feat(picker): on_show + impl for lines to show with current cursor

lua/snacks/picker/config/defaults.lua

@@ -75,7 +75,9 @@ local M = {}
 ---@field icons? snacks.picker.icons
 ---@field source? string
 ---@field on_change? fun(picker:snacks.Picker, item:snacks.picker.Item) called when the cursor changes
+---@field on_show? fun(picker:snacks.Picker) called when the picker is shown
 ---@field layouts? table<string, snacks.picker.Layout>
+---@field main? snacks.picker.main.Config
 local defaults = {
   prompt = " ",
   sources = {},

lua/snacks/picker/config/sources.lua

@@ -266,6 +266,13 @@ M.lines = {
     preview = "main",
     preset = "ivy",
   },
+  ---@param picker snacks.Picker
+  on_show = function(picker)
+    local cursor = vim.api.nvim_win_get_cursor(picker.main)
+    local info = vim.api.nvim_win_call(picker.main, vim.fn.winsaveview)
+    picker.list:view(cursor[1], info.topline)
+    picker:show_preview()
+  end,
 }
 
 -- Loclist

lua/snacks/picker/core/picker.lua

@@ -263,6 +263,9 @@ function M:show()
     self.preview.win:show()
   end
   self.input.win:focus()
+  if self.opts.on_show then
+    self.opts.on_show(self)
+  end
 end
 
 ---@return fun():snacks.picker.Item?