Difference between opts = {} and config = true

[georgejean]

Sorry if my question seems stupid. Suppose all my plugins are lazy-loaded. I have read the docs:

and I don't understand when using config = true rather than opts = {} (which can be filled later if necessary) in a plugin Spec.
For example, is there any differences between these three plugin Specs ?

{
    "nvim-pack/nvim-spectre",
  keys = {
    { "<leader>rp", function() require("spectre").open() end, desc = "Replace in files (Spectre)" },
  },
  }

{
    "nvim-pack/nvim-spectre",
  keys = {
    { "<leader>rp", function() require("spectre").open() end, desc = "Replace in files (Spectre)" },
  },
  opts = {}
  }

{
    "nvim-pack/nvim-spectre",
  keys = {
    { "<leader>rp", function() require("spectre").open() end, desc = "Replace in files (Spectre)" },
  },
  config = true
  }

Which are the typical cases when config = true should be used ?

[folke]

The first one will not be setup().

The other two are equivalent.

Initially, only config existed. config=true.

Later I added opts. opts={} is the preferred way. For most plugins you can always use opts, only in very complex use-cases you would need to add a config() function.

[georgejean]

Thank you very much for your quick answer !
In config doc, it is said config is executed when the plugin loads. Here, all my plugins are lazy-loaded : why the first Spec wouldn't be setup when loaded (i.e. when <leader>rp pressed)?

[folke]

Because you didn't specify a config function or a opts function. The plugin would just be added to the rtp. So for vimscript plugins and some lua plugins that's enough. But most lua plugins also need setup()

[georgejean]

Ok ! It makes more sense to me now. Thanks !