Use Bazel-Central-Registry backed binaries

[UebelAndre]

Now that M4, Bison, and Flex exist in the Basel-Central-Registry, I was wondering if there was any interest in swapping the toolchains to use binaries backed by those modules instead of the generated targets within the relevant set of rules (rules_flex and rules_bison including). I think it would be valuable to separate out the concerns of building each tool with the rule and action interfaces.

[jmillikin]

The current build logic in these rulesets has a lot of complexity to get working binaries, so I wouldn't want to swap the guts over to a different build unless there was some solid plan for dealing with gnulib (etc).

However, it should be possible to configure the toolchain shim repositories (e.g. m4_toolchain_repository) to point to binaries at any location. Right now there's a hardcoded assumption that the m4 build target is {m4_repo} + "//bin:m4" but that's pretty easy to add an override for.

[UebelAndre]

Can you enumerate the complexities? I would like the BCR versions to be accurate to the original build system as much as possible to produce results consistent with standard/non-bazel releases of each tool.

[jmillikin]

https://github.com/jmillikin/rules_m4/blob/v0.3/m4/internal/gnulib/gnulib.bzl#L123-L176

https://github.com/jmillikin/rules_m4/blob/v0.3/m4/rules/m4_repository.bzl#L128-L158

Similar code exists in rules_bison.

I warn you ahead of time, reading those patches will bring no joy to your life. If your build logic works well enough to produce working binaries on the targets you care about (Linux/macOS + gcc + glibc is easiest) then I wouldn't worry too much about trying to exactly match either rules_m4 or ./configure && make.

[UebelAndre]

https://github.com/jmillikin/rules_m4/blob/v0.3/m4/internal/gnulib/gnulib.bzl#L123-L176

https://github.com/jmillikin/rules_m4/blob/v0.3/m4/rules/m4_repository.bzl#L128-L158

Similar code exists in rules_bison.

I warn you ahead of time, reading those patches will bring no joy to your life. If your build logic works well enough to produce working binaries on the targets you care about (Linux/macOS + gcc + glibc is easiest) then I wouldn't worry too much about trying to exactly match either rules_m4 or ./configure && make.

Thank you! Is there some sort of benchmark I can use to make sure the BCR modules satisfy your needs? I'm still hopeful there's a path to moving the BUILD targets to BCR and having a more visible and focused place to discuss issues around building the tools themselves.