Re: [PATCH 0/2] Sparse index: fetch, pull, ls-files

Derrick Stolee [off-list ref] writes:

quoted

But what makes sure, after all of the above happens, that no new
changes that assume it can walk the full index enters in the
codebase?

In other words, after "fetch" is declared "sparse clean" with patch
[1/2], what effort from us will it take to stay clean?

The tests in t1092 that use the "ensure_not_expanded" helper are
intended to be regression tests that would start failing if the
sparse index starts expanding in a new way. I think this is what
you mean by staying "sparse clean".

It is more like how would we help a new piece of code, which does
not even consider the possibility that the in-core index might be
sparse, and instead blindly walks the in-core index entries, doing
something unexpected (to both the author of the new code and to
those who are aware of the sparse-index feature) when it sees an
"tree" entry.  We'll hopefully see a breakage and the developer who
added such a new piece of code can keep both halves?

One direction I could see is that as new features are contributed
that change how the index is used, these features are not
automatically tested with sparse-checkout and the sparse index.
In this case, we will need to increase our awareness when reviewing
such features to ensure that they could fit within the sparse index
model (or are sufficiently protected by ensure_full_index() in their
first version).

Yup, making developers aware of the issue is probably the good first
thing to do.