setup: fix memory leaks with `struct repository_format`

After we set up a `struct repository_format`, it owns various pieces of
allocated memory. We then either use those members, because we decide we
want to use the "candidate" repository format, or we discard the
candidate / scratch space. In the first case, we transfer ownership of
the memory to a few global variables. In the latter case, we just
silently drop the struct and end up leaking memory.

Introduce an initialization macro `REPOSITORY_FORMAT_INIT` and a
function `clear_repository_format()`, to be used on each side of
`read_repository_format()`. To have a clear and simple memory ownership,
let all users of `struct repository_format` duplicate the strings that
they take from it, rather than stealing the pointers.

Call `clear_...()` at the start of `read_...()` instead of just zeroing
the struct, since we sometimes enter the function multiple times. Thus,
it is important to initialize the struct before calling `read_...()`, so
document that. It's also important because we might not even call
`read_...()` before we call `clear_...()`, see, e.g., builtin/init-db.c.

Teach `read_...()` to clear the struct on error, so that it is reset to
a safe state, and document this. (In `setup_git_directory_gently()`, we
look at `repo_fmt.hash_algo` even if `repo_fmt.version` is -1, which we
weren't actually supposed to do per the API. After this commit, that's
ok.)

We inherit the existing code's combining "error" and "no version found".
Both are signalled through `version == -1` and now both cause us to
clear any partial configuration we have picked up. For "extensions.*",
that's fine, since they require a positive version number. For
"core.bare" and "core.worktree", we're already verifying that we have a
non-negative version number before using them.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/repository.c b/repository.c
index 7b02e1d..df88705 100644
--- a/repository.c
+++ b/repository.c
@@ -148,7 +148,7 @@ int repo_init(struct repository *repo,
 	      const char *gitdir,
 	      const char *worktree)
 {
-	struct repository_format format;
+	struct repository_format format = REPOSITORY_FORMAT_INIT;
 	memset(repo, 0, sizeof(*repo));
 
 	repo->objects = raw_object_store_new();
@@ -165,6 +165,7 @@ int repo_init(struct repository *repo,
 	if (worktree)
 		repo_set_worktree(repo, worktree);
 
+	clear_repository_format(&format);
 	return 0;
 
 error: