[PATCH 02/10] merge-recursive.c: call a new unpack_trees_options_init() function

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

In the preceding commit we introduced a new UNPACK_TREES_OPTIONS_INIT
macro, but "merge-recursive.c" could not be converted to it since
it (re-)initializes a "struct unpack_trees_options" on the heap.

In order to convert use the macro as the source of truth for
initialization we need to not only convert the initialization in
unpack_trees_start(), but also call the new
unpack_trees_options_init() just after the CALLOC_ARRAY() in
merge_start().

When we call merge_trees() we'll call merge_start() followed by
merge_trees_internal(), and it will call unpack_trees_start() before
it does much of anything. So it's covered by an initialization in
unpack_trees_start().

But when merge_recursive() is called it will call merge_start()
followed by merge_recursive_internal(), which won't call
unpack_trees_start() until its own call call to
merge_trees_internal(), but in the meantime it might end up using that
calloc'd "struct unpack_trees_options".

This was OK before, as setup_unpack_trees_porcelain() would call
strvec_init(), and our "struct dir_struct" in turn is OK with being
NULL'd. Let's convert the former to macro initialization, we'll deal
with the latter in a subsequent commit.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 merge-recursive.c | 3 ++-
 unpack-trees.c    | 8 ++++++--
 unpack-trees.h    | 5 ++++-
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/merge-recursive.c b/merge-recursive.c
index e594d4c3fa1..d24a4903f1d 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -405,7 +405,7 @@ static int unpack_trees_start(struct merge_options *opt,
 	struct tree_desc t[3];
 	struct index_state tmp_index = { NULL };
 
-	memset(&opt->priv->unpack_opts, 0, sizeof(opt->priv->unpack_opts));
+	unpack_trees_options_init(&opt->priv->unpack_opts);
 	if (opt->priv->call_depth)
 		opt->priv->unpack_opts.index_only = 1;
 	else
@@ -3704,6 +3704,7 @@ static int merge_start(struct merge_options *opt, struct tree *head)
 
 	CALLOC_ARRAY(opt->priv, 1);
 	string_list_init_dup(&opt->priv->df_conflict_file_set);
+	unpack_trees_options_init(&opt->priv->unpack_opts);
 	return 0;
 }
 
diff --git a/unpack-trees.c b/unpack-trees.c
index 8ea0a542da8..393c1f35a5d 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -108,8 +108,6 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 	const char **msgs = opts->msgs;
 	const char *msg;
 
-	strvec_init(&opts->msgs_to_free);
-
 	if (!strcmp(cmd, "checkout"))
 		msg = advice_enabled(ADVICE_COMMIT_BEFORE_MERGE)
 		      ? _("Your local changes to the following files would be overwritten by checkout:\n%%s"
@@ -189,6 +187,12 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 		opts->unpack_rejects[i].strdup_strings = 1;
 }
 
+void unpack_trees_options_init(struct unpack_trees_options *o)
+{
+	struct unpack_trees_options blank = UNPACK_TREES_OPTIONS_INIT;
+	memcpy(o, &blank, sizeof(*o));
+}
+
 void clear_unpack_trees_porcelain(struct unpack_trees_options *opts)
 {
 	strvec_clear(&opts->msgs_to_free);
diff --git a/unpack-trees.h b/unpack-trees.h
index ecf256cbcea..892b65ea623 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -91,7 +91,10 @@ struct unpack_trees_options {
 	struct checkout_metadata meta;
 };
 
-#define UNPACK_TREES_OPTIONS_INIT { 0 }
+#define UNPACK_TREES_OPTIONS_INIT { \
+	.msgs_to_free = STRVEC_INIT, \
+}
+void unpack_trees_options_init(struct unpack_trees_options *o);
 
 int unpack_trees(unsigned n, struct tree_desc *t,
 		 struct unpack_trees_options *options);
-- 
2.33.0.1404.g83021034c5d