michael@0: .. _environment_variables:
michael@0: 
michael@0: ================================================
michael@0: Environment Variables Impacting the Build System
michael@0: ================================================
michael@0: 
michael@0: Various environment variables have an impact on the behavior of the
michael@0: build system. This document attempts to document them.
michael@0: 
michael@0: AUTOCLOBBER
michael@0:    If defines, the build system will automatically clobber as needed.
michael@0:    The default behavior is to print a message and error out when a
michael@0:    clobber is needed.
michael@0: 
michael@0:    This variable is typically defined in a :ref:`mozconfig <mozconfig>`
michael@0:    file via ``mk_add_options``.
michael@0: 
michael@0: REBUILD_CHECK
michael@0:    If defined, the build system will print information about why
michael@0:    certain files were rebuilt.
michael@0: 
michael@0:    This feature is disabled by default because it makes the build slower.
michael@0: 
michael@0: MACH_NO_TERMINAL_FOOTER
michael@0:    If defined, the terminal footer displayed when building with mach in
michael@0:    a TTY is disabled.
michael@0: 
michael@0: MACH_NO_WRITE_TIMES
michael@0:    If defined, mach commands will not prefix output lines with the
michael@0:    elapsed time since program start. This option is equivalent to
michael@0:    passing ``--log-no-times`` to mach.
michael@0: 
michael@0: MOZ_PSEUDO_DERECURSE
michael@0:    Activate an *experimental* build mode where make directory traversal
michael@0:    is derecursified. This mode should result in faster build times at
michael@0:    the expense of busted builds from time-to-time. The end goal is for
michael@0:    this build mode to be the default. At which time, this variable will
michael@0:    likely go away.
michael@0: 
michael@0:    A value of ``1`` activates the mode with full optimizations.
michael@0: 
michael@0:    A value of ``no-parallel-export`` activates the mode without
michael@0:    optimizations to the *export* tier, which are known to be slightly
michael@0:    buggy.
michael@0: 
michael@0:    A value of ``no-skip`` activates the mode without optimizations to skip
michael@0:    some directories during traversal.
michael@0: 
michael@0:    Values may be combined with a comma.