CMake: Add a global QT_QML_NO_CACHEGEN cmake variable

A new QT_QML_NO_CACHEGEN cmake variable can be set to disable
compilation of qml files into bytecode or C++ code.

The variable can be set either in a specific directory scope or in
the root of the project (to disable qml compilation for all targets).

This is just a more global version of the NO_CACHEGEN option that can
be passed to qt6_add_qml_module.

For projects with many qml files, this reduces the build time,
allowing faster development iteration times.
It is more convenient than passing NO_CACHEGEN to each created
qml module.

[ChangeLog][Build System] A new QT_QML_NO_CACHEGEN cmake variable can
be set to disable compilation of qml files for all project qml files.

Task-number: QTBUG-125631
Task-number: QTBUG-126205
Task-number: QTBUG-128323
Change-Id: I963c14ad0d07bf1f6d6205afdd0a8a90e73f025d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
(cherry picked from commit 69254dfc91c19e3005968a46bc6dbf7d8197712d)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 40 insertions, 1 deletions

diff --git a/src/qml/Qt6QmlMacros.cmake b/src/qml/Qt6QmlMacros.cmake
index f1c5b0c3ee..aa50da4324 100644
--- a/src/qml/Qt6QmlMacros.cmake
+++ b/src/qml/Qt6QmlMacros.cmake
@@ -332,6 +332,10 @@ function(qt6_add_qml_module target)
         )
     endif()
 
+    if(QT_QML_NO_CACHEGEN)
+        set(arg_NO_CACHEGEN TRUE)
+    endif()
+
     # Other arguments and checking for invalid combinations
     if (NOT arg_TARGET_PATH)
         # NOTE: This will always be used for copying things to the build
@@ -2758,7 +2762,7 @@ function(qt6_target_qml_sources target)
     if(arg_NO_LINT)
         set(no_lint TRUE)
     endif()
-    if(arg_NO_CACHEGEN)
+    if(arg_NO_CACHEGEN OR QT_QML_NO_CACHEGEN)
         set(no_cachegen TRUE)
     endif()
     if(no_qmldir MATCHES "NOTFOUND" OR arg_NO_QMLDIR_TYPES)
diff --git a/src/qml/doc/src/cmake/cmake-variables.qdoc b/src/qml/doc/src/cmake/cmake-variables.qdoc
index de984c88ef..7b5547a1ac 100644
--- a/src/qml/doc/src/cmake/cmake-variables.qdoc
+++ b/src/qml/doc/src/cmake/cmake-variables.qdoc
@@ -73,4 +73,39 @@ subdirectories} that define QML Modules.
 
 */
 
+/*!
+\page cmake-variable-qt-qml-no-cachegen.html
+\ingroup cmake-variables-qtqml
+
+\title QT_QML_NO_CACHEGEN
+
+\brief Disables compilation of QML files into bytecode or C++ code.
+\cmakevariablesince 6.8.1
+
+\c QT_QML_NO_CACHEGEN is a CMake variable that can be set to disable the compilation of QML files
+into bytecode or C++ code for QML targets created by
+\l{qt6_add_qml_module}{qt6_add_qml_module()}.
+
+It has the same effect as setting the \c{NO_CACHEGEN} option of
+\l{qt6_add_qml_module}{qt6_add_qml_module()}, but allows doing so on a per-directory or project
+basis.
+
+Turn on this option to reduce the number of build steps necessary to complete a build, and
+thereby shorten the develop-debug iteration cycle.
+
+To minimize application size, turn off this option, and instead use
+\l{QT_DISCARD_FILE_CONTENTS}{QT_DISCARD_FILE_CONTENTS} to remove the QML files embedded into the
+resource system.
+
+The variable can be set in the project's CMakeLists.txt as follows:
+\badcode
+set(QT_QML_NO_CACHEGEN TRUE)
+qt_add_qml_module(MyModule
+    URI MyModule
+    VERSION 1.0
+    ...
+)
+\endcode
+
+*/