Support multiline inputs in non TTY contexts

[basile-henry]

This PR add supports for multiline inputs (via the Validator API) for the case where stdin isn't a TTY (or is an unsupported terminal).

I have added a new example input_multiline to make quickly showcase how this works.

This lets us do:

echo -e "(\n\n)" | cargo run --example input_multiline

And have readline correctly read this as a single multiline input instead of 3 separate inputs (if it was called in a loop).
Even in the single line case, there was a difference between the TTY and the non-TTY versions of readline: the non-TTY version would keep the trailing newline character.

My main motivation for this change is to be able to easily test a REPL made using rustyline by piping my inputs in without having to mock the TTY part of it. It also make rustyline more consistent this way.

[basile-henry]

I have also added support to handle backspace characters in non TTY mode.

This makes the following work:

➜ echo -e "([)\n\b\b\n])" | cargo run --example input_multiline 2> /dev/null
Input: ([
])

[gwenn]

Sorry, but there should be no ANSI escape sequence (colors) in the input stream.
See #215 (comment)

[basile-henry]

there should be no ANSI escape sequence (colors) in the input stream

I don't really understand what you mean. I don't think I have added anything ANSI dependent in the input stream. Are you referring to '\b'? I believe that is a ASCII control character. And by the looks of it python-prompt-toolkit also supports it.

Or are you referring to the output stream, and I need to filter out ANSI sequences in the messages from the validator?

[gwenn]

there should be no ANSI escape sequence (colors) in the input stream

I don't really understand what you mean. I don't think I have added anything ANSI dependent in the input stream. Are you referring to '\b'? I believe that is a ASCII control character. And by the looks of it python-prompt-toolkit also supports it.

Or are you referring to the output stream, and I need to filter out ANSI sequences in the messages from the validator?

Sorry I was completely wrong !

[basile-henry]

Since I have fixed an edge case in the way the Invalid case worked the quick example is now this:

➜ echo -e "([)\n\b\n])" | cargo run --example input_multiline 2> /dev/null
Input: ([
])

Notice how I don't need to backspace the \n anymore, because the input is invalid the newline isn't entered, so \b char applies to ) instead.

[gwenn]

Thanks and sorry for the long delay.

[basile-henry]

No worries, thanks for reviewing and taking the feature in! 😄

[gwenn]

Version 9.0.0 released.