Clarification of history_request status and future plans

[krassowski]

history_request is currently described as not in use in the main notebook interface and says that some options may be removed in the future (in a note added 7 years ago).

jupyter_client/docs/messaging.rst

Lines 805 to 813 in 6ea7118

	Most of the history messaging options are not used by Jupyter frontends, and
	many kernels do not implement them. If you're implementing these messages in
	a kernel, the 'tail' request is the most useful; this is used by the Qt
	console, for example. The notebook interface does not use history messages
	at all.
	This interface was designed by exposing all the main options of IPython's
	history interface. We may remove some options in a future version of the
	message spec.

While the above is true as of today, two pull request against JupyterLab propose exposing the history information in the notebook interface (which will likely propagate to Jupyter Notebook v7.x) as opt-in features:

• Notebook execution history jupyterlab/jupyterlab#15062
• Experimental inline completer jupyterlab/jupyterlab#15160

The former uses the same request as presently implemented in JupyterLab console:

{
  output: false,
  raw: true,
  hist_access_type: 'tail',
  n: 500
}

and the latter makes use of search function:

{
  output: false,
  raw: true,
  hist_access_type: 'search',
  pattern: linePrefix + '*',
  unique: true,
  n: this._maxSuggestions
}

Aside: I find the pattern option specification a bit unclear e.g. whether there are escaping characters which would allow to escape . and * wildcards.

Once these pull requests are merged and released, the history request API will gain more prominence and more kernels will want to implement it. It might be then harder to change the APIs.

1. Which options were planned for removal? Should those be deprecated? Are those any of options proposed in the pull requests mentioned above?
2. Are there any other changes/addition that we want to expose out of IPython?

[krassowski]

CC @andrewfulton9 @Carreau