Drop support for local middleware/adapter functions

[teamon]

TODO

• Remove support for local middleware
• Remove support for local adapter
• Keep support for anon fun adapter
• Remove all references in docs (plug)
• Add info to migration guide
• Add test to migration test

Context

What is local middleware?

defmodule Client do
  use Tesla
  plug :some_local_function

  def some_local_function(env, next) do
    # ...
  end
end

Pros

• No need to create a separate module for something trivial

Cons

• Additional complexity
• Conflicting API with now-removed aliases support
• The function must be public anyway

The local middleware can be replaced with simply module:

defmodule Client do
  defmodule LocalMiddleware do
    def call(env, next, _opts) do
      # ...
    end
  end

  use Tesla
  plug LocalMiddleware
end

Question

Is local function middleware widely used or not?

/cc @amatalai @hodak @any-other-tesla-user

[amatalai]

I have 3 custom middlewares in current project and I never considered using local middleware. Simply because writing defmodule isn't tremendous amount of work and it's easier to reuse them later.

btw, have local middleware been documented anywhere?

[teamon]

That's a good sign!

Unfortunately yes - https://hexdocs.pm/tesla/Tesla.Builder.html#plug/2 (and adapter too)