[PRISM] allow enabling Prism via flag or env var

[HParker]

Enable Prism using either --prism

ruby --prism test.rb

or via env var

RUBY_PRISM=1 ruby test.rb

This uses Prism to load the first file and files loaded with require. This does not use Prism for eval, but that can be done in a followup.

[jemmaissroff]

Looks good, just one q about if we can reduce dependencies

[jemmaissroff]

Is there a way we can do this without adding this dependency?

[HParker]

I think, as long as rb_iseq_new_main_prism takes a pm_string_t and pm_options_t, we need those types available.

Maybe we can hide the types behind a void * or a VALUE? Would that be better?

I looked into if we could move this to prism_compile.c instead of defining this in iseq.c, but prism_compile.c doesn't know about iseq_alloc.

Also, it looks like iseq.c already depends on prism/prism.h via prism_compile.h.

Is the idea in reducing dependencies to decouple things, or is the worry this will make compile times longer since changes in prism will require a recompile on all things that use iseq.h?

[jemmaissroff]

The smell is actually a bit of common.mk. Historically we've been trying to keep the dependencies to a minimum to make it easier to pull Prism out if the Ruby core team ever decides to do something like that. But I hink in this case, you're right, it's not really worth the void * casting.

[mame]

@jemmaissroff @HParker Hey, this is a user-facing feature. Please file a ticket on bugs.ruby-lang.org and get matz's approval to merge it. Please revert it for now. cc/ @kddnewton

[hsbt]

Command line option and Environmental variables need to discuss naming and get approval from Matz.

[HParker]

Thank you @mame and @hsbt. I opened #9133 to revert this change so the conversation about the feature flag can happen. Please feel free to merge it.

I apologize for not following the correct process.

[mame]

@HParker Thank you! Sorry for the hassle. I think we should discuss the following before merging it, for example.

• What to do with the command-line option when prism becomes the default parser in the future.
  • Just remove it, or leave it as a "do nothing" option?
• What are the appropriate names.
  • In Ruby, not absolutely but the names of features for professional use tend to be long and verbose, while those used by ordinary users tend to be short.
• Whether to print a warning when this mode is used.

[hsbt]

@HParker Thank you for your quick action ❤️

[HParker]

@mame and @hsbt,

Sorry for the hassle

No thank you both for the noticing and helping me learn the correct process! ❤️

I included mame's questions in the ticket. I think those are all really good points and many things I didn't consider enough.