Re: [PATCH] sparse-index: avoid crash on intent-to-add entry outside the cone

[Derrick Stolee <stolee@gmail.com>]

On 7/29/2026 5:51 PM, Junio C Hamano wrote:
> "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> From: Derrick Stolee <stolee@gmail.com>
>>
>> When collapsing a full index to a sparse index, the recursive
>> convert_to_sparse_rec() walks the cache tree to determine if any
>> of the cache tree entries can be used to represent a sparse directory.
>>
>> As it goes, the method tracks how many cache entries are being represented
>> by the cache tree entry. The cache tree node's 'entry_count' represents how
>> many cache entries are covered by the node.
>>
>> However, this value can be negative, representing that a node is invalid,
>> and is no longer reflecting the number of cache entries fit within. This can
>> happen when the user uses 'git add --intent-to-add' to mark an untracked
>> file with the intent-to-add bit to avoid committing without finishing the
>> add.
> 
> Yes.  If the code were not anticipating this, I can understand how a
> bug can arise ;-)
> 
>> Theoretically, we could scan to find the range of entries that match this
>> directory and determine if they truly do have an intent-to-add bit and then
>> collapse as many child trees as possible (the ones with valid cache tree
>> nodes). That would be a non-trivial change for performance-only benefit.
>> Since this combination of the intent-to-add and sparse index features has so
>> far gone undetected by real users, this scenario is unlikely to be worth
>> such a change.
> 
> I tend to agree.  That does sound nasty.

>> +		span = ct->down[pos]->cache_tree->entry_count;
>> +		if (span < 0) {
>> +			/* cache-tree entry is invalidated, cannot collapse. */
>> +			istate->cache[num_converted++] = ce;
>> +			i++;
>> +			continue;
>> +		}
> 
> OK.  That is an easy and safe cop-out that is much better than segfaulting.
> 
> Shall we mark the topic for 'next'?
Thanks for taking a look. yes, this should be a pretty safe change that
can merge.

Thanks,
-Stolee