[PATCH v2 01/12] diffcore-break: guard against NULLed queue entries in merge loop

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

The outer loop in `diffcore_merge_broken()` sets `q->queue[j]` to NULL
when it merges a broken pair back together, and has a NULL check to skip
such entries on subsequent iterations. The inner loop, however, lacks
this guard: when it scans forward looking for a matching peer, it can
encounter a slot that was NULLed by a previous outer-loop iteration and
dereference it unconditionally.

In practice this requires at least two broken pairs whose peers
both survive rename/copy detection and appear later in the queue,
which is rare but not impossible.

Add the same `if (!pp) continue` guard to the inner loop.

Pointed out by Coverity.

Assisted-by: Claude Opus 4.6
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 diffcore-break.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/diffcore-break.c b/diffcore-break.c
index 17b5ad1fed..b5bcc956cc 100644
--- a/diffcore-break.c
+++ b/diffcore-break.c
@@ -289,6 +289,8 @@ void diffcore_merge_broken(void)
 			 */
 			for (j = i + 1; j < q->nr; j++) {
 				struct diff_filepair *pp = q->queue[j];
+				if (!pp)
+					continue;
 				if (pp->broken_pair &&
 				    !strcmp(pp->one->path, pp->two->path) &&
 				    !strcmp(p->one->path, pp->two->path)) {
-- 
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