fix: improve startup time by deferring executable check (#970)

lua/fzf-lua/defaults.lua

@@ -141,17 +141,18 @@ M.defaults = {
       _ctor = previewers.fzf.cmd,
     },
     bat = {
-      cmd   = vim.fn.executable("batcat") == 1 and "batcat" or "bat",
+      -- reduce startup time by deferring executable check to previewer constructor (#970)
+      cmd   = function() return vim.fn.executable("batcat") == 1 and "batcat" or "bat" end,
       args  = "--color=always --style=numbers,changes",
       _ctor = previewers.fzf.bat_async,
     },
     bat_native = {
-      cmd   = vim.fn.executable("batcat") == 1 and "batcat" or "bat",
+      cmd   = function() return vim.fn.executable("batcat") == 1 and "batcat" or "bat" end,
       args  = "--color=always --style=numbers,changes",
       _ctor = previewers.fzf.bat,
     },
     bat_async = {
-      cmd   = vim.fn.executable("batcat") == 1 and "batcat" or "bat",
+      cmd   = function() return vim.fn.executable("batcat") == 1 and "batcat" or "bat" end,
       args  = "--color=always --style=numbers,changes",
       _ctor = previewers.fzf.bat_async,
     },
@@ -198,8 +199,9 @@ M.defaults = {
     codeaction_native = {
       _ctor     = previewers.fzf.codeaction,
       diff_opts = { ctxlen = 3 },
-      pager     = vim.fn.executable("delta") == 1
-          and "delta --width=$FZF_PREVIEW_COLUMNS" or nil,
+      pager     = function()
+        return vim.fn.executable("delta") == 1 and "delta --width=$FZF_PREVIEW_COLUMNS" or nil
+      end,
     },
   },
 }

lua/fzf-lua/previewer/codeaction.lua

@@ -228,6 +228,9 @@ function M.native:new(o, opts, fzf_win)
   M.native.super.new(self, o, opts, fzf_win)
   setmetatable(self, M.native)
   self.pager = opts.preview_pager == nil and o.pager or opts.preview_pager
+  if type(self.pager) == "function" then
+    self.pager = self.pager()
+  end
   self.diff_opts = o.diff_opts
   return self
 end

lua/fzf-lua/previewer/fzf.lua

@@ -12,6 +12,9 @@ function Previewer.base:new(o, opts)
   o = o or {}
   self.type = "cmd";
   self.cmd = o.cmd;
+  if type(self.cmd) == "function" then
+    self.cmd = self.cmd()
+  end
   self.args = o.args or "";
   self.opts = opts;
   return self