assert fails on pattern matching with typed binary pattern matching

[ityonemo]

Environment

Erlang/OTP 22 [erts-10.7] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe]
Elixir 1.10.2 (compiled with Erlang/OTP 21)

Linux Mint 19.2 ~ (Ubuntu Bionic)

Current behavior

code:

defmodule StringAssertTest do
  use ExUnit.Case

  test "passes" do
    input = "foobar"
    assert <<trap::binary-size(3)>> <> "bar" = input
    assert trap == "foo"
  end

  test "failsbad" do
    input = "foobar"
    assert <<trap::binary-size(3)>> <> "baz" = input
    assert trap == "foo"
  end

end

** (FunctionClauseError) no function clause matching in String.Unicode.length/1
    (elixir 1.10.2) lib/elixir/unicode/unicode.ex:266: String.Unicode.length({:<<>>, [line: 12], [{:"::", [line: 12], [{:trap, [line: 12], nil}, {:-, [line: 12], [{:binary, [line: 12], nil}, {:size, [line: 12], [3]}]}]}]})
    (ex_unit 1.10.2) lib/ex_unit/diff.ex:766: ExUnit.Diff.parse_string/1
    (ex_unit 1.10.2) lib/ex_unit/diff.ex:731: ExUnit.Diff.diff_string_concat/3
    (elixir 1.10.2) lib/task/supervised.ex:90: Task.Supervised.invoke_mfa/2
    (elixir 1.10.2) lib/task/supervised.ex:35: Task.Supervised.reply/5
    (stdlib 3.12) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Function: &ExUnit.Diff.compute/3
    Args: [{:<>, [expanded: {:<<>>, [], [{:"::", [], [{:<<>>, [line: 12], [{:"::", [line: 12], [{:trap, [line: 12], nil}, {:-, [line: 12], [{:binary, [line: 12], nil}, {:size, [line: 12], [3]}]}]}]}, {:binary, [], nil}]}, "baz"]}, line: 12], [{:<<>>, [line: 12], [{:"::", [line: 12], [{:trap, [line: 12], nil}, {:-, [line: 12], [{:binary, [line: 12], nil}, {:size, [line: 12], [3]}]}]}]}, "baz"]}, "foobar", {:match, []}]

this error stops the vm completely.

Expected behavior

Simple fail