Fix set_next_input with prompt_toolkit 1.0.10

[takluyver]

Closes gh-10229

Please don't merge this just yet.

@jonathanslenders I discovered after updating that we can no longer set text in the buffer with a pre_run function, because pre_run_callables reset the buffer immediately after that. I've worked around this by adding another callable to pre_run_callables which sets the text that I want, but I don't know if this is the right way to do it, or whether it works with previous releases of prompt_toolkit.

[jonathanslenders]

Hi @takluyver,
I didn't realize you were relying on this.
This merge request is correct, but it will indeed not work for earlier versions of prompt_toolkit.
You may want to test for hasattr(self.pt_cli, 'pre_run_callables').
What is actually the use case for this? Why are you setting a text?

[takluyver]

Thanks, I've pushed a fix that only uses pre_run_callables if the attribute is there, and otherwise just sets the document directly.

There are a few features in IPython that put some text at the next prompt; probably the most obvious is the %recall magic - %recall 1-3 will get inputs 1, 2 and 3 from your history, concatenate them and put them at the next prompt. They all go through a method shell.set_next_input().

[takluyver]

We're getting a number of bug reports that I believe this would fix, if someone would like to review it.

[takluyver]

@meeseeksdev backport to 5.x