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/*!
\page qt_add_qml_module.html
\ingroup cmake-commands-qtqml

\title qt_add_qml_module
\target qt6_add_qml_module

\brief Defines a QML module.

\cmakecommandsince 6.2

\section1 Synopsis

\badcode
qt_add_qml_module(
    target
    URI uri
    VERSION version
    [PAST_MAJOR_VERSIONS ...]
    [STATIC | SHARED]
    [PLUGIN_TARGET plugin_target]
    [OUTPUT_DIRECTORY output_dir]
    [RESOURCE_PREFIX resource_prefix]
    [CLASS_NAME class_name]
    [TYPEINFO typeinfo]
    [IMPORTS ...]
    [OPTIONAL_IMPORTS ...]
    [DEPENDENCIES ...]
    [IMPORT_PATH ...]
    [SOURCES ...]
    [QML_FILES ...]
    [RESOURCES ...]
    [OUTPUT_TARGETS out_targets_var]
    [DESIGNER_SUPPORTED]
    [FOLLOW_FOREIGN_VERSIONING]
    [NO_PLUGIN_OPTIONAL]
    [NO_CREATE_PLUGIN_TARGET]
    [NO_GENERATE_PLUGIN_SOURCE]
    [NO_GENERATE_QMLTYPES]
    [NO_GENERATE_QMLDIR]
    [NO_LINT]
    [NO_CACHEGEN]
    [NO_RESOURCE_TARGET_PATH]
    [NO_IMPORT_SCAN]
)

\endcode

\versionlessCMakeCommandsNote qt6_add_qml_module()

\section1 Description

This command defines a QML module that can consist of C++ sources, \c{.qml}
files, or both. It ensures that essential module details are provided and that
they are consistent. It also sets up and coordinates things like cached
compilation of \c{.qml} sources, resource embedding, linting checks, and
auto-generation of some key module files.

\section2 Target Structure

A QML module can be structured in a few different ways. The following scenarios
are the typical arrangements:

\section3 Separate backing and plugin targets

This is the recommended arrangement for most QML modules. All of the module's
functionality is implemented in the \e backing target, which is given as the
first command argument. C++ sources, \c{.qml} files, and resources should all
be added to the backing target. The backing target is a library that should be
installed in the same location as any other library defined by the project.

The source directory structure under which the backing target is created should
match the target path of the QML module (the target path is the module's URI
with dots replaced by forward slashes). If the source directory structure
doesn't match the target path, \c{qt_add_qml_module()} will issue a warning.

The following example shows a suitable source directory structure for a QML
module with a URI of \c{MyThings.Panels}. The call to \c{qt_add_qml_module()}
would be in the \c{CMakeLists.txt} file shown.

\badcode
src
 +-- MyThings
      +-- Panels
           +-- CMakeLists.txt
\endcode

A separate \e plugin target is associated with the QML module. It is used at
runtime to load the module dynamically when the application doesn't already
link to the backing target. The plugin target will also be a library and is
normally installed to the same directory as the module's
\l{Module Definition qmldir Files}{qmldir} file.

The plugin target should ideally contain nothing more than a trivial
implementation of the plugin class. This allows the plugin to be designated as
optional in the \c qmldir file. Other targets can then link directly to the
backing target and the plugin will not be needed at runtime, which can improve
load-time performance. By default, a C++ source file that defines a minimal
plugin class will be automatically generated and added to the plugin target.
For cases where the QML module needs a custom plugin class implementation, the
\l{NO_GENERATE_PLUGIN_SOURCE} and usually the \l{NO_PLUGIN_OPTIONAL} options
will be needed.

\section3 Plugin target with no backing target

A QML module can be defined with the plugin target serving as its own backing
target. In this case, the module must be loaded dynamically at runtime and
cannot be linked to directly by other targets. To create this arrangement,
the \c PLUGIN_TARGET keyword must be used, with the \c target repeated as the
plugin target name. For example:

\badcode
qt_add_qml_module(someTarget
    PLUGIN_TARGET someTarget
    ...
)
\endcode

While this arrangement may seem marginally simpler to deploy, a separate
backing target should be preferred where possible due to the potentially better
load-time performance.

