[PATCH v3 1/6] setup.c: initialize the_repository correctly in all cases

There are many ways for any command to access a git repository:

- most of them will try to discover the .git dir via
  setup_git_directory() and friends

- the server side programs already know where the repo is and prepare
  with enter_repo()

- special commands that deal with repo creation (init/clone) use
  init_db() once the new repo is ready for access.

- somebody accesses $GIT_DIR before any of above functions are called
  and accidentally sets up a git repository by set_git_dir() alone

"the_repository" is partially set up via set_git_dir() at some point
in all four cases. The hash algorithm though is configured later after
.git/config is read.

So far proper repo initialization is done only for the first case [1].
The second case is not covered (but that's fine [3]). The third case
was found and worked around in [2]. The fourth case is a buggy one,
which should be fixed already by jk/no-looking-at-dotgit-outside-repo
and never happens again.

This patch makes sure all cases initialize the hash algorithm in
the_repository correctly. Both second and third cases must run
check_repo_format() before "entering" it. Eventually we probably just
rename this function to init_repo() or something.

[1] 78a6766802 (Integrate hash algorithm support with repo setup -
    2017-11-12)

[2] e26f7f19b6 (repository: pre-initialize hash algo pointer -
    2018-01-19)

[3] the reason server side is still running ok with no hash algo before
    [2] is because the programs that use enter_repo() do very
    little (and unlikely to hash anything) then spawn a new
    program (like pack-objects or upload-archive) to do the heavy
    lifting. These programs already use setup_git_directory() or the
    gently version

Signed-off-by: Nguyễn Thái Ngọc Duy <redacted>
---
 builtin/init-db.c | 3 ++-
 cache.h           | 3 ++-
 path.c            | 2 +-
 setup.c           | 5 ++++-
 4 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/builtin/init-db.c b/builtin/init-db.c
index c9b7946bad..d119d9906b 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c

@@ -9,6 +9,7 @@
 #include "builtin.h"
 #include "exec_cmd.h"
 #include "parse-options.h"
+#include "repository.h"
 
 #ifndef DEFAULT_GIT_TEMPLATE_DIR
 #define DEFAULT_GIT_TEMPLATE_DIR "/usr/share/git-core/templates"

@@ -369,7 +370,7 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	 * config file, so this will not fail.  What we are catching
 	 * is an attempt to reinitialize new repository with an old tool.
 	 */
-	check_repository_format();
+	check_repository_format(the_repository);
 
 	reinit = create_default_files(template_dir, original_git_dir);
 

diff --git a/cache.h b/cache.h
index 21fbcc2414..6b97138264 100644
--- a/cache.h
+++ b/cache.h

@@ -894,6 +894,7 @@ extern int repository_format_precious_objects;
 extern char *repository_format_partial_clone;
 extern const char *core_partial_clone_filter_default;
 
+struct repository;
 struct repository_format {
 	int version;
 	int precious_objects;

@@ -926,7 +927,7 @@ int verify_repository_format(const struct repository_format *format,
  * set_git_dir() before calling this, and use it only for "are we in a valid
  * repo?".
  */
-extern void check_repository_format(void);
+extern void check_repository_format(struct repository *);
 
 #define MTIME_CHANGED	0x0001
 #define CTIME_CHANGED	0x0002

diff --git a/path.c b/path.c
index da8b655730..a544252198 100644
--- a/path.c
+++ b/path.c

@@ -827,7 +827,7 @@ const char *enter_repo(const char *path, int strict)
 
 	if (is_git_directory(".")) {
 		set_git_dir(".");
-		check_repository_format();
+		check_repository_format(the_repository);
 		return path;
 	}
 

diff --git a/setup.c b/setup.c
index c5d55dcee4..a82103832e 100644
--- a/setup.c
+++ b/setup.c

@@ -1180,11 +1180,14 @@ int git_config_perm(const char *var, const char *value)
 	return -(i & 0666);
 }
 
-void check_repository_format(void)
+/* optionally configure "repo" to the correct format */
+void check_repository_format(struct repository *repo)
 {
 	struct repository_format repo_fmt;
 	check_repository_format_gently(get_git_dir(), &repo_fmt, NULL);
 	startup_info->have_repository = 1;
+	if (repo)
+		repo_set_hash_algo(repo, repo_fmt.hash_algo);
 }
 
 /*

-- 
2.16.1.435.g8f24da2e1a