Weird 'incompatible types' warning

[mat-hek]

Environment

• Elixir & Erlang/OTP versions (elixir --version):

Erlang/OTP 24 [erts-12.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]

Elixir 1.14.0-dev (bdcf887) (compiled with Erlang/OTP 23)

Happens on Elixir 1.12.3 and 1.13.3 as well

• Operating system: Mac OS 11.6

Current behavior

Compiling this:

defmodule A do
  def fun(state, key) do
    key0 = key
    state = %{state | key0 => true}
    key1 = key
    state = %{state | key1 => true}
    state
  end
end

gives this warning:

warning: incompatible types:

    map() !~ var2

in expression:

    # a.exs:6
    state = %{state | key1 => true}

where "state" was given the type map() in:

    # a.exs:6
    state = %{state | key1 => true}

Conflict found at
  a.exs:6: A.fun/2

Expected behavior

No warning should be reported

[michallepicki]

I can look into it over the weekend :)

[michallepicki]

Bug introduced by #10320

I reduced it a bit more to:

defmodule A do
  def fun(map0, key0) do
    map1 = %{map0 | key0 => true}
    key1 = key0
    map2 = %{map1 | key1 => true}
    map2
  end
end

which still warns, while this compiles cleanly:

defmodule A do
  def fun(map0, key0) do
    map1 = %{map0 | key0 => true}
    key1 = key0
    %{map1 | key1 => true}
  end
end

[michallepicki]

#10320 is mostly refactoring. One thing that it changed is that when validating a map update, the extra "open" map argument was moved to the end of map args list, where it probably should be - before it was prepended to the start of the map args list for non-struct map updates. I'll look into the implementation of map updates validation introduced in #10316 , maybe it can be improved.