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Details

Type: Bug
Resolution: Fixed
Priority: P2: Important
Fix Version/s: 6.5.2, 6.7.0 FF
Affects Version/s: 6.3.2, 6.5.0
Component/s: Build System: CMake
Labels:
- Reported_by_support_1H23
- Reported_by_support_standard
Environment:
Windows 10
Visual Studio 2019 16.11.19
MSVC 19.29.30146
CMake version 3.24.2
Ninja 1.11.1

Platform/s:

Windows
Commits:
e0ec19de4 (dev), 99aeb7594 (6.5), 470fee321 (dev), 1e303cdbd (6.6), a945c542d (6.5), b6f777824 (tqtc/lts-6.2), ec5fee55e (6.5.2)

Description

Hi,

I was trying out the new qt_add_qml_module CMake-macro that came with Qt 6.2 to create reusable QML modules.

In Visual Studio I noticed that it will always re-build rcc files even when nothing has changed.

I used the following example project https://gitlab.com/kelteseth/qt6-cmake-qml-plugin-example-project and QT 6.3.2 via vcpkg.

After a full project build and without changing any source files, the rcc-generated files still always get recompiled when MSBuild gets invoked:

1>------ Build started: Project: DownloadManager_qmlcache_autogen, Configuration: Debug x64 ------
2>------ Build started: Project: DownloadManagerplugin_init_autogen, Configuration: Debug x64 ------
3>------ Build started: Project: TestProject_qmlimportscan, Configuration: Debug x64 ------
4>------ Build started: Project: DownloadManager_autogen, Configuration: Debug x64 ------
1>Automatic MOC for target DownloadManager_qmlcache
2>Automatic MOC for target DownloadManagerplugin_init
4>Automatic MOC for target DownloadManager
5>------ Build started: Project: DownloadManager_automoc_json_extraction, Configuration: Debug x64 ------
5>Running AUTOMOC file extraction for target DownloadManager
6>------ Build started: Project: DownloadManager, Configuration: Debug x64 ------
6>Running moc --collect-json for target DownloadManager
6>Automatic QML type registration for target DownloadManager
6>Generating .rcc/qmlcache/DownloadManager_DownloadManager/TestMain_qml.cpp
6>Generating .rcc/qmlcache/DownloadManager_DownloadManager/DownloadManagerControls_qml.cpp
6>DownloadManagerControls_qml.cpp
6>TestMain_qml.cpp
6>downloadmanager_qmltyperegistrations.cpp
6>DownloadManager.vcxproj -> F:\Temp\testbuild\Debug\DownloadManager.lib
7>------ Build started: Project: TestProject, Configuration: Debug x64 ------
7>Automatic MOC for target TestProject
7>TestProject.vcxproj -> F:\Temp\testbuild\Debug\TestProject.exe
========== Build: 7 succeeded, 0 failed, 7 up-to-date, 0 skipped ==========

Even with only two QML-resources, the build already takes more than 4 seconds every time. The Visual Studio re-build times on larger projects with more resources would be horribly slow.

Through the verbose MSBuild output I figured out that the source of the resource-build being triggered lies in the _automoc_json_extraction Utility-target. It gets re-generated every time because the output file mentioned in the custom build step is never created:

<ItemGroup>
    <CustomBuild Include="F:\Temp\testbuild\CMakeFiles\da9815ec55e86dcf9777446cf05e6423\DownloadManager_automoc_json_extraction.rule">
      <Message Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">Running AUTOMOC file extraction for target DownloadManager</Message>
      <Command Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">setlocal
G:\vcpkg\installed\x64-windows\tools\Qt6\bin\cmake_automoc_parser.exe --cmake-autogen-cache-file F:/Temp/testbuild/CMakeFiles/DownloadManager_autogen.dir/ParseCache_Debug.txt --cmake-autogen-info-file F:/Temp/testbuild/CMakeFiles/DownloadManager_autogen.dir/AutogenInfo.json --output-file-path F:/Temp/testbuild/meta_types/DownloadManager_json_file_list.txt --timestamp-file-path F:/Temp/testbuild/meta_types/DownloadManager_json_file_list.txt.timestamp --cmake-autogen-include-dir-path F:/Temp/testbuild/DownloadManager_autogen/include_Debug --cmake-multi-config
if %errorlevel% neq 0 goto :cmEnd
:cmEnd
endlocal &amp; call :cmErrorLevel %errorlevel% &amp; goto :cmDone
:cmErrorLevel
exit /b %1
:cmDone
if %errorlevel% neq 0 goto :VCEnd</Command>
      <AdditionalInputs Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">G:\vcpkg\installed\x64-windows\tools\Qt6\bin\cmake_automoc_parser.exe;%(AdditionalInputs)</AdditionalInputs>
      <Outputs Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">F:\Temp\testbuild\CMakeFiles\DownloadManager_automoc_json_extraction</Outputs>
      <LinkObjects Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">false</LinkObjects>
      <VerifyInputsAndOutputsExist Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">false</VerifyInputsAndOutputsExist>

If i manually create the file "F:\Temp\testbuild\CMakeFiles\DownloadManager_automoc_json_extraction" the target is not re-built, but consequentially actual re-builds may not get triggered when necessary.

When using Ninja as the CMake generator, everything behaves as expected and no files are re-built without changes. Thus, this seems to be an issue that specifically affects only the Visual Studio CMake generators.