fix(daemon): suppress GCC 16 -Warray-bounds false positive

[deepin-wm]

背景

ddm 的 Build ddm on Arch Linux 工作流在 master 基线上因 -Werror=array-bounds 中断，导致所有 ddm PR 的该检查都是红的。触发 run：https://github.com/linuxdeepin/ddm/actions/runs/37735447997

src/daemon/DdeSeatdControl.cpp:391:15: error: array subscript 'unsigned int[0]' is partly outside array bounds of 'const char [1]' [-Werror=array-bounds=]
/usr/include/qt6/QtCore/qbytearray.h:65:23: note: object 'QByteArray::_empty' of size 1
cc1plus: all warnings being treated as errors

这是 archlinux:latest 滚动到 GCC 16 之后暴露的既有问题，与任何 PR 的改动都无关（最初触发它的 PR #112 只改了 2 个 workflow 文件的 on: 触发条件）。

根因

QByteArray::constData() 在空数据时可能返回 1 字节的静态 QByteArray::_empty（const char[1]）。GCC 15/16 的 -Warray-bounds 无法把 size() 的返回值与 constData() 返回的指针关联起来，于是把「源码来自 1 字节静态对象」这条不可达路径当成可能路径，对 4 字节的 memcpy 报错。

原代码并没有越界：src/daemon/DdeSeatdControl.cpp:389 的循环条件已经是 while (m_eventBuffer.size() >= static_cast<int>(sizeof(ControlHeader)))，进入循环体时缓冲区至少有 sizeof(ControlHeader) = 4 字节，第 391 行的 memcpy 是安全的。

改动内容

src/daemon/DdeSeatdControl.cpp 一处，1 文件 / +7 行：

• 对该条 memcpy 局部使用 QT_WARNING_PUSH / QT_WARNING_DISABLE_GCC("-Warray-bounds") / QT_WARNING_POP，只关闭 GCC 的这一次误报；
• 上方加注释说明「while 已保证长度」以及「GCC 15/16 对 QByteArray::constData() 的误报成因」，避免后来人误以为这里本来就可能越界。

为什么这么改

• 抑制范围最小，只作用于这一条语句；没有重复添加长度判断，没有改变线格式、字节序或运行时行为。
• QT_WARNING_DISABLE_GCC 只对 GCC 生效，不会掩盖 clang 的真实告警。
• 没有改成逐字节拷贝之类的等价写法：原代码本身是正确的，改写反而会引入与线格式相关的风险。

验证

• 在 archlinux:latest 容器（GCC 16.2.1 / Qt 6.12.0，编译参数与 workflow 完全一致 -DCMAKE_CXX_FLAGS="-Wall -Wextra -Werror"）中先复现同一报错，应用本改动后完整构建 53/53 个 target 通过、链接产出 src/daemon/ddm、退出码 0。
• 本 PR 上的 Arch Linux 工作流变绿即闭环。

关联

• Multica Issue: WM-566

Summary by Sourcery

Prevent GCC 15/16 false-positive array-bounds warnings from failing daemon builds without changing runtime behavior.

Bug Fixes:

• Suppress the GCC 15/16 false-positive -Warray-bounds diagnostic that breaks Arch Linux daemon builds.

Enhancements:

• Document why the guarded event-buffer copy is safe and limit warning suppression to that specific operation.

[deepin-ci-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

The PR fixes Arch/GCC 15–16 build failures by locally suppressing an array-bounds false positive caused by GCC’s inability to connect QByteArray::size() with constData(), while retaining the existing size guard and unchanged safe memcpy behavior.

Flow diagram for guarded event-buffer header copy

flowchart TD
    A[m_eventBuffer.append] --> B{m_eventBuffer.size >= sizeof ControlHeader}
    B -- No --> C[Exit loop]
    B -- Yes --> D[QT_WARNING_PUSH]
    D --> E[QT_WARNING_DISABLE_GCC -Warray-bounds]
    E --> F[memcpy from m_eventBuffer.constData to header]
    F --> G[QT_WARNING_POP]
    G --> H[Process ControlHeader]
    H --> B

Loading

File-Level Changes

Change	Details	Files
Narrowly suppress GCC’s false-positive array-bounds diagnostic for the validated event-header copy.	Document that the loop guard guarantees enough buffered bytes for the copy. Wrap only the affected memcpy with QT_WARNING_PUSH, QT_WARNING_DISABLE_GCC("-Warray-bounds"), and QT_WARNING_POP. Keep the suppression GCC-specific and preserve existing runtime behavior, protocol handling, and byte order.	src/daemon/DdeSeatdControl.cpp

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[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: deepin-wm, zccrs

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