_callable_to_source_string

# File activesupport/lib/active_support/testing/assertions.rb, line 329
        def _callable_to_source_string(callable)
          if defined?(RubyVM::InstructionSequence) && callable.is_a?(Proc)
            iseq = RubyVM::InstructionSequence.of(callable)
            source =
              if iseq.script_lines
                iseq.script_lines.join("\n")
              elsif File.readable?(iseq.absolute_path)
                File.read(iseq.absolute_path)
              end

            return callable unless source

            location = iseq.to_a[4][:code_location]
            return callable unless location

            lines = source.lines[(location[0] - 1)..(location[2] - 1)]
            lines[-1] = lines[-1].byteslice(...location[3])
            lines[0] = lines[0].byteslice(location[1]...)
            source = lines.join.strip

            # We ignore procs defined with do/end as they are likely multi-line anyway.
            if source.start_with?("{")
              source.delete_suffix!("}")
              source.delete_prefix!("{")
              source.strip!
              # It won't read nice if the callable contains multiple
              # lines, and it should be a rare occurrence anyway.
              # Same if it takes arguments.
              if !source.include?("\n") && !source.start_with?("|")
                return source
              end
            end
          end

          callable
        end