Re: dired-do-find-regexp failure with latin-1 encoding

[Dmitry Gutov <dgutov@yandex.ru>]

On 29.11.2020 21:37, Juri Linkov wrote:

>> Do we want to search the "binary" files at all? Right now we simply filter
>> such matches out (see the definition of xref-matches-in-files), and I have
>> seen no complaints.
> 
> There are two cases: a really binary file, and a legit ascii file
> with an occasional ^@ char.  And grep can't distinguish one from another.
> There is an option --binary-files=binary, but unfortunately it doesn't help,
> it still outputs "Binary file matches".

Makes sense.

> So xref parser needs to be smart enough to detect whether the matched line
> contains binary garbage when '-a' is used, or it's purely ascii.

I guess we can do that, but then some people might be a bit unhappy 
about not being able to search inside such files? It could be useful on 
occasion, too (TBC below *).

> Moreover, I think we should apply the same heuristics to the grep output
> in grep.el and add '-a' to the grep command by default.

I guess we should. Or do the LC_ALL thing. I'm still unclear on the 
difference in effect between the two.

> Then grep.el
> should prettify the lines with real binary garbage e.g. by hiding groups of
> bytes between 0 and 32, or adding a 'display' property with ellipsis.

Why not. xref could also do something like that.

>> Our interpreter is our regexp with which we parse. But I suppose as long as
>> Grep doesn't insert unexpected newlines, the parser will be fine.
> 
> For grep output a bigger problem is that grep on binary data
> might output too long lines before the terminating newline.

(*) We already have this kind of problem with "normal" files which 
contain minified assets (JS or CSS). The file contents are usually 
normal ASCII, but it's just one line which can reach several MBs in length.

The usual way to deal with that is with project-ignores and 
grep-find-ignored-files. That works for both cases.

>>> I actually don't think I understand why we need -a in this case, since
>>> Grep looks for null bytes to decide this is a binary file, and encoded
>>> non-ASCII characters don't have null bytes 9except if they are in
>>> UTF-16).
>>
>> Good question.
> 
> The grep manual says that binary data are either output bytes that
> are improperly encoded for the current locale, or null input bytes.

So... if we add LC_ALL=C but not '-a' we will allow the "improperly 
encoded" case but not the "null input bytes" one?