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Changes to the Gradle build

With MontiCore version 7.6.0, the monticore gradle plugin has been replaced with the de.monticore.generator plugin. It supports the default use case for the MontiCore generator out of the box.

Default Project Setup

plugins {
    id "de.monticore.generator" version "$version"
    id "java-library"
// And thats it - no further task definitions required!

The de.monticore.generator plugin automatically adds a MCGenTask named generateMCGrammars task, which builds all grammars in the src/main/grammars folder. Unlike with the old MCTask, which required one task per grammar, the new MCGenTask task builds all grammars incrementally. The generated java files are automatically added to the sources.

A work action is created for every grammar which is required to be worked on and thus, multiple grammars can be build in parallel.


The automatically added generateMCGrammars task is configured with some defaults, which can be modified via the build file. For example, the following build file snippet changes the output directory:

generateMCGrammars {
    outputDir = file "$projectDir/target/mc"

The following table shows the main configuration options

Option Description Type Default
grammar (, input) The grammar files ConfigurableFileCollection src/main/grammars
handWrittenCodeDir (, hwc, handcodedPath ) Directories for detecting hand-written code that needs to be integrated. ConfigurableFileCollection src/main/java
handWrittenGrammarDir (, hwg) Directories for detecting hand-written grammar modifications that need to be integrated. ConfigurableFileCollection src/main/grammarsHC
templatePath (, tmplDir) Directories for detecting hand-written templates to integrate. ConfigurableFileCollection src/main/resources
configTemplate template to configure the integration of hand-written templates. Thus, it can only be used in conjunction with a valid templatePath. String absent
script Groovy script to control the generation workflow. String monticore_standard.groovy
modelPath Directories in which symbols or grammars are searched. ConfigurableFileCollection absent
outputDir Directory to which the output should be written to Directory $buildDir/generated-sources/monticore/sourcecode (only added for the default generateMCGrammars task)
reportDir Directory to which the reports should be written to Directory $buildDir/mc_reports/task_$taskname
debug Enables developer logging and boolean false
genDST Whether domain specific transformation infrastructure should be generated (only suitable for TR grammars) boolean false
genTag Whether tagging infrastructure should be generated (only suitable for TagDefinition grammars) boolean false
groovyHook1 Groovy script that is hooked into the workflow of the standard script at hook point one, which is called after initialization, before the actual workflow begins. File absent
groovyHook2 Groovy script that is hooked into the workflow of the standard script at hook point two, which is called before the generation step. File absent
moreArgs Additional arguments passed to the Tool. List<String> []


In most cases, adding the plugin should be enough. The following snippets show examples, in which the default configuration is modified:

Different ModelPath

generateMCGrammars {
    modelPath("$projectDir/src/main/grammars", "$projectDir/src/notquitemain/grammars")

*Note:* We have introduced a breaking change to the `modelPath()` behavior:
It is no longer possible to specify multiple directories by calling `modelPath(...)` multiple times,
 instead a comma-seperated list is to be used.
The legacy usage now aborts with a descriptive error.

### Different workflow script

generateMCGrammars {
    script = "de/monticore/monticore_noreports.groovy"

Specify Groovy Hooks

generateMCGrammars {
    groovyHook1 = file "$projectDir/gs1.groovy"
    groovyHook2 = file "$projectDir/gs2.groovy"


generateMCGrammars {
  configTemplate = "ct.ftl"
  templatePath "$projectDir/src/main/tpl"
Note: Incremental building after changes to the templatePath directory contents is not supported. Instead, a full-rebuild is enforced.

Custom MCGenTask

A generateTRGrammars task to generate TR grammars:

tasks.register("generateTRGrammars", MCGenTask) {
    grammar.setFrom(tasks.named("generateMCGrammars", MCGenTask.class).get().getTROutput())
    outputDir = file derivOutDir
    modelPath.from(file grammarOutDir) // the directory hierarchy is required here
    if (findProperty("ci") != null) {
      script = "de/monticore/monticore_noreports.groovy"
// Note: The output directory has to manually be added to the java sources 
sourceSets { += derivOutDir

// In case the derivOutDir does not contribute to the main source set, make sure to add the dependsOn
compileTRJava.dependsOn (tasks.named("generateTRGrammars"))

Improvements over the old MCTask

  • Improved incremental build support
  • Added Gradle build cache support
  • Added parallel task execution support
  • Using Gradle task definitions which can be used for Gradle plugins of MontiCore language tools

Implementation specifics

MontiCore suffers from a memory leak caused by the GroovyInterpreter. The parallel, isolated execution of the generator intensifies this memory leak (which is why we limit it using --max-workers=4). This might be fixed by 8078641 in jdk 18+.