Re: make -n executes RCS commands

[Aaron S. Hawley]

On Thu, 20 Jan 2005, Paul D. Smith wrote:

> The builtin rule for checking things out of source uses the "+" prefix
> character.  You can find the builtin rules with the -p option, something
> like this:
>
>     $ make -pf /dev/null
>         ...
>     # default
>     CHECKOUT,v = +$(if $(wildcard $@),,$(CO) $(COFLAGS) $< $@)
>         ...
>     %:: RCS/%,v
>     #  commands to execute (built-in):
>             $(CHECKOUT,v)
>
> The "+" token tells GNU make to run this command line even if -n is
> given.

I sorta figured that Make's implicit rule for RCS-files was forced (marked
recursive).  Perhaps all the implicit rules that are always executed
shoulud be included in the manual.

What is it about RCS-files that requires their implicit rule to be marked
recursive?

It's not clear to me.  Obviously, Make knows what the name of a
checked-out file is.  So are there cases where it is absolutely necessary
for Make to know the contents of a checked-out file?  the only time I can
think of Make needing a checked-out file in order to proceed is the
following dependency:

Makefile: Makefile,v

thanks,
/a