[PATCH 3/5] Makefile: simplify $(test_bindir_programs) rule by splitting it up

When the @@PROG@@ substitution was added in [1] it was a simple matter of doing a:

	's|@@PROG@@|$(@F)|'

Then when t/helpers were added in [2] followed by the ".exe" needing to be appended in [3] this previously simple rule ended up as a dense one-liner.

It has been pointed out that this is hard to read[4], but the problem isn't the "design of the Makefile syntax". It's we now have to after-the-fact determine if we were dealing with a bin-wrapper/ that needed to have $(X) appended, a t/helper/, or a non-binary (currently only git-cvsserver).

That would be a problem in any language. We're starting out with three lists, and then end up having to heuristically determine given a member of any of those lists which list that member came from. Let's just stop doing that and keep track of what member belongs to which list.

We can do this by splitting up the single "bin-wrappers/%" rule into a rule for each of the three lists. With the "cmd_munge_script_sed_shell_path_arg" define added in a preceding commit this is easy, we just need to add a sister template to the existing "cmd_munge_script" added in [5].

There is then an an in-flight change[6] that generalizes this to support "scalar". That change needed to further special-case the pre-image here, as we couldn't rely on the "git%" heuristic to mean "not from the $(TEST_PROGRAMS_NEED_X) variable".

With this conflicting change that special-casing becomes unnecessary. The conflict between the two can be resolved entirely in favor of this change, as the other change adds "scalar" to "$(BINDIR_PROGRAMS_NEED_X)", and we are no longer losing track of which members belong to that list.

This change can be tested with e.g.:

	git checkout master &&
	make SHELL_PATH=/bin/bash X=.exe &&
	mv bin-wrappers bin-wrappers.master &&
	<apply this change> &&
	make SHELL_PATH=/bin/bash X=.exe &&
	diff -ru bin-wrappers{.master,}

Which will show an empty diff, i.e. we've correctly dealt with the combination of $(SHELL_PATH), $(X) and these three variables here.

1. ea925196f1b (build dashless "bin-wrappers" directory similar to
   installed bindir, 2009-12-02)
2. e6e7530d10b (test helpers: move test-* to t/helper/ subdirectory,
   2016-04-13)
3. 3a94cb31d52 (bin-wrappers: append `.exe` to target paths if
   necessary, 2019-07-29)
4. https://lore.kernel.org/git/sso99so6-n28s-rq86-8q20-4456r3pn869r@tzk.qr/
5. 46bac904581 (Do not install shell libraries executable, 2010-01-31)
6. https://lore.kernel.org/git/4d69e5eaccb8873eece666a3d2bb2b22abdde7ea.1661961746.git.gitgitgadget@gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Makefile | 35 +++++++++++++++++++++++++++--------
 1 file changed, 27 insertions(+), 8 deletions(-)