Regression in map key pattern matching

[zachallaun]

Elixir and Erlang/OTP versions

Erlang/OTP 26 [erts-14.0] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [jit:ns]

Elixir 1.15.0-rc.0 (3cdb388) (compiled with Erlang/OTP 24)

Operating system

Ubuntu-20.04

Current behavior

On 1.15.0-rc.0 on both OTP 25 and 26:

iex(1)> %{<<0>> => nil} = %{<<0>> => nil}
error: cannot use variable integer as map key inside a pattern. Map keys in patterns can only be literals (such as atoms, strings, tuples, and the like) or an existing variable matched with the pin operator (such as ^some_var)
  iex:1

** (CompileError) cannot compile code (errors have been logged)

Expected behavior

On 1.14.4:

iex(1)> %{<<0>> => nil} = %{<<0>> => nil}
%{<<0>> => nil}

Found courtesy of stream_data 😄