Export multiline prompt functions

[josevalim]

Both shell:default_multiline_prompt/1 and
shell:inverted_space_prompt/1 have been exported.

shell:prompt_width/1 is now also available as a
helper function for custom prompt implementations.

[github-actions]

CT Test Results

       3 files     145 suites   1h 37m 59s ⏱️
3 373 tests 3 072 ✔️ 301 💤 0 ❌
3 892 runs  3 538 ✔️ 354 💤 0 ❌

Results for commit 8fc5c40.

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[josevalim]

On a second though, it may be better to expose the underlying prim_tty:npwcwidthstring/1 function, so it is easier for others to build their own prompts, including the default one. However, prim_tty is not public. Perhaps we can expose it on edlin, shell, or some other module?

[dgud]

You can set the prompt with the documented:
shell:prompt_func(PromptFunc)
but there needs to be a
shell:multiline_prompt_func(MPF)

[frazze-jobb]

I agree, the prim_tty:npwcwidthstring/1 will need to be made available through some public module I suggest shell.
And we need a call as @dgud mentioned to set the multiline prompt via the shell module.
Since the shell_prompt and multiline_prompt is related, it would probably make more sense to have both the default_mulitline_prompt and inverted_space_prompt available through the shell module. And documentation of them in the shell module.

[josevalim]

I will send a PR this week with most of these changes. :)

[josevalim]

I have rebased and moved the multiline prompt functions to shell, with tests and docs. I did not add a convenience API for setting the shell multiline prompt programatically.

I have decided to rename prim_tty:npwcwidthstring/1 to shell:prompt_width/1, as the first name was a good match for prim_tty (and its internal functions) but it felt out of replace in the shell module. I will be glad to rename it to something else.

[frazze-jobb]

Thanks @josevalim, I think it looks good, just the failing testcase that needs fixing.
I can try to find time to create the convenience API shell:multiline_prompt_func(MPF) later in a separate PR.

[josevalim]

I changed the test but I realized now that edlin:inverted_space_prompt was somewhat public then, even if not documented. Should we keep it around for compatibility or will we tell people to update their flags accordingly, given this is still new (experimental?)?

[frazze-jobb]

Still experimental so. And it makes more sense to me to have it in shell