FileMerge quits immediately after launching from SourceTree

Question

I regularly use Atlassian SourceTree (on Mac OS X) to launch FileMerge to resolve git merge conflicts. Out of the blue it has stopped working: when I right click and select

Answer 1

If Xcode has recently updated itself, you may need to agree to the new license terms. If you have not agreed to the license terms, FileMerge (when launched from SourceTree) will quit immediately.

To check for this, open a shell and run as your usual user:

$ opendiff

If the license is the problem, it will tell you. To agree to the new license terms, you'll need to run open diff using sudo:

$ sudo opendiff

After agreeing to the license terms, you can now retry launching FileMerge from SourceTree using Resolve Conflicts > Launch External Merge Tool. FileMerge should launch and behave normally.