Added Yarn Berry compatibility flag

CHANGELOG.md

@@ -8,6 +8,7 @@ Last public release: [![Maven Central](https://maven-badges.herokuapp.com/maven-
 
 * update Dependency: Jackson (2.13.0), Mockito (4.1.0), JUnit (5.8.1), Hamcrest (2.2; now a direct dependency)
 * remove Dependency: Powermock
+* Added better support for Yarn 2.x and above (Berry)
 
 ### 1.11.4
 * Support node arm64 binaries since v16 major release

README.md

@@ -139,6 +139,10 @@ Node/Yarn will only be "installed" locally to your project.
 It will not be installed globally on the whole system (and it will not interfere with any Node/Yarn installations already 
 present). 
 
+If your project is using Yarn Berry (2.x or above), the Yarn version is handled per project but a Yarn 1.x install is still needed as a "bootstrap".
+The plugin will try to detect `.yarnrc.yml` file in the current Maven project/module folder, at the root of the multi-module project if relevant, and in the folder from which the `mvn` command was run. 
+If detected, the plugin will assume your project is using Yarn Berry. It will install the 1.x Yarn version you specify with `yarnVersion` as bootstrap, then hand over to your project-specific version.   
+
 Have a look at the example `POM` to see how it should be set up with Yarn: 
 https://github.com/eirslett/frontend-maven-plugin/blob/master/frontend-maven-plugin/src/it/yarn-integration/pom.xml
 

frontend-maven-plugin/src/main/java/com/github/eirslett/maven/plugins/frontend/mojo/InstallNodeAndYarnMojo.java

@@ -1,5 +1,7 @@
 package com.github.eirslett.maven.plugins.frontend.mojo;
 
+import java.io.File;
+import java.util.stream.Stream;
 import org.apache.maven.execution.MavenSession;
 import org.apache.maven.plugins.annotations.Component;
 import org.apache.maven.plugins.annotations.LifecyclePhase;
@@ -16,6 +18,8 @@
 @Mojo(name = "install-node-and-yarn", defaultPhase = LifecyclePhase.GENERATE_RESOURCES, threadSafe = true)
 public final class InstallNodeAndYarnMojo extends AbstractFrontendMojo {
 
+    private static final String YARNRC_YAML_FILE_NAME = ".yarnrc.yml";
+
     /**
      * Where to download Node.js binary from. Defaults to https://nodejs.org/dist/
      */
@@ -65,6 +69,22 @@ protected boolean skipExecution() {
         return this.skip;
     }
 
+    /**
+     * Checks whether a .yarnrc.yml file exists at the project root (in multi-module builds, it will be the Reactor project)
+     *
+     * @return true if the .yarnrc.yml file exists, false otherwise
+     */
+    private boolean isYarnrcYamlFilePresent() {
+        Stream<File> filesToCheck = Stream.of(
+                new File(session.getCurrentProject().getBasedir(), YARNRC_YAML_FILE_NAME),
+                new File(session.getRequest().getMultiModuleProjectDirectory(), YARNRC_YAML_FILE_NAME),
+                new File(session.getExecutionRootDirectory(), YARNRC_YAML_FILE_NAME)
+        );
+
+        return filesToCheck
+                .anyMatch(File::exists);
+    }
+
     @Override
     public void execute(FrontendPluginFactory factory) throws InstallationException {
         ProxyConfig proxyConfig = MojoUtils.getProxyConfig(this.session, this.decrypter);
@@ -75,12 +95,12 @@ public void execute(FrontendPluginFactory factory) throws InstallationException
                 .setUserName(server.getUsername()).install();
             factory.getYarnInstaller(proxyConfig).setYarnDownloadRoot(this.yarnDownloadRoot)
                 .setYarnVersion(this.yarnVersion).setUserName(server.getUsername())
-                .setPassword(server.getPassword()).install();
+                .setPassword(server.getPassword()).setIsYarnBerry(isYarnrcYamlFilePresent()).install();
         } else {
             factory.getNodeInstaller(proxyConfig).setNodeDownloadRoot(this.nodeDownloadRoot)
                 .setNodeVersion(this.nodeVersion).install();
             factory.getYarnInstaller(proxyConfig).setYarnDownloadRoot(this.yarnDownloadRoot)
-                .setYarnVersion(this.yarnVersion).install();
+                .setYarnVersion(this.yarnVersion).setIsYarnBerry(isYarnrcYamlFilePresent()).install();
         }
     }
 

frontend-plugin-core/src/main/java/com/github/eirslett/maven/plugins/frontend/lib/YarnInstaller.java

@@ -23,6 +23,8 @@ public class YarnInstaller {
 
     private String yarnVersion, yarnDownloadRoot, userName, password;
 
+    private boolean isYarnBerry;
+
     private final Logger logger;
 
     private final InstallConfig config;
@@ -43,6 +45,11 @@ public YarnInstaller setYarnVersion(String yarnVersion) {
         return this;
     }
 
+    public YarnInstaller setIsYarnBerry(boolean isYarnBerry) {
+        this.isYarnBerry = isYarnBerry;
+        return this;
+    }
+
     public YarnInstaller setYarnDownloadRoot(String yarnDownloadRoot) {
         this.yarnDownloadRoot = yarnDownloadRoot;
         return this;
@@ -85,8 +92,13 @@ private boolean yarnIsAlreadyInstalled() {
                     logger.info("Yarn {} is already installed.", version);
                     return true;
                 } else {
-                    logger.info("Yarn {} was installed, but we need version {}", version, yarnVersion);
-                    return false;
+                    if (isYarnBerry && Integer.parseInt(version.split("\\.")[0]) > 1) {
+                        logger.info("Yarn Berry {} is installed.", version);
+                        return true;
+                    } else{
+                        logger.info("Yarn {} was installed, but we need version {}", version, yarnVersion);
+                        return false;
+                    }
                 }
             } else {
                 return false;