feat(highlight): update default color scheme

Problem: Default color scheme is suboptimal.

Solution: Start using new color scheme. Introduce new `vim` color scheme
for opt-in backward compatibility.

------
Main design ideas
- Be "Neovim branded".
- Be minimal for 256 colors with a bit more shades for true colors.
- Be accessible through high enough contrast ratios.
- Be suitable for dark and light backgrounds via exchange of dark and
  light palettes.

------
Palettes

- Have dark and light variants. Implemented through exporeted
  `NvimDark*` and `NvimLight*` hex colors.

- Palettes have 4 shades of grey for UI elements and 6 colors (red,
  yellow, green, cyan, blue, magenta).

- Actual values are computed procedurally in Oklch color space based on
  a handful of hyperparameters.

- Each color has a 256 colors variant with perceptually closest color.

------
Highlight groups

Use:

- Grey shades for general UI according to their design.

- Bold text for keywords (`Statement` highlight group). This is an
  important choice to increase accessibility for people with color
  deficiencies, as it doesn't rely on actual color.

- Green for strings, `DiffAdd` (as background), `DiagnosticOk`, and some
  minor text UI elements.

- Cyan as main syntax color, i.e. for function usage (`Function`
  highlight group), `DiffText`, `DiagnosticInfo`, and some minor text UI
  elements.

- Red to generally mean high user attention, i.e. errors; in particular
  for `ErrorMsg`, `DiffDelete`, `DiagnosticError`.

- Yellow very sparingly only with true colors to mean mild user
  attention, i.e. warnings. That is, `DiagnosticWarn` and `WarningMsg`.

- Blue very sparingly only with true colors as `DiagnosticHint` and some
  additional important syntax group (like `Identifier`).

- Magenta very carefully (if at all).

------
Notes

- To make tests work without relatively larege updates, each one is
  prepended with an equivalent of the call `:colorscheme vim`.

  Plus some tests which spawn new Neovim instances also now use 'vim'
  color scheme.

  In some cases tests are updated to fit new default color scheme.

7 files changed, 51 insertions, 33 deletions

diff --git a/test/functional/ui/cursor_spec.lua b/test/functional/ui/cursor_spec.lua
index 05057ca080..7bec5eaac6 100644
--- a/test/functional/ui/cursor_spec.lua
+++ b/test/functional/ui/cursor_spec.lua
@@ -215,7 +215,7 @@ describe('ui/cursor', function()
           m.hl_id = 64
           m.attr = {background = Screen.colors.DarkGray}
       end
-      if m.id_lm then m.id_lm = 67 end
+      if m.id_lm then m.id_lm = 69 end
     end
 
     -- Assert the new expectation.
diff --git a/test/functional/ui/embed_spec.lua b/test/functional/ui/embed_spec.lua
index 9729f65355..3bc3af9853 100644
--- a/test/functional/ui/embed_spec.lua
+++ b/test/functional/ui/embed_spec.lua
@@ -26,6 +26,12 @@ local function test_embed(ext_linegrid)
       [3] = {bold = true, foreground = Screen.colors.Blue1},
       [4] = {bold = true, foreground = Screen.colors.Green},
       [5] = {bold = true, reverse = true},
+      [6] = {foreground = Screen.colors.NvimDarkGrey3, background = Screen.colors.NvimLightGrey1};
+      [7] = {foreground = Screen.colors.NvimDarkRed};
+      [8] = {foreground = Screen.colors.NvimDarkCyan};
+      [9] = {foreground = Screen.colors.NvimLightGrey3, background = Screen.colors.NvimDarkGrey1};
+      [10] = {foreground = Screen.colors.NvimLightRed};
+      [11] = {foreground = Screen.colors.NvimLightCyan};
     })
   end
 
@@ -36,10 +42,10 @@ local function test_embed(ext_linegrid)
                                                                   |
                                                                   |
                                                                   |
-                                                                  |
-      Error detected while processing pre-vimrc command line:     |
-      E121: Undefined variable: invalid                           |
-      Press ENTER or type command to continue^                     |
+      {6:                                                            }|
+      {7:Error detected while processing pre-vimrc command line:}     |
+      {7:E121: Undefined variable: invalid}                           |
+      {8:Press ENTER or type command to continue}^                     |
     ]])
 
     feed('<cr>')
@@ -64,11 +70,11 @@ local function test_embed(ext_linegrid)
                                                                   |
                                                                   |
                                                                   |
-      {5:                                                            }|
-      Error detected while processing pre-vimrc command line:     |
-      foo                                                         |
-      {1:bar}                                                         |
-      {4:Press ENTER or type command to continue}^                     |
+      {9:                                                            }|
+      {7:Error detected while processing pre-vimrc command line:}     |
+      {7:foo}                                                         |
+      {10:bar}                                                         |
+      {11:Press ENTER or type command to continue}^                     |
     ]])
   end)
 
