ui-shared: don't list branches when there is no repository

print_header() fills the branch switcher from the main ref store whenever
ctx.repo is set. For a request which prints a page before
prepare_repo_cmd() has cleared ctx.repo -- an unknown page name for a
repository whose repo.path is broken, for instance -- the ref store has
never been initialized, and get_main_ref_store() aborts after the
response has already begun:

    BUG: refs.c:2301: reference backend is unknown
    get_main_ref_store
    print_header at ui-shared.c:1057
    cgit_print_error_page(fmt="Invalid request")

Add cgit_have_repository() to say whether the repository for this request
was opened, and skip the switcher when it was not.

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

3 files changed, 15 insertions, 1 deletions

diff --git a/cgit.h b/cgit.h
index 7d7ece7..b8b7712 100644
--- a/cgit.h
+++ b/cgit.h
@@ -334,6 +334,8 @@ extern struct cgit_repo *cgit_get_repoinfo(const char *url);
 extern void cgit_repo_config(struct cgit_repo *repo, const char *name,
 			     const char *value);
 
+extern int cgit_have_repository(void);
+
 extern int chk_zero(int result, char *msg);
 extern int chk_positive(int result, char *msg);
 extern int chk_non_negative(int result, char *msg);
diff --git a/shared.c b/shared.c
index a39394d..e79c3da 100644
--- a/shared.c
+++ b/shared.c
@@ -13,6 +13,18 @@
 struct cgit_repolist cgit_repolist;
 struct cgit_context ctx;
 
+/* Returns true when the git repository belonging to this request was opened
+ * successfully. Some requests print a page for a repository which could not
+ * be opened, e.g. because repo.path is wrong, and the object database and
+ * ref stores must not be touched in that case: they would abort with
+ * "reference backend is unknown" or dereference the not yet known hash
+ * algorithm.
+ */
+int cgit_have_repository(void)
+{
+	return startup_info->have_repository;
+}
+
 int chk_zero(int result, char *msg)
 {
 	if (result != 0)
diff --git a/ui-shared.c b/ui-shared.c
index 9f7625c..a6a828d 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -1042,7 +1042,7 @@ static void print_header(void)
 		cgit_index_link("index", NULL, NULL, NULL, NULL, 0, 1);
 		html(" : ");
 		cgit_summary_link(ctx.repo->name, NULL, NULL, NULL);
-		if (ctx.env.authenticated) {
+		if (ctx.env.authenticated && cgit_have_repository()) {
 			html("</td><td class='form'>");
 			html("<form method='get'>\n");
 			cgit_add_hidden_formfields(0, 1, ctx.qry.page);