feat: standalone autodetect for DM Wayland sessions

README.md

@@ -323,9 +323,11 @@ composited onto the output in a second render pass instead of being drawn
 into a host window.
 
 The auto-detection fires only when none of `KICK_MODE`, `WLR_BACKENDS`,
-`WAYLAND_DISPLAY` or `DISPLAY` is set **and** kick's stdin is a real VT
-(`/dev/tty<digits>`): there must be nothing to nest into, and SSH sessions,
-terminal emulators and pipes never match the VT shape test. The chosen mode
+`WAYLAND_DISPLAY` or `DISPLAY` is set **and** either kick's stdin is a real
+VT (`/dev/tty<digits>`) or the login advertises a Wayland session
+(`XDG_SESSION_TYPE=wayland`, as every display manager/greeter sets): there
+must be nothing to nest into, and SSH sessions, terminal emulators and
+pipes match neither test, so they keep the nested default. The chosen mode
 is logged at startup as `[mode] standalone|nested (reason)`. Escape hatches,
 in precedence order:
 

kick.c

@@ -12141,16 +12141,22 @@ static bool parse_screen_mode(const char *val) {
     return true;
 }
 
-/* True when this process was started from a Linux virtual console: our
-   controlling terminal is a real VT (/dev/tty<digits>) and there is no
-   ambient graphical session (neither WAYLAND_DISPLAY nor DISPLAY) that
-   nested mode could open its window in.  SSH sessions, terminal emulators
-   and pipes all fail the tty shape test (/dev/pts/N, /dev/ttyS*, not a tty),
-   so they keep the nested default. */
+/* True when this process is the graphical session itself (standalone) rather
+   than a client of one (nested): our controlling terminal is a real VT
+   (/dev/tty<digits>) and there is no ambient graphical session (neither
+   WAYLAND_DISPLAY nor DISPLAY) that nested mode could open its window in --
+   or a display manager launched us as its Wayland session (XDG_SESSION_TYPE
+   says so; every major DM/greeter sets it, and the VT test can never fire
+   there since stdin is no virtual console).  SSH sessions, terminal
+   emulators and pipes all fail both tests (/dev/pts/N, /dev/ttyS*, not a
+   tty; no session type), so they keep the nested default. */
 static bool started_on_console(void) {
     char name[64];
     if (getenv("WAYLAND_DISPLAY") || getenv("DISPLAY"))
         return false;
+    const char *session_type = getenv("XDG_SESSION_TYPE");
+    if (session_type && strcmp(session_type, "wayland") == 0)
+        return true;
     if (!isatty(STDIN_FILENO))
         return false;
     if (ttyname_r(STDIN_FILENO, name, sizeof(name)) != 0)
@@ -12511,13 +12517,15 @@ int main(int argc, char *argv[]) {
        drives a native output directly (DRM, or headless for tests); the
        default nested mode blits a headless output into a host window.
        With neither variable set, launching from a Linux virtual console
-       picks standalone automatically so plain `kick` works at a TTY;
-       KICK_MODE=nested pins the old behaviour there. */
+       or as a display manager's Wayland session picks standalone
+       automatically so plain `kick` works at a TTY and in lightdm/greetd
+       entries; KICK_MODE=nested pins the old behaviour there. */
     server.standalone = false;
     const char *mode_reason = "default";
     {
         const char *mode = getenv("KICK_MODE");
         const char *wlr_backends = getenv("WLR_BACKENDS");
+        const char *session_type = getenv("XDG_SESSION_TYPE");
         if (mode && strcmp(mode, "standalone") == 0) {
             server.standalone = true;
             mode_reason = "KICK_MODE";
@@ -12526,7 +12534,10 @@ int main(int argc, char *argv[]) {
             mode_reason = "KICK_MODE";
         } else if (!wlr_backends || !wlr_backends[0]) {
             server.standalone = started_on_console();
-            mode_reason = server.standalone ? "console" : "default";
+            if (server.standalone)
+                mode_reason = (session_type &&
+                        strcmp(session_type, "wayland") == 0) ?
+                    "session" : "console";
         }
         if (wlr_backends && wlr_backends[0]) {
             server.standalone = true;

tests/test_smoke.py

@@ -4636,6 +4636,35 @@ def test_mode_autodetect_stays_nested_without_console():
         s.close()
 
 
+def test_mode_autodetect_standalone_wayland_session():
+    """A display manager launching kick as its Wayland session (no KICK_MODE,
+    no WLR_BACKENDS, no displays, piped stdin like lightdm provides) must
+    pick standalone via XDG_SESSION_TYPE: the VT shape test can never fire
+    there, and without this the session tries to nest into nothing and the
+    login loops back to the greeter."""
+    env = dict(os.environ)
+    log = _fresh_log()
+    dump_dir = _mk_dump_dir()
+    proc = subprocess.Popen(
+        ["env", "-i",
+         "PATH=" + env["PATH"],
+         "HOME=" + env.get("HOME", "/"),
+         "XDG_RUNTIME_DIR=" + env.get("XDG_RUNTIME_DIR", "/tmp"),
+         "XDG_SESSION_TYPE=wayland",
+         "KICK_LOG=1",
+         "KICK_DUMP_DIR=" + dump_dir,
+         "stdbuf", "-oL", BIN],
+        stdin=subprocess.PIPE, stdout=open(log, "ab"), stderr=subprocess.STDOUT,
+        preexec_fn=_preexec_death(os.getpid()),
+    )
+    s = Session(proc, log, dump_dir)
+    try:
+        s.wait_for(r"\[mode\] standalone \(session\)")
+        assert "[mode] nested" not in s.read_log()
+    finally:
+        s.close()
+
+
 @pytest.mark.flaky
 def test_x11_leader_window_never_becomes_tab():
     """A GTK-style X11 app (unmapped leader window created first, real frame