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From:   Junio C Hamano <gitster@pobox.com>
To:     Jeff King <peff@peff.net>
Cc:     Jonathan Nieder <jrnieder@gmail.com>,
        Sam Kuper <sam.kuper@uclmail.net>, git@vger.kernel.org
Subject: Re: Bug report: "Use of uninitialized value $_ in print"
References: <CAD-Jur+6m1SjqHVWBxW5HnTjutSVrkP+dEXdYmFHzoUf0FGdNA@mail.gmail.com>
        <20180302070434.GG238112@aiede.svl.corp.google.com>
        <20180302104608.GB11074@sigill.intra.peff.net>
Date:   Fri, 02 Mar 2018 08:53:34 -0800
In-Reply-To: <20180302104608.GB11074@sigill.intra.peff.net> (Jeff King's
        message of "Fri, 2 Mar 2018 05:46:08 -0500")
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Jeff King <peff@peff.net> writes:

> Because the array is full of "undef". See parse_diff(), which does this:
>
>   my @diff = run_cmd_pipe("git", @diff_cmd, "--", $path);
>   ...
>   @colored = run_cmd_pipe(@display_cmd);
>   ...
>   for (my $i = 0; $i < @diff; $i++) {
>           ...
>           push @{$hunk[-1]{TEXT}}, $diff[$i];
>           push @{$hunk[-1]{DISPLAY}},
>                (@colored ? $colored[$i] : $diff[$i]);
>   }
>
> If the @colored output is shorter than the normal @diff output, we'll
> push a bunch of "undef" onto the DISPLAY array (the ternary there is
> because sometimes @colored is completely empty if the user did not ask
> for color).

An obvious sanity check would be to ensure @colored == @diff

                push @{$hunk[-1]{DISPLAY}},
        -            (@colored ? $colored[$i] : $diff[$i]);
        +            (@colored && @colored == @diff ? $colored[$i] : $diff[$i]);
         }

or something like that?