I had accidentally posted to bug-m...@gnu.org first, but this belongs to bug-automake@gnu.org.
Paul Smith wrote: > On Mon, 2021-05-03 at 12:55 +0200, Frank Heckenbach wrote: > > The manual ( > > https://www.gnu.org/software/automake/manual/html_node/Multiple-Outputs.html > > ) > > describes various ways to handle commands with multiple outputs. > > Just to remind, this is the mailing list for GNU make... the above > manual is for automake which is a different project; we have no input > into or control over their manual. You should be emailing their list. Oops! I see that now. I had googled for "gnu make multiple outputs" and got that page, and since it described make features without any reference to automake, I didn't notice where I was. (And the last paragraph links to the GNU make manual which is formatted exactly the same, to add to the confusion.) > > One intermediate solution that's said to work except with phony > > dependencies doesn't actually seem to work: > > > > % cat Makefile > > all: data.c data.h > > data.c data.h: data.foo > > touch data.c data.h > > data.h: data.c > > > > % rm -f data.[ch]; touch data.foo; make -j > > touch data.c data.h > > touch data.c data.h > > > > It says "[...] therefore a parallel make will have to serialize the > > builds of data.c and data.h, and will detect that the second is no > > longer needed once the first is over." This doesn't seem to be so. > > > > Am I missing something? > > This example is wrong. You need the data.h target to have a recipe > associated with it; it could be rewritten as: > > data.h: data.c ; > > (note the extra semicolon). Now it will work. This gives me this error: Makefile:4: warning: overriding recipe for target 'data.h' Makefile:3: warning: ignoring old recipe for target 'data.h' It goes away if I take out data.h in the first rule (not sure what other consequences this might have). This suggestion still stands (to the automake manual maintainers): > > More importantly (at least to me), the final paragraph of the page > > should really be first. After reading about increasingly more > > complex solutions to handle various corner cases, I found it *much* > > easier to just turn my rule into a pseudo-pattern rule a la: > > > > %ata.c %ata.h: %ata.foo > > Of course, this can't work if there's no common stem between the > targets. Yes. I'd prefer if "%" could match the empty string ... (Anyway, I'd rather rename my files to create a common stem than go through the contortions in the final example. ;) > It also requires GNU make, which is a restriction that not > all automake projects may be willing to accept. Indeed, the manual page says so. > In newer versions of GNU make there's a "grouped targets" feature which > allows explicit rules to behave like implicit rules WRT multiple > targets. With emphasis on newer! 4.2.1 (my current default) accepts "&:", but still runs the recipe twice. Only 4.3 seems to work correctly. > But again, this is only helpful for automake projects which > are willing to require a new-enough version of GNU make. Or non-automake projects which require GNU make, such as mine.
