index: split up nt_init() in two I'd like to make nt_init() take a pointer to a nodetree to initialize, but it currently also allocates the nodetree. This patch prepares for that change by making nt_init() be about initializing an existing node tree and by creating a new index_init_nt() that creates the nodetree. Differential Revision: https://phab.mercurial-scm.org/D4114

index: make most "nt_*" functions take a nodetree Now that the nodetree has a pointer to the index, we can pass the nodtree instead of the index. There are few "nt_*" functions left after this. I'll deal with them soon. Differential Revision: https://phab.mercurial-scm.org/D4113

index: add pointer from nodetree back to index This is always a cycle right now, but it will not be for the nodetree instances I'm planning to add later (see earlier patch). Differential Revision: https://phab.mercurial-scm.org/D4112

index: remove side-effect from failed nt_new() As pointed out by Yuya in the review of D4108, if realloc() fails, we would end up with an invalid nodetree instance (with nt->nodes set to NULL), which means that if it was later accessed again it would likely segfault. It's probably unlikely that much else happens in the process if it ran out memory, but we should of course do our best to handle it. This patch makes it so we don't update the nodetree in this case. Differential Revision: https://phab.mercurial-scm.org/D4154

index: remove side-effect from failed nt_init() As pointed out by Yuya in the review of D4108, if we run into the "overflow in nt_init" case (which I think normally happens only in repos with at least 2^26=64Mi revisions), we would leave the node tree half-initialized. Differential Revision: https://phab.mercurial-scm.org/D4153

index: use PyMem_Free() to free nodeetree instance As Yuya pointed out in the review of D4108, PyMem_Malloc() and PyMem_Free() should be paired. IIUC, PyMem_Malloc() may use a different allocator than malloc(), so using free() with a pointer from PyMem_Malloc() may be very wrong. Differential Revision: https://phab.mercurial-scm.org/D4152

linelog: fix infinite loop vulnerability Checking `len(lines)` is not a great way of detecting infinite loops, as demonstrated in the added test. Therefore check instruction count instead. The original C implementation does not have this problem. There are a few other places where the C implementation enforces more strictly, like `a1 <= a2`, `b1 <= b2`, `rev > 0`. But they are optional. Test Plan: Add a test. The old code forces the test to time out. Differential Revision: https://phab.mercurial-scm.org/D4151