Re: New feature: Post-requisites

[Alejandro Colomar]

Hi Edward, thutt,

On 7/22/22 15:36, Edward Welbourne wrote:
> Alejandro Colomar (Friday, July 22, 2022 14:05)
>  > I'd like to suggest a new feature: post-requisites.
>  >
>  > As the word suggests, as pre-requisites are satisfied before a given
>  > target, post-requisites would be satisfied _after_ a given target.
>
> and just as a prerequisite can be built at any time before, but must be
> built before, the post-requisite can be run at any time after, but must
> be built after.  So if several targets that are being built require some
> given post-requisite, it waits until all of them have been built.

Exactly.  I didn't word it, but I meant it :)

>  > Why would someone ever need that in a Makefile:
>  >
>  > In an install target for a library, you may want to run ldconfig(8)
>  > after any install targets have executed.
>  >
>  > In an install target for the linux man-pages, you may want to run
>  > mandb(8)  after any pages have been installed in the system.
>
> I think the traditional solution to this would be to make the install
> depend on rules that get individual files installed and have its command
> run the post-install steps, or have the install rule depend on a set of
> post-install rules (each of which does one post-install task), that in
> turn depend on all the files whose updates would trigger them.  However,
> the problem with that is that if I want to just update the one man page,
> the mandb(8) run that's needed following it won't be run unless I build
> the mandb-run rule, that depends on *all* my man pages.  So I can't do
> fine-grained targeted "build this one thing" parts of my build process.

Yeah, those are the current workarounds to this missing feature.  As you 
explained, they are very suboptimal.

> Post-requisites would take care of that; if I build and install an
> update to any man page, then mandb gets run, regardless of what else I
> am also building, aside from mandb's run happening after any of those
> that need it to be done later.

thutt, this answers your question.

>  > The proposed syntax would be similar to that of order only
>  > prerequisites, but using '>' instead of '|':
>  >
>  > [
>  > [...]
>  >
>  > $(DESTDIR)$(man3dir)/foo.3: man3/foo.3 | $(DESTDIR)$(man3dir) > 
> update-mandb
>  >         $(info INSTALL  $@)
>  >         @$(INSTALL_DATA) -T $< $@
>  >
>  > $(DESTDIR)$(man3dir)/bar.3: man3/bar.3 | $(DESTDIR)$(man3dir) > 
> update-mandb
>  >         $(info INSTALL  $@)
>  >         @$(INSTALL_DATA) -T $< $@
>  >
>  > .PHONY: update-mandb
>  > update-mandb:
>  >         $(info MANDB)
>  >         @mandb
>  >
>  > .PHONY: install
>  > install: $(DESTDIR)$(man3dir)/foo.3 $(DESTDIR)$(man3dir)/bar.3
>  > ]
>  >
>  > So that `make install` would install foo.3 and bar.3, and after all of
>  > the pages have been installed, mandb(8) would be run.
>  > And `make /usr/local/share/man/man3/foo.3` would install foo.3, and
>  > after it, it would run mandb(8).
>  >
>  > Does that make sense to you?
>
> and if my package (e.g. perl) has a whole library of man pages, I'd be
> able to do updates to just one (or a few) of them at a time and get
> mandb run after that update, regardless of which subset of pages I
> update, rather than only being able to get that run when I install the
> whole library.
>
> I guess it would also be useful for tidying away scratch directories and
> the like, used by rules for their transient or intermediate files.
>
> It sounds like a neat idea.  I wonder how practical it would be to
> implement ...

Yep, that's the idea.  I hope it's as easy to implement as it's to describe.

Cheers,

Alex

>       Eddy.

--
Alejandro Colomar
<http://www.alejandro-colomar.es/>

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