On Jul 11, 2013, at 10:41 AM, Junio C Hamano <gitster@xxxxxxxxx> wrote:
> Doug Bell <madcityzen@xxxxxxxxx> writes:
>
>> The docs seem to say that doing
>>
>> git show-ref --head --tags
>>
>> would show both the HEAD ref and all the tag refs. However, doing
>> both --head and either of --tags or --heads would filter out the HEAD
>> ref.
>>
>> Signed-off-by: Doug Bell <madcityzen@xxxxxxxxx>
>> ---
>
> I think this patch fell through the cracks, and looking at it, I am
> somewhat torn.
>
> The command help for "--head" says "show the HEAD reference", which
> may mean:
>
> (1) in addition to everything else the command would do if there
> weren't this option specified, show HEAD;
>
> (2) show the HEAD and nothing else; or
>
> (3) add HEAD to the candidates to be shown, but apply the usual
> filtering rule based on --heads, --tags and/or pattern
> arguments.
>
> While the last interpretation is what we have used since the
> beginning of the command at 358ddb62 (Add "git show-ref" builtin
> command, 2006-09-15), I tend to agree with you that the first
> interpretation may make more sense, at least from the end user's
> point of view.
>
> But at a deeper level, it makes the command somewhat inconsistent.
>
> What happens in the command is
>
> - We iterate over "candidates to be shown", which is usually
> "everything under refs/", but with "--head", HEAD is added to
> this set. For each of these candidates:
>
> - if one or more <pattern> parameters are given, reject the
> candidate ref if it does not tail-match with any of the
> patterns;
>
> - if either "--heads" or "--tags" is given, among the ones that
> pass <pattern> filter, check if they:
>
> - begin with "refs/heads/" (if "--heads" is given); or
> - begin with "refs/tags/" (if "--tags" is given).
>
> and reject those that don't.
>
> - show it if it is still surviving after these two tests.
>
> And taht is why "git show-ref --tags master v1.3.0" shows only the
> v1.3.0 tag without showing the master branch, and giving "--heads"
> instead of "--tags" yields only the master branch without the tag.
>
> The semantics your patch wants, by changing the definition of
> "--head" from (3) to (1), is:
>
> - If "--head" is given, show HEAD no matter what.
>
> - Iterate over everything under refs/, and for each of them, do the
> same filter-and-show as we currently do (see above).
>
> While I think the new semantics is also understandable as the
> current one, and personally I think it is a better behaviour than
> the current one, it will require an update to the document to
> highlight that "--head" is special-cased in a big way, to bypass all
> the filtering that is applied to normal refs.
>
> A few additional observations (these are not complaints to this
> patch and please do not take them as such):
>
> - The command help says "(can be combined with heads)" for "--tags"
> and vice versa, but does not mention their interaction with
> "--head". This is because we take interpretation (3) above and
> do not treat "--head" as a mechanism to add to <pattern>
> parameter like these two.
>
> - The command help for "--heads" and "--tags" says "only show
> heads/tags", which technically does not contradict with "can be
> combined with" above, but a logical consequence of combining
> ought to be showing nothing, as a ref cannot be a head (an old
> nomenclature for a "branch") and a tag at the same time.
>
> I think we should find a word better than "only" to use here, but I
> am not sure what would be a good phrase to use.
>
The reason I had initially wanted both --tags and --head was I wanted to compare HEAD against all the tags to see which one(s) I was on (if any). I was eventually pointed to `git describe`, but I ended up just using show-ref without any options and filtering the result using Perl (the entire application is in Perl, so this wasn't a big deal). Then, yeah, I figured it was confusing enough to either patch the code or the docs.
For the doc changes, I think if it's explained that by default it show-ref shows refs/{tags,heads,remotes}, it becomes easier to explain what the options will end up doing. I'll put together a second patch.--
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