A first draft of tab-completion for prompts

[untitaker]

See #173. This is not ready for merge yet.

• Missing tests, changelog entry, and isn't yet used in click.Path/File.
• Is a very myopic implementation. Users will ask for custom completion
  functions, which bash's read of course doesn't support.

[untitaker]

And i just found out that readline from the stdlib might be helpful...

[untitaker]

I suggest that types can define custom readline completers.

[untitaker]

A problem i am currently running into is that the prompt text doesn't get reshown after showing all suggestions. This is because click outputs the prompt text manually instead of passing it to raw_input. I tried some of the hooks in the readline module without success.

[mitsuhiko]

We cannot use readline because of licensing issues unfortunately. Readline is GPL licensed :-/

[untitaker]

From the readline docs:

On MacOS X the readline module can be implemented using the libedit library
instead of GNU readline.

The configuration file for libedit is different from that of GNU readline.
If you programmatically load configuration strings you can check for the
text “libedit” in readline.__doc__ to differentiate between GNU readline
and libedit.

Since libedit is BSD, this seems to be a greyzone.

Shouldn't GPL be enforced on CPython itself if its stdlib is depending on readline?

[untitaker]

Also, https://mail.python.org/pipermail/python-list/2010-April/574100.html

[untitaker]

Rebased and reverted accidental change to index.rst. Any updates on this?

[untitaker]

I think https://github.com/jonathanslenders/python-prompt-toolkit could be used as optdepends for this.

[msabramo]

Doesn't merge cleanly anymore.

[untitaker]

Yeah, this is a dead end.