\section3 Executable as a QML module

An executable target can act as a backing target for a QML module. In this case,
there will be no plugin library, since the QML module will always be loaded
directly as part of the application. The \c{qt_add_qml_module()} command will
detect when an executable is used as the backing target and will automatically
disable the creation of a separate plugin. Do not use any of the options with
\c{PLUGIN} in their name when using this arrangement.

When an executable is used as the backing target, the source directory structure
is not expected to match the QML module's target path.
See \l{qmlcachegen-auto}{Caching compiled QML sources} for additional target
path differences for compiled-in resources.


\target qmldir-autogeneration
\section2 Auto-generating \c{qmldir} and typeinfo files

By default, a \l{Module Definition qmldir Files}{qmldir} file and a typeinfo
file will be auto-generated for the QML module being defined. The contents of
those files are determined by the various arguments given to this command, as
well as the sources and \c{.qml} files added to the backing target.
The \l OUTPUT_DIRECTORY argument determines where the \c qmldir and typeinfo
files will be written to. If the QML module has a plugin, that plugin will also
be created in the same directory as the \c qmldir file.

If using a statically built Qt, the backing target's \c{.qml} files will be
scanned during the CMake configure run to determine the imports used by the
module and to set up linking relationships (the \c{NO_IMPORT_SCAN} keyword
can be given to disable this). When a \c{.qml} file is added to or
removed from the module, CMake will normally re-run automatically and the
relevant files will be re-scanned, since a \c{CMakeLists.txt} file will have
been modified. During the course of development, an existing \c{.qml} file may
add or remove an import or a type. On its own, this would not cause CMake to
re-run automatically, so you should explicitly re-run CMake to force the
\c qmldir file to be regenerated and any linking relationships to be updated.

The backing target's C++ sources are scanned at build time to generate a
typeinfo file and a C++ file to register the associated types. The generated
C++ file is automatically added to the backing target as a source.
This requires \c AUTOMOC to be enabled on the target. The project is
responsible for ensuring this, usually by setting the \c CMAKE_AUTOMOC variable
to \c TRUE before calling \c qt_add_qml_module(), or by passing in an existing
target with the \c AUTOMOC target property already set to \c TRUE. It isn't an
error to have \c AUTOMOC disabled on the target, but the project is then
responsible for handling the consequences. This may include having to manually
generate the typeinfo file instead of allowing it to be auto-generated with
missing details, and adding C++ code to register the types.

Projects should prefer to use the auto-generated typeinfo and \c qmldir files
where possible. They are easier to maintain and they don't suffer from the same
susceptibility to errors that hand-written files do. Nevertheless, for
situations where the project needs to provide these files itself, the
auto-generation can be disabled. The \c NO_GENERATE_QMLDIR option disables the
\c qmldir auto-generation and the \c NO_GENERATE_QMLTYPES option disables the
typeinfo and C++ type registration auto-generation. If the auto-generated
typeinfo file is acceptable, but the project wants to use a different name for
that file, it can override the default name with the \c TYPEINFO option (but
this should not typically be needed).

\target qmlcachegen-auto
\section2 Caching compiled QML sources

All \c{.qml}, \c{.js}, and \c{.mjs} files added to the module via the
\c QML_FILES argument will be compiled to bytecode and cached directly in the
backing target. This improves load-time performance of the module. The original
uncompiled files are also stored in the backing target's resources, as these
may still be needed in certain situations by the QML engine.

