Running 'mach build' in fx-team tip I get: [...] 45:25.21 327 compiler warnings present. Error running mach: ['build'] The error occurred in code that was called by the mach command. This is either a bug in the called code itself or in the way that mach is calling it. You should consider filing a bug for this issue. If filing a bug, please include the full output of mach, including this error message. The details of the failure are as follows: IOError: [Errno 2] No such file or directory: u'/Users/past/src/fx-team/obj-ff-dbg/.mozbuild/warnings.json' File "/Users/past/src/fx-team/python/mozbuild/mozbuild/mach_commands.py", line 115, in build warnings_database.save_to_file(warnings_path) File "/Users/past/src/fx-team/python/mozbuild/mozbuild/compilation/warnings.py", line 268, in save_to_file with open(filename, 'wb') as fh: The error message is correct, there is no .mozbuild directory in my objdir at all. Could it be a regression from bug 857984?