[mix format] What is considered to be relevant when calculating line length?

It seems to me that credo and mix format currently calculate the
line length differently.

This experiment is running

• credo --strict (v0.8.10)
• mix format --check-formatted (Elixir 1.6.1 on Erlang/OTP 20.2.3)

and here is the noticed behaviour and the change I did to reconcile:

         xxxxxxxxxxx: %{
           xxxxxxxxxxxxxxxx: %{
             xxxx: get_in(xxxxxxxxxxx, [:xxxxxxx, :xxxxxxxxxxxxxxxx, :xxxx]),
+            # credo:disable-for-lines:2 Credo.Check.Readability.MaxLineLength
             xxxxxxxxxxxxxx:
-              get_in(xxxxxxxxxxx,
-                [:xxxxxxx, :xxxxxxxxxxxxxxxx, :xxxxxxxxxxxxxx]),
+              get_in(xxxxxxxxxxx, [:xxxxxxx, :xxxxxxxxxxxxxxxx, :xxxxxxxxxxxxxx]),
             xxxxxxxx:
               get_in(xxxxxxxxxxx, [:xxxxxxx, :xxxxxxxxxxxxxxxx, :xxxxxxxx])
           },

The old code wrapped around the 80 character limit. credo is happy, but
mix format wants everything on one line, as the closing parenthesis and
comma seem to not be counted in the line length.

Don’t know if this is worth opening an issue on GitHub - elixir-lang/elixir: Elixir is a dynamic, functional language for building scalable and maintainable applications · GitHub
or if this is desired and expected behaviour.

PS: @AstonJ please help me triage this post if I didn’t figure out the best place for it?