The resource path of each file is determined by its path relative to the
current source directory (\c CMAKE_CURRENT_SOURCE_DIR). This resource path is
appended to a prefix formed by concatenating the \l{RESOURCE_PREFIX} and
the target path (but see \l NO_RESOURCE_TARGET_PATH for an exception to this).
Ordinarily, the project should aim to place \c{.qml} files in
the same relative location as they would have in the resources. If the \c{.qml}
file is in a different relative directory to its desired resource path, its
location in the resources needs to be explicitly specified. This is done by
setting the \c QT_RESOURCE_ALIAS source file property, which must be set before
the \c{.qml} file is added. For example:

\badcode
set_source_files_properties(path/to/somewhere/MyFrame.qml PROPERTIES
    QT_RESOURCE_ALIAS MyFrame.qml
)

qt_add_qml_module(someTarget
    URI MyCo.Frames
    RESOURCE_PREFIX /my.company.com/imports
    QML_FILES
        path/to/somewhere/MyFrame.qml
        AnotherFrame.qml
)
\endcode

In the above example, the target path will be \c{MyCo/Frames}. After
taking into account the source file properties, the two \c{.qml} files will be
found at the following resource paths:

\list
\li \c{/my.company.com/imports/MyCo/Frames/MyFrame.qml}
\li \c{/my.company.com/imports/MyCo/Frames/AnotherFrame.qml}
\endlist

In the rare case that you want to override the automatic selection of the
qmlcachegen program to be used, you may set the \c QT_QMLCACHEGEN_EXECUTABLE
target property on the module target. For example:

\badcode
set_target_properties(someTarget PROPERTIES
    QT_QMLCACHEGEN_EXECUTABLE qmlcachegen
)
\endcode

This explicitly selects qmlcachegen as the program to be used, even if
better alternatives are available.

Furthermore, you can pass extra arguments to qmlcachegen, by setting the
\c QT_QMLCACHEGEN_ARGUMENTS option. In particular, the \c --only-bytecode
option will turn off compilation of QML script code to C++. For example:

\badcode
set_target_properties(someTarget PROPERTIES
    QT_QMLCACHEGEN_ARGUMENTS "--only-bytecode"
)
\endcode

\target qmllint-auto
\section2 Linting QML sources

A separate linting target will be automatically created if any \c{.qml} files
are added to the module via the \c QML_FILES keyword, or by a later call to
\l{qt6_target_qml_sources}{qt_target_qml_sources()}. The name of the linting
target will be the \c target followed by \c{_qmllint}. An \c{all_qmllint}
target which depends on all the individual \c{*_qmllint} targets is also
provided as a convenience.

\target qml-cmake-singletons
\section2 Singletons

If a QML module has \c{.qml} files which provide singleton types, these files
need to have their \c QT_QML_SINGLETON_TYPE source property set to \c TRUE, to
ensure that the \c singleton command is written into the
\l{Module Definition qmldir Files}{qmldir} file. This must be done in addition
to the QML file containing the \c {pragma Singleton} statement.

See \l{qt_target_qml_sources_example}{qt_target_qml_sources()} for an example on
how to set the \c QT_QML_SINGLETON_TYPE property.

\section1 Arguments

The \c target specifies the name of the backing target for the QML module.
By default, it is created as a shared library if Qt was built as shared
libraries, or as a static library otherwise. This choice can be explicitly
overridden with the \c STATIC or \c SHARED options.

The plugin target associated with the QML module can be specified using the
\c PLUGIN_TARGET argument. The \c PLUGIN_TARGET can be the same as the backing
\c target, in which case there will be no separate backing target.
If \c PLUGIN_TARGET is not given, it defaults to \c target with \c plugin
appended. For example, a backing target called \c mymodule would have a default
plugin name of \c mymoduleplugin. The plugin target's name will be used to
populate a \c{plugin} line in the generated
\l{Module Definition qmldir Files}{qmldir} file. Therefore, you must not try to
change the plugin's output name by setting target properties like
\c OUTPUT_NAME or any of its related properties.

The backing \c target and the plugin target (if different) will be created by
the command, unless they already exist. Projects should generally let them be
created by the command so that they are created as the appropriate target type.
If the backing \c target is a static library, the plugin will also be created
as a static library. If the backing \c target is a shared library, the plugin
will be created as a module library. If an existing \c target is passed in and
it is an executable target, there will be no plugin. If you intend to always
link directly to the backing target and do not need a plugin, it can be
disabled by adding the \c NO_PLUGIN option. Specifying both \c NO_PLUGIN and
\c PLUGIN_TARGET is an error.

