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Please review the following information to ensure ** the GNU Free Documentation License version 1.3 requirements ** will be met: https://www.gnu.org/licenses/fdl-1.3.html. ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \contentspage list-of-language-items.html \previouspage PropertyOptions \nextpage Scanner \qmltype Rule \inqmlmodule QbsLanguageItems \ingroup list-of-items \keyword QML.Rule \brief Creates transformers for input tags. In \QBS, rules create \e transformers that produce output files from input files. The term \e transformer refers to a list of \l{Command and JavaScriptCommand}{commands}. These commands are created in a rule's \l{prepare} script. They do the actual work, either directly or by executing external commands. \section1 A Simple Example The following rule takes text files and replaces Windows-style line endings with their Unix-style counterparts. We will look at it one piece at a time. \quotefromfile ../examples/rule/rule.qbs \skipto Rule \printuntil multiplex: false A \e {multiplex rule} creates one transformer that takes all input artifacts with the matching input file tag and creates one or more output artifacts. We are setting the respective property to \c false here, indicating that we want to create one transformer per input file. \note This is actually the default, so the above assignment is not required. \printuntil inputs: ["txt_input"] Here we are specifying that our rule is interested in input files that have the tag \c "txt_input". Such files could be source files, in which case you would tag them using a \l{Group}. Or they could in turn get generated by a different rule, in which case that rule would assign the file tag. The files matching the tag will be available in the \l{prepare} script under the name \c inputs (see \l{inputs and outputs}{The inputs and outputs Variables}). \printuntil } Here we are specifying that for every input file, we want to create one output file whose name is the same as the input file, but with an additional extension. Because we are giving a relative path, \QBS will prepend that path by the product's build directory. In addition, we tell \QBS that the output files should get the file tag \c "txt_output". This enables other rules to use these files as inputs. You must always assign suitable file tags to your output artifacts, or the rule will not be run. See \l{Rules and Product Types} for details. If you want to create more than one output file per input file, you simply provide multiple \l Artifact items. The set of output artifacts will be available in the prepare script under the name \c outputs (see \l{inputs and outputs}{The inputs and outputs Variables}). \printuntil /^\s{4}\}/ The prepare script shown above puts everything together by creating the command that does the actual transformation of the file contents, employing the help of the \l{TextFile Service}{TextFile} class. As you can see, the return value is an array, meaning you can provide several commands to implement the rule's functionality. For instance, if we had provided two \c Artifact items, we might have also provided two commands, each of them creating one output file. For the \c input and \c output variables used in the code, see the next section. \target inputs and outputs \section1 The \c inputs and \c outputs Variables We already mentioned that the input and output artifacts are available in the prepare script via the variables \c inputs and \c outputs, respectively. These variables are JavaScript objects whose property keys are file tags and whose property values are lists of objects representing the artifacts matching these tags. In our example, the \c inputs variable has a single property \c txt_input, whose value is a list with one element. Similarly, the \c outputs variable also has one single property \c txt_output, again with a list containing one element. The actual artifact objects have the following properties: \table \header \li Property \li Description \row \li \c baseName \li The file name without any extension. \row \li \c completeBaseName \li The file name without the last extension. \row \li \c fileName \li The name of the file (that is, \c filePath without any directory components). \row \li \c filePath \li The full file path. \row \li \c fileTags \li The list of the artifact's file tags. \endtable The artifact object contains a property for every module that is used in the product. That can be used to access the module's properties. For instance, for an artifact in a C++ product, \c{artifact.cpp.defines} is the list of defines that will be passed when compiling the respective file. But what about the variables \c input and \c output that appeared in our example? These are simply convenience variables which are available in the case that the \c inputs and \c outputs variables contain only one artifact, respectively. So in our example, instead of \c input we also could have written \c {inputs.txt_input[0]}, which is considerably more verbose. \section1 Rules and Product Types It is important to know that when figuring out which rules to execute, \QBS starts at the product type and then looks for a way to produce artifacts with matching file tags from source files, using a chain of rules that are connected by their respective input and output tags. For instance, consider this simple C++ project: \code Product { type: ["application"] Depends { name: "cpp" } files: ["main.cpp"] } \endcode Here's how this product is built: \list 1 \li \QBS looks for a rule that can produce artifacts with the file tag \c{"application"}. Such a rule is found in the \l{cpp} module (namely, the rule that invokes the linker). \li Since the rule found in the previous step takes inputs of type \c{"obj"}, \QBS now looks for a rule that produces artifacts of that type. Again, such a rule is found in the \c cpp module (the rule that runs the compiler). \li The rule found in the previous step takes inputs of type \c{"cpp"}. No rule is found that creates such artifacts, but we do have a source file with a matching type (because the \c cpp module contains a \l{FileTagger} which attached that type to \c{"main.cpp"} due to its file extension). \li Now that there is a chain of rules leading from a source file tag to the product type, the commands of these rules are executed one after the other until we end up with our executable. \endlist \section1 A Complete Example The following code snippet shows a single \l{Rule} within a \l{Product} and summarizes the previous sections. \note The product's type is set up to the \c "txt_output" file tag to tell \QBS that the product depends on output artifacts produced by the custom rule. Otherwise the rule would not be executed. \quotefile ../examples/rule/rule.qbs */ /*! \qmlproperty bool Rule::multiplex Determines whether this is a multiplex rule. \defaultvalue \c false */ /*! \qmlproperty stringList Rule::inputs A list of file tags the input artifacts must match. All output artifacts will depend on all artifacts in the product with the given input file tags. Also, these artifacts are available in the \c inputs variable of the \l{prepare} script. \nodefaultvalue */ /*! \qmlproperty stringList Rule::auxiliaryInputs A list of file tags. This rule will be dependent on every other rule that produces artifacts that are compatible with the value of this property. Unlike \l{inputs}, this property has no effect on the content of the \c inputs variable of the \l{prepare} script. All rules in this product and rules of product dependencies that produce target artifacts are considered. \nodefaultvalue */ /*! \qmlproperty stringList Rule::excludedInputs A list of file tags. Connections to rules that produce these file tags are prevented. \nodefaultvalue \since Qbs 1.12 */ /*! \qmlproperty stringList Rule::inputsFromDependencies A list of file tags that the artifacts of product dependencies must match. For example, the product \a foo might appear as follows in the current product: \code Depends { name: "foo" } \endcode All artifacts of \a foo that match the given file tags will appear in the \c inputs variable of the \l{prepare} script. \nodefaultvalue */ /*! \qmlproperty var Rule::outputArtifacts An array of output artifacts, specified as JavaScript objects. For example: \code outputArtifacts: [{ filePath: "myfile.cpp", fileTags: ["cpp"], cpp: { cxxLanguageVersion: "c++11" } }] \endcode For a description of the possible properties, see the documentation of the \l{Artifact} item. Output artifacts can be specified either by this property or by \l{Artifact} items. Use this property if the set of outputs is not fixed but depends the input's content. If no file tags are provided, \QBS will apply all \l{FileTagger}{file taggers} known in the current context to the output file name. The user may set the property \c{explicitlyDependsOn} on artifact objects, which is similar to \l{Rule::explicitlyDependsOn}{Rule.explicitlyDependsOn}. \nodefaultvalue */ /*! \qmlproperty stringList Rule::outputFileTags If output artifacts are specified by \l{outputArtifacts}, this property must specify a list of file tags that the rule potentially produces. \nodefaultvalue */ /*! \qmlproperty bool Rule::condition If \c true, the rule is enabled, otherwise it does nothing. \defaultvalue \c true */ /*! \qmlproperty stringList Rule::explicitlyDependsOn A list of file tags. Each artifact that matches the file tags is added to the dependencies of each output node. All artifacts in the current product are considered. \nodefaultvalue */ /*! \qmlproperty stringList Rule::explicitlyDependsOnFromDependencies A list of file tags. Each artifact that matches the file tags is added to the dependencies of each output node. Only target artifacts of products that this product depends on are considered. \nodefaultvalue \since Qbs 1.12 */ /*! \qmlproperty script Rule::prepare A script that prepares the commands to transform the inputs to outputs. The code in this script is treated as a function with the signature \c{function(project, product, inputs, outputs, input, output, explicitlyDependsOn)}. The argument \c{input} is \c{undefined} if there's more than one input artifact for this rule. Similarly, \c{output} is only defined if there is exactly one output artifact. \nodefaultvalue */ /*! \qmlproperty bool Rule::requiresInputs Specifies whether a rule's commands should be created even if no inputs are available. Enabling this property can be useful if you are not sure whether input files exist, and you want \QBS to create an output file even if they do not. Set to \c true if the rule declares any inputs, \c false otherwise. */ /*! \qmlproperty bool Rule::alwaysRun If \c true, the rule's commands are always executed, even if all output artifacts are up to date. \defaultvalue \c false */