[ruby-core:123381] [Ruby Bug#21618] Allow to use the build-in prism version to parse code

Issue #21618 has been updated by Eregon (Benoit Daloze).


Taking the concerns from the description:

Earlopain (Earlopain _) wrote:
> Consider that some syntax will be disallowed in the next ruby version. I would have to specify the ruby version I want to parse as in order to not run into syntax errors: `Prism.parse("foo", version: RUBY_VERSION)`. But doing so is not feasable because `prism` is distributed out of sync with ruby itself.
> If the user already has prism in their lockfile, the user may run a prism version that doesn't yet know about lets say ruby 4.0 and thus raise.

If it's locked to an older prism in lockfile, it's expected to not work. Same as any other gem really. Need to update in lockfile.

> Similarly, it may parse as an older patch version that has subtle behaviour differences.

If the differences are relevant those could be handled in Prism. They are probably just bug fixes and if so then the fixed behavior seems always best.

IOW, I think they are theoretical concerns.
Is there a concrete realistic problem with using `Prism.parse_file(filepath, version: RUBY_VERSION)` where the solution is not trivial?

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Bug #21618: Allow to use the build-in prism version to parse code
https://bugs.ruby-lang.org/issues/21618#change-114753

* Author: Earlopain (Earlopain _)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
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Prism is a multi-version parser, which is a great feature.

If one calls `Prism.parse("foo")`, it will always use the latest version prism knows about. This may or may not be the version that is currently executing. This is problematic when one wants to introspect code the same way that the currently running ruby version would.

Consider that some syntax will be disallowed in the next ruby version. I would have to specify the ruby version I want to parse as in order to not run into syntax errors: `Prism.parse("foo", version: RUBY_VERSION)`. But doing so is not feasable because `prism` is distributed out of sync with ruby itself. If the user already has prism in their lockfile, the user may run a prism version that doesn't yet know about lets say ruby 4.0 and thus raise. Similarly, it may parse as an older patch version that has subtle behaviour differences.

`ripper` does not have this issue because it is always tied to the ruby version and it is not distributed as a gem, so what the user has will always be exactly what ruby shipped with. I wish for a similar API that utilizes the prism version bundled with ruby itself.

Libraries like `rails` have moved from ripper to prism because of its superior developer experience but it risks breaking in unexpected ways with new `prism` versions that know about more recent syntax. `error_highlight` for example also suffers from the same defect.

It seems like prism currently has 34 methods that optionally take a version (per the rbi file). Many of these are trivial helper methods like `Prism.parse_success?` (does the parse result have any errors?). I would be happy with supporting only the minimal functions like `Prism.parse` and `Prism.parse_file`. Currently I don't have a use-case for any of the other methods. Pretty much just functions to mirror `RubyVM::InstructionSequence.compile_file` and `RubyVM::InstructionSequence.compile`.

It would be optimal if I would be able to transparently call `Prism.parse("foo", version: "current")` (or maybe even have an unspecified version mean the build-in prism version) but I am not sure how feasable that is since I'm pretty sure logic for this would have to live in ruby itself.

@kddnewton does this feature request make sense? Do you have any other ideas/inputs?



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