Add custom highlight groups

README.md

@@ -73,6 +73,21 @@ end)
 }
 ```
 
+## Appearance
+
+The appearance of the hover window can be customized with the following
+highlight groups:
+
+* `HoverWindow` (defaults to: `NormalFloat`)
+* `HoverBorder` (defaults to: `FloatBorder`)
+* `HoverSourceLine` (defaults to: `TabLine`)
+* `HoverActiveSource` (defaults to: `TabLineSel`)
+* `HoverInactiveSource` (defaults to: `TabLineFill`)
+* `HoverFloatingError` (defaults to: `DiagnosticFloatingError`)
+* `HoverFloatingWarn` (defaults to: `DiagnosticFloatingWarn`)
+* `HoverFloatingInfo` (defaults to: `DiagnosticFloatingInfo`)
+* `HoverFloatingHint` (defaults to: `DiagnosticFloatingHint`)
+
 ## Built in Providers
 
 ### LSP

lua/hover.lua

@@ -33,6 +33,7 @@ end
 ---@param user_config Hover.Config
 function M.setup(user_config)
   require('hover.config').set(user_config)
+  require('hover.highlights').setup()
 end
 
 return M

lua/hover/actions.lua

@@ -4,6 +4,7 @@ local npcall = vim.F.npcall
 local has_winbar = vim.fn.has('nvim-0.8') == 1
 
 local async = require('hover.async')
+local highlights = require('hover.highlights').HIGHLIGHT_GROUPS
 
 local providers = require('hover.providers').providers
 local get_config = require('hover.config').get
@@ -34,9 +35,9 @@ local function add_title(bufnr, winnr, active_provider_id)
 
   for _, p in ipairs(providers) do
     if is_enabled(p, bufnr) then
-      local hl = p.id == active_provider_id and 'TabLineSel' or 'TabLineFill'
+      local hl = p.id == active_provider_id and highlights.HoverActiveSource or highlights.HoverInactiveSource
       title[#title + 1] = string.format('%%#%s# %s ', hl, p.name)
-      title[#title + 1] = '%#Normal# '
+      title[#title + 1] = '%#' .. highlights.HoverSourceLine .. '# '
       winbar_length = winbar_length + #p.name + 2 -- + 2 for whitespace padding
     end
   end

lua/hover/highlights.lua

@@ -0,0 +1,39 @@
+local M = {}
+
+---@enum HoverHighlightGroup
+M.HIGHLIGHT_GROUPS = {
+  HoverWindow = 'HoverWindow',
+  HoverBorder = 'HoverBorder',
+  HoverActiveSource = 'HoverActiveSource',
+  HoverInactiveSource = 'HoverInactiveSource',
+  HoverSourceLine = 'HoverSourceLine',
+  HoverFloatingError = 'HoverFloatingError',
+  HoverFloatingWarn = 'HoverFloatingWarn',
+  HoverFloatingInfo = 'HoverFloatingInfo',
+  HoverFloatingHint = 'HoverFloatingHint',
+}
+
+---@type table<HoverHighlightGroup, string>
+M.HIGHLIGHT_GROUP_DEFAULTS = {
+  [M.HIGHLIGHT_GROUPS.HoverWindow] = 'NormalFloat',
+  [M.HIGHLIGHT_GROUPS.HoverBorder] = 'FloatBorder',
+  [M.HIGHLIGHT_GROUPS.HoverSourceLine] = 'TabLine',
+  [M.HIGHLIGHT_GROUPS.HoverActiveSource] = 'TabLineSel',
+  [M.HIGHLIGHT_GROUPS.HoverInactiveSource] = 'TabLineFill',
+  [M.HIGHLIGHT_GROUPS.HoverFloatingError] = 'DiagnosticFloatingError',
+  [M.HIGHLIGHT_GROUPS.HoverFloatingWarn] = 'DiagnosticFloatingWarn',
+  [M.HIGHLIGHT_GROUPS.HoverFloatingInfo] = 'DiagnosticFloatingInfo',
+  [M.HIGHLIGHT_GROUPS.HoverFloatingHint] = 'DiagnosticFloatingHint',
+}
+
+function M.setup()
+  for highlight, value in pairs(M.HIGHLIGHT_GROUP_DEFAULTS) do
+    local existing = vim.api.nvim_get_hl(0, { name = highlight })
+
+    if vim.tbl_isempty(existing) then
+      vim.api.nvim_set_hl(0, highlight, { link = value })
+    end
+  end
+end
+
+return M

lua/hover/providers/diagnostic.lua

@@ -1,13 +1,14 @@
+local highlights = require('hover.highlights').HIGHLIGHT_GROUPS
 local api, if_nil = vim.api, vim.F.if_nil
 
 -- Most of this is taken straight from vim.diagnostic.open_float,
 -- with some tweaks to remove some unnecessary parts
 
 local highlight_map = {
-  [vim.diagnostic.severity.ERROR] = 'DiagnosticFloatingError',
-  [vim.diagnostic.severity.WARN] = 'DiagnosticFloatingWarn',
-  [vim.diagnostic.severity.INFO] = 'DiagnosticFloatingInfo',
-  [vim.diagnostic.severity.HINT] = 'DiagnosticFloatingHint',
+  [vim.diagnostic.severity.ERROR] = highlights.HoverFloatingError,
+  [vim.diagnostic.severity.WARN] = highlights.HoverFloatingWarn,
+  [vim.diagnostic.severity.INFO] = highlights.HoverFloatingInfo,
+  [vim.diagnostic.severity.HINT] = highlights.HoverFloatingHint,
 }
 
 --- @return vim.diagnostic.Opts.Float
@@ -149,18 +150,18 @@ local function execute(opts, done)
   end
 
   local lines = {} --- @type string[]
-  local highlights = {} --- @type table[]
+  local _highlights = {} --- @type table[]
 
   for i, diagnostic in ipairs(diagnostics) do
     if type(prefix_opt) == 'function' then
       --- @cast prefix_opt fun(...): string?, string?
