fix: allow treeland to start without any users

[Groveer]

Summary

Fix treeland crash when no system users exist. The compositor previously assumed the "dde" user always exists and would crash via assertion, undefined behavior, or qFatal. This PR ensures treeland can start gracefully in the absence of users.

Changes

1. session.cpp: fall back to getpwuid(getuid()) when getpwnam("dde") fails in ensureSession, ensuring globalSession() is never null
2. usermodel.cpp: guard empty user list before calling .first() to avoid undefined behavior
3. usermodel.cpp: replace qFatal with qCWarning + early return for graceful D-Bus degradation (Accounts service unavailable)
4. treeland.cpp: replace Q_ASSERT(globalSession) with a runtime null check

Related: WM-82

Summary by Sourcery

Ensure Treeland starts and degrades gracefully when no system users or global session are available.

Bug Fixes:

• Avoid crashing when the Accounts service fails to provide a user list by logging a warning and aborting initialization of the user model.
• Prevent undefined behavior when no users are returned by guarding access to the first user entry.
• Allow session creation to succeed even when the requested username has no passwd entry by falling back to the current process user, while handling failure explicitly.
• Avoid Treeland startup crashes due to a null global session by converting the assert into a runtime check with critical logging and early return.

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Groveer

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Details

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[sourcery-ai]

Reviewer's Guide

Ensures Treeland and its greeter start gracefully when no system users or the expected "dde" user exist by adding runtime fallbacks and null/empty checks, and by downgrading fatal errors to logged warnings where appropriate.

Sequence diagram for Treeland startup and session fallback

sequenceDiagram
    participant Treeland
    participant Helper
    participant SessionManager
    participant passwd_db

    Treeland->>Helper: helper
    Helper->>SessionManager: globalSession()
    SessionManager->>passwd_db: getpwnam(username)
    alt passwd entry found
        passwd_db-->>SessionManager: passwd
        SessionManager-->>Helper: Session
    else passwd entry missing
        passwd_db-->>SessionManager: null
        SessionManager->>passwd_db: getpwuid(getuid())
        alt current user passwd found
            passwd_db-->>SessionManager: passwd
            SessionManager-->>Helper: Session
        else current user passwd missing
            passwd_db-->>SessionManager: null
            SessionManager-->>Helper: nullptr
        end
    end
    Helper-->>Treeland: globalSession
    alt globalSession is null
        Treeland->>Treeland: qCCritical(lcTlCore)
        Treeland->>Treeland: return
    else globalSession valid
        Treeland->>Treeland: proceed initialization
    end

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Sequence diagram for UserModel initialization with empty or failing user list

sequenceDiagram
    participant UserModel
    participant AccountsManager as Manager

    UserModel->>Manager: userList()
    alt userList has error
        Manager-->>UserModel: error
        UserModel->>UserModel: qCWarning(lcTlGreeter)
        UserModel->>UserModel: return
    else userList ok
        Manager-->>UserModel: uids
        UserModel->>UserModel: populate d->users
        alt currentUserName is empty
            alt d->users is empty
                UserModel->>UserModel: qCWarning(lcTlGreeter)
            else d->users not empty
                UserModel->>UserModel: qCWarning(lcTlGreeter)
                UserModel->>UserModel: d->currentUserName = d->users.first()->userName()
            end
        else currentUserName set
            UserModel->>UserModel: keep currentUserName
        end
    end

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File-Level Changes

Change	Details	Files
Make session creation resilient when the expected username passwd entry is missing by falling back to the current process user.	Include unistd.h to access getuid Log a warning when getpwnam for the requested username fails and document the fallback behavior Fallback to getpwuid(getuid()) when getpwnam fails Log a critical error and return nullptr if getpwuid also fails before constructing the Session	src/session/session.cpp
Harden the greeter user model against Accounts service failures and an empty user list to avoid crashes and undefined behavior.	Replace qFatal on failed userList() retrieval with a categorized warning and early return Guard access to d->users.first() with an isEmpty check before defaulting currentUserName Adjust warning messages to reflect either no users found or fallback to first user	src/greeter/usermodel.cpp
Prevent Treeland from crashing on startup when globalSession is null by replacing an assertion with a runtime check and early exit, and update copyright years.	Update the copyright header years from 2023 to 2023-2026 Replace Q_ASSERT(globalSession) with an if check that logs a critical error and returns early when globalSession is null	src/core/treeland.cpp

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[sourcery-ai]

Hey - I've left some high level feedback:

• In SessionManager::ensureSession, falling back from the requested username to getuid() may be surprising; consider logging the original username and/or propagating a distinct error or status so callers can distinguish between “requested user not found” and “fallback to current user.”
• The early return in Treeland::Treeland when globalSession is null leaves a partially initialized object; consider moving the check to a factory or init method that can fail explicitly rather than returning from the constructor, or set an explicit "invalid" state that callers can query.
• When UserModel returns early due to a failure in userList(), ensure all dependent code paths can handle an empty d->users and d->currentUserName gracefully; if needed, add a simple validity flag or getter to make this state explicit to consumers.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `SessionManager::ensureSession`, falling back from the requested `username` to `getuid()` may be surprising; consider logging the original username and/or propagating a distinct error or status so callers can distinguish between “requested user not found” and “fallback to current user.”
- The early `return` in `Treeland::Treeland` when `globalSession` is null leaves a partially initialized object; consider moving the check to a factory or init method that can fail explicitly rather than returning from the constructor, or set an explicit "invalid" state that callers can query.
- When `UserModel` returns early due to a failure in `userList()`, ensure all dependent code paths can handle an empty `d->users` and `d->currentUserName` gracefully; if needed, add a simple validity flag or getter to make this state explicit to consumers.

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[deepin-bot]

TAG Bot

New tag: 0.8.15
DISTRIBUTION: unstable
Suggest: synchronizing this PR through rebase #1163