core: remove support for ".include" stanza

Six years ago we declared it obsolete and removed it from the docs
(c073a0c4a5ffbf6677dd6af02e7c7d59b2b901ab) and added a note about it in
NEWS. Two years ago we add warning messages about it, indicating the
feature will be removed (41b283d0f1f4abd85d0bbeeb7f71bb30f87cfab9) and
mentioned it in NEWS again.

Let's now kill it for good.

NEWS

@@ -357,6 +357,11 @@ CHANGES WITH 246 in spe:
           The optional positional argument to "systemctl reboot" is now
           being deprecated in favor of this option.
 
+        * Support for the .include syntax in unit files has been removed. The
+          concept has been obsolete for 6 years and we started warning about
+          its pending removal 2 years ago (also see NEWS file below). It's
+          finally gone now.
+
 CHANGES WITH 245:
 
         * A new tool "systemd-repart" has been added, that operates as an

man/systemd.unit.xml

@@ -226,9 +226,6 @@
     <filename>foo-.service.d/10-override.conf</filename> would override
     <filename>service.d/10-override.conf</filename>.</para>
 
-    <!-- Note that we do not document .include here, as we consider it mostly obsolete, and want
-         people to use .d/ drop-ins instead. -->
-
     <para>Note that while systemd offers a flexible dependency system
     between units it is recommended to use this functionality only
     sparingly and instead rely on techniques such as bus-based or

src/core/load-fragment.c

@@ -4864,7 +4864,7 @@ int unit_load_fragment(Unit *u) {
                         r = config_parse(u->id, fragment, f,
                                          UNIT_VTABLE(u)->sections,
                                          config_item_perf_lookup, load_fragment_gperf_lookup,
-                                         CONFIG_PARSE_ALLOW_INCLUDE,
+                                         0,
                                          u,
                                          NULL);
                         if (r == -ENOEXEC)

src/fuzz/fuzz-unit-file.c

@@ -74,7 +74,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
                         name, name, f,
                         UNIT_VTABLE(u)->sections,
                         config_item_perf_lookup, load_fragment_gperf_lookup,
-                        CONFIG_PARSE_ALLOW_INCLUDE,
+                        0,
                         u,
                         NULL);
 

src/shared/conf-parser.c

@@ -159,7 +159,7 @@ static int parse_line(
                 char *l,
                 void *userdata) {
 
-        char *e, *include;
+        char *e;
 
         assert(filename);
         assert(line > 0);
@@ -173,35 +173,6 @@ static int parse_line(
         if (*l == '\n')
                 return 0;
 
-        include = first_word(l, ".include");
-        if (include) {
-                _cleanup_free_ char *fn = NULL;
-
-                /* .includes are a bad idea, we only support them here
-                 * for historical reasons. They create cyclic include
-                 * problems and make it difficult to detect
-                 * configuration file changes with an easy
-                 * stat(). Better approaches, such as .d/ drop-in
-                 * snippets exist.
-                 *
-                 * Support for them should be eventually removed. */
-
-                if (!(flags & CONFIG_PARSE_ALLOW_INCLUDE)) {
-                        log_syntax(unit, LOG_ERR, filename, line, 0, ".include not allowed here. Ignoring.");
-                        return 0;
-                }
-
-                log_syntax(unit, LOG_WARNING, filename, line, 0,
-                           ".include directives are deprecated, and support for them will be removed in a future version of systemd. "
-                           "Please use drop-in files instead.");
-
-                fn = file_in_same_dir(filename, strstrip(include));
-                if (!fn)
-                        return -ENOMEM;
-
-                return config_parse(unit, fn, NULL, sections, lookup, table, flags, userdata, NULL);
-        }
-
         if (!utf8_is_valid(l))
                 return log_syntax_invalid_utf8(unit, LOG_WARNING, filename, line, l);
 

src/shared/conf-parser.h

@@ -16,8 +16,7 @@
 
 typedef enum ConfigParseFlags {
         CONFIG_PARSE_RELAXED       = 1 << 0, /* Do not warn about unknown non-extension fields */
-        CONFIG_PARSE_ALLOW_INCLUDE = 1 << 1, /* Allow the deprecated .include stanza */
-        CONFIG_PARSE_WARN          = 1 << 2, /* Emit non-debug messages */
+        CONFIG_PARSE_WARN          = 1 << 1, /* Emit non-debug messages */
 } ConfigParseFlags;
 
 /* Argument list for parsers of specific configuration settings. */

src/shared/install.c

@@ -1304,7 +1304,7 @@ static int unit_file_load(
                          "-Target\0"
                          "-Timer\0",
                          config_item_table_lookup, items,
-                         CONFIG_PARSE_ALLOW_INCLUDE, info,
+                         0, info,
                          NULL);
         if (r < 0)
                 return log_debug_errno(r, "Failed to parse %s: %m", info->name);