Add IRB fix command to rerun with corrected spelling (references ruby/did_you_mean#179)

[krsinghshubham]

Add IRB fix command to rerun with corrected spelling (references ruby/did_you_mean#179)

Summary

Adds a native fix command to IRB that reruns the previous command with corrected spelling when a "Did you mean?" error occurs. This implements the feature requested in ruby/did_you_mean#179.

Example

irb(main):001> ac
# => NameError (undefined local variable or method 'ac' for main)
#    Did you mean?  acc
#    Type `fix` to rerun with the correction.

irb(main):002> fix
# Rerunning with: acc
# => ...

irb(main):001> 1.zeor?
# => NoMethodError (undefined method `zeor?' for 1:Integer)
#    Did you mean?  zero?
#    Type `fix` to rerun with the correction.

irb(main):002> fix
# Rerunning with: 1.zero?
# => true

Why This Change in IRB (Not did_you_mean)?

The Problem

The fix command was originally implemented as an extension in the did_you_mean gem via PR ruby/did_you_mean#204 (https://github.com/ruby/did_you_mean). However, this implementation introduced a load order problem.

• did_you_mean is a default gem—Ruby loads it at boot, before any application code
• IRB loads later (e.g., when running rails console or irb)
• When did_you_mean loads, IRB isn't defined yet, so the extension never loads
• Result: The fix command didn't work in Rails console or when IRB loads after app initialization

Why IRB Should Own This Feature

1. It's a REPL feature – The fix command is an IRB command (like exit, load, help). It belongs in the REPL layer.

2. IRB has the context – IRB already has the eval loop, exception handling, and access to the last executed code. It's the natural place for this logic.

3. did_you_mean provides the API – The did_you_mean gem adds #corrections to exceptions (NameError, NoMethodError, KeyError, etc.). IRB simply uses this public API—no patching or extension loading required.

4. No load order issues – When IRB runs, both IRB and did_you_mean are loaded. IRB can check exception.respond_to?(:corrections) and use the fix command natively.

5. Clean separation of concerns – did_you_mean = spell-checking. IRB = REPL behavior. Each gem does one thing well.

What IRB Gets from did_you_mean

IRB uses only the public API that did_you_mean provides:

• exception.respond_to?(:corrections) – Check if the exception has suggestions
• exception.corrections – Get the suggested corrections (e.g., ["zero?"])
• DidYouMean::Levenshtein.distance – Optional; used for edit-distance filtering when available. If did_you_mean isn't loaded (e.g., --disable-did_you_mean), the fix command still works but skips the distance filter.

No internal APIs, no patching, no extension loading.

Implementation Details

Files Changed

• lib/irb/command/fix.rb (new) – Fix command and LastError storage
• lib/irb.rb – Store last correctable exception, show discoverability hint
• lib/irb/default_commands.rb – Register fix and dym commands

Supported Error Types

NoMethodError, NameError, KeyError, NoMatchingPatternKeyError, LoadError

Correction Logic

• Single suggestion only (edit distance ≤ 2 when did_you_mean is available)
• Replacement patterns: identifiers, symbols, strings
• dym alias for users who use fix as a variable

Discoverability

When a fix is available, IRB shows: Type \fix` to rerun with the correction.`

References

• ruby/did_you_mean#179 – Original feature request
• thefuck – Similar concept for shell commands

[krsinghshubham]

Hi, this PR adds the IRB fix command to rerun with corrected spelling when a "Did you mean?" error occurs (see ruby/did_you_mean#179).

@tompng @st0012 @aycabta I’d appreciate a review when you have time. Thanks.

[hsbt]

Please remove PR_DESCRIPTION.md at least. That file is unrelated for this repository.

[krsinghshubham]

Please remove PR_DESCRIPTION.md at least. That file is unrelated for this repository.

Done