cgit: don't initialize notes when there is no repository

prepare_repo_env() calls load_display_notes() unconditionally, even when
setup_git_directory_gently() has just reported that repo.path is not a
repository. init_notes() then resolves the default notes ref and
dereferences the repository's hash algorithm, which is still NULL:

    EXC_BAD_ACCESS (code=1, address=0x18)
    get_oid_basic(str="refs/notes/commits", len=18) at object-name.c:688
    -> if (len == r->hash_algo->hexsz && !get_oid_hex(str, oid)) {

A typo in repo.path therefore took out the request. On Linux this
segfaults; on macOS nothing consumes the Mach exception, so the faulting
instruction is retried forever and the worker process spins at 100% CPU
instead of dying.

Only load the notes once a repository has been opened. prepare_repo_cmd()
reports the failure immediately afterwards, so such a request now renders
"Failed to open <repo>: No such file or directory".

Signed-off-by: Saya Andy <saya.andy@posteo.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/cgit.c b/cgit.c
index ca318e8..5bf52f8 100644
--- a/cgit.c
+++ b/cgit.c
@@ -587,9 +587,12 @@ static void prepare_repo_env(int *nongit)
 
 	/* Setup the git directory and initialize the notes system. Both of these
 	 * load local configuration from the git repository, so we do them both while
-	 * the HOME variables are unset. */
+	 * the HOME variables are unset. Initializing the notes system requires an
+	 * actual repository, as it would otherwise dereference the not yet known
+	 * hash algorithm. */
 	setup_git_directory_gently(nongit);
-	load_display_notes(NULL);
+	if (!*nongit)
+		load_display_notes(NULL);
 }
 
 static int prepare_repo_cmd(int nongit)