Support 2.7 syntax

[paracycle]

Problem

Sorbet does not currently handle some new Ruby 2.7 syntax like the "forward all arguments syntax", "beginless range" and "numbered block parameters"

An example of some syntax failing can be seen here

Proposed solution

Update Sorbet parser to handle the new 2.7 syntax.

[Morriar]

I've recently been working on solving this issue.

Here's an update on what if done, and what remains to do based on the reference for 2.7.

Merged:

• Import tests for ruby27 parser and add a few features
• Parse embedded ivars/cvars starting with digit as str
• Reject CSend inside left hand side of mass assign
• Allow comments before leading dot
• Fix rescue parsing in multi assignment
• Reject circular argument reference
• + ruby27.y: dsym should be treated as string. whitequark/parser#560 (merged in Import tests for ruby27 parser and add a few features #3226)
• + ruby27.y: removed opt_block_args_tail: tOROP rule. whitequark/parser#635 (ruby27: remove opt_block_args_tail: tOROP rule #3333)
• ruby27.y: hoisted out f_rest_marg. whitequark/parser#594 (ruby27: hoisted out f_rest_marg #3314)
• Add beginless ranges support (ruby27: Add begin-less ranges support #3313)
• **kwnil (Add support for ruby 2.7 **nil syntax #3330)
• Numbered parameters (ruby27: Introduce numbered parameters support #3344)
• Fix parsing of "\\\n" escaped sequences in various literals. whitequark/parser#539 (Fix line continuations in literals #3362)
• - ruby*.y: fixed context inside lambda args and module. whitequark/parser#709 (Fix parsing context for lambdas and modules #3363)
• Parameter forwarding (ruby27: Support forwarding arguments syntax #3420)
• Pattern matching (Introduce Ruby27 pattern matching limited support #3444)

Todo:

• **kwnil related errors
• Resolve grammar conflicts

I will update this list as it goes.

[iliabylich]

FYI There's more work to backport:

• + ruby27.y: removed opt_block_args_tail: tOROP rule. whitequark/parser#635 (to allow def foo(var: bar { || var }); end)
• + ruby27.y: dsym should be treated as string. whitequark/parser#560 (doesn't affect the grammar, but may cause conflicts in the future if not backported)
• ruby27.y: hoisted out f_rest_marg. whitequark/parser#594 (same)
• Add kwnilarg for **nil argument whitequark/parser#606 (new syntax def m(**nil); end, not sure why it's not in the list)

whitequark/parser notable bugfixes:

• Fix parsing of "\\\n" escaped sequences in various literals. whitequark/parser#539 (doesn't seem to be valuable for sorbet)
• - ruby*.y: fixed context inside lambda args and module. whitequark/parser#709 (I have no idea why nobody noticed it, maybe failing test cases are too esoteric? Also, does sorbet/parser have parsing context?)

[Morriar]

• + ruby27.y: dsym should be treated as string. whitequark/parser#560 is already merged with Import tests for ruby27 parser and add a few features #3226
• Add kwnilarg for **nil argument whitequark/parser#606 wasn't mentioned but I have it in the same branch than forward parameters, seemed related (I updated the list to make it visible).

I'll add the other ones to the list. Thanks for pointing this!

[jez]

This issue seems stale, and I don't think it's useful to have one big issue. If there are still parts of Ruby 2.7 syntax that Sorbet doesn't parse correctly, feel free to open individual issues.