rfc for improving command suggestions

[nlf]

this is intended to improve discoverability of a working command when a user runs something that does not work, notably this is an approach to addressing the needs of users who expect npm foo to work. instead of making an assumption that they want a script or binary, we will suggest that they try an explicit command that does one of those actions.

References

Related to #336
Related to #332
Related to #279

[isaacs]

So if we do this, we could have the commands do something like throw Object.assign(new Error('unknown command'), { suggestions: listOfEveryAvailableCommand }) and let the Levenshtein distance pick the best ones to prompt?

[isaacs]

I think (ironically) this RFC is blending together a few things into one, and in the spirit of this RFC, it should be made explicit. They are:

1. Unknown top level commands suggesting run/exec
2. Misspelling affordances (like npm isntall)
3. Unambiguous partial abbrev spellings for known things (like npm ins for npm install)
4. "Blessed" affordances/shorthands like the npm i alias for npm install

For (1), I think that this is exactly the right approach, and seems to be where we keep landing every time we discuss the tradeoffs involved in making npm tsc work like yarn.

For (2), this seems reasonable enough, though it is a breaking change, and definitely not uncontroversial. We could do a lot worse than copying git, and we have enough commands that some of the affordances have started to get a bit cluttered.

For (3), it's worth noting that git recently added support for abbreviations on command-line switches, but not on top level commands. If a command is an unambiguous abbreviation for a known top-level command, it seems like we have enough to know what the user intended.

For (4), I think the list could be examined and we could make some changes, but I am going to die on the hill of npm i and npm t continuing to work as they currently do. Making the user type out the full word for those common commands just seems rude.

Ideas for a follow-up RFC:

• Config option to tell npm to just take the first suggestion.
• Config options to define shorthands and aliases.
• Choice in the prompt to save the suggestion as an alias when we do have an interactive mode, so users who truly cannot stop typing hlep can opt into the affordance.
• Similar rejection/suggestion for CLI configs, in some future time when we can drop support for parsing unknown config options.