when xcode license was not accepted there should be a helpful error message

[fabian@…]

For example I just installed valgrind and got this error (for some reason xcode didn't have the EULA marked as accepted anymore):

$ sudo port install valgrind
...
--->  Building valgrind
Error: org.macports.build for port valgrind returned: command execution failed
To report a bug, follow the instructions in the guide:
    http://guide.macports.org/#project.tickets
Error: Processing of port valgrind failed
frankfa@palmtree:~/repo/nativesdk (1) $ sudo port install valgrind
--->  Computing dependencies for valgrind
--->  Building valgrind
Error: org.macports.build for port valgrind returned: command execution failed
Please see the log file for port valgrind for details:
    /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_devel_valgrind/valgrind/main.log
To report a bug, follow the instructions in the guide:
    http://guide.macports.org/#project.tickets
Error: Processing of port valgrind failed

So I

$ cat /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_devel_valgrind/valgrind/main.log 
...
:info:build You have not agreed to the Xcode license agreements, please run 'xcodebuild -license' (for user-level acceptance) or 'sudo xcodebuild -license' (for system-wide acceptance) from within a Terminal window to review and agree to the Xcode license agreements.
...

And the error is clear. However, for less experienced users, it might be very confusing. How about adding a less generic error message for this case, or maybe even run xcodebuild -license for the user if this happens.

[larryv (Lawrence Velázquez)]

We should not (and probably cannot) agree to the license for the user, but perhaps we can test for license acceptance before starting a build and fail more gracefully.