commit 746d94dfa3a4c965501cde5bb0a59a168cc2ab44
from: Neels Hofmeyr <neels@hofmeyr.de>
date: Mon Oct 12 04:01:33 2020 UTC

diff_main: don't run algo if left or right are empty

commit - acfce337ad1e68d4ab00bd78bdb6dd459acc3c46
commit + 746d94dfa3a4c965501cde5bb0a59a168cc2ab44
blob - 1380f79ea94f4492b19d3d7e5851c1205e4383da
blob + 73eeffeb2f2c32acdb1121c77d1186c4504bc025
--- lib/diff_main.c
+++ lib/diff_main.c
@@ -470,14 +470,19 @@ diff_run_algo(const struct diff_algo_config *algo_conf
 	      struct diff_state *state)
 {
 	int rc;
-	ARRAYLIST_FREE(state->temp_result);
 
 	if (!algo_config || !algo_config->impl
-	    || !state->recursion_depth_left) {
-		debug("MAX RECURSION REACHED, just dumping diff chunks\n");
+	    || !state->recursion_depth_left
+	    || !state->left.atoms.len || !state->right.atoms.len) {
+		debug("Fall back to diff_algo_none():%s%s%s\n",
+		      (!algo_config || !algo_config->impl) ? " no-cfg" : "",
+		      (!state->recursion_depth_left) ? " max-depth" : "",
+		      (!state->left.atoms.len || !state->right.atoms.len)?
+			      " trivial" : "");
 		return diff_algo_none(algo_config, state);
 	}
 
+	ARRAYLIST_FREE(state->temp_result);
 	ARRAYLIST_INIT(state->temp_result, DIFF_RESULT_ALLOC_BLOCKSIZE);
 	rc = algo_config->impl(algo_config, state);
 	switch (rc) {