Merge branch 'jk/patch-ids-no-merges' into maint

"git log --cherry-pick" used to include merge commits as candidates
to be matched up with other commits, resulting a lot of wasted time.
The patch-id generation logic has been updated to ignore merges to
avoid the wastage.

* jk/patch-ids-no-merges:
  patch-ids: refuse to compute patch-id for merge commit
  patch-ids: turn off rename detection

patch-ids.c

@@ -4,9 +4,18 @@
 #include "sha1-lookup.h"
 #include "patch-ids.h"
 
+static int patch_id_defined(struct commit *commit)
+{
+	/* must be 0 or 1 parents */
+	return !commit->parents || !commit->parents->next;
+}
+
 int commit_patch_id(struct commit *commit, struct diff_options *options,
 		    unsigned char *sha1, int diff_header_only)
 {
+	if (!patch_id_defined(commit))
+		return -1;
+
 	if (commit->parents)
 		diff_tree_sha1(commit->parents->item->object.oid.hash,
 			       commit->object.oid.hash, "", options);
@@ -45,6 +54,7 @@ int init_patch_ids(struct patch_ids *ids)
 {
 	memset(ids, 0, sizeof(*ids));
 	diff_setup(&ids->diffopts);
+	ids->diffopts.detect_rename = 0;
 	DIFF_OPT_SET(&ids->diffopts, RECURSIVE);
 	diff_setup_done(&ids->diffopts);
 	hashmap_init(&ids->patches, (hashmap_cmp_fn)patch_id_cmp, 256);
@@ -76,6 +86,9 @@ struct patch_id *has_commit_patch_id(struct commit *commit,
 {
 	struct patch_id patch;
 
+	if (!patch_id_defined(commit))
+		return NULL;
+
 	memset(&patch, 0, sizeof(patch));
 	if (init_patch_id_entry(&patch, commit, ids))
 		return NULL;
@@ -88,6 +101,9 @@ struct patch_id *add_commit_patch_id(struct commit *commit,
 {
 	struct patch_id *key = xcalloc(1, sizeof(*key));
 
+	if (!patch_id_defined(commit))
+		return NULL;
+
 	if (init_patch_id_entry(key, commit, ids)) {
 		free(key);
 		return NULL;