In certain situations, the project may want to delay creating the plugin target
until after the call. The \c NO_CREATE_PLUGIN_TARGET option can be given in
that situation. The project is then expected to call
\l{qt6_add_qml_plugin}{qt_add_qml_plugin()} on the plugin target once it has
been created. When  \c NO_CREATE_PLUGIN_TARGET is given, \c PLUGIN_TARGET must
also be provided to explicitly name the plugin target.

Every QML module must define a \c URI. It should be specified in dotted URI
notation, such as \c{QtQuick.Layouts}. It must not contain anything other than
alphanumeric or dot characters. Other QML modules may use this name in
\l{qtqml-syntax-imports.html}{import statements} to import the module. The
\c URI will be used in the \c module line of the generated
\l{Module Definition qmldir Files}{qmldir} file. The \c URI is also used to
form the \e{target path} by replacing dots with forward slashes.

A QML module must also define a \c VERSION in the form \c{Major.Minor}, where
both \c Major and \c Minor must be integers. An additional \c{.Patch}
component may be appended, but will be ignored. A list of earlier major
versions the module provides types for can also optionally be given after the
\c PAST_MAJOR_VERSIONS keyword (see below).
See \l{qtqml-modules-identifiedmodules.html}{Identified Modules} for further
in-depth discussion of the module URI and version numbering.

A list of additional major versions the module provides may be given using the
\c PAST_MAJOR_VERSIONS keyword. For each of those versions and each QML file
without a \c QT_QML_SOURCE_VERSIONS setting an additional entry in the
\l{Module Definition qmldir Files}{qmldir} file will be generated to specify
the extra version. Furthermore, the generated module registration code will
register the past major versions using \l{qmlRegisterModule()} on the C++ side.
The module registration code is automatically generated for your QML module,
unless you specify \c{NO_GENERATE_QMLTYPES} (but use of this option is strongly
discouraged). Usage of \c PAST_MAJOR_VERSIONS adds some overhead when your
module is imported. You should increment the major version of your module as
rarely as possible. Once you can rely on all QML files importing this module to
omit the version in their imports, you can safely omit \c{PAST_MAJOR_VERSIONS}.
All the QML files will then import the latest version of your module. If you
have to support versioned imports, consider supporting only a limited number of
past major versions.

\target RESOURCE_PREFIX
\c RESOURCE_PREFIX is intended to encapsulate a namespace for the project and
will often be the same for all QML modules that the project defines. It should
be chosen to avoid clashing with the resource prefix of anything else used by
the project or likely to be used by any other project that might consume it.
A good choice is to incorporate the domain name of the organization the project
belongs to. A common convention is to append \c{/imports} to the domain name to
form the resource prefix. For example:

\badcode
qt_add_qml_module(someTarget
    RESOURCE_PREFIX /my.company.com/imports
    ...
)
\endcode

\target NO_RESOURCE_TARGET_PATH
When various files are added to the compiled-in resources, they are placed
under a path formed by concatenating the \c RESOURCE_PREFIX and the target path.
For the special case where the backing target is an executable, it may be
desirable to place the module's \c{.qml} files and other resources directly
under the \c RESOURCE_PREFIX instead. This can be achieved by specifying the
\c NO_RESOURCE_TARGET_PATH option, which may only be used if the backing target
is an executable.

\target OUTPUT_DIRECTORY
\c OUTPUT_DIRECTORY specifies where the plugin library, \c qmldir and typeinfo
files are generated. When this keyword is not given, the default value will be
the target path (formed from the \c URI) appended to the value of the
\l QT_QML_OUTPUT_DIRECTORY variable.
If that variable is not defined, the default depends on the type of backing
target. For executables, the value will be the target path appended to
\c{${CMAKE_CURRENT_BINARY_DIR}}, whereas for other targets it will be just
\c{${CMAKE_CURRENT_BINARY_DIR}}. When the structure of the source tree
matches the structure of QML module target paths (which is highly recommended),
\l QT_QML_OUTPUT_DIRECTORY often isn't needed. In order to match the structure
of the target paths, you have to call your directories \e exactly like the
segments of your module URI. For example, if your module URI is
\c{MyUpperCaseThing.mylowercasething}, you need to put this in a directory
called \c{MyUpperCaseThing/mylowercasething/}.

