Disable feature/dircache files when dircache module is disabled.

To make Tor still work, we define a minimal dircache_stub.c file
that defines the entry points to the module that can actually be
seen by the compiler when we're building with dircache and relay
disabled.

src/core/include.am

@@ -91,10 +91,6 @@ LIBTOR_APP_A_SOURCES = 				\
 	src/feature/control/control_proto.c	\
 	src/feature/control/fmt_serverstatus.c  \
 	src/feature/control/getinfo_geoip.c	\
-	src/feature/dircache/conscache.c	\
-	src/feature/dircache/consdiffmgr.c	\
-	src/feature/dircache/dircache.c		\
-	src/feature/dircache/dirserv.c		\
 	src/feature/dirclient/dirclient.c	\
 	src/feature/dirclient/dlstatus.c	\
 	src/feature/dircommon/consdiff.c	\
@@ -183,6 +179,13 @@ MODULE_RELAY_SOURCES = 						\
 	src/feature/relay/relay_sys.c				\
 	src/feature/relay/transport_config.c
 
+# The Directory Cache module.
+MODULE_DIRCACHE_SOURCES = \
+	src/feature/dircache/conscache.c	\
+	src/feature/dircache/consdiffmgr.c	\
+	src/feature/dircache/dircache.c		\
+	src/feature/dircache/dirserv.c
+
 # The Directory Authority module.
 MODULE_DIRAUTH_SOURCES =					\
 	src/feature/dirauth/authmode.c				\
@@ -209,6 +212,12 @@ else
 LIBTOR_APP_A_STUB_SOURCES += src/feature/relay/relay_stub.c
 endif
 
+if BUILD_MODULE_DIRCACHE
+LIBTOR_APP_A_SOURCES += $(MODULE_DIRCACHE_SOURCES)
+else
+LIBTOR_APP_A_STUB_SOURCES += src/feature/dircache/dircache_stub.c
+endif
+
 if BUILD_MODULE_DIRAUTH
 LIBTOR_APP_A_SOURCES += $(MODULE_DIRAUTH_SOURCES)
 else
@@ -222,6 +231,7 @@ if UNITTESTS_ENABLED
 
 # Add the sources of the modules that are needed for tests to work here.
 LIBTOR_APP_TESTING_A_SOURCES += $(MODULE_RELAY_SOURCES)
+LIBTOR_APP_TESTING_A_SOURCES += $(MODULE_DIRCACHE_SOURCES)
 LIBTOR_APP_TESTING_A_SOURCES += $(MODULE_DIRAUTH_SOURCES)
 
 src_core_libtor_app_testing_a_SOURCES = $(LIBTOR_APP_TESTING_A_SOURCES)

src/feature/dircache/dircache_stub.c

@@ -0,0 +1,152 @@
+/* Copyright (c) 2001-2004, Roger Dingledine.
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2020, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * @file dircache_stub.c
+ * @brief Stub declarations for use when dircache module is disabled.
+ **/
+
+#include "core/or/or.h"
+#include "feature/dircache/consdiffmgr.h"
+#include "feature/dircache/dircache.h"
+#include "feature/dircache/dirserv.h"
+#include "feature/dircommon/dir_connection_st.h"
+
+int
+directory_handle_command(dir_connection_t *conn)
+{
+  (void) conn;
+  tor_assert_nonfatal_unreached_once();
+  return -1;
+}
+
+int
+connection_dirserv_flushed_some(dir_connection_t *conn)
+{
+  (void) conn;
+  tor_assert_nonfatal_unreached_once();
+  return -1;
+}
+
+int
+directory_fetches_from_authorities(const or_options_t *options)
+{
+  (void) options;
+  return 0;
+}
+
+int
+directory_fetches_dir_info_early(const or_options_t *options)
+{
+  (void) options;
+  return 0;
+}
+
+int
+directory_fetches_dir_info_later(const or_options_t *options)
+{
+  (void) options;
+  return 0;
+}
+
+int
+directory_caches_unknown_auth_certs(const or_options_t *options)
+{
+  (void) options;
+  return 0;
+}
+
+int
+directory_caches_dir_info(const or_options_t *options)
+{
+  (void) options;
+  return 0;
+}
+
+int
+directory_permits_begindir_requests(const or_options_t *options)
+{
+  (void) options;
+  return 0;
+}
+
+int
+directory_too_idle_to_fetch_descriptors(const or_options_t *options,
+                                        time_t now)
+{
+  (void)options;
+  (void)now;
+  return 0;
+}
+
+cached_dir_t *
+dirserv_get_consensus(const char *flavor_name)
+{
+  (void) flavor_name;
+  return NULL;
+}
+
+void
+dir_conn_clear_spool(dir_connection_t *conn)
+{
+  if (!conn)
+    return;
+  tor_assert_nonfatal_once(conn->spool == NULL);
+}
+
+void
+consdiffmgr_enable_background_compression(void)
+{
+}
+
+void
+dirserv_set_cached_consensus_networkstatus(const char *networkstatus,
+                                           size_t networkstatus_len,
+                                           const char *flavor_name,
+                                           const common_digests_t *digests,
+                                           const uint8_t *sha3_as_signed,
+                                           time_t published)
+{
+  (void)networkstatus;
+  (void)networkstatus_len;
+  (void)flavor_name;
+  (void)digests;
+  (void)sha3_as_signed;
+  (void)published;
+}
+
+int
+consdiffmgr_add_consensus(const char *consensus,
+                          size_t consensus_len,
+                          const networkstatus_t *as_parsed)
+{
+  (void)consensus;
+  (void)consensus_len;
+  (void)as_parsed;
+  return 0;
+}
+
+int
+consdiffmgr_register_with_sandbox(struct sandbox_cfg_elem_t **cfg)
+{
+  (void)cfg;
+  return 0;
+}
+
+int
+consdiffmgr_cleanup(void)
+{
+  return 0;
+}
+
+void
+consdiffmgr_free_all(void)
+{
+}
+
+void
+dirserv_free_all(void)
+{
+}