Handling typos in commands and subcommands

[Hind-M]

Hey there!
We are using CLI11 in our project, and we were wondering if there is anything that we can use to handle typos in set commands/subcommands?
For now if we run for example:

mamba instal test

The printed error would be:

The following arguments were not expected: test instal
Run with --help for more information.

Which is ok as we can guess that instal is not the right command, but that gets more confusing if multiple arguments are used as the error is not really explicit and does not point to the exact offending argument.

For example:

mamba reqoquery whoneeds _openmp_mutex

outputs:

The following arguments were not expected: _openmp_mutex whoneeds reqoquery
Run with --help for more information.

Furthermore, the arguments in the output are written in the reverse order of the command.

cf. mamba-org/mamba#3856

Maybe the error with multiple arguments could be more explicit, or we could use some kind of validation methods if available?
Additionally, if suggestions are supported in CLI11 that would be awesome!

Thanks!

[cxw42]

Git's "the most similar commands are..." output would be a neat feature!

[phlptp]

Any thought on what a good measure for "close" strings would be? It should be possible to insert a method into one of the app/subcommand callbacks that can check this and return a useful message, but not sure what a good simple algorithm for what the "best" match should be.

[cxw42]

I could think of a few options, roughly in increasing order of complexity:

• Prefix matches only
• Hamming distance < N
  • N determined empirically? Perhaps based on the lengths of the subcommands?
• Levenshtein distance within a threshold (looks like git uses this)

For a first cut, how about something like this (assuming the shortest subcommand has at least two characters):

1. Space-pad input and all subcommands to same length
2. Compute Hamming distance for each subcommand
3. Select subcommands with distance <= N (N == 1 if the shortest subcommand has only two characters, otherwise 2?)

• Edit Or maybe choose N based on the number of chars the user typed? If the user typed more chars, give the user more options?

5. Sort the remaining by "is input prefix of the candidate?" first, then distance ascending, then ASCII order ascending.
   (Made up on the spot as a draft :D so no guarantees!)

[phlptp]

I made a PR, with an example that does this, curious to continue the discussion of what this would look like. I definitely don't think it would be the default behavior, but not completely against some code included in CLI11 that would make it really easy to set up.