The need for specifying the \c OUTPUT_DIRECTORY keyword should be rare, but if
it is used, it is likely that the caller will also need to add to the
\l IMPORT_PATH to ensure that \l{qmllint-auto}{linting},
\l{qmlcachegen-auto}{cached compilation} of qml sources,
\l{qt6_import_qml_plugins}{automatic importing} of plugins in static builds,
and \l{qt_deploy_qml_imports}{deploying imported QML modules} for non-static
builds all work correctly.

\target NO_GENERATE_PLUGIN_SOURCE
By default, \c{qt_add_qml_module()} will auto-generate a \c{.cpp} file that
implements the plugin class named by the \c CLASS_NAME argument. The generated
\c{.cpp} file will be automatically added to the plugin target as a source file
to be compiled. If the project wants to provide its own implementation of the
plugin class, the \c NO_GENERATE_PLUGIN_SOURCE option should be given. Where no
\c CLASS_NAME is provided, it defaults to the \c URI with dots replaced by
underscores, then \c Plugin appended. Unless the QML module has no plugin, the
class name will be recorded as a \c classname line in the generated
\l{Module Definition qmldir Files}{qmldir} file.

\target NO_PLUGIN_OPTIONAL
If the \c NO_PLUGIN_OPTIONAL keyword is given, then the plugin is recorded in
the generated \c qmldir file as non-optional. If all of a QML module's
functionality is implemented in its backing target and the plugin target is
separate, then the plugin can be optional, which is the default and recommended
arrangement. The auto-generated plugin source file satisfies this requirement.
Where a project provides its own \c{.cpp} implementation for the plugin, that
would normally mean the \c NO_PLUGIN_OPTIONAL keyword is also needed because
the plugin will almost certainly contain functionality that the QML module
requires.

Type registration is automatically performed for the backing target's C++
sources that are processed by AUTOMOC. This will generate a typeinfo file in the
\l{OUTPUT_DIRECTORY}{output directory}, the file name being the \c target name
with \c{.qmltypes} appended. This file name can be changed using the
\c TYPEINFO option if desired, but this should not normally be necessary.
The file name is also recorded as a \c typeinfo entry in the generated
\l{Module Definition qmldir Files}{qmldir} file. Automatic type registration
can be disabled using the \c NO_GENERATE_QMLTYPES option, in which case no
typeinfo file will be generated, but the project will still be expected to
generate a typeinfo file and place it in the same directory as the generated
\c qmldir file.

\c IMPORTS provides a list of other QML modules that this module imports. Each
module listed here will be added as an \c{import} entry in the generated
\l{Module Definition qmldir Files}{qmldir} file. If a QML file imports the
this module, it also imports all the modules listed under \c{IMPORTS}.
Optionally, a version can be specified by appending it after a slash, such as
\c{QtQuick/2.0}. Omitting the version will cause the greatest version available
to be imported. You may only specify the major version, as in \c{QtQuick/2}. In
that case the greatest minor version available with the given major version will
be imported. Finally, \c{auto} may be given as version (\c{QtQuick/auto}). If
\c{auto} is given, the version that the current module is being imported with is
propagated to the module to be imported. Given an entry \c{QtQuick/auto} in a
module \c{YourModule}, if a QML file specifies \c{import YourModule 3.14}, this
results in importing  version \c{3.14} of \c{QtQuick}. For related modules that
follow a common versioning scheme, you should use \c{auto}.

\c OPTIONAL_IMPORTS provides a list of other QML modules that this module
\e may import at run-time. These are not automatically imported by the QML
engine when importing the current module, but rather serve as hints to tools
like \c qmllint. Versions can be specified in the same way as for \c IMPORTS.
Each module listed here will be added as an \c{optional import} entry in the
generated \l{Module Definition qmldir Files}{qmldir} file.

