Find all tools with AC_CHECK_TOOL

[jamesjer]

The Fedora Linux project is preparing to rebuild all of its OCaml packages with OCaml 5.0.0. This means that, for the first time in some years, we have bytecode-only architectures (ppc64le, for example). The configure run fails on such architectures if ocamlfind is installed. Line 81 of configure.ac does this:

AC_SUBST([OCAMLC], [["$OCAMLFIND ocamlc"]])

But running ocamlfind ocamlc prints nothing, at least with ocamlfind 1.9.6 and OCaml 5.0.0. The same goes for ocamlopt, ocamldoc, ocamldep, and ocamlmklib. This commit uses AC_CHECK_TOOL to find all of them, and ocamlfind is used only to look for the result, seq, and uchar modules. Note that OCAMLC is already set further up in configure.ac.

[shindere]

Many thanks for your report, @jamesjer.

I have been able to reproduce the problem you mention locally with the latest main branch.

Also, I do not doubt that your PR fixes the issue. Neither do I doubt
that there is room for improvement in the way configure works -- I expect to give it a proper thought later.

Meanwhile, I came up with PR #42 which I believe does fix the issue you report.

Would you mind giving it a try and letting me know whether it indeed solves the issue you wanted to address with this present PR, please?

[jamesjer]

No, I am afraid that does not solve the issue. I tested by building on a Fedora 40 ppc64le box, which has OCaml 5.1.1, so ppc64le is a bytecode architecture. Problems are evident while configure runs:

checking OCaml target OS type... ocamlfind: Not supported in your configuration: ocamlopt
checking for flambda2... ocamlfind: Not supported in your configuration: ocamlopt
false

After running make all, the ocamldep step succeeds, but then the build fails immediately:

make[1]: Entering directory '/builddir/build/BUILD/stdcompat-20.1'
ocamlfind ocamlopt -c  -bin-annot -no-alias-deps -g -nolabels -I . -alert -deprecated stdcompat__native.mli -o stdcompat__native.cmi
ocamlfind: Not supported in your configuration: ocamlopt
make[1]: Leaving directory '/builddir/build/BUILD/stdcompat-20.1'
make[1]: *** [Makefile:1794: stdcompat__native.cmi] Error 2
make: *** [Makefile:938: all] Error 2

[shindere]

Okay, a bunch of thanks for the report, I will investigate further. Meanwhile I may still merge this PR because, even if I understand it is not enough, I still think it really is a step in the right direction.

[shindere]

Okay I do reproduce now, thanks. I was actually testing another scenario, i.e. bytecode-only and _no_ ocamlfind installed, and that now works thanks to #42. The thing which is actually still broken, even with #42, is bytecode-only and ocamlfind installed. In this scenario I get the same output than you for configure and will now work on fixing that.