From: Junio C Hamano <gitster@pobox.com>
Date: Tue, 29 Apr 2025 19:39:41 GMT
Subject: Re: [PATCH v3] diff: check range before dereferencing an array element
Message-ID: <xmqqcycu69ky.fsf@gitster.g>
In-Reply-To: <pull.1887.v3.git.1745926679028.gitgitgadget@gmail.com>

"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> Before accessing an array element at a given index, it should be
> verified that the index is within the desired bounds, not afterwards,
> otherwise it may not make sense to even access the array element in the
> first place. This is the point of CodeQL's
> `cpp/offset-use-before-range-check` rule.
>
> This CodeQL rule unfortunately is also triggered by the
> `fill_es_indent_data()` code, even though the condition `off < len - 1`
> does not even need to guarantee that the offset is in bounds (`s` points
> to a NUL-terminated string, for which `s[off] == '\r'` would fail before
> running out of bounds).
>
> Let's work around this rare false positive to help us use an otherwise
> mostly useful tool is a worthy thing to do.

Thanks. I have almost forgotten about this one. The above
explanation works very well.