Subject: bug#20629: 25.0.50; Regression: TAGS broken, can't find anything in C++ files.

From: Dmitry Gutov <[email-masked]>
Date: Sat, 30 May 2015 18:03:18 +0300

On 05/30/2015 05:31 PM, Eli Zaretskii wrote:

> Feel free to describe a full recipe for comparing.  I needed to guess
> what you wanted me to test; I'd be happy to just follow instructions
> and report back what I saw.

I'd rather not bother (let's see if we can conclude this thread of 
discussion without that). The patch in question is at 
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=20629#59, and I'm 
officially withdrawing it.

>> - Like you mentioned, it's not always that qualified name occurs in the
>> pattern. Sometimes it's creates using curly braces and such, and thus
>> can only occur in an explicit tag name (which the discussed patch won't
>> account for). Thus, some qualified names would be present in
>> completions, and some won't. This is bad.
>
> Do you have an actual example?  AFAIU, this shouldn't happen: etags
> only decides that an explicit tag name is unneeded when it can be
> deduced from the pattern.  So if the explicit tag is not in TAGS, it
> means etags.el can find it in the pattern.  (Qualified tag names that
> are constructed by etags are never in the pattern, so they will always
> get explicit tag names.)

I believe that the current choice is between "etags produces unqualified 
tags" and "etags produces both qualified and unqualified tags for lines 
where the distinction appies" (2 entries per line).

In the latter case the patch above is extraneous. So above I'm 
describing the situation where etags produces unqualified tags (which it 
currently does, by default).

> Yes, but I'd like to make a decision before making the change for
> placing 2 entries, so that the number of backward-incompatible changes
> could be minimized.

I think that would be a mistake. Rather, we should make the choice based 
on correctness.

> Because if tag-exact-match-p finds a match, tag-implicit-name-match-p
> will not be invoked, AFAIU.

It would, but that's not the point. But yes, the above would make sense. 
Anyway...

> And AFAIU we don't, because the match methods are invoked in order,
> until one of them yields a match.

Of course the difference in tag-implicit-name-match-p behavior will only 
matter when tag-exact-match-p returns nil for the entry in question. 
Which is the case in the example I've given in the previous email.

> Which is why there's an explicit tag there.  But I'm afraid I don't
> see what you meant to demonstrate by this example.  Which code will
> look for 'edit-abbrevs-map, and under what circumstances?

find-tag, for instance. After being asked by the user. Like I said, it's 
a contrived example (users don't usually bother with names as tricky as 
this one), but I can try to cook up a more realistic one, if you insist.

An Elisp identifier can actually include a quote if it's escaped, but 
that's not the case with edit-abbrevs-map.

>> It's harder to present a realistic case of a user looking for one thing
>> and getting another, but the point is, is the Etags parser decided that
>> the implicit tag doesn't match the explicit tag, we should ignore the
>> former (because we don't really know the way they mismatch).
>
> I think we already do.

Currently, we don't put the implicit tag into the completion table if 
the explicit tag is present.

But we do match implicit tags during navigation, even when an explicit 
tag is there.

The aforementioned patch would include the implicit tag in the 
completion table anyway. I'm now saying we don't want that, and we also 
don't want navigation to match implicit tags in the entries that contain 
an explicit tag as well.