# Re: diffutils: C labels misdetected as functions

2 messages from 2007-07-22 to 2007-07-22. Participants: Simon Arlott, Junio C Hamano.
Thread: https://gitlist.dev/t/9151

## Simon Arlott, 2007-07-22 19:16

Subject: Re: diffutils: C labels misdetected as functions
Message-ID: <46A3AD07.1070504@simon.arlott.org.uk>
URL: https://gitlist.dev/e/46A3AD07.1070504%40simon.arlott.org.uk
In-Reply-To: <87abtogu6u.fsf@penguin.cs.ucla.edu>

```
On 22/07/07 19:38, Paul Eggert wrote:
> Simon Arlott <simon@fire.lp0.eu> writes:
> 
>> The patch below stops diffutils treating C labels starting in column 1 as function names.
> 
> That patch alone wouldn't suffice, since -p is documented as implying
> -F '^[[:alpha:]$_]'.  If the behavior changes, we'd also have to
> change the documentation to match.

Ok.

> I'm not sure the change is a good idea.  It would complicate the
> documentation and therefore the user interface, without that much

Complicated documentation means a bug shouldn't be fixed?

> benefit.  And it wouldn't suffice in general, since it would still
> mishandle labels followed by comments or by white space.

Yes, the regexp needs changing further to ignore comments...

"[[:alpha:]$_][^:]*$" perhaps? Although that ignores functions with
comments on the same line containing a :.

> Also, for long C functions some people might rather see a top-level
> (unindented) label highlighted than the function name highlighted, so
> they might prefer the current behavior.

"-p  --show-c-function  Show which C function each change is in."

It's not "--show-c-function-or-label".

> Anyway, to work around your problem without changing "diff", you can
> use "diff -u -F '^[[:alpha:]$_](|.*[^:])$'" instead of "diff -u -p".

Perhaps git could do this (or similar) as a workaround? (Cc:ed)

> Or you can put a single space before the labels in question: they'll
> still stand out plenty.

The code should definitely not need to be modified to work around a
diff bug.

-- 
Simon Arlott

```

## Junio C Hamano, 2007-07-22 21:30

Subject: Re: diffutils: C labels misdetected as functions
Message-ID: <7vtzrwqg87.fsf@assigned-by-dhcp.cox.net>
URL: https://gitlist.dev/e/7vtzrwqg87.fsf%40assigned-by-dhcp.cox.net
In-Reply-To: <46A3AD07.1070504@simon.arlott.org.uk>

```
Simon Arlott <simon@fire.lp0.eu> writes:

> On 22/07/07 19:38, Paul Eggert wrote:
>> 
>> Anyway, to work around your problem without changing "diff", you can
>> use "diff -u -F '^[[:alpha:]$_](|.*[^:])$'" instead of "diff -u -p".
>
> Perhaps git could do this (or similar) as a workaround? (Cc:ed)
>
>> Or you can put a single space before the labels in question: they'll
>> still stand out plenty.
>
> The code should definitely not need to be modified to work around a
> diff bug.

I think the word "bug" is just about documentation.  Promising
"show C function" and including labels and/or not showing all
functions would be a bug, but given that diff is about showing
textual differences between two text files with arbitrary kind
of contents, I do not think it is reasonable to take that "show
C function" promise too literally.

To avoid this, the description of the feature could be reworded
to "shows lines that match pattern '^[[:alpha:]$_]' on context
lines, intent of the option being that the pattern tends to
match the beginning of function in C language and help the
reader to locate the context more easily, with a caveat that the
pattern matching is not meant to capture all functions nor only
functions --- there will be false matches."

But that would be too long.  And as Paul showed, you can narrow
or widen the set of lines that are shown with the -F option.  I
do not think this deserves to be called a "bug".

You can define your own customized "function name" pattern in
your .git/config (or $HOME/.gitconfig) file to be used by the
git-diff family with recent enough git via the attributes
mechanism, but I do not think we should change the default,
unless GNU diff changes its default.  Personally I'd rather not
see it change, though.

```