       local prefix0, prefix_hl_group0 = prefix_opt(diagnostic, i, #diagnostics)
-      prefix, prefix_hl_group = prefix0 or '', prefix_hl_group0 or 'NormalFloat'
+      prefix, prefix_hl_group = prefix0 or '', prefix_hl_group0 or highlights.HoverWindow
     end
     if type(suffix_opt) == 'function' then
       --- @cast suffix_opt fun(...): string?, string?
       local suffix0, suffix_hl_group0 = suffix_opt(diagnostic, i, #diagnostics)
-      suffix, suffix_hl_group = suffix0 or '', suffix_hl_group0 or 'NormalFloat'
+      suffix, suffix_hl_group = suffix0 or '', suffix_hl_group0 or highlights.HoverWindow
     end
     --- @type string?
     local hiname = highlight_map[assert(diagnostic.severity)]
@@ -173,7 +174,7 @@ local function execute(opts, done)
       local pre = j == 1 and prefix or string.rep(' ', #prefix)
       local suf = j == #message_lines and suffix or ''
       table.insert(lines, pre .. message_lines[j] .. suf)
-      table.insert(highlights, {
+      table.insert(_highlights, {
         hlname = hiname,
         prefix = {
           length = j == 1 and #prefix or 0,
@@ -190,7 +191,7 @@ local function execute(opts, done)
   local float_bufnr = api.nvim_create_buf(false, true)
   api.nvim_buf_set_lines(float_bufnr, 0, -1, true, lines)
 
-  for i, hl in ipairs(highlights) do
+  for i, hl in ipairs(_highlights) do
     local line = lines[i]
     local prefix_len = hl.prefix and hl.prefix.length or 0
     local suffix_len = hl.suffix and hl.suffix.length or 0

lua/hover/util.lua

@@ -1,3 +1,5 @@
+local highlights = require("hover.highlights").HIGHLIGHT_GROUPS
+local highlight_defaults = require("hover.highlights").HIGHLIGHT_GROUP_DEFAULTS
 local api = vim.api
 
 local M = {}
@@ -61,14 +63,14 @@ end
 
 ---@type ({[1]: string, [2]: string}|string)[]
 local default_border = {
-  { '', 'NormalFloat' },
-  { '', 'NormalFloat' },
-  { '', 'NormalFloat' },
-  { ' ', 'NormalFloat' },
-  { '', 'NormalFloat' },
-  { '', 'NormalFloat' },
-  { '', 'NormalFloat' },
-  { ' ', 'NormalFloat' },
+  { '',  highlights.HoverBorder },
+  { '',  highlights.HoverBorder },
+  { '',  highlights.HoverBorder },
+  { ' ', highlights.HoverBorder },
+  { '',  highlights.HoverBorder },
+  { '',  highlights.HoverBorder },
+  { '',  highlights.HoverBorder },
+  { ' ', highlights.HoverBorder },
 }
 
 --- @param width integer
@@ -297,6 +299,14 @@ function M.open_floating_preview(contents, bufnr, syntax, opts)
   local float_option = make_floating_popup_options(width, height, opts)
   local hover_winid = api.nvim_open_win(floating_bufnr, false, float_option)
 
+  -- Set custom highlights for the window
+  local _winhl = {}
+  for hl, link in pairs(highlight_defaults) do
+    table.insert(_winhl, link .. ':' .. hl)
+  end
+  local winhl = table.concat(_winhl, ',')
+  vim.api.nvim_set_option_value('winhl', winhl, { win = hover_winid })
+
   if do_stylize then
     vim.wo[hover_winid].conceallevel = 2
     vim.wo[hover_winid].concealcursor = 'n'