feat(highlights): add fzf-lua

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https://github.com/ibhagwan/fzf-lua

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We should probably mention in the README about this setting for generating highlights for fzf.

require("fzf-lua").setup({ fzf_colors = true })

I've been using this plugin for a while now, but I just learned about this setting recently. 😀

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Some updates.

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Hey @ramojus, this PR has all the changes from the PR with blink.

[ramojus]

Hey, sorry for the delays, I'm quite busy lately.

I'm just wondering if we really need to support this plugin? We have telescope, which is much more popular. Does this plugin have anything that telescope doesn't?
Otherwise the PR looks good, I would have a few minor comments and it can be merged.

[ramojus]

Also just saw that this plugin has a telescope profile. In terms of highlight groups, with your changes, does it look similar to telescope when that profile is applied?

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I'm just wondering if we really need to support this plugin?

Why Fzf-Lua
Personally, I think it's a matter of personal preference, but I find it slightly faster. I'm an Fzf user, and I would greatly appreciate it if this plugin were supported by this beautiful colorscheme. There's no real reason not to support it. By doing so, we can potentially attract more users.

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Also just saw that this plugin has a telescope profile. In terms of highlight groups, with your changes, does it look similar to telescope when that profile is applied?

It looks like this.

[emretuna]

I was waiting for that one great!

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@ramojus I've removed variables

[ramojus]

Thanks for the screenshots, that looks surprisingly good! We should make telescope look more like this :D
But of course, it's not viable unless telescope supports darker backdrop.

This is a difficult plugin as there are a lot of scenarios. I've pulled your changes to take a deeper look. There are some things I don't like about this plugin that I haven't found a way to fix:

• Current result being bold (seems unnecessary - distracting).
  
• Backdrop removed when searching colorschemes. I get it, it's for colorscheme preview, but ideally fzf background would then be lighter when searching colorschemes.
  
• Line numbers in preview having their default dark background. (This is probably fine as long as the preview has Normal background)
  
  I was thinking of making the backgrounds lighter, but with this issue, probably better to leave it as is.

As you know this plugin better than I do, I would appreciate any help with these issues. Otherwise, not a deal breaker.

I will also submit some review comments.

[ramojus]

Currently there is no easy way to change normal bg or preview bg without changing a whole lot of highlight groups manually.

I think it's okay to use some variables for highlights as long as it offers readability and/or maintainability improvements. Here we could have a variable normal for FzfLuaNormal, this variable could then be reused in other highlight groups. Similarly we could have a variable preview_normal.

A fine alternative would be to reuse FzfLuaNormal and FzfLuaPreviewNormal with linking and hl.get function.

[ramojus]

Here I would suggest: (normal being FzfLuaNormal)

    local groups = require("mellifluous.highlights.custom_groups").get(colors)

    hl.set("FzfLuaCursorLine", { bg = groups.MenuButtonSelected(normal.bg).bg, fg = normal.fg })

I don't think there's any reason to have lighter fg for this group, keeping the same fg as for other results will offer more consistency.

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Oh, apparently, FzfLuaCursorLine is intended for the preview window. I was confused about the naming convention and removed it.

[ramojus]

This group goes nicely here:

    hl.set("FzfLuaFzfHeader", { fg = colors.fg4 })

[ramojus]

Nice work, really. I like that we also retain some similarity with fzf cli, mainly by keeping that FzfLuaFzfPointer visible, but also not distracting.
One more issue here:

The background of that title doesn't match with normal background. Not sure which highlight group sets it, as I don't get this title by default.

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• Current result being bold (seems unnecessary - distracting).
  

Not sure how to fix this. I've explicitly unset bold and set nocombine, but it seems to be ignored.

• Backdrop removed when searching colorschemes. I get it, it's for colorscheme preview, but ideally fzf background would then be lighter when searching colorschemes.
  

I think it's fine. And probably there's nothing we can do about it.

• Line numbers in preview having their default dark background. (This is probably fine as long as the preview has Normal background)
  
  I was thinking of making the backgrounds lighter, but with this issue, probably better to leave it as is.

Fixed.

One more issue here:

The background of that title doesn't match with normal background. Not sure which highlight group sets it, as I don't get this title by default.

Nice catch! Fixed.

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