atom: add a mock for struct atom

And define a macro specifically for fuzzer so we know when to build the
mock.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/atom.c

@@ -134,3 +134,29 @@ void destroy_atoms(struct atom *a) {
 	assert(atoms->atom_to_name == NULL);
 	free(a);
 }
+
+#if defined(UNIT_TEST) || defined(CONFIG_FUZZER)
+
+static inline int mock_atom_getter(struct cache *cache, const char *atom_name attr_unused,
+                                   size_t atom_len attr_unused, struct cache_handle **value,
+                                   void *user_data attr_unused) {
+	auto atoms = container_of(cache, struct atom_impl, c);
+	xcb_atom_t atom = (xcb_atom_t)HASH_COUNT(atoms->atom_to_name) + 1;
+	struct atom_entry *entry = ccalloc(1, struct atom_entry);
+	entry->atom = atom;
+	HASH_ADD_INT(atoms->atom_to_name, atom, entry);
+	*value = &entry->entry;
+	return 0;
+}
+
+struct atom *init_mock_atoms(void) {
+	return init_atoms_impl(NULL, mock_atom_getter);
+}
+
+#else
+
+struct atom *init_mock_atoms(void) {
+	abort();
+}
+
+#endif

src/atom.h

@@ -74,3 +74,9 @@ const char *get_atom_name(struct atom *a, xcb_atom_t, xcb_connection_t *c);
 const char *get_atom_name_cached(struct atom *a, xcb_atom_t atom);
 
 void destroy_atoms(struct atom *a);
+
+/// A mock atom object for unit testing. Successive calls to get_atom will return
+/// secutive integers as atoms, starting from 1. Calling get_atom_name with atoms
+/// previously seen will result in the string that was used to create the atom; if
+/// the atom was never returned by get_atom, it will abort.
+struct atom *init_mock_atoms(void);

src/meson.build

@@ -98,7 +98,7 @@ endif
 
 if cc.has_argument('-fsanitize=fuzzer')
   c2_fuzz = executable('c2_fuzz', srcs + ['fuzzer/c2.c'],
-	c_args: cflags + ['-fsanitize=fuzzer', '-Dmain=__main__'],
+	c_args: cflags + ['-fsanitize=fuzzer', '-DCONFIG_FUZZER'],
 	link_args: ['-fsanitize=fuzzer'],
 	dependencies: [ base_deps, deps, test_h_dep ],
 	build_by_default: false,

src/picom.c

@@ -2791,10 +2791,16 @@ static void session_run(session_t *ps) {
 	ev_run(ps->loop, 0);
 }
 
+#ifdef CONFIG_FUZZER
+#define PICOM_MAIN(...) no_main(__VA_ARGS__)
+#else
+#define PICOM_MAIN(...) main(__VA_ARGS__)
+#endif
+
 /**
  * The function that everybody knows.
  */
-int main(int argc, char **argv) {
+int PICOM_MAIN(int argc, char **argv) {
 	// Set locale so window names with special characters are interpreted
 	// correctly
 	setlocale(LC_ALL, "");