\c DEPENDENCIES provides a list of other QML modules that this module depends
on, but doesn't necessarily import. It would typically be used for dependencies
that only exist at the C++ level, such as a module registering a class to QML
which is a subclass of one defined in another module. The module version of the
dependencies must be specified along with the module name, in the same form as
used for \c IMPORTS and \c OPTIONAL_IMPORTS. Each module listed here will be
added as a \c{depends} entry in the generated
\l{Module Definition qmldir Files}{qmldir} file.

\target IMPORT_PATH
\c IMPORT_PATH can be used to add to the search paths where other QML modules
that this one depends on can be found. The other modules must have their
\c qmldir file under their own target path below one of the search paths.

\c SOURCES specifies a list of non-QML sources to be added to the backing
target. It is provided as a convenience and is equivalent to adding the sources
to the backing target with the built-in \c{target_sources()} CMake command.

\c QML_FILES lists the \c{.qml}, \c{.js} and \c{.mjs} files for the module.
These will be automatically \l{qmlcachegen-auto}{compiled into bytecode} and
embedded in the backing target unless the \c NO_CACHEGEN option is given.
The uncompiled file is always stored in the embedded resources of the backing
target, even if \c NO_CACHEGEN is specified. Unless the \c NO_LINT option is
given, the uncompiled files will also be
\l{Linting QML sources}{processed by \c qmllint} via a separate custom build
target. The files will also be used to populate type information in the
generated \l{Module Definition qmldir Files}{qmldir} file.
See \l{qt6_target_qml_sources}{qt_target_qml_sources()} for further details on
the source file properties that can be set on these files or if files need to
be added to the backing target after this command has been called.

\c RESOURCES lists any other files needed by the module, such as images
referenced from the QML code. These files will be added as compiled-in
resources (see \l RESOURCE_PREFIX for an explanation of the base point they
will be located under). If needed, their relative location can
be controlled by setting the \c QT_RESOURCE_ALIAS source property, just as for
\c{.qml} files (see \l{qmlcachegen-auto}{Caching compiled QML sources}).

\c NO_GENERATE_QMLDIR can be given to disable the automatic generation of the
\c qmldir file. This should normally be avoided, but for cases where the
project needs to provide its own \c qmldir file, this option can be used.

If the backing target is a static library and that static library will be
installed, \c OUTPUT_TARGETS should be given to provide a variable in which to
store a list of additional targets that will also need to be installed.
These additional targets are generated internally by \c{qt_add_qml_module()}
and are referenced by the backing target's linking requirements as part of
ensuring that resources are set up and loaded correctly.

The \c DESIGNER_SUPPORTED keyword should be given if the QML module supports
Qt Quick Designer. When present, the generated \c qmldir file will contain
a \c designersupported line. See \l{Module Definition qmldir Files} for how
this affects the way Qt Quick Designer handles the plugin.

The \c FOLLOW_FOREIGN_VERSIONING keyword relates to base types of your own
C++-defined QML types that live in different QML modules. Typically, the
versioning scheme of your module does not match that of the module providing
the base types. Therefore, by default all revisions of the base types are
made available in any import of your module. If \c FOLLOW_FOREIGN_VERSIONING
is given, the version information attached to the base types and their
properties is respected. So, an \c {import MyModule 2.8} will then only make
available versioned properties up to version \c{2.8} of any base types outside
\c{MyModule}.
This is mostly useful if you want to keep your module version in sync
with other modules you're basing types on. In that case you might want your custom
types to not expose properties from a module's base type version greater than the one being
imported.

For static Qt builds, \c{qmlimportscanner} is run at configure time to scan the
\c{.qml} files of a QML module and identify the QML imports it uses (see
\l{qt6_import_qml_plugins}{qt_import_qml_plugins()}). For non-static Qt builds,
if the target is an executable, a similar scan is performed at build time
to provide the information needed by deployment scripts (see
\l{qt_deploy_qml_imports()}). Both scans can be disabled by providing the
\c{NO_IMPORT_SCAN} option. Doing so means the project takes on the
responsibility of ensuring all required plugins are instantiated and linked for
static builds. For non-static builds the project must manually work out
and deploy all QML modules used by an executable target.
*/
