feat(overrides): improve highlight-group overrides

- Assigning `false` or an empty table to a highlight group clears it

- Assigning `false` to groups/specs/palettes clears previous settings
  from the config store (like `reset()` but finer-grained)

- (internal) Use `false` instead of `link = ''` to mark groups which
  should be cleared when set

- Improve `github-theme.group`

- Improve/cleanup code and other minor improvements (code-sharing,
  simplification, etc.)

CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### What's New?
 
 -   Added new highlight groups for mini.nvim (#333 by @echasnovski)
+-   Improved highlight-group overrides (#349)
+-   Assigning `false` or an empty table to a highlight group clears it
+-   Assigning `false` to groups/specs/palettes clears previous settings from the config store
 
 ### Changes
 

lua/github-theme/_test/util.lua

@@ -29,7 +29,7 @@ function M.get_hl(group, link)
   })
 end
 
-if vim.fn.has('nvim-0.10.0') == false or vim.fn.has('nvim-0.10.0') == 0 then
+if vim.fn.has('nvim-0.10.0') == 0 or vim.fn.has('nvim-0.10.0') == false then
   function M.get_hl(group, link)
     return api.nvim_get_hl(0, {
       name = group,

lua/github-theme/group.lua

@@ -1,23 +1,9 @@
 local collect = require('github-theme.lib.collect')
 local template = require('github-theme.util.template')
-
+local override = require('github-theme.override')
 local M = {}
 
-local function override(groups, spec, ovr)
-  ovr = template.parse(ovr, spec)
-  -- If `set = {}` in override,
-  -- the corresponding group is deleted.
-  -- https://github.com/projekt0n/github-nvim-theme/issues/249
-  for k, v in pairs(ovr) do
-    if v.link == '' then
-      groups[k] = nil
-    end
-  end
-  return collect.deep_extend(groups, ovr)
-end
-
 function M.from(spec)
-  local ovr = require('github-theme.override').groups
   local config = require('github-theme.config').options
 
   if not spec then
@@ -26,7 +12,7 @@ function M.from(spec)
   local editor = require('github-theme.group.editor').get(spec, config)
   local syntax = require('github-theme.group.syntax').get(spec, config)
 
-  local result = collect.deep_extend(editor, syntax)
+  local res = collect.deep_extend(editor, syntax)
 
   local default_enable_value = config.module_default
   local mod_names = require('github-theme.config').module_names
@@ -38,25 +24,29 @@ function M.from(spec)
     opts.enable = opts.enable == nil and default_enable_value or opts.enable
 
     if opts.enable then
-      result = collect.deep_extend(
-        result,
+      res = collect.deep_extend(
+        res,
         require('github-theme.group.modules.' .. name).get(spec, config, opts)
       )
     end
   end
 
-  local function apply_ovr(key, groups)
-    return ovr[key] and override(groups, spec, ovr[key]) or groups
+  local ovr = override.groups
+
+  if ovr.all then
+    override.extend_groups(res, template.parse(ovr.all, spec), {})
   end
 
-  result = apply_ovr('all', result)
-  result = apply_ovr(spec.palette.meta.name, result)
+  if ovr[spec.palette.meta.name] then
+    override.extend_groups(res, template.parse(ovr[spec.palette.meta.name], spec), {})
+  end
 
-  return result
+  return res
 end
 
 function M.load(name)
   name = name or require('github-theme.config').theme
   return M.from(require('github-theme.spec').load(name))
 end
+
 return M

lua/github-theme/init.lua

@@ -82,15 +82,15 @@ M.setup = function(opts)
     config.set_options(opts.options)
   end
 
-  if opts.palettes then
+  if opts.palettes ~= nil then
     override.palettes = opts.palettes
   end
 
-  if opts.specs then
+  if opts.specs ~= nil then
     override.specs = opts.specs
   end
 
-  if opts.groups then
+  if opts.groups ~= nil then
     override.groups = opts.groups
   end
 

lua/github-theme/override.lua

@@ -11,27 +11,48 @@ function M.hash()
   return require('github-theme.lib.hash')(getmetatable(M).__index) or 0
 end
 
-local function check_link(tbl)
-  for _, theme in pairs(tbl) do
-    for _, opts in pairs(theme) do
-      opts.link = opts.link or ''
+---Extends `groups` with `overrides`. `groups` is modified in-pace.
+---@generic T: table<string, table|false>
+---@param groups T a table of highlight groups
+---@param overrides T | nil
+---@param nullval any the marker to use for cleared groups
+---@return T groups
+function M.extend_groups(groups, overrides, nullval)
+  for grp_name, grp in pairs(overrides or {}) do
+    if grp == false or next(grp) == nil then
+      -- clear the group
+      groups[grp_name] = nullval
+    else
+      -- `link` is not compatible with other settings
+      if grp.link then
+        groups[grp_name] = { link = grp.link }
+      else
+        groups[grp_name] = vim.tbl_deep_extend('force', groups[grp_name] or {}, grp)
+
+        -- Clear previous `link`, or `grp.link = false`
+        groups[grp_name].link = nil
+      end
     end
   end
+
+  return groups
 end
 
 setmetatable(M, {
   __newindex = function(self, k, v)
     local store = getmetatable(self).__index
+
     if type(store[k]) == 'table' then
       if not v then
         store[k] = {}
-        return
-      end
-      if k == 'groups' then
-        check_link(v)
+      elseif k == 'groups' then
+        for theme, grps in pairs(v) do
+          store.groups[theme] = store.groups[theme] or {}
+          M.extend_groups(store.groups[theme], grps, false)
+        end
+      else
+        store[k] = vim.tbl_deep_extend('force', store[k], v)
       end
-      store[k] = collect.deep_extend(store[k], v)
-      store.has_override = true
     end
   end,
 })