Allow to control where the replace refs are looked for

It can be useful to have grafts or replace refs for specific use-cases while
keeping the default "view" of the repository pristine (or with a different
set of grafts/replace refs).

It is possible to use a different graft file with GIT_GRAFT_FILE, but while
replace refs are more powerful, they don't have an equivalent override.

Add a GIT_REPLACE_REF_BASE environment variable to control where git is
going to look for replace refs.

Signed-off-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/replace.c

@@ -104,9 +104,9 @@ static int for_each_replace_name(const char **argv, each_replace_name_fn fn)
 			continue;
 		}
 		full_hex = sha1_to_hex(sha1);
-		snprintf(ref, sizeof(ref), "refs/replace/%s", full_hex);
+		snprintf(ref, sizeof(ref), "%s%s", git_replace_ref_base, full_hex);
 		/* read_ref() may reuse the buffer */
-		full_hex = ref + strlen("refs/replace/");
+		full_hex = ref + strlen(git_replace_ref_base);
 		if (read_ref(ref, sha1)) {
 			error("replace ref '%s' not found.", full_hex);
 			had_error = 1;
@@ -134,7 +134,7 @@ static void check_ref_valid(unsigned char object[20],
 			    int force)
 {
 	if (snprintf(ref, ref_size,
-		     "refs/replace/%s",
+		     "%s%s", git_replace_ref_base,
 		     sha1_to_hex(object)) > ref_size - 1)
 		die("replace ref name too long: %.*s...", 50, ref);
 	if (check_refname_format(ref, 0))

cache.h

@@ -397,6 +397,7 @@ static inline enum object_type object_type(unsigned int mode)
 #define EXEC_PATH_ENVIRONMENT "GIT_EXEC_PATH"
 #define CEILING_DIRECTORIES_ENVIRONMENT "GIT_CEILING_DIRECTORIES"
 #define NO_REPLACE_OBJECTS_ENVIRONMENT "GIT_NO_REPLACE_OBJECTS"
+#define GIT_REPLACE_REF_BASE_ENVIRONMENT "GIT_REPLACE_REF_BASE"
 #define GITATTRIBUTES_FILE ".gitattributes"
 #define INFOATTRIBUTES_FILE "info/attributes"
 #define ATTRIBUTE_MACRO_PREFIX "[attr]"
@@ -622,6 +623,7 @@ extern unsigned long pack_size_limit_cfg;
  * been sought but there were none.
  */
 extern int check_replace_refs;
+extern char *git_replace_ref_base;
 
 extern int fsync_object_files;
 extern int core_preload_index;

environment.c

@@ -47,6 +47,7 @@ const char *askpass_program;
 const char *excludes_file;
 enum auto_crlf auto_crlf = AUTO_CRLF_FALSE;
 int check_replace_refs = 1;
+char *git_replace_ref_base;
 enum eol core_eol = EOL_UNSET;
 enum safe_crlf safe_crlf = SAFE_CRLF_WARN;
 unsigned whitespace_rule_cfg = WS_DEFAULT_RULE;
@@ -110,6 +111,7 @@ const char * const local_repo_env[] = {
 	GRAFT_ENVIRONMENT,
 	INDEX_ENVIRONMENT,
 	NO_REPLACE_OBJECTS_ENVIRONMENT,
+	GIT_REPLACE_REF_BASE_ENVIRONMENT,
 	GIT_PREFIX_ENVIRONMENT,
 	GIT_SHALLOW_FILE_ENVIRONMENT,
 	GIT_COMMON_DIR_ENVIRONMENT,
@@ -156,6 +158,7 @@ static void setup_git_env(void)
 	struct strbuf sb = STRBUF_INIT;
 	const char *gitfile;
 	const char *shallow_file;
+	const char *replace_ref_base;
 
 	git_dir = getenv(GIT_DIR_ENVIRONMENT);
 	if (!git_dir)
@@ -173,6 +176,9 @@ static void setup_git_env(void)
 					   "info/grafts", &git_graft_env);
 	if (getenv(NO_REPLACE_OBJECTS_ENVIRONMENT))
 		check_replace_refs = 0;
+	replace_ref_base = getenv(GIT_REPLACE_REF_BASE_ENVIRONMENT);
+	git_replace_ref_base = xstrdup(replace_ref_base ? replace_ref_base
+							  : "refs/replace/");
 	namespace = expand_namespace(getenv(GIT_NAMESPACE_ENVIRONMENT));
 	namespace_len = strlen(namespace);
 	shallow_file = getenv(GIT_SHALLOW_FILE_ENVIRONMENT);

log-tree.c

@@ -96,11 +96,12 @@ static int add_ref_decoration(const char *refname, const unsigned char *sha1, in
 
 	assert(cb_data == NULL);
 
-	if (starts_with(refname, "refs/replace/")) {
+	if (starts_with(refname, git_replace_ref_base)) {
 		unsigned char original_sha1[20];
 		if (!check_replace_refs)
 			return 0;
-		if (get_sha1_hex(refname + 13, original_sha1)) {
+		if (get_sha1_hex(refname + strlen(git_replace_ref_base),
+				 original_sha1)) {
 			warning("invalid replace ref %s", refname);
 			return 0;
 		}

refs.c

@@ -2106,7 +2106,8 @@ int for_each_remote_ref_submodule(const char *submodule, each_ref_fn fn, void *c
 
 int for_each_replace_ref(each_ref_fn fn, void *cb_data)
 {
-	return do_for_each_ref(&ref_cache, "refs/replace/", fn, 13, 0, cb_data);
+	return do_for_each_ref(&ref_cache, git_replace_ref_base, fn,
+			       strlen(git_replace_ref_base), 0, cb_data);
 }
 
 int head_ref_namespaced(each_ref_fn fn, void *cb_data)