shared/install: report invalid unit files slightly better

When a unit file is invalid, we'd return an error without any details:
$ systemctl --root=/ enable testing@instance.service
Failed to enable: Invalid argument.

Fix things to at least print the offending file name:
$ systemctl enable testing@instance.service
Failed to enable unit: File testing@instance.service: Invalid argument

$ systemctl --root=/ enable testing@instance.service
Failed to enable unit, file testing@instance.service: Invalid argument.

A real fix would be to pass back a proper error message from conf-parser.
But this would require major surgery, since conf-parser functions now
simply print log errors, but we would need to return them over the bus.
So let's just print the file name, to indicate where the error is.

(Incomplete) fix for #4210.

2 files changed, 30 insertions, 16 deletions

diff --git a/src/shared/install.c b/src/shared/install.c
index ff1ecbe7ff..f44f80560a 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -1205,7 +1205,7 @@ static int unit_file_load(
                          config_item_table_lookup, items,
                          true, true, false, info);
         if (r < 0)
-                return r;
+                return log_debug_errno(r, "Failed to parse %s: %m", info->name);
 
         info->type = UNIT_FILE_TYPE_REGULAR;
 
@@ -1495,7 +1495,9 @@ static int install_info_discover(
                 const LookupPaths *paths,
                 const char *name,
                 SearchFlags flags,
-                UnitFileInstallInfo **ret) {
+                UnitFileInstallInfo **ret,
+                UnitFileChange **changes,
+                unsigned *n_changes) {
 
         UnitFileInstallInfo *i;
         int r;
@@ -1505,10 +1507,12 @@ static int install_info_discover(
         assert(name);
 
         r = install_info_add_auto(c, paths, name, &i);
-        if (r < 0)
-                return r;
+        if (r >= 0)
+                r = install_info_traverse(scope, c, paths, i, flags, ret);
 
-        return install_info_traverse(scope, c, paths, i, flags, ret);
+        if (r < 0)
+                unit_file_changes_add(changes, n_changes, r, name, NULL);
+        return r;
 }
 
 static int install_info_symlink_alias(
@@ -2225,7 +2229,8 @@ int unit_file_add_dependency(
 
         config_path = runtime ? paths.runtime_config : paths.persistent_config;
 
-        r = install_info_discover(scope, &c, &paths, target, SEARCH_FOLLOW_CONFIG_SYMLINKS, &target_info);
+        r = install_info_discover(scope, &c, &paths, target, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                  &target_info, changes, n_changes);
         if (r < 0)
                 return r;
         r = install_info_may_process(target_info, &paths, changes, n_changes);
@@ -2237,7 +2242,8 @@ int unit_file_add_dependency(
         STRV_FOREACH(f, files) {
                 char ***l;
 
-                r = install_info_discover(scope, &c, &paths, *f, SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
+                r = install_info_discover(scope, &c, &paths, *f, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                          &i, changes, n_changes);
                 if (r < 0)
                         return r;
                 r = install_info_may_process(i, &paths, changes, n_changes);
@@ -2290,7 +2296,8 @@ int unit_file_enable(
         config_path = runtime ? paths.runtime_config : paths.persistent_config;
 
         STRV_FOREACH(f, files) {
-                r = install_info_discover(scope, &c, &paths, *f, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
+                r = install_info_discover(scope, &c, &paths, *f, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                          &i, changes, n_changes);
                 if (r < 0)
                         return r;
                 r = install_info_may_process(i, &paths, changes, n_changes);
@@ -2403,7 +2410,7 @@ int unit_file_set_default(
         if (r < 0)
                 return r;
 
-        r = install_info_discover(scope, &c, &paths, name, 0, &i);
+        r = install_info_discover(scope, &c, &paths, name, 0, &i, changes, n_changes);
         if (r < 0)
                 return r;
         r = install_info_may_process(i, &paths, changes, n_changes);
@@ -2433,7 +2440,8 @@ int unit_file_get_default(
         if (r < 0)
                 return r;
 
-        r = install_info_discover(scope, &c, &paths, SPECIAL_DEFAULT_TARGET, SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
+        r = install_info_discover(scope, &c, &paths, SPECIAL_DEFAULT_TARGET, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                  &i, NULL, NULL);
         if (r < 0)
                 return r;
         r = install_info_may_process(i, &paths, NULL, 0);
@@ -2465,7 +2473,8 @@ static int unit_file_lookup_state(
         if (!unit_name_is_valid(name, UNIT_NAME_ANY))
                 return -EINVAL;
 
-        r = install_info_discover(scope, &c, paths, name, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
+        r = install_info_discover(scope, &c, paths, name, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                  &i, NULL, NULL);
         if (r < 0)
                 return r;
 
@@ -2552,7 +2561,7 @@ int unit_file_exists(UnitFileScope scope, const LookupPaths *paths, const char *
         if (!unit_name_is_valid(name, UNIT_NAME_ANY))
                 return -EINVAL;
 
-        r = install_info_discover(scope, &c, paths, name, 0, NULL);
+        r = install_info_discover(scope, &c, paths, name, 0, NULL, NULL, NULL);
         if (r == -ENOENT)
                 return 0;
         if (r < 0)
@@ -2770,7 +2779,8 @@ static int preset_prepare_one(
         if (install_info_find(plus, name) || install_info_find(minus, name))
                 return 0;
 
-        r = install_info_discover(scope, &tmp, paths, name, SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
+        r = install_info_discover(scope, &tmp, paths, name, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                  &i, changes, n_changes);
         if (r < 0)
                 return r;
         if (!streq(name, i->name)) {
@@ -2783,7 +2793,8 @@ static int preset_prepare_one(
                 return r;
 
         if (r > 0) {
-                r = install_info_discover(scope, plus, paths, name, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
+                r = install_info_discover(scope, plus, paths, name, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                          &i, changes, n_changes);
                 if (r < 0)
                         return r;
 
@@ -2791,7 +2802,8 @@ static int preset_prepare_one(
                 if (r < 0)
                         return r;
         } else
-                r = install_info_discover(scope, minus, paths, name, SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
+                r = install_info_discover(scope, minus, paths, name, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                          &i, changes, n_changes);
 
         return r;
 }
diff --git a/src/test/test-install-root.c b/src/test/test-install-root.c
index db1c928660..1686054d2a 100644
--- a/src/test/test-install-root.c
+++ b/src/test/test-install-root.c
@@ -326,7 +326,9 @@ static void test_default(const char *root) {
         assert_se(unit_file_get_default(UNIT_FILE_SYSTEM, root, &def) == -ENOENT);
 
         assert_se(unit_file_set_default(UNIT_FILE_SYSTEM, root, "idontexist.target", false, &changes, &n_changes) == -ENOENT);
-        assert_se(n_changes == 0);
+        assert_se(n_changes == 1);
+        assert_se(changes[0].type == -ENOENT);
+        assert_se(streq_ptr(changes[0].path, "idontexist.target"));
         unit_file_changes_free(changes, n_changes);
         changes = NULL; n_changes = 0;