Skip to main content

POM-leading for DSL projects

· 3 min read
Toine Hartman-Rijksen

In this post we report on important changes to dependency resolution and project configuration in Rascal 0.43.0 and Rascal LSP 2.23.0.

Since some time, Rascal projects have been gradually moving away from the manifest-based project configuration towards Maven's POM. Library depencies need to be specified in the POM. These libraries are resolved (and, if needed, downloaded) in the local Maven repository and used by Rascal tools like the VS Code extension (IDE features) and the Maven plugin (mvn compile).

However, the rascal and rascal-lsp dependencies were treated differently. In many cases, it was not even necessary to explicitly specifiy them in the POM, because they were implicitly added. And even if specified, their version would often be ignored in the IDE, due to implementation constraints.

Not anymore! In the past year, we have reworked many parts of Rascal and the VS Code extension. This allows the extension (and the maven plugin) to follow the POM more closely, leading to predictable and transparent dependency versions in Rascal projects (also enabled by the removal of library schemes). REPLs in VS Code and type-checks in the IDE will now use the Rascal standard library version from the POM, and language servers registered using registerLanguage will run with the specified Rascal and LSP versions.

In order to work with the newest release of the VS Code extension, new and existing projects should be set up with the proper dependencies. Rascal language projects might require code changes as well. Note that the VS Code extension will both inform you about this, and often offer a quick-fix for the problem.

Modifying existing Rascal projects​

Any new or existing project requires an explicit dependency on Rascal 0.43.0 in the POM:

<dependencies>
    <dependency>
        <groupId>org.rascalmpl</groupId>
        <artifactId>rascal</artifactId>
        <version>0.43.0</version>
    </dependency>
    <!-- other dependencies -->
</dependencies>

Modifying existing language projects​

Language projects are projects that use the util::LanguageServer library and/or use registerLanguage in the REPL. These projects require additional changes. First of all, they need a POM dependency on the newly released version of Rascal LSP, since this dependency is not implicitly derived from the development environment anymore.

<dependencies>
    <dependency>
        <groupId>org.rascalmpl</groupId>
        <artifactId>rascal-lsp</artifactId>
        <version>2.23.0</version>
    </dependency>
    <!-- other dependencies -->
</dependencies>

In any call to registerLanguage, the parameter should now contain a complete path config. This path config can be obtained by util::Reflective::getProjectPathConfig with the interpreter_external mode. This mode ensures that the the path config will be strictly based on the POM.

import util::LanguageServer;
import util::Reflective;

void main() {
    PathConfig pcfg = getProjectPathConfig(|project://my-project|, mode=interpreter_external());
    registerLanguage(language(pcfg, ....));
}

Under the hood, each registered language will run in a dedicated process. Languages are thus completely isolated in case of a crash, improving the robustness of the language server, especially when registering multiple languages. As a consequence, the memory of the extension might increased in case multiple languages are registered in parallel.