From: Phillip Wood <phillip.wood123@gmail.com>
To: Jeff King <peff@peff.net>, phillip.wood@dunelm.org.uk
Cc: Ryan Zoeller <rtzoeller@rtzoeller.com>,
Junio C Hamano <gitster@pobox.com>,
git@vger.kernel.org
Subject: Re: [RFC 0/1] Leading whitespace as a function identification heuristic?
Date: Fri, 25 Sep 2020 20:01:07 +0100 [thread overview]
Message-ID: <005de229-ad05-437c-7b83-8f6502b4e27d@gmail.com> (raw)
In-Reply-To: <20200925184319.GA660343@coredump.intra.peff.net>
Hi Peff
On 25/09/2020 19:43, Jeff King wrote:
> On Fri, Sep 25, 2020 at 10:11:33AM +0100, Phillip Wood wrote:
>
>> If I've understood correctly when ...code 2... contains changes that are
>> themselves indented then we'll pick the wrong function header for example
>>
>> void foo() {
>> void bar() {
>> ...code 1...
>> }
>> for (...) {
>> // if this line is changed we pick bar rather
>> // than foo because it is the first function
>> // header with a smaller indentation than the
>> // first changed line.
>> }
>> }
>>
>> Unfortunately I suspect code like that is not uncommon and the diff would
>> regress with this simple heuristic. It might be possible to recalculate the
>> required indentation as we walk backwards up the file though, so when we hit
>> the "for" line we reduce the maximum indentation allowed for a match and so
>> skip "bar" as a function header.
>
> Thanks, that's a great counter-example I hadn't considered.
>
> Yes, I agree that adjusting the desired indentation as we walk backwards
> would work. That's assuming indentation is hierarchical, but I think
> that's implied by the existence of this feature at all.
>
> Another possible corner case: tabs vs spaces. If I have:
>
> <space><space><space><space><space><space><space><space>foo
> <tab><tab>bar
>
> which is more indented? Counting isspace(), it is the first one. But
> visually, it would _usually_ be the second one. But of course it would
> depend on your tabstops.
>
> The above example is obviously stupid and contrived, but I wonder if
> there are legitimate confusing cases where people mix tabs and spaces
> (e.g., mixed tabs and spaces to align function parameters, etc).
To calculate the indentation for diff
--color-moved-ws=allow-indentation-change in fill_es_indent_data() we
use the tabwidth whitespace attribute to calculate the width of a tab in
spaces
int tab_width = es->flags & WS_TAB_WIDTH_MASK;
/* calculate the visual width of indentation */
while(1) {
if (s[off] == ' ') {
width++;
off++;
} else if (s[off] == '\t') {
width += tab_width - (width % tab_width);
while (s[++off] == '\t')
width += tab_width;
} else {
break;
}
}
I think we could probably do something similar here assuming it is the
visual width of the indentation that we care about.
Best Wishes
Phillip
> -Peff
>
next prev parent reply other threads:[~2020-09-25 19:01 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 21:59 [RFC 0/1] Leading whitespace as a function identification heuristic? Ryan Zoeller
2020-09-23 21:59 ` [RFC 1/1] xdiff: use leading whitespace in function heuristic Ryan Zoeller
2020-09-24 6:45 ` [RFC 0/1] Leading whitespace as a function identification heuristic? Junio C Hamano
2020-09-24 21:17 ` Jeff King
2020-09-24 22:01 ` Ryan Zoeller
2020-09-25 9:11 ` Phillip Wood
2020-09-25 18:43 ` Jeff King
2020-09-25 19:01 ` Phillip Wood [this message]
2020-09-25 19:05 ` Jeff King
2020-09-25 18:12 ` Johannes Sixt
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