feat: enable to preview themes (#980)

doc/telescope.txt

@@ -670,6 +670,9 @@ builtin.colorscheme({opts})                            *builtin.colorscheme()*
     Parameters: ~
         {opts} (table)  options to pass to the picker
 
+    Fields: ~
+        {enable_preview} (boolean)  if true, will preview the selected color
+
 
 builtin.marks({opts})                                        *builtin.marks()*
     Lists vim marks and their value, jumps to the mark on `<cr>`

lua/telescope/builtin/init.lua

@@ -254,6 +254,7 @@ builtin.buffers = require('telescope.builtin.internal').buffers
 
 --- Lists available colorschemes and applies them on `<cr>`
 ---@param opts table: options to pass to the picker
+---@field enable_preview boolean: if true, will preview the selected color
 builtin.colorscheme = require('telescope.builtin.internal').colorscheme
 
 --- Lists vim marks and their value, jumps to the mark on `<cr>`

lua/telescope/builtin/internal.lua

@@ -635,26 +635,101 @@ internal.buffers = function(opts)
 end
 
 internal.colorscheme = function(opts)
-  local colors = vim.list_extend(opts.colors or {}, vim.fn.getcompletion('', 'color'))
+  local before_color = vim.api.nvim_exec('colorscheme', true)
+  local need_restore = true
 
-  pickers.new(opts,{
+  local colors = opts.colors or { before_color }
-    prompt = 'Change Colorscheme',
+  if not vim.tbl_contains(colors, before_color) then
+    table.insert(colors, 1, before_color)
+  end
+
+  colors = vim.list_extend(
+    colors,
+    vim.tbl_filter(function(color)
+      return color ~= before_color
+    end, vim.fn.getcompletion(
+      '',
+      'color'
+    ))
+  )
+
+  local previewer
+  if opts.enable_preview then
+    -- define previewer
+    local bufnr = vim.api.nvim_get_current_buf()
+    local p = vim.api.nvim_buf_get_name(bufnr)
+
+    -- don't need previewer
+    if vim.fn.buflisted(bufnr) ~= 1 then
+      local deleted = false
+      local function del_win(win_id)
+        if win_id and vim.api.nvim_win_is_valid(win_id) then
+          utils.buf_delete(vim.api.nvim_win_get_buf(win_id))
+          pcall(vim.api.nvim_win_close, win_id, true)
+        end
+      end
+
+      previewer = previewers.new {
+        preview_fn = function(_, entry, status)
+          if not deleted then
+            deleted = true
+            del_win(status.preview_win)
+            del_win(status.preview_border_win)
+          end
+          vim.cmd('colorscheme ' .. entry.value)
+        end,
+      }
+    else
+      -- show current buffer content in previewer
+      previewer = previewers.new_buffer_previewer {
+        get_buffer_by_name = function()
+          return p
+        end,
+        define_preview = function(self, entry)
+          if vim.loop.fs_stat(p) then
+            conf.buffer_previewer_maker(p, self.state.bufnr, { bufname = self.state.bufname })
+          else
+            local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
+            vim.api.nvim_buf_set_lines(self.state.bufnr, 0, -1, false, lines)
+          end
+          vim.cmd('colorscheme ' .. entry.value)
+        end,
+      }
+    end
+  end
+
+  local picker = pickers.new(opts, {
+    prompt_title = 'Change Colorscheme',
     finder = finders.new_table {
-      results = colors
+      results = colors,
     },
-    -- TODO: better preview?
     sorter = conf.generic_sorter(opts),
+    previewer = previewer,
     attach_mappings = function(prompt_bufnr)
       actions.select_default:replace(function()
         local selection = action_state.get_selected_entry()
-
         actions.close(prompt_bufnr)
-        vim.cmd("colorscheme " .. selection.value)
+
+        need_restore = false
+        vim.cmd('colorscheme ' .. selection.value)
       end)
 
       return true
+    end,
+  })
+
+  if opts.enable_preview then
+    -- rewrite picker.close_windows. restore color if needed
+    local close_windows = picker.close_windows
+    picker.close_windows = function(status)
+      close_windows(status)
+      if need_restore then
+        vim.cmd('colorscheme ' .. before_color)
       end
-  }):find()
+    end
+  end
+
+  picker:find()
 end
 
 internal.marks = function(opts)