list-objects-filter-options: clean up use of ALLOC_GROW

Introduce a new macro ALLOC_GROW_BY which automatically zeros the added
array elements and takes care of updating the nr value. Use the macro in
code introduced earlier in this patchset.

Signed-off-by: Matthew DeVore <matvore@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 29 insertions, 10 deletions

diff --git a/cache.h b/cache.h
index bf20337ef4..cf5d70c196 100644
--- a/cache.h
+++ b/cache.h
@@ -660,6 +660,9 @@ int daemonize(void);
  * at least 'nr' entries; the number of entries currently allocated
  * is 'alloc', using the standard growing factor alloc_nr() macro.
  *
+ * Consider using ALLOC_GROW_BY instead of ALLOC_GROW as it has some
+ * added niceties.
+ *
  * DO NOT USE any expression with side-effect for 'x', 'nr', or 'alloc'.
  */
 #define ALLOC_GROW(x, nr, alloc) \
@@ -673,6 +676,25 @@ int daemonize(void);
 		} \
 	} while (0)
 
+/*
+ * Similar to ALLOC_GROW but handles updating of the nr value and
+ * zeroing the bytes of the newly-grown array elements.
+ *
+ * DO NOT USE any expression with side-effect for any of the
+ * arguments.
+ */
+#define ALLOC_GROW_BY(x, nr, increase, alloc) \
+	do { \
+		if (increase) { \
+			size_t new_nr = nr + (increase); \
+			if (new_nr < nr) \
+				BUG("negative growth in ALLOC_GROW_BY"); \
+			ALLOC_GROW(x, new_nr, alloc); \
+			memset((x) + nr, 0, sizeof(*(x)) * (increase)); \
+			nr = new_nr; \
+		} \
+	} while (0)
+
 /* Initialize and use the cache information */
 struct lock_file;
 void preload_index(struct index_state *index,
diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index 2506dc8327..44bc1153d1 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c
@@ -120,14 +120,12 @@ static int parse_combine_subfilter(
 	struct strbuf *subspec,
 	struct strbuf *errbuf)
 {
-	size_t new_index = filter_options->sub_nr++;
+	size_t new_index = filter_options->sub_nr;
 	char *decoded;
 	int result;
 
-	ALLOC_GROW(filter_options->sub, filter_options->sub_nr,
-		   filter_options->sub_alloc);
-	memset(&filter_options->sub[new_index], 0,
-	       sizeof(*filter_options->sub));
+	ALLOC_GROW_BY(filter_options->sub, filter_options->sub_nr, 1,
+		      filter_options->sub_alloc);
 
 	decoded = url_percent_decode(subspec->buf);
 
@@ -255,13 +253,12 @@ int parse_list_objects_filter(
 
 		string_list_append(&filter_options->filter_spec, xstrdup("+"));
 		filter_spec_append_urlencode(filter_options, arg);
-		ALLOC_GROW(filter_options->sub, filter_options->sub_nr + 1,
-			   filter_options->sub_alloc);
-		filter_options = &filter_options->sub[filter_options->sub_nr++];
-		memset(filter_options, 0, sizeof(*filter_options));
+		ALLOC_GROW_BY(filter_options->sub, filter_options->sub_nr, 1,
+			      filter_options->sub_alloc);
 
 		parse_error = gently_parse_list_objects_filter(
-			filter_options, arg, &errbuf);
+			&filter_options->sub[filter_options->sub_nr - 1], arg,
+			&errbuf);
 	}
 	if (parse_error)
 		die("%s", errbuf.buf);