diffcore-rename, merge-ort: add wrapper functions for filepair alloc/dealloc

We want to be able to allocate filespecs and filepairs using a mem_pool.
However, filespec data will still remain outside the pool (perhaps in
the future we could plumb the pool through the various diff APIs to
allocate the filespec data too, but for now we are limiting the scope).
Add some extra functions to allocate these appropriately based on the
non-NULL-ness of opt->priv->pool, as well as some extra functions to
handle correctly deallocating the relevant parts of them.  A future
commit will make use of these new functions.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diffcore-rename.c

@@ -1328,6 +1328,47 @@ static void handle_early_known_dir_renames(struct dir_rename_info *info,
 	rename_src_nr = new_num_src;
 }
 
+static void free_filespec_data(struct diff_filespec *spec)
+{
+	if (!--spec->count)
+		diff_free_filespec_data(spec);
+}
+
+MAYBE_UNUSED
+static void pool_free_filespec(struct mem_pool *pool,
+			       struct diff_filespec *spec)
+{
+	if (!pool) {
+		free_filespec(spec);
+		return;
+	}
+
+	/*
+	 * Similar to free_filespec(), but only frees the data.  The spec
+	 * itself was allocated in the pool and should not be individually
+	 * freed.
+	 */
+	free_filespec_data(spec);
+}
+
+MAYBE_UNUSED
+void pool_diff_free_filepair(struct mem_pool *pool,
+			     struct diff_filepair *p)
+{
+	if (!pool) {
+		diff_free_filepair(p);
+		return;
+	}
+
+	/*
+	 * Similar to diff_free_filepair() but only frees the data from the
+	 * filespecs; not the filespecs or the filepair which were
+	 * allocated from the pool.
+	 */
+	free_filespec_data(p->one);
+	free_filespec_data(p->two);
+}
+
 void diffcore_rename_extended(struct diff_options *options,
 			      struct strintmap *relevant_sources,
 			      struct strintmap *dirs_removed,

diffcore.h

@@ -127,6 +127,8 @@ struct diff_filepair {
 #define DIFF_PAIR_MODE_CHANGED(p) ((p)->one->mode != (p)->two->mode)
 
 void diff_free_filepair(struct diff_filepair *);
+void pool_diff_free_filepair(struct mem_pool *pool,
+			     struct diff_filepair *p);
 
 int diff_unmodified_pair(struct diff_filepair *);
 

merge-ort.c

@@ -690,6 +690,48 @@ static void path_msg(struct merge_options *opt,
 	strbuf_addch(sb, '\n');
 }
 
+MAYBE_UNUSED
+static struct diff_filespec *pool_alloc_filespec(struct mem_pool *pool,
+						 const char *path)
+{
+	struct diff_filespec *spec;
+	size_t len;
+
+	if (!pool)
+		return alloc_filespec(path);
+
+	/* Same code as alloc_filespec, except allocate from pool */
+	len = strlen(path);
+
+	spec = mem_pool_calloc(pool, 1, st_add3(sizeof(*spec), len, 1));
+	memcpy(spec+1, path, len);
+	spec->path = (void*)(spec+1);
+
+	spec->count = 1;
+	spec->is_binary = -1;
+	return spec;
+}
+
+MAYBE_UNUSED
+static struct diff_filepair *pool_diff_queue(struct mem_pool *pool,
+					     struct diff_queue_struct *queue,
+					     struct diff_filespec *one,
+					     struct diff_filespec *two)
+{
+	struct diff_filepair *dp;
+
+	if (!pool)
+		return diff_queue(queue, one, two);
+
+	/* Same code as diff_queue, except allocate from pool */
+	dp = mem_pool_calloc(pool, 1, sizeof(*dp));
+	dp->one = one;
+	dp->two = two;
+	if (queue)
+		diff_q(queue, dp);
+	return dp;
+}
+
 static void *pool_calloc(struct mem_pool *pool, size_t count, size_t size)
 {
 	if (!pool)