The upstream emsdk / emscripten cmake toolchain file sets the CMake global property TARGET_SUPPORTS_SHARED_LIBS to FALSE, claiming that creation of true shared libraries is not supported. See the following comment: https://github.com/emscripten-core/emscripten/pull/8362#issuecomment-3050586255 Despite that, Qt for a while now set the global property to TRUE both when building Qt and user projects, and things mostly worked. This was done in QtWasmHelpers.cmake for shared lib Qt builds. And in Qt6CoreConfigExtras.cmake.in for user projects in both shared or static qt builds (which actually affects repos other than qtbase as well). Starting with CMake 3.30, which introduced policy CMP0164, if it's set to NEW, and TARGET_SUPPORTS_SHARED_LIBS is FALSE, CMake will refuse to create shared library targets (even IMPORTED ones) with an error like: CMake Error at lib/cmake/Qt6Core/Qt6CoreTargets.cmake:50 (add_library): ADD_LIBRARY called with SHARED option but the target platform does not support dynamic linking. Call Stack (most recent call first): lib/cmake/Qt6Core/Qt6CoreConfig.cmake:57 (include) lib/cmake/Qt6/Qt6Config.cmake:240 (find_package) CMakeLists.txt:7 (find_package) This usually popped up when configuring a user project or a qt repo other than qtbase, when Qt is built with CMake 3.30. That's because the auto-generated *Targets.cmake always enables all policies up to the version of the used CMake version, with a command like cmake_policy(VERSION 2.8.3...3.31) The Qt6CoreConfigExtras.cmake file is included after the Targets file, so its setting of TARGET_SUPPORTS_SHARED_LIBS to TRUE is too late. To avoid this error, introduce a new _qt_internal_handle_target_supports_shared_libs helper function that sets TARGET_SUPPORTS_SHARED_LIBS to TRUE in Qt6ConfigExtras.cmake. This will be executed before any imported target creation in Qt*Targets.cmake files. Because Qt6ConfigExtras.cmake is not loaded during the initial configuration of the qtbase build, also replace the call in QtWasmHelpers.cmake. Make it consistent and call the function regardless of a shared or static Qt build. Allow opting out of the TARGET_SUPPORTS_SHARED_LIBS assignment by passing -DQT_NO_ENABLE_TARGET_SUPPORTS_SHARED_LIBS=ON. Incidentally, CMake 4.2 is introducing it's own support for Emscripten, and will set TARGET_SUPPORTS_SHARED_LIBS to TRUE if it detects that the emsdk toolchain file is not loaded. Pick-to: 6.8 6.9 6.10 Task-number: QTBUG-140211 Change-Id: I9313476abd885bcbe60309e62fe1d6ae568769e8 Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io> Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>