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

[Dmitry Gutov <dgutov@yandex.ru>]

On 05/30/2015 08:01 PM, Francesco Potortì wrote:

> Sorry if I don't closely follow the discussion (I do not know all the
> internals of etags.el), and consequently sorry if I am misanderstanding
> anything.  In that case, please discard my observations below.

I don't think I'm misunderstanding: it's mainly a problem of terminology.

> I fear I can read in the above quotes a fundamental misunderstanding.
> If Emacs (etags.el or anything else) treats implicit tags differently
> from explicit tags, that's an error.

It has different predicates, to determine whether point is after an 
"implicit tag name" for a given string. Or whether it's after an 
"explicit tag name", or some other kind of match.

> Implicit tags are semantically the same as explicit tags.  Whether a tag
> is implicit or explicit, it's only a matter of efficiency in building
> the TAGS file. For a given TAGS file entry, there is either no tag, or
> an implicit tag, or an explicit tag.

Maybe we should say that there's always a "tag name", for a given entry. 
And we can determine it by looking at the tag name field, or, in the 
absence of it, implicitly determine from the pattern.

It's easier to call the value of the tag name field an "explicit tag", 
and the value that we can derive from the pattern an "implicit tag". And 
if the explicit tag is present, naturally they'll be different.

> The latter two cases should be
> treated exactly alike by whichever program is reading the TAGS file.
> Nor is it possible that for a given entry its implicit tag does not
> match its explicit tag, because either the former or the latter are
> present, not both.

This confirms that we should always disregard implicit tag when the 
explicit tag is present.