Check that colorscheme has true color support

Unfortunately neovim has no support for hlget() yet [0], so this got a
little bit more complicated there.

Also what the hell is wrong with Lua to overcomplicate basic things such
as getting the name of the colorscheme. Apparently we have to use the
generic vimscript command interface [1] just for this.

It's kind of funny how the Lua API now has `api.nvim_cmd()`,
`api.nvim_exec()` and `api.nvim_exec2()` similar to how libc has evolved
to have 1000 alternatives to strcpy() and every year they release a new
version that is apparently safer.
So when will we get `api.nvim_exec3()`? ;)

[0] neovim/neovim#16270
[1] neovim/neovim#18201

Author: vimpostor

autoload/tpipeline/debug.vim

@@ -21,7 +21,8 @@ func tpipeline#debug#info()
 	let tmux = systemlist("tmux -V")[-1]
 	let jobstate = tpipeline#job_state()
 	let os = tpipeline#debug#os()
-	let result = #{left: left, right: right, tmux: tmux, plugin_version: tpipeline#version#string(), job_state: jobstate, job_errors: s:stderr, os: os}
+	let bad_colors = len(tpipeline#debug#get_bad_hl_groups())
+	let result = #{left: left, right: right, tmux: tmux, plugin_version: tpipeline#version#string(), job_state: jobstate, job_errors: s:stderr, os: os, bad_colors: bad_colors}
 
 	if has('nvim')
 		let stl = g:tpipeline_statusline
@@ -50,4 +51,24 @@ func tpipeline#debug#log_err(line)
 	call add(s:stderr, a:line)
 endfunc
 
+func tpipeline#debug#is_truecolor(s)
+	return empty(a:s) || a:s == 'fg' || a:s== 'bg' || a:s == '#NONE' || a:s =~ '#\x\{6}'
+endfunc
+
+func tpipeline#debug#is_truecolor_group(id)
+	let syn = synIDtrans(a:id)
+	let fg = tolower(synIDattr(syn, 'fg'))
+	let bg = tolower(synIDattr(syn, 'bg'))
+	return tpipeline#debug#is_truecolor(fg) && tpipeline#debug#is_truecolor(bg)
+endfunc
+
+func tpipeline#debug#get_bad_hl_groups()
+	if has('nvim')
+		let hls = luaeval('vim.tbl_keys(vim.api.nvim_get_hl(0, {}))')->map({_, v -> #{id: hlID(v), name: v}})
+	else
+		let hls = hlget()
+	endif
+	return hls->filter({_, v -> !tpipeline#debug#is_truecolor_group(v.id)})->map({_, v -> v.name})
+endfunc
+
 call tpipeline#debug#init()

lua/tpipeline/health.lua

@@ -4,7 +4,7 @@ M.check = function()
 	vim.health.report_start("tpipeline report")
 	local info = vim.fn['tpipeline#debug#info']()
 
-	ver = vim.version()
+	local ver = vim.version()
 	if vim.version.lt(ver, {0, 6, 0}) then
 		vim.health.report_error(string.format("Neovim version %d.%d is not supported, use 0.6 or higher", ver.major, ver.minor))
 	else
@@ -22,6 +22,14 @@ M.check = function()
 	else
 		vim.health.report_warn("Job reported errors", info.job_errors)
 	end
+
+	if info.bad_colors > 0 then
+		local groups = vim.fn['tpipeline#debug#get_bad_hl_groups']()
+		local colorscheme = vim.api.nvim_exec2("colorscheme", {output = true}).output
+		vim.health.report_warn(string.format("The colorscheme %s contains %d highlight groups that don't properly support truecolor. These colors might not render correctly in tmux.\nBad highlight groups are: %s", colorscheme, info.bad_colors, vim.inspect(groups)))
+	else
+		vim.health.report_ok("Colorscheme has true color support")
+	end
 end
 
 return M