[RFC PATCH 1/2] packfile API: add and use a pack_name_to_ext() utility function

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

Add and use a pack_name_to_ext() utility function for the copy/pasted
cases of creating a FOO.ext file given a string like FOO.pack.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 pack-bitmap.c   |  6 +-----
 pack-revindex.c |  5 +----
 packfile.c      | 14 ++++++++++----
 packfile.h      |  9 +++++++++
 4 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/pack-bitmap.c b/pack-bitmap.c
index 97909d48da3..0c3770d038d 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -302,11 +302,7 @@ char *midx_bitmap_filename(struct multi_pack_index *midx)
 
 char *pack_bitmap_filename(struct packed_git *p)
 {
-	size_t len;
-
-	if (!strip_suffix(p->pack_name, ".pack", &len))
-		BUG("pack_name does not end in .pack");
-	return xstrfmt("%.*s.bitmap", (int)len, p->pack_name);
+	return pack_name_to_ext(p->pack_name, "bitmap");
 }
 
 static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
diff --git a/pack-revindex.c b/pack-revindex.c
index 08dc1601679..69dc5688796 100644
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -179,10 +179,7 @@ static int create_pack_revindex_in_memory(struct packed_git *p)
 
 static char *pack_revindex_filename(struct packed_git *p)
 {
-	size_t len;
-	if (!strip_suffix(p->pack_name, ".pack", &len))
-		BUG("pack_name does not end in .pack");
-	return xstrfmt("%.*s.rev", (int)len, p->pack_name);
+	return pack_name_to_ext(p->pack_name, "rev");
 }
 
 #define RIDX_HEADER_SIZE (12)
diff --git a/packfile.c b/packfile.c
index 835b2d27164..bd6ad441bf5 100644
--- a/packfile.c
+++ b/packfile.c
@@ -191,15 +191,12 @@ int load_idx(const char *path, const unsigned int hashsz, void *idx_map,
 int open_pack_index(struct packed_git *p)
 {
 	char *idx_name;
-	size_t len;
 	int ret;
 
 	if (p->index_data)
 		return 0;
 
-	if (!strip_suffix(p->pack_name, ".pack", &len))
-		BUG("pack_name does not end in .pack");
-	idx_name = xstrfmt("%.*s.idx", (int)len, p->pack_name);
+	idx_name = pack_name_to_ext(p->pack_name, "idx");
 	ret = check_packed_git_idx(idx_name, p);
 	free(idx_name);
 	return ret;
@@ -2266,3 +2263,12 @@ int is_promisor_object(const struct object_id *oid)
 	}
 	return oidset_contains(&promisor_objects, oid);
 }
+
+char *pack_name_to_ext(const char *pack_name, const char *ext)
+{
+	size_t len;
+
+	if (!strip_suffix(pack_name, ".pack", &len))
+		BUG("pack_name does not end in .pack");
+	return xstrfmt("%.*s.%s", (int)len, pack_name, ext);
+}
diff --git a/packfile.h b/packfile.h
index a3f6723857b..6890c57ebdb 100644
--- a/packfile.h
+++ b/packfile.h
@@ -195,4 +195,13 @@ int is_promisor_object(const struct object_id *oid);
 int load_idx(const char *path, const unsigned int hashsz, void *idx_map,
 	     size_t idx_size, struct packed_git *p);
 
+/**
+ * Given a string like "foo.pack" and "ext" returns an xstrdup()'d
+ * "foo.ext" string. Used for creating e.g. PACK.{bitmap,rev,...}
+ * filenames from PACK.pack.
+ *
+ * Will BUG() if the expected string can't be created from the
+ * "pack_name" argument.
+ */
+char *pack_name_to_ext(const char *pack_name, const char *ext);
 #endif
-- 
2.36.1.952.g6652f7f0e6b