deliciouslytyped/make-groupedtargets

Some resources on multi-output/multi-target/grouped targets with (gnu) make

Note: this text was pulled from an issue post without editing, the phrasing may be odd.

This post is going to be a bit off topic, but it seems as good a place as any to summarize some things;

this seems like one of those somewhat more obscure features of make that is(was?) bafflingly missing decent support. Edit: (I mean in make itself, not remake.) With the research I've been able to manage, things do seem to point to gmake's pattern rules being the cleanest, albeit still hacky solution to multiple-output targets. This may have been fixed by "grouped targets" in 4.3, see [3] and [4].

A link I haven't seen mentioned here yet is https://www.gnu.org/software/automake/manual/html_node/Multiple-Outputs.html , which goes quite in depth with the pertinent issues. (It is also this article which leads to my bafflement to the lack of a decent solution; you can't expect everyday developers to have to deal with this, and I myself don't understand the contents of that article yet). Given that it's in the automake documentation, maybe automake has support for dealing with this, but I haven't gotten to the point of researching that.

Perhaps the issues listed in that document are also a good test for remakes debugging capabilities.

To aggregate some of the above, the most useful things I've found on the topic so far are: [1] https://www.gnu.org/software/automake/manual/html_node/Multiple-Outputs.html [2] https://www.cmcrossroads.com/article/rules-multiple-outputs-gnu-make - as linked previously (I actually found this because I didn't believe that was pattern rules were really gmake's solution...) [3] https://lists.gnu.org/archive/html/info-gnu/2020-01/msg00004.html linked above, has some content:

* New feature: Grouped explicit targets
  Pattern rules have always had the ability to generate multiple targets with
  a single invocation of the recipe.  It's now possible to declare that an
  explicit rule generates multiple targets with a single invocation.  To use
  this, replace the ":" token with "&:" in the rule.  To detect this feature
  search for 'grouped-target' in the .FEATURES special variable.
  Implementation contributed by Kaz Kylheku <address@hidden>

This looks interesting, and I should look into it. If not for this thread, I don't think I would have ever found this. Grouped targets appear to be documented at [4] https://www.gnu.org/software/make/manual/html_node/Multiple-Targets.html

There is a little bit of exposition at https://stackoverflow.com/a/63935393 and a common pitfall seems to be trying to use it with older versions: https://stackoverflow.com/a/63162448 , https://stackoverflow.com/questions/61345698/gnu-make-grouped-targets-are-not-grouped

Here is a proposed solution for the lack of an automatic variable expanding to all grouped targets; https://stackoverflow.com/questions/60402075/is-there-an-automatic-variable-for-all-grouped-targets-in-makefile/60441626#60441626

https://lwn.net/Articles/810247/ reports to have a portable implementation of grouped targets at https://github.com/david-a-wheeler/make-booster

Also I should probably correct my terminology, people seem to say multi-target, though I don't think that's obviously the same thing as multi-output. Maybe the term is now grouped targets.

• If indeed grouped targets are what's wanted for multiple-outputs, the automake documentation should be updated to reflect this.

Now if only The GNU Make Book or Managing Projects With GNU Make was updated. :)

If anyone has any additional resources to add to this list, that would be cool; please open an issue or a PR.