A test tries to compare equality of `Vec`s, approximately `x.sort() == y.sort()`,
but `sort()` uses in-place mutation, and returns `unit`, not the input `slice`,
so the lists are never actually compared.

It's possible for a call to `File::open()` to succeed even if reading from
that `File` isn't actually possible due to the `File` being a directory.
In such cases, `Lines` can return `Err` infinitely,
causing `filter_map()` to diverge while searching for a nonexistant `Ok`.

This is a semantic change.
`filter_map()` can filter multiple errors before returning lines again,
while `map_while()` will stop iterating entirely at the first `Err`.

However, errors are unlikely at all since the `file` argument is currently
always a preallocated temporary file for collecting `Command` output.
This merely mitigates the worst case if `lines_from_file()` is ever used
in a way where this error could occur.

replace `Vec<String>` with `Vec<&str>` to reduce allocation

all ranges are already iterators

`append(true)` implies `write(true)`

Why was this used in the first place? Does anyone depend on this particular format?

allocation should be avoided when possible since it's relatively slow