Merge stack before printing

[zhiburt]

Could you @fdncred try it?

close?: #9264

[fdncred]

@zhiburt Doesn't seem to work. Here's my test.

1. save preview-theme.nu from some theme items do not change colors when requested #9264 (comment)
2. source preview-theme.nu
3. cd nu_scripts
4. preview and i randomly picked apprentice
5. which then puts this on the command line use themes/themes/apprentice.nu; $env.config.color_config = (apprentice); preview_theme | table -e and hit enter
6. I get this
   
   Which you can tell it's not working because the header and row index (which are the same color) {fg: #87af87, attr: b} are not being drawn in that color. the green header and cyan index are from my current theme, before i use'd the one above.

If i run the command in 5 above again, i get this

One last comment here. After the first screenshot is shown with the preview_theme | table -e, if I do a ls, the theme is applied, even though the table that is drawn right after doesn't show it.

[fdncred]

This is so strange. If I do the commands on separate lines, it seems to work.

[fdncred]

It seems this may have something to do with how nushell is handling one-liners with multiple commands separated with semicolons? like all the stuff that is changing in this pr may not be happening on this type of one-liner?

[zhiburt]

I think must be addressed.
I got lazy a bit here and just followed @kubouch suggestion for this case.

Let me know if it works.

[fdncred]

wow, this is working great! still playing but just wow!!!

[fdncred]

@zhiburt I'm ready to merge this but can we have more descriptive fn names for merge_env2 and merge_env3?

[fdncred]

Thanks @zhiburt!

[kubouch]

I didn't have time to look into it yet but we shouldn't clone the EngineState before every print, that will be super slow.

[zhiburt]

Precisely clone will make it slower.
The same for table.

I am not sure to which degree though; you could test it.

Ideally the env shall be just merged somewhere in nu-engine/eval; but I haven't cracked this one.