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From:   Eric Sunshine <sunshine@sunshineco.com>
Date:   Tue, 26 Jun 2018 17:13:05 -0400
Message-ID: <CAPig+cRzZ-Nd2b-M8v0NUsLX_gkKwLqyakgcRhwGf3CzsWwxBA@mail.gmail.com>
Subject: Re: [PATCH 29/29] t/test-lib: teach --chain-lint to detect broken
 &&-chains in subshells
To:     Jeff King <peff@peff.net>
Cc:     Junio C Hamano <gitster@pobox.com>, Git List <git@vger.kernel.org>,
        Jonathan Nieder <jrnieder@gmail.com>,
        Stefan Beller <sbeller@google.com>,
        Elijah Newren <newren@gmail.com>,
        Jonathan Tan <jonathantanmy@google.com>
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On Tue, Jun 26, 2018 at 5:01 PM Jeff King <peff@peff.net> wrote:
> On Tue, Jun 26, 2018 at 04:46:18PM -0400, Eric Sunshine wrote:
> > Some of these dangers can be de-thoothed during the linting phase by
> > defining do-nothing shell functions:
> >
> >     cp () { :; }
> >     mv () { :; }
> >     ln () { :; }
> >
> > That, at least, makes the scariest case ("rm") much less so.
>
> Now that's an interesting idea. We can't catch every dangerous action
> (notably ">" would be hard to override), but it should be pretty cheap
> to cover some obvious ones.

Taking the idea a bit further, the 'sed' script could also throw away
strings of "../" inside subshells, which would help defang the more
difficult cases, like "echo x >../git.c". There are pathological
cases, of course, which it wouldn't catch:

    P=../git.c
    test_expect_success 'foo' '
        (
            cd dir &&
            echo x >$P
        )
    '

but it does help mitigate the issue for the most typical cases.