.\" $FreeBSD: head/tools/build/options/WITH_META_MODE 301889 2016-06-14 16:20:25Z bdrewery $
Creates
.Xr make 1
meta files when building, which can provide a reliable incremental build when
using
.Xr filemon 4 .
The meta file is created in the OBJDIR as
.Pa target.meta .
These meta files track the command ran, its output, and the current directory.
The
.Xr filemon 4
module is required unless
.Va NO_FILEMON
is defined.
When the module is loaded, any files used by the commands executed will be
tracked as
dependencies for the target in its meta file.
The target will be considered out-of-date and rebuilt if any of the following
are true compared to the last build:
.Bl -bullet -compact
.It
The command to execute changes.
.It
The current working directory changes.
.It
The target's meta file is missing.
.It
The target's meta file is missing filemon data when filemon is loaded
and a previous run did not have it loaded.
.It
[requires
.Xr filemon 4 ]
Files read, executed or linked to are newer than the target.
.It
[requires
.Xr filemon 4 ]
Files read, written, executed or linked are missing.
.El
The meta files can also be useful for debugging.
.Pp
The build will hide commands ran unless
.Va NO_SILENT
is defined.
Errors will cause
.Xr make 1
to show some of its environment for further debugging.
.Pp
The build operates as it normally would otherwise.
This option originally invoked a different build system but that was renamed
to
.Va WITH_DIRDEPS_BUILD .
.Pp
Currently this also enforces
.Va WITHOUT_SYSTEM_COMPILER .