Subject: Re: [PATCH v2 0/2] object-name: fix resolution of object names containing curly braces

From: Junio C Hamano <[email-masked]>
Date: Sat, 04 Jan 2025 09:51:56 -0800

Elijah Newren <[email-masked]> writes:

>> In general what would we do if a string can be interpreted in
>> multiple ways in _different_ parts of the object-name codepaths.  We
>> all know that "affed" would trigger the "ambiguous object name"
>> error if there are more than one object whose object name begins
>> with "affed", but if "${garbage}-gaffed" can be interpreted as the
>> name of an object whose object name begins with "affed" and also can
>> be interpreted as the name of another object that sits at a path
>> that ends with "-gaffed" in some tree object, regardless of how the
>> leading part "${garbage}" looks like, it would be desirable if we
>> declared such a string as "ambiguous" the same way.
>
> How would that be desirable?

In "a:b/c-0-gabcde", *if* "a:b/c-0" *were* a valid way to spell a
valid refname, then the whole thing is an ambiguous object name,
i.e. it could be "something reachable from object 'a:b/c' whose
object name begins with abcde", or it could be "object at the path
b/c-0-gabcde in a tree-ish a", and in such a case our code should be
set up to allow us to give a "that's ambiguous" error, instead of
yielding the first possible interpretation (i.e. if we happen to
have checked the describe name first and "$garbage-0-gabcde", we
yield "abcde" before even checking if $garbage part gives a possible
leading part of a tree-ish; but if a future refactoring of the code
flips the order of checking, we may end up yielding 'an object at a
path, which ends with -0-gabcde, sitting in a tree-ish', without
checking if that could be a valid describe name).

Of course we should make sure that the syntax cannot be ambiguous
when we introduce a new syntax to represent a new feature ;-)

Now, I think ":" has always been a byte that is invalid as a part of
any refname, so "${garbage}-gabcde" with a colon in ${garbage}
cannot be a describe name.  So in the above about "a:b/c-0" is an
impossible example, but I was wondering more about the general
principle we should follow.