Identify(h) advertised over D-Bus but call returns UnknownMethod (Qt 6.11)

[svan71]

SUMMARY | 问题概要

org.desktopspec.ApplicationManager1.Identify is present in D-Bus introspection (signature h → soa{sa{sv}}), but live method calls with a valid unix:fd (h) fail with:

org.freedesktop.DBus.Error.UnknownMethod
No such method 'Identify' in interface 'org.desktopspec.ApplicationManager1'
at object path '/org/desktopspec/ApplicationManager1' (signature 'h')

This leaves Treeland's treeland-session-helper with an empty appId when resolving a newly mapped toplevel, which breaks prelaunch splash matching (real window + lingering Loading... splash / dual SurfaceWrappers).

Related design discussions: #276 (pidfd→pid TOCTOU), #278 (Identify via pid design). This report is specifically about registration/dispatch: the method is advertised but not invokable.

Environment | 环境

Component	Version
OS	Arch Linux x86_64
dde-application-manager	1.2.58 (Arch extra, also reproduced with a clean rebuild of the same tag)
Qt	6.11.1 (qt6-base)
Session	Treeland / Wayland (DDE)
treeland (stock)	0.8.15 (session-helper calls Identify)

Steps to reproduce | 复现步骤

1. Start a Treeland/DDE session with Application Manager running.
2. Confirm introspection lists the method:

busctl --user introspect org.desktopspec.ApplicationManager1 \
  /org/desktopspec/ApplicationManager1 \
  org.desktopspec.ApplicationManager1 | grep Identify
# → .Identify  method  h  soa{sa{sv}}

3. Launch an app that uses prelaunch splash (e.g. Deepin Terminal) from the launcher, or call Identify the same way Treeland does (Qt QDBusInterface / official app-identifier / Gio) with a real process pidfd.
4. Observe session-helper / client error:

DBus Identify failed ... method= "Identify" error=
"No such method 'Identify' in interface 'org.desktopspec.ApplicationManager1'
 at object path '/org/desktopspec/ApplicationManager1' (signature 'h')"
respond sent N ""

Expected | 期望

• Introspected Identify(h) is invokable.
• Successful calls return a non-empty application id (and instance path / info as documented).

Actual | 实际

• Introspect shows Identify.
• Call with signature h returns UnknownMethod.
• Callers (including stock treeland-session-helper) treat this as failure and respond with an empty appId.

Additional notes | 补充

• Reproduced with:
  • Qt D-Bus client (same path treeland-session-helper uses)
  • Gio
  • Official app-identifier tooling
• A fresh rebuild of AM 1.2.58 still exhibits the failure on this host.
• Minimal standalone Qt D-Bus servers that export a method with signature h work on the same Qt 6.11 stack — so this appears AM registration/adaptor-path specific, not a blanket “Qt 6.11 cannot handle h” issue.
• Method body exists in AM source (ApplicationManager1Service::Identify(const QDBusUnixFileDescriptor &...)).
• Workaround used on the compositor side: if Identify fails, parse the process cgroup unit name app-DDE-<id>@*.service as a fallback appId (local treeland-session-helper patch only; not a substitute for fixing AM).

Impact | 影响

Prelaunch splash cannot be matched to the real toplevel when appId resolve is empty → dual windows / stuck Loading splash until prelaunchSplashTimeoutMs (typically ~5s). Visible with Terminal, Calculator, Chrome, etc. under Treeland on Arch + Qt 6.11.

Happy to provide more logs, a minimal Qt caller, or test a patch build.

[svan71]

Downstream impact

When Identify fails this way, Treeland session-helper responds with an empty appId and prelaunch splash cannot attach to the real toplevel (dual Loading window / dual SurfaceWrapper until timeout).

Tracked on the compositor side: linuxdeepin/treeland#1169