@@ -78,11 +84,11 @@ local function test_embed(ext_linegrid)
                                                                   |
                                                                   |
                                                                   |
-                                                                  |
-      Error detected while processing pre-vimrc command line:     |
-      foo                                                         |
-      bar                                                         |
-      Press ENTER or type command to continue^                     |
+      {6:                                                            }|
+      {7:Error detected while processing pre-vimrc command line:}     |
+      {7:foo}                                                         |
+      {7:bar}                                                         |
+      {8:Press ENTER or type command to continue}^                     |
     ]], condition=function()
       eq(Screen.colors.Green, screen.default_colors.rgb_bg)
     end}
@@ -144,7 +150,7 @@ describe('--embed --listen UI', function()
     helpers.skip(helpers.is_os('win'))
     clear()
     local child_server = assert(helpers.new_pipename())
-    funcs.jobstart({nvim_prog, '--embed', '--listen', child_server, '--clean'})
+    funcs.jobstart({nvim_prog, '--embed', '--listen', child_server, '--clean', '--cmd', 'colorscheme vim'})
     retry(nil, nil, function() neq(nil, uv.fs_stat(child_server)) end)
 
     local child_session = helpers.connect(child_server)
diff --git a/test/functional/ui/float_spec.lua b/test/functional/ui/float_spec.lua
index 2902b4a4a5..eca8ee6422 100644
--- a/test/functional/ui/float_spec.lua
+++ b/test/functional/ui/float_spec.lua
@@ -1185,7 +1185,7 @@ describe('float window', function()
 
     it('defaults to NormalFloat highlight and inherited options', function()
       command('set number')
-      command('hi NormalFloat guibg=#333333')
+      command('hi NormalFloat guibg=#333333 guifg=NONE')
       feed('ix<cr>y<cr><esc>gg')
       local win = meths.open_win(0, false, {relative='editor', width=20, height=4, row=4, col=10})
       if multigrid then
@@ -1271,7 +1271,7 @@ describe('float window', function()
       command('set colorcolumn=1')
       command('set cursorline')
       command('set foldcolumn=1')
-      command('hi NormalFloat guibg=#333333')
+      command('hi NormalFloat guibg=#333333 guifg=NONE')
       feed('ix<cr>y<cr><esc>gg')
       local win = meths.open_win(0, false, {relative='editor', width=20, height=4, row=4, col=10, style='minimal'})
       if multigrid then
@@ -1399,7 +1399,7 @@ describe('float window', function()
       command('set colorcolumn=1')
       command('set cursorline')
       command('set foldcolumn=1')
-      command('hi NormalFloat guibg=#333333')
+      command('hi NormalFloat guibg=#333333 guifg=NONE')
       feed('ix<cr>y<cr><esc>gg')
       local win = meths.open_win(0, false, {relative='editor', width=20, height=4, row=4, col=10, style='minimal'})
       if multigrid then
@@ -1528,7 +1528,7 @@ describe('float window', function()
       command('set cursorline')
       command('set foldcolumn=1')
       command('set statuscolumn=%l%s%C')
-      command('hi NormalFloat guibg=#333333')
+      command('hi NormalFloat guibg=#333333 guifg=NONE')
       feed('ix<cr>y<cr><esc>gg')
       meths.open_win(0, false, {relative='editor', width=20, height=4, row=4, col=10, style='minimal'})
       if multigrid then
@@ -5921,7 +5921,7 @@ describe('float window', function()
     describe('float shown after pum', function()
       local win
       before_each(function()
-        command('hi NormalFloat guibg=#333333')
+        command('hi NormalFloat guibg=#333333 guifg=NONE')
         feed('i')
         funcs.complete(1, {'aa', 'word', 'longtext'})
         if multigrid then
diff --git a/test/functional/ui/hlstate_spec.lua b/test/functional/ui/hlstate_spec.lua
index 55f873e827..b35d61744f 100644
--- a/test/functional/ui/hlstate_spec.lua
+++ b/test/functional/ui/hlstate_spec.lua
@@ -72,7 +72,7 @@ describe('ext_hlstate detailed highlights', function()
       [6] = {{}, {{hi_name = "StatusLineNC", ui_name = "StatusLineNC", kind = "ui"}}},
       [7] = {{}, {{hi_name = "MsgArea", ui_name = "MsgArea", kind = "ui"}}},
     })
-    command("hi clear VertSplit")
+    command("hi clear WinSeparator")
     command("vsplit")
 
