[BUG] Assertion failed: (child->real_type == OBJ_REF_DELTA), function find_unresolved_deltas_1, file builtin/index-pack.c

Hi!

See also https://code.google.com/p/support/issues/detail?id=31571

Executing the command

git clone https://code.google.com/p/mapsforge/

fails with the error message

Assertion failed: (child->real_type == OBJ_REF_DELTA), function find_unresolved_deltas_1, file builtin/index-pack.c

Bisecting the code I found that 7218a215efc7ae46f7ca8d82 (from 2011, first released in git 1.7.7) is the first bad commit. It is also the one to introduce that assertion.

The idea behind that commit seems simple: instead of just sorting by base hash, also sort by type. Then when iterating over the matching objects, we can rely on the type and don't have to check that.

So far, so good. But the problem here is that the sorting is based on the "type" attribute, while the assertion and the case distinction it replaces was based on "real_type". I guess that at the point where the sorting takes place, these two should be identical. But once resolve_delta gets called, the real_type is changed to that of the base object. Which means that the original case distinction did more than just drop deltas of the wrong type: it also prevented resolution of already-resolved deltas. Therefore the change caused stuff to fail which used to work before. In this particular instance, the real_type changed from OBJ_REF_DELTA to OBJ_TREE which caused the assertion to fail.

I'm not sure whether this kind of duplicate resolution is something normal or indicates some breakage in the repository in question. If it is considered normal (although rare, otherwise others would have complained by now), then someone should likely turn the assertion back into a normal conditional. If this is a broken repository, then I think it should be reported as such, since in my book a failed assertion indicates a problem with the program itself, not its input data.

Thank you very much,
 Martin von Gagern