Implement hash -p to set a command path

[eswarseeram]

Adds support for the -p option in the hash builtin in Oil Shell.

• Allows manually mapping a command to a specific path.
• Updates the internal hash table for shell commands.

[andychu]

Thank you for looking into this! We like to start with spec tests -- te.g. there are related ones in spec/command_.test.sh

https://github.com/oils-for-unix/oils/wiki/Spec-Tests

$ test/spec.sh command_ -r 8-15
command_.test.sh
case    line    dash    bash    mksh    zsh     osh
  8      57     pass    pass    pass    pass    pass    $PATH lookup
  9      70     pass    pass    pass    ok      pass    filling $PATH cache, then insert the same command earlier in cache
 10     101     pass    pass    ok      ok      pass    filling $PATH cache, then deleting command
 11     133     pass    pass    pass    pass    pass    Non-executable on $PATH
 12     154     pass    ok      ok      ok      pass    hash without args prints the cache
 13     171     pass    pass    BUG     pass    pass    hash with args
 14     190     BUG     BUG     pass    pass    ok      hash -r doesn't allow additional args
 15     197     pass    pass    pass    pass    pass    Executing command with same name as directory in PATH (#2429)

                dash    bash    mksh    zsh     osh
        pass    7       6       5       5       7
        ok      0       1       2       3       1
        BUG     1       1       1       0       0
        total   8       8       8       8       8

[andychu]

To add a flag, see

HASH_SPEC = FlagSpec('hash')
HASH_SPEC.ShortFlag('-r')

in frontend/flag_def.py . And then regenerated code with build/py.sh all

https://github.com/oils-for-unix/oils/wiki/Oils-Dev-Cheat-Sheet

And then you can use arg.p

According to help hash, it is a flag that takes an argument, not 2 arguments. -p pathname

So that's ShortFlag('-p', args.String)

[eswarseeram]

Updated hash -p flag implementation as per maintainer feedback. Only single argument is taken now.

[andychu]

As mentioned, this would still need spec tests