Re: [PATCH 2/2] refs: add GIT_REF_URI to specify reference backend and directory

When set, this variable is used to obtain the main reference store for
all Git commands. The variable is checked in `get_main_ref_store()`
when lazily assigning `repo->refs_private`. We cannot initialize this
earlier in `repo_set_gitdir()` because the repository's hash algorithm
isn't known at that point, and the reftable backend requires this
information during initialization.

When used with worktrees, the specified directory is treated as the
reference directory for all worktree operations.

Add a new test file 't1423-ref-backend.sh' to test this environment
variable.

Signed-off-by: Karthik Nayak <redacted>
---
 Documentation/git.adoc |   8 ++++
 environment.h          |   1 +
 refs.c                 |  53 +++++++++++++++++++++++-
 t/meson.build          |   1 +
 t/t1423-ref-backend.sh | 109 +++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 171 insertions(+), 1 deletion(-)

diff --git a/Documentation/git.adoc b/Documentation/git.adoc
index ce099e78b8..a1d1078f42 100644
--- a/Documentation/git.adoc
+++ b/Documentation/git.adoc

@@ -584,6 +584,14 @@ double-quotes and respecting backslash escapes. E.g., the value
 	repositories will be set to this value. The default is "files".
 	See `--ref-format` in linkgit:git-init[1].
 
+`GIT_REF_URI`::
+    Specify which reference backend and path to be used, if not specified the
+    backend is inferred from the configuration and $GIT_DIR is used as the
+    path.
++
+Expects the format '<ref_backend>://<path>', where the 'backend' specifies the
+reference backend and the 'path' specifies the directory used by the backend.

+
 Git Commits
 ~~~~~~~~~~~
 `GIT_AUTHOR_NAME`::

diff --git a/environment.h b/environment.h
index 51898c99cd..9bc380bba4 100644
--- a/environment.h
+++ b/environment.h

@@ -42,6 +42,7 @@
 #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
 #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
 #define GIT_ATTR_SOURCE_ENVIRONMENT "GIT_ATTR_SOURCE"
+#define GIT_REF_URI_ENVIRONMENT "GIT_REF_URI"
 
 /*
  * Environment variable used to propagate the --no-advice global option to the

diff --git a/refs.c b/refs.c
index 23f46867f2..0922f08c9f 100644
--- a/refs.c
+++ b/refs.c

@@ -2186,15 +2186,66 @@ static struct ref_store *get_ref_store_for_dir(struct repository *r,
 	return maybe_debug_wrap_ref_store(dir, ref_store);
 }
 
+static struct ref_store *get_ref_store_from_uri(struct repository *repo,
+						const char *uri)
+{
+	struct string_list ref_backend_info = STRING_LIST_INIT_DUP;
+	enum ref_storage_format format;
+	struct ref_store *store = NULL;
+	char *format_string;
+	char *dir;
+
+	if (!uri || !uri[0]) {
+		error("reference backend uri is empty");
+		goto cleanup;
+	}
+
+	if (string_list_split(&ref_backend_info, uri, ":", 2) != 2) {
+		error("invalid reference backend uri format '%s'", uri);
+		goto cleanup;
+	}
+
+	format_string = ref_backend_info.items[0].string;
+	dir = ref_backend_info.items[1].string + 2;
+
+	if (!dir || !dir[0]) {
+		error("invalid path in uri '%s'", uri);
+		goto cleanup;
+	}
+
+	format = ref_storage_format_by_name(format_string);
+	if (format == REF_STORAGE_FORMAT_UNKNOWN) {
+		error("unknown reference backend '%s'", format_string);
+		goto cleanup;
+	}
+
+	store = get_ref_store_for_dir(repo, dir, format);