feat(utils): support extracting fallback color

lua/lualine/components/diagnostics/config.lua

@@ -26,28 +26,28 @@ function M.apply_default_colors(opts)
   local default_diagnostics_color = {
     error = {
       fg = utils.extract_color_from_hllist(
-        'fg',
+        { 'fg', 'sp' },
         { 'DiagnosticError', 'LspDiagnosticsDefaultError', 'DiffDelete' },
         '#e32636'
       ),
     },
     warn = {
       fg = utils.extract_color_from_hllist(
-        'fg',
+        { 'fg', 'sp' },
         { 'DiagnosticWarn', 'LspDiagnosticsDefaultWarning', 'DiffText' },
         '#ffa500'
       ),
     },
     info = {
       fg = utils.extract_color_from_hllist(
-        'fg',
+        { 'fg', 'sp' },
         { 'DiagnosticInfo', 'LspDiagnosticsDefaultInformation', 'Normal' },
         '#ffffff'
       ),
     },
     hint = {
       fg = utils.extract_color_from_hllist(
-        'fg',
+        { 'fg', 'sp' },
         { 'DiagnosticHint', 'LspDiagnosticsDefaultHint', 'DiffChange' },
         '#273faf'
       ),

lua/lualine/utils/utils.lua

@@ -36,23 +36,26 @@ end
 
 --- retrieves color value from highlight group name in syntax_list
 --- first present highlight is returned
----@param scope string
+---@param scope string|table
 ---@param syntaxlist table
 ---@param default string
 ---@return string|nil
 function M.extract_color_from_hllist(scope, syntaxlist, default)
+  scope = type(scope) == 'string' and { scope } or scope
   for _, highlight_name in ipairs(syntaxlist) do
     if vim.fn.hlexists(highlight_name) ~= 0 then
       local color = M.extract_highlight_colors(highlight_name)
+      for _, sc in ipairs(scope) do
         if color.reverse then
-        if scope == 'bg' then
+          if sc == 'bg' then
-          scope = 'fg'
+            sc = 'fg'
           else
-          scope = 'bg'
+            sc = 'bg'
           end
         end
-      if color[scope] then
+        if color[sc] then
-        return color[scope]
+          return color[sc]
+        end
       end
     end
   end

tests/spec/utils_spec.lua

@@ -24,6 +24,41 @@ describe('Utils', function()
     vim.cmd('hi clear hl2')
   end)
 
+  it('can extract individual highlight color', function()
+    local fg_clr = '#aabbcc'
+    local bg_clr = '#889977'
+    local sp_clr = '#997788'
+    local def_clr = '#ff0000'
+    local hl_std = { fg = fg_clr, bg = bg_clr }
+    local hl_rvs = { fg = fg_clr, bg = bg_clr, reverse = true }
+    local hl_ul = { sp = sp_clr, undercurl = true }
+    local hl_ul_rvs = { fg = fg_clr, bg = bg_clr, sp = sp_clr, reverse = true, undercurl = true }
+    -- create highlights
+    vim.cmd(string.format('hi hl_std guifg=%s guibg=%s', hl_std.fg, hl_std.bg))
+    vim.cmd(string.format('hi hl_rvs guifg=%s guibg=%s gui=reverse', hl_rvs.fg, hl_rvs.bg))
+    vim.cmd(string.format('hi hl_ul guisp=%s gui=undercurl', hl_ul.sp))
+    vim.cmd(string.format('hi hl_ul_rvs guifg=%s guibg=%s guisp=%s gui=reverse,undercurl', hl_ul_rvs.fg, hl_ul_rvs.bg, hl_ul_rvs.sp))
+    -- Can extract color from primary highlight group
+    eq(utils.extract_color_from_hllist('fg', {'hl_std','hl_ul'}, def_clr), fg_clr)
+    -- Can extract color from fallback highlight group
+    eq(utils.extract_color_from_hllist('fg', {'hl_noexist','hl_std'}, def_clr), fg_clr)
+    -- Can fall back to default color on nonexistent color
+    eq(utils.extract_color_from_hllist('fg', {'hl_ul'}, def_clr), def_clr)
+    -- Can fall back to default color on nonexistent highlight group
+    eq(utils.extract_color_from_hllist('fg', {'hl_noexist'}, def_clr), def_clr)
+    -- Can extract fallback color
+    eq(utils.extract_color_from_hllist({'fg','sp'}, {'hl_ul'}, def_clr), sp_clr)
+    -- Can extract reverse color
+    eq(utils.extract_color_from_hllist('fg', {'hl_rvs'}, def_clr), bg_clr)
+    -- Can extract fallback reverse color
+    eq(utils.extract_color_from_hllist({'sp','fg'}, {'hl_rvs'}, def_clr), bg_clr)
+    -- clear highlights
+    vim.cmd('hi clear hl_std')
+    vim.cmd('hi clear hl_rvs')
+    vim.cmd('hi clear hl_ul')
+    vim.cmd('hi clear hl_ul_rvs')
+  end)
+
   it('can shrink list with holes', function()
     local list_with_holes = {
       '2',