fix(accounts): guard userList against unavailable Accounts service

[zccrs]

Problem

DAccountsManager::userList() 在 org.freedesktop.Accounts 不可用时直接解引用空 QArrayDataPointer<QDBusObjectPath>（needsDetach(this=0x0)），导致 SIGSEGV（exit 139）。gdb 栈：

#0 QArrayDataPointer<QDBusObjectPath>::needsDetach(this=0x0)
#1 QMovableArrayOps<QDBusObjectPath>::emplace
#2 DAccountsManager::userList() at daccountsmanager.cpp:52
#3 UserModel::UserModel at treeland/src/greeter/usermodel.cpp:64
#4 Helper::init -> QQmlEngine::singletonInstance<UserModel>

在 treeland 启动时必现：Helper::init 无条件实例化 UserModel QML 单例，dde-system-daemon（org.deepin.dde.Accounts1）因 Go concurrent map 竞态崩溃后，org.freedesktop.Accounts 虽在但 QDBusPendingReply::value() 的解包路径在部分传输下返回 QDBusArgument 而非 QList<QDBusObjectPath>，原有 !isValid 检查不足，遍历空指针列表触发崩溃。treeland 侧虽已加 isServiceRegistered 防护（ca5936d），库侧仍需健壮。

Fix

• 调用前 QDBusConnection::systemBus().interface()->isServiceRegistered("org.freedesktop.Accounts")，不可用时直接返回 DUnexpected{ServiceUnknown}，避免发 DBus
• waitForFinished 后同时检查 isError() || !isValid()
• const auto value = reply.value() 拷贝后遍历，跳过空 path()，避免解包失败时的空 QList 解引用

已在 archlinux + accounts-daemon 788 + treeland build/src/treeland 验证：原库 ./build/src/treeland 必 SIGSEGV，补丁库 LD_LIBRARY_PATH=/tmp/dtk_build/src 后正常启动至锁屏/多任务视图，无崩溃。

Test

• ./tmp/test3 直接调用 DAccountsManager::userList() 返回 4 用户正常
• treeland 原分支 + 补丁库：timeout 4 treeland 从 EXIT:139 变为 EXIT:124（wayland-0.lock 正常退出），无 SIGSEGV
• cmake --build /tmp/dtk_build 通过

Log: fix accounts userList SIGSEGV when service unavailable

Summary by Sourcery

Harden account user listing against unavailable services and malformed D-Bus responses.

Bug Fixes:

• Prevent crashes in DAccountsManager::userList() when the Accounts D-Bus service is unavailable or returns invalid user data.
• Return a service-unavailable error instead of issuing D-Bus requests when org.freedesktop.Accounts is not registered.

Enhancements:

• Improve validation of D-Bus replies and ignore empty user object paths during user list processing.

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: zccrs

The full list of commands accepted by this bot can be found here.

Details

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• debian/deepin/OWNERS

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Hardens DAccountsManager::userList() against an unavailable Accounts service and invalid D-Bus payloads, preventing the startup-time SIGSEGV while preserving normal user enumeration.

Sequence diagram for guarded Accounts user listing

sequenceDiagram
    participant UserModel
    participant DAccountsManager
    participant DBus as QDBusConnection
    participant Accounts as org.freedesktop.Accounts

    UserModel->>DAccountsManager: userList()
    DAccountsManager->>DBus: isServiceRegistered(org.freedesktop.Accounts)
    alt service unavailable
        DBus-->>DAccountsManager: false
        DAccountsManager-->>UserModel: DUnexpected ServiceUnknown
    else service available
        DBus-->>DAccountsManager: true
        DAccountsManager->>Accounts: listCachedUsers()
        DAccountsManager->>Accounts: waitForFinished()
        alt reply.isError() or !reply.isValid()
            Accounts-->>DAccountsManager: error reply
            DAccountsManager-->>UserModel: DUnexpected reply error
        else valid reply
            Accounts-->>DAccountsManager: QList<QDBusObjectPath>
            DAccountsManager->>DAccountsManager: getUIDFromObjectPath(user.path())
            DAccountsManager-->>UserModel: QList<quint64>
        end
    end

Loading

File-Level Changes

Change	Details	Files
Adds defensive handling for unavailable or malformed Accounts D-Bus responses before constructing the user list.	Checks whether org.freedesktop.Accounts is registered before issuing the request and returns ServiceUnknown when unavailable. Treats both D-Bus errors and invalid replies as failures. Copies the reply value before iteration and skips entries with empty object paths to avoid null/failed-demarshalling crashes.	src/accounts/daccountsmanager.cpp

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[sourcery-ai]

Hey - I've reviewed your changes and they look great!

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[zccrs]

Closed in favor of linuxdeepin/dtksystemsettings#148 — dtk6 will auto-sync from main repo.