setup: refactor repo format reading and verification

When we want to know if we're in a git repository of
reasonable vintage, we can call check_repository_format_gently(),
which does three things:

  1. Reads the config from the .git/config file.

  2. Verifies that the version info we read is sane.

  3. Writes some global variables based on this.

There are a few things we could improve here.

One is that steps 1 and 3 happen together. So if the
verification in step 2 fails, we still clobber the global
variables. This is especially bad if we go on to try another
repository directory; we may end up with a state of mixed
config variables.

The second is there's no way to ask about the repository
version for anything besides the main repository we're in.
git-init wants to do this, and it's possible that we would
want to start doing so for submodules (e.g., to find out
which ref backend they're using).

We can improve both by splitting the first two steps into
separate functions. Now check_repository_format_gently()
calls out to steps 1 and 2, and does 3 only if step 2
succeeds.

Note that the public interface for read_repository_format()
and what check_repository_format_gently() needs from it are
not quite the same, leading us to have an extra
read_repository_format_1() helper. The extra needs from
check_repository_format_gently() will go away in a future
patch, and we can simplify this then to just the public
interface.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/cache.h b/cache.h
index 867e73e..4fc42b5 100644
--- a/cache.h
+++ b/cache.h
@@ -750,6 +750,30 @@ extern int grafts_replace_parents;
 extern int repository_format_version;
 extern int repository_format_precious_objects;
 
+struct repository_format {
+	int version;
+	int precious_objects;
+	int is_bare;
+	char *work_tree;
+	struct string_list unknown_extensions;
+};
+
+/*
+ * Read the repository format characteristics from the config file "path" into
+ * "format" struct. Returns the numeric version. On error, -1 is returned,
+ * format->version is set to -1, and all other fields in the struct are
+ * undefined.
+ */
+int read_repository_format(struct repository_format *format, const char *path);
+
+/*
+ * Verify that the repository described by repository_format is something we
+ * can read. If it is, return 0. Otherwise, return -1, and "err" will describe
+ * any errors encountered.
+ */
+int verify_repository_format(const struct repository_format *format,
+			     struct strbuf *err);
+
 /*
  * Check the repository format version in the path found in get_git_dir(),
  * and die if it is a version we don't understand. Generally one would