Ecto.Multi caused dialyzer warnings because of MapSet.t() reference in `:names`

[jeroenvisser101]

Elixir version

1.18.4

Database and Version

postgres 17.5

Ecto Versions

3.13.2

Database Adapter and Versions (postgrex, myxql, etc)

N/A

Current behavior

1. Create a new app, create a new file called test.ex with these contents:

      defmodule MyApp.Test do
        def test do
          Ecto.Multi.new()
          |> Ecto.Multi.run(:test, fn _changes -> :ok end)
        end
      end

2. Run dialyzer
3. Observe multiple mismatches between names: MapSet.t() (expected) and names: #MapSet<...map: internal(_)...>

Expected behavior

No error.

A consideration may be to make Ecto.Multi.names() an opaque type as well. I'm no longer sure that that's the right thing to do.

[jeroenvisser101]

Relevant ElixirForum post: https://elixirforum.com/t/ecto-new-broken-after-recent-update/71497/3
And relevant Elixir commit: elixir-lang/elixir@5c621f2

[v0idpwn]

There's nothing wrong with Ecto's usage of MapSet. The issue is upstream, an interaction of inlining and opaque types, and has been fixed in elixir-lang/elixir#14581