[ruby-core:105309] [Ruby master Feature#18159] Integrate functionality of dead_end gem into Ruby

Issue #18159 has been updated by mame (Yusuke Endoh).


In today's dev meeting, we discussed this. Basically, no one was opposed to the concept. But some concerns were discussed.

@ko1 and @knu were concerned about whether the heuristic algorithm was mature enough. If dead_end prints a misguided summary, it may rather confuse users. They wanted to take an experimental period after dead_end is integrated to the ruby core. There are only three months until Ruby 3.1 release, so they suggested to try the integration towards Ruby 3.2.

@nobu and I briefly read the source code, and had some concerns about the implementation details:

* Currently, there are no good way to allow dead_end to hook a syntax error and extend its message. The redefinition of `Kernel#require` is never a preferable way. (discussed later)
* The implementation uses timeout, five seconds by default. The heuristic algorithm may take so long time?
* The gem includes "exe/dead_end" command. Should it be shipped with the ruby tarball, too?
* dead_end seems to extend NoMethodError to show a code snippet where the error occurs (if it is not running in production?). Does this conflict with error_highlight?

If dead_end is integrated to the core, we want to avoid the redefinition of `Kernel#require` and `require_relative`. It does not work well against an syntax error of an entrypoint file (a file passed the ruby interpreter). But unfortunately, there is no good API for the feature. `did_you_mean` and `error_highlight` extend the error message of NameError by defining `NameError#message`. It would be good if dead_end can do the same (define `SyntaxError#message`), but unfortunately it does not work because the current parser outputs an error message directly to tty, not via `SyntaxError#message`. @nobu is now trying to sort it out to allow the following API design. @schneems What do you think?

```
class SyntaxError
  attr_reader :file_path # the file path that caused this syntax error

  def message
    dead_end_error_message = DeadEnd.call(source: File.read(file_path), ...)

    "#{ super }\n\nDeadEnd: Unmatched `end` detected ..." + dead_end_error_message
  end
end
```

----------------------------------------
Feature #18159: Integrate functionality of dead_end gem into Ruby
https://bugs.ruby-lang.org/issues/18159#change-93719

* Author: duerst (Martin Dst)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 3.1
----------------------------------------
Missing 'end' errors are difficult to fix. We should integrate the functionality of the dead_end gem (https://github.com/zombocom/dead_end) into Ruby similar to how we integrated did_you_mean. It would greatly help programming Ruby, in particular for beginners.

See also Ruby Kaigi Takeout 2021 talk by Richard Schneeman https://rubykaigi.org/2021-takeout/presentations/schneems.html.



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