- Convert the opt-in for qml.req to an opt-out OBS-URL: https://build.opensuse.org/request/show/867108 OBS-URL: https://build.opensuse.org/package/show/KDE:Qt5/qml-autoreqprov?expand=0&rev=5
172 lines
8.5 KiB
Plaintext
172 lines
8.5 KiB
Plaintext
qml-autoreqprov - Automatic generation of Provides and Requires for QML imports
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======
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QML is a user interface specification and programming language. Each QML file
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can have import statements at the top, which can either reference files or
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directories directly or modules by identifier and version (major.minor).
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If any of those import statements can't be satisfied, loading fails. For imports
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which are provided by other packages, this maps naturally to Requires statements
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in RPM packages, which enforce that all imports are satisfied on package
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installation.
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Direct file/directory imports are ignored here, as those are usually contained
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within a single package and thus not relevant for inter-package dependencies.
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TLDR for packagers
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------------------
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Packages with system-wide QML modules get Provides like
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`qt5qmlimport(QtQuick.Controls.2) = 15` automatically. Imports in .qml files
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map to RPM requires like `qt5qmlimport(QtQuick.Controls.2) >= 15`. This can be
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disabled with `%global %_disable_qml_requires 1` in .spec files. It's important
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to check that all dependendencies are fulfilled, as in some cases a needed
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`qmlimport` Provides is missing. See the "Internal and private exports" section
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for how to deal with that.
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How the QML engine imports modules
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----------------------------------
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For each module import, the QML engine looks into the import cache to find any
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suitable export with identical identifier and major version and same/higher
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minor version. If there is no match, it goes through the QML import path (with
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a system-wide default) in order with the module identifier and version appended
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in various ways and reads the qmldir file inside. If the qmldir file mentions
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plugins, those are loaded and it can register the exported types. If the import
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can't be satisfied (due to a version mismatch), the search continues.
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Mapping to RPM capabilities
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---------------------------
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The goal is that all imports for .qml files within a package are satisfied by
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RPM dependencies of that package. This is achieved by adding Provides to
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packages which satisfy a specific module import and Requires to the packages
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with QML files inside. The capability has to include both the full module
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identifier and version. As modules with a different major version are pretty
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much independent, the major version is part of the capabilities' name and the
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minor version is used as the capabilities' version. Additionally, the system
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import paths are specific to a Qt major version, this is also included. The end
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result are QML modules providing capabilities like:
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`Provides: qt5qmlimport(QtQuick.Controls.2) = 15`
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On the import side, packages with QML files get requirements like:
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`Requires: qt5qmlimport(QtQuick.Controls.2) >= 13`
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for a statement like `import QtQuick.Controls 2.13`. The `>=` is there so that
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modules with a higher minor version satisfy it as well.
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Generating Requires from .qml files
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-----------------------------------
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As can be seen, mapping QML import statements to RPM requires is
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straightforward, and even made easier by using the `qmlimportscanner` tool from
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qtdeclarative combined with `jq` to convert its JSON output with some filtering
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directly into the capabilities format for RPM.
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There is one tricky part though: QML files are (intentionally) not tied to any
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specific version of Qt, while QML modules are (though the Qt version specific
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import paths and binary plugins). So when generating the list of required
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imports, those are tied to a specific Qt major version. Currently this is
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automatically detected by looking at which versions of qmlimportscanner are
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installed. If multiple versions are found, the requires scanner aborts. This
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can be overwritten by setting a variable in the .spec file (unfortunately not
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possible per subpackage):
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`%global %__qml_requires_opts --qtver 5`
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Currently, only .qml files directly part of the package are handled, so if
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those are part of a resources file embedded into an executable or library, they
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will not be read. Making this possible needs more research and effort.
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Generating Provides from qmldir files
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-------------------------------------
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Every module installed into the QML import path contains aqmldir` file with
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metainformation. They usually contain a `module` line which specifies the
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identifier (those which don't are ignored) and a list of exports and plugins.
