string_list API users: use string_list_init_{no,}dup

Follow-up on the introduction of string_list_init_nodup() and
string_list_init_dup() in the series merged in bd4232fac3 (Merge
branch 'ab/struct-init', 2021-07-16) and convert code that implicitly
relied on xcalloc() being equivalent to the initializer to use
xmalloc() and string_list_init_{no,}dup() instead.

In the case of get_unmerged() in merge-recursive.c we used the
combination of xcalloc() and assigning "1" to "strdup_strings" to get
what we'd get via string_list_init_dup(), let's use that instead.

Adjacent code in cmd_format_patch() will be changed in a subsequent
commit, since we're changing that let's change the other in-tree
patterns that do the same. Let's also convert a "x == NULL" to "!x"
per our CodingGuidelines, as we need to change the "if" line anyway.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/log.c

@@ -231,7 +231,8 @@ static void cmd_log_init_finish(int argc, const char **argv, const char *prefix,
 	}
 
 	if (mailmap) {
-		rev->mailmap = xcalloc(1, sizeof(struct string_list));
+		rev->mailmap = xmalloc(sizeof(struct string_list));
+		string_list_init_nodup(rev->mailmap);
 		read_mailmap(rev->mailmap);
 	}
 
@@ -2173,8 +2174,10 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 		prepare_bases(&bases, base, list, nr);
 	}
 
-	if (in_reply_to || thread || cover_letter)
-		rev.ref_message_ids = xcalloc(1, sizeof(struct string_list));
+	if (in_reply_to || thread || cover_letter) {
+		rev.ref_message_ids = xmalloc(sizeof(*rev.ref_message_ids));
+		string_list_init_nodup(rev.ref_message_ids);
+	}
 	if (in_reply_to) {
 		const char *msgid = clean_message_id(in_reply_to);
 		string_list_append(rev.ref_message_ids, msgid);

builtin/shortlog.c

@@ -81,8 +81,10 @@ static void insert_one_record(struct shortlog *log,
 		format_subject(&subject, oneline, " ");
 		buffer = strbuf_detach(&subject, NULL);
 
-		if (item->util == NULL)
-			item->util = xcalloc(1, sizeof(struct string_list));
+		if (!item->util) {
+			item->util = xmalloc(sizeof(struct string_list));
+			string_list_init_nodup(item->util);
+		}
 		string_list_append(item->util, buffer);
 	}
 }

merge-recursive.c

@@ -522,10 +522,10 @@ static struct stage_data *insert_stage_data(struct repository *r,
  */
 static struct string_list *get_unmerged(struct index_state *istate)
 {
-	struct string_list *unmerged = xcalloc(1, sizeof(struct string_list));
+	struct string_list *unmerged = xmalloc(sizeof(struct string_list));
 	int i;
 
-	unmerged->strdup_strings = 1;
+	string_list_init_dup(unmerged);
 
 	/* TODO: audit for interaction with sparse-index. */
 	ensure_full_index(istate);