Fix unicode bug with "format_raw_parse_error" sample

lib/absinthe/phase/parse.ex

@@ -104,7 +104,8 @@ defmodule Absinthe.Phase.Parse do
   @spec format_raw_parse_error({:lexer, String.t(), {line :: pos_integer, column :: pos_integer}}) ::
           Phase.Error.t()
   defp format_raw_parse_error({:lexer, rest, {line, column}}) do
-    <<sample::binary-size(10), _::binary>> = rest
+    sample = String.slice(rest, 0, 10)
+
     message = "Parsing failed at `#{sample}`"
     %Phase.Error{message: message, locations: [%{line: line, column: column}], phase: __MODULE__}
   end

test/absinthe/phase/parse_test.exs

@@ -29,6 +29,34 @@ defmodule Absinthe.Phase.ParseTest do
            ] == bp.execution.validation_errors
   end
 
+  @graphql "aa;bbbbbbbb—cc"
+  test "should provide sample of parsing failure respecting unicode boundary" do
+    assert {:error, bp} = Absinthe.Phase.Parse.run(@graphql, jump_phases: false)
+
+    assert [
+             %Absinthe.Phase.Error{
+               extra: %{},
+               locations: [%{column: 3, line: 1}],
+               message: "Parsing failed at `;bbbbbbbb—`",
+               phase: Absinthe.Phase.Parse
+             }
+           ] == bp.execution.validation_errors
+  end
+
+  @graphql ";"
+  test "should provide sample of parsing failure on very short query strings" do
+    assert {:error, bp} = Absinthe.Phase.Parse.run(@graphql, jump_phases: false)
+
+    assert [
+             %Absinthe.Phase.Error{
+               extra: %{},
+               locations: [%{column: 1, line: 1}],
+               message: "Parsing failed at `;`",
+               phase: Absinthe.Phase.Parse
+             }
+           ] == bp.execution.validation_errors
+  end
+
   @graphql """
   query {
     user {