     screen:expect([[
diff --git a/test/functional/ui/output_spec.lua b/test/functional/ui/output_spec.lua
index 7b93b74eac..1dbbe76bac 100644
--- a/test/functional/ui/output_spec.lua
+++ b/test/functional/ui/output_spec.lua
@@ -22,7 +22,7 @@ describe("shell command :!", function()
   before_each(function()
     clear()
     screen = child_session.screen_setup(0, '["'..helpers.nvim_prog..
-      '", "-u", "NONE", "-i", "NONE", "--cmd", "'..helpers.nvim_set..'"]')
+      '", "-u", "NONE", "-i", "NONE", "--cmd", "colorscheme vim", "--cmd", "'..helpers.nvim_set..'"]')
     screen:expect([[
       {1: }                                                 |
       {4:~                                                 }|
diff --git a/test/functional/ui/quickfix_spec.lua b/test/functional/ui/quickfix_spec.lua
index df43871e60..9f072915e2 100644
--- a/test/functional/ui/quickfix_spec.lua
+++ b/test/functional/ui/quickfix_spec.lua
@@ -89,7 +89,7 @@ describe('quickfix selection highlight', function()
   end)
 
   it('using QuickFixLine highlight group', function()
-    command('highlight QuickFixLine guibg=Red')
+    command('highlight QuickFixLine guibg=Red guifg=NONE gui=NONE')
 
     command('copen')
 
@@ -124,7 +124,7 @@ describe('quickfix selection highlight', function()
 
   it('combines with CursorLine', function()
     command('set cursorline')
-    command('highlight QuickFixLine guifg=Red')
+    command('highlight QuickFixLine guifg=Red guibg=NONE gui=NONE')
     command('highlight CursorLine guibg=Fuchsia')
 
     command('copen')
@@ -160,7 +160,7 @@ describe('quickfix selection highlight', function()
 
   it('QuickFixLine background takes precedence over CursorLine', function()
     command('set cursorline')
-    command('highlight QuickFixLine guibg=Red')
+    command('highlight QuickFixLine guibg=Red guifg=NONE gui=NONE')
     command('highlight CursorLine guibg=Fuchsia')
 
     command('copen')
diff --git a/test/functional/ui/screen_basic_spec.lua b/test/functional/ui/screen_basic_spec.lua
index 7cc1accd3f..4ef7565ec5 100644
--- a/test/functional/ui/screen_basic_spec.lua
+++ b/test/functional/ui/screen_basic_spec.lua
@@ -8,9 +8,15 @@ local funcs, meths = helpers.funcs, helpers.meths
 
 describe('screen', function()
   local screen
-  local nvim_argv = {helpers.nvim_prog, '-u', 'NONE', '-i', 'NONE', '-N',
-                     '--cmd', 'set shortmess+=I background=light noswapfile belloff= noshowcmd noruler',
-                     '--embed'}
+  local nvim_argv = {
+    helpers.nvim_prog,
+    '-u', 'NONE',
+    '-i', 'NONE',
+    '-N',
+    '--cmd', 'set shortmess+=I background=light noswapfile belloff= noshowcmd noruler',
+    '--cmd', 'colorscheme vim',
+    '--embed',
+  }
 
   before_each(function()
     local screen_nvim = spawn(nvim_argv)
@@ -997,9 +1003,15 @@ describe('Screen default colors', function()
   local function startup(light, termcolors)
     local extra = (light and ' background=light') or ''
 
-    local nvim_argv = {helpers.nvim_prog, '-u', 'NONE', '-i', 'NONE', '-N',
-                       '--cmd', 'set shortmess+=I noswapfile belloff= noshowcmd noruler'..extra,
-                       '--embed'}
+    local nvim_argv = {
+      helpers.nvim_prog,
+      '-u', 'NONE',
+      '-i', 'NONE',
+      '-N',
+      '--cmd', 'set shortmess+=I noswapfile belloff= noshowcmd noruler'..extra,
+      '--cmd', 'colorscheme vim',
+      '--embed',
+    }
     local screen_nvim = spawn(nvim_argv)
     set_session(screen_nvim)
     screen = Screen.new()
@@ -1017,7 +1029,7 @@ describe('Screen default colors', function()
   it('can be set to light', function()
     startup(true, false)
     screen:expect{condition=function()
-      eq({rgb_fg=Screen.colors.White, rgb_bg=0, rgb_sp=Screen.colors.Red,
+      eq({rgb_bg=Screen.colors.White, rgb_fg=0, rgb_sp=Screen.colors.Red,
           cterm_bg=0, cterm_fg=0}, screen.default_colors)
     end}
   end)