Re: [PATCH v2 4/4] gitdiffcore doc: mention new preliminary step for rename detection

From: Elijah Newren <newren@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Derrick Stolee <stolee@gmail.com>,
	Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>,
	Git Mailing List <git@vger.kernel.org>,
	Derrick Stolee <dstolee@microsoft.com>,
	Jonathan Tan <jonathantanmy@google.com>,
	Taylor Blau <me@ttaylorr.com>, Jeff King <peff@peff.net>
Subject: Re: [PATCH v2 4/4] gitdiffcore doc: mention new preliminary step for rename detection
Date: Tue, 9 Feb 2021 09:44:28 -0800	[thread overview]
Message-ID: <CABPp-BGM8N_PaS_M148DoteO3dHNq+gvmNbigHuHsgkVjocCww@mail.gmail.com> (raw)
In-Reply-To: <xmqqo8gt2mxh.fsf@gitster.c.googlers.com>

On Tue, Feb 9, 2021 at 9:03 AM Junio C Hamano <gitster@pobox.com> wrote:
>
> Derrick Stolee <stolee@gmail.com> writes:
>
> >> +Note that when rename detection is on but both copy and break
> >> +detection are off, rename detection adds a preliminary step that first
> >> +checks files with the same basename.  If files with the same basename
> >
> > I find myself wanting a definition of 'basename' here, but perhaps I'm
> > just being pedantic. A quick search clarifies this as a standard term [1]
> > of which I was just ignorant.
> >
> > [1] https://man7.org/linux/man-pages/man3/basename.3.html
> >
> >> +are sufficiently similar, it will mark them as renames and exclude
> >> +them from the later quadratic step (the one that pairwise compares all
> >> +unmatched files to find the "best" matches, determined by the highest
> >> +content similarity).
>
> While I do not think `basename` is unacceptably bad, we should aim
> to do better.  For "direc/tory/hello.txt", both "hello.txt" or
> "hello" are what would come up to people's mind with the technical
> term "basename" (i.e. basename as opposed to dirname, vs basename as
> opposed to filename with .extension).
>
> Avoiding this ambiguity and using a word understandable by those not
> versed well with UNIX/POSIX lingo may be done at the same time,
> hopefully.
>
> For example, can we frame the description around this key sentence:
>
>     The heuristics is based on an observation that a file is often
>     moved across directories while keeping its filename the same.
>
> The term "filename" alone can be ambiguous (i.e. both "hello.txt"
> and "direc/tory/hello.txt" are valid interpretations in the earlier
> example), but in the context of a sentence that talks about "moved
> across directories", the former would become the only valid one.  We
> can even say just "name" and there is no ambiguity in the above "key
> sentence".
>
> Then keeping that in mind, we can rewrite the above you quoted like
> so without going technical and without risking ambiguity, like this:
>
>     ... a preliminary step that checks if files are moved across
>     directories while keeping their filenames the same.  If there is
>     a file added to a directory whose contents is sufficiently
>     similar to a file with the same name that got deleted from a
>     different directory, ...

Nice, I like it!