, I am changing it because TehOne answered this more general form of the question.
I would have though this would have been asked already on Stackoverflow. I found the answer elsewhere, but I am asking/answering here. It's now a community wiki.
When I was looking for how to do this, I found this post to be invaluable:
http://blogs.msdn.com/jmanning/articles/535573.aspx
The long procedure is provided in a Rory Primrose blog posting
The short answer is the argument list for compare is:
/x /e /ub /wl /dl %6 /dr %7 %1 %2
and the argument list for merge is:
/x /e /ub /wl /dl %6 /dr %7 %1 %2 %4
Sometimes Winmerge does not return 0 and TFS will think the merge was canceled. You need to use the following wrapper batch file for merging:
@rem winmergeFromTFS.bat
@rem 2007-08-01
@rem File created by Paul Oliver to get Winmerge to play nicely with TFS
@rem
@rem To use, tell TFS to use this command as the merge command
@rem And then set this as your arguments:
@rem %6 %7 %1 %2 %4
"C:\Program Files\WinMerge\WinMerge.exe" /x /e /ub /wl /dl %1 /dr %2 %3 %4 %5
exit 0
And then you set the argument list to:
%6 %7 %1 %2 %
exit 0
For SourceGear DiffMerge, you need to change the default command line to:
C:\Program Files (x86)\SourceGear\Vault Client\sgdm.exe
I found the parameters in this thread on the SourceGear support forums, as well as on James Manning's blog mentioned by @TehOne, but the arguments given there are incorrect and result in the auto-merge being executed in reverse, i.e. old code overwrites new code. The correct arguments are:
/m /t1=%6 /t2=%7 /t3=%8 /c=%9 %1 %3 %2 /r=%4