How to delay effect of "include" directive in Makefile.am until make (avoid "include" being seen by Automake)?

Question

My Makefile.am includes a file (with various defined variables), for example:

include make.config

...

The problem is that this file is in turn generated by a tool (i.e. config.generator.sh) based on some input file (i.e. input.dat). The straightforward and wrong idea would be to add a rule to generate make.config:

make.config : input.dat
    config.generator.sh input.dat > make.config

include make.config

...

Although this content is perfectly working makefile on its own without automake, the idea is doomed with automake. The make.config file is included by automake before I even have a chance to execute make (and it fails as the file is not yet generated):

automake: cannot open < make.config: No such file or directory

Is there a way to postpone effect of include directive until make is run (possibly by using another directive)?

There is probably a way to simply run arbitrary commands before any makefile generation is done (i.e. AC_CONFIG_COMMANDS*). But the question is more complicated because the config.generator.sh is supposed to use executables which are in turn also generated during the same build process (so there is a dependency chain which logically has to be managed by makefiles from the same project). The documentation simply confirms the logic without providing alternatives.

Answer 1

I've come across the same annoying problem today when moving my OCaml project to Autotools. My solution is to use autoconf's substitution to go around automake. For the above example, I'd add a substitution to configure.ac:

AC_SUBST([include_make_config], ["include make.config"])

and adjust Makefile.am, replacing the include directive with the autoconf variable reference:

make.config : input.dat
    config.generator.sh input.dat > make.config

@include_make_config@
...

automake doesn't touch the @include_make_config@ line so it gets carried over into the generated Makefile.in. When autoconf takes over, it substitutes the variable with include make.config in the final Makefile.

Note: I use this with OCaml's ocamldep dependency generator.

Answer 2

The solution is described in this email of Automake's mailing list.

The idea is to use include directives inside small regular "wrapper" makefile and include Automake-generated Makefile into it (note the upper case M). Because makefile is not an Automake template, the include works as expected triggering builds for non-existing files.

Note that:

• By default make utility will search for makefile first (not for Makefile) making this approach working seamlessly.
• It is still recommended to specify all rules inside Makefile.am and keep the "wrapper" makefile simple. The rules for non-existing files will naturally come from the generated Makefile anyway.