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Just the module identifier is not enough to generate the capability, major and
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corresponding minor version(s) are also needed. For each major version, only
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the highest minor version is stored, as it also satisfies imports with a lower
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minor version.
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Handling direct exports are easy, as they mention the major and minor version
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directly, which combined with the Qt version (derived from the location the
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qmldir file is installed to) results in a capability. For plugins, it's not as
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easy though, those actually have to be loaded to get their registrations.
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While `qtdeclarative` provides a tool called `qmlplugindump`, which lists all
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exported types in a QML format, it uses the QML engine for loading plugins,
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which requires the module identifier and a version. In addition to that, it
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just doesn't work at all sometimes and does not provide all necessary
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information (like pure module exports, which just bump the available minor
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version without exporting any new type revisions).
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To get a list of all versioned exports made by a plugin, a new tool called
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`qmlpluginexports` specifically for that was written. It uses private API to
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load a plugin without specifying a version and then iterates through all known
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types to get their versions. It also handles lazy registration using
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QQmlModuleRegistration and qmlRegisterModule by implementing the underlying
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modules, which overrides the symbols in the Qt libraries (symbols in
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executables have higher priority than public symbols from shared objects) to
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store the information and then forwarding the call to the Qt library.
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As loading a plugin also triggers loading of all dependencies, it's possible
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that those register their own exports as well. So only exports including the
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module identifier from the `qmldir` file are used and others are ignored. For
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instance, the plugin for `QtQuick.Controls.2` also registers
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`QtQuick.Controls.impl.2`.
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Internal and private exports
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----------------------------
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The automatic generation of import requirements uses every module import in
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installed .qml files. In some cases, those imports are not for system-wide
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modules, but for imports provided by code in shared libraries and executables,
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usable only in .qml files loaded by those. Provides for those can't be
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generated, but the requirement will be, which makes the package unsatisfiable
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due to missing dependencies. How to deal with that depends on the export
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itself.
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RPM dependencies are inter-package, so if an export is only used within a
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package (for instance, an application with its UI), it's fine to filter it
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out from requires and provides like this:
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```
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%global __requires_exclude (org.kde.private.kcms.kwin.effects)|(org.kde.kcms.kwinrules)
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%global __provides_exclude (org.kde.private.kcms.kwin.effects)|(org.kde.kcms.kwinrules)
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```
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Truly private exports are usually not found by the generation of provided
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capabilities, so the latter is normally not necessary.
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The opposite case is when an application or library registers exports for use
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by other packages (e.g. Plasma applets) which aren't available as system wide
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QML imports. Those shouldn't simply be filtered out, as other packages actually
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make use of it. Instead, the capability has to be provided manually, e.g.
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```
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Provides: qt5qmlimport(org.kde.plasma.configuration.2) = 0
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Provides: qt5qmlimport(org.kde.plasma.plasmoid.2) = 0
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```
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qtdeclarative-imports-provides
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------------------------------
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The qml-autoreqprov scripts need qmlimportscanner from qtdeclarative to
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generate Requires and for `qmldir` files with `plugin` lines `qmlpluginexports`
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is required. The latter needs qtdeclarative to be built. This is a problem,
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because qtdeclarative provides important exports, which have to be available as
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RPM capabilities as well. Making qml-autoreqprov and its dependencies available
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during build of qtdeclarative would cause a build cycle. To work around that,
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a "stub" package installs qtdeclarative during build and runs the provides
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generator for each relevant qtdeclarative package, to map the exports to the
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corresponding package.
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TODO
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----
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Is special treatment for baselibs.conf needed?
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How do .qmlc files relate to this?
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RPM doesn't seem to merge "foo >= 10" and "foo >= 11", so there are redundant
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requirements generated. As the generator is run for each file separately, it's
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not directly possible to work around that.
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