Feature request for an API to check if a syntax invalid code can be syntax valid by appending continuation tokens

[tompng]

It would be helpful if Prism have an API that works like this.

Prism.parse('1 + [').input_continuable? #=> true
Prism.parse('1 + ]').input_continuable? #=> false
Prism.parse('tap do').input_continuable? #=> true
Prism.parse('end.tap do').input_continuable? #=> false

Some other naming idea: end_of_input_error? error_recoverable?

Background

When IRB receives end[ENTER], IRB immediately evaluates it because "end\n" + code is always syntax invalid.

irb(main):001> end
(irb):1: syntax error found (SyntaxError)

When IRB receives tap do[ENTER], IRB waits for the next line input because "tap do\n" + code can be syntax valid.

irb(main):001> tap do
irb(main):002>

Both end and tap do are syntax invalid code. IRB needs to distinguish these two type of syntax errors.
IRB currently uses SyntaxError#message and regexps. This check logic is fragile.
Implementation in IRB: https://github.com/ruby/irb/blob/8b63f05160aa90e0205cf392b10cb85d6ecfa9a3/lib/irb/ruby-lex.rb#L229-L276

[kddnewton]

If you get:

def foo
  a +
end

tap do

right now it would match :recoverable_error. What is the desired behavior in this case? You would need to go back in and put content after the a + to make it valid. Should that not be recoverable?