v2, 5 partsDocumentation/Makefile: conditionally include doc.dep

>
>
> The 'clean' target is noticeably slow on cygwin, even for a 'do-nothing'
> invocation of 'make clean'. For example, the second 'make clean' below:
>
>   $ make clean >/dev/null 2>&1
>   $ make clean
>   GIT_VERSION = 2.29.0
>   ...
>   make[1]: Entering directory '/home/ramsay/git/Documentation'
>       GEN mergetools-list.made
>       GEN cmd-list.made
>       GEN doc.dep
>   ...
>   $
>
> has been timed at 23.339s, using git v2.29.0, on my laptop (on old core
> i5-4200M @ 2.50GHz, 8GB RAM, 1TB HDD).
>
> Notice that, since the 'doc.dep' file does not exist, make takes the
> time (about 8s) to generate several files in order to create the doc.dep
> include file. (If an 'include' file is missing, but a target for the
> said file is present in the Makefile, make will execute that target
> and, if that file now exists, throw away all its internal data and
> re-read and re-parse the Makefile). Having spent the time to include
> the 'doc.dep' file, the 'clean' target immediately deletes those files.
>
> In order to eliminate such wasted effort, use the value of the internal
> $(MAKECMDGOALS) variable to only '-include doc.dep' when the target is
> not 'clean'. (This drops the time down to 12.364s, on my laptop, giving
> an improvement of 47.02%).

> 
> All this makes sense, but I had to do "make doc.dep" and take a look
> at that file to understand why:
> 
> doc.dep contains make rules with targets and dependencies that will
> not be used in "make clean".
> 
> This is in my opinion the important information. Maybe mention
> something like that in the commit message?

> Notice that, since the 'doc.dep' file does not exist, make takes the
> time (about 8s) to generate several files in order to create the doc.dep
> include file. (If an 'include' file is missing, but a target for the
> said file is present in the Makefile, make will execute that target
> and, if that file now exists, throw away all its internal data and
> re-read and re-parse the Makefile). Having spent the time to include
> the 'doc.dep' file, the 'clean' target immediately deletes those files.
>
> In order to eliminate such wasted effort, use the value of the internal
> $(MAKECMDGOALS) variable to only '-include doc.dep' when the target is
> not 'clean'. (This drops the time down to 12.364s, on my laptop, giving
> an improvement of 47.02%).

> Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
> ---
>  Documentation/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/Documentation/Makefile b/Documentation/Makefile
> index 80d1908a44..652d57a1b6 100644
> --- a/Documentation/Makefile
> +++ b/Documentation/Makefile
> @@ -286,7 +286,9 @@ doc.dep : $(docdep_prereqs) $(wildcard *.txt) $(wildcard config/*.txt) build-doc
>  	$(PERL_PATH) ./build-docdep.perl >$@+ $(QUIET_STDERR) && \
>  	mv $@+ $@
>  
> +ifneq ($(MAKECMDGOALS),clean)
>  -include doc.dep
> +endif
>  
>  cmds_txt = cmds-ancillaryinterrogators.txt \
>  	cmds-ancillarymanipulators.txt \

> 
> Nicely explained.  It might be worth saying
> 
>     ... the clean target immediately deletes those files.  The rules
>     and definitions of doc.dep however does not affect what 'clean'
>     target removes otherwise, so we can do without all this.