support installing yarn version from package.json engines

fixes #798

frontend-maven-plugin/src/it/yarn-version-from-engines/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "example",
+  "version": "0.0.1",
+  "engines": {
+    "yarn": "^1.10"
+  },
+  "dependencies": {
+    "less": "~3.0.2"
+  },
+  "scripts": {
+    "prebuild": "npm install"
+  }
+}

frontend-maven-plugin/src/it/yarn-version-from-engines/pom.xml

@@ -0,0 +1,50 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.github.eirslett</groupId>
+    <artifactId>example</artifactId>
+    <version>0</version>
+    <packaging>pom</packaging>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>com.github.eirslett</groupId>
+                <artifactId>frontend-maven-plugin</artifactId>
+                <!-- NB! Set <version> to the latest released version of frontend-maven-plugin, like in README.md -->
+                <version>@project.version@</version>
+
+                <configuration>
+                    <installDirectory>target</installDirectory>
+                </configuration>
+
+                <executions>
+
+                    <execution>
+                        <id>install node and yarn</id>
+                        <goals>
+                            <goal>install-node-and-yarn</goal>
+                        </goals>
+                        <configuration>
+                            <nodeVersion>v16.0.0</nodeVersion>
+                            <yarnVersion>engines</yarnVersion>
+                        </configuration>
+                    </execution>
+
+                    <execution>
+                        <id>yarn install</id>
+                        <goals>
+                            <goal>yarn</goal>
+                        </goals>
+                        <!-- Optional configuration which provides for running any npm command -->
+                        <configuration>
+                            <arguments>install</arguments>
+                        </configuration>
+                    </execution>
+
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>

frontend-maven-plugin/src/it/yarn-version-from-engines/verify.groovy

@@ -0,0 +1,6 @@
+assert new File(basedir, 'target/node').exists() : "Node was not installed in the custom install directory";
+assert new File(basedir, 'node_modules').exists() : "Node modules were not installed in the base directory";
+assert new File(basedir, 'node_modules/less/package.json').exists() : "Less dependency has not been installed successfully";
+
+String buildLog = new File(basedir, 'build.log').text
+assert buildLog.contains('BUILD SUCCESS') : 'build was not successful'

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

@@ -5,7 +5,14 @@
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.Arrays;
-
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.vdurmont.semver4j.Requirement;
+import com.vdurmont.semver4j.Semver;
 import org.apache.commons.io.FileUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -31,6 +38,8 @@ public class YarnInstaller {
 
     private final FileDownloader fileDownloader;
 
+    private Requirement yarnVersionRequirement;
+
     YarnInstaller(InstallConfig config, ArchiveExtractor archiveExtractor, FileDownloader fileDownloader) {
         logger = LoggerFactory.getLogger(getClass());
         this.config = config;
@@ -64,7 +73,53 @@ public void install() throws InstallationException {
             if (yarnDownloadRoot == null || yarnDownloadRoot.isEmpty()) {
                 yarnDownloadRoot = DEFAULT_YARN_DOWNLOAD_ROOT;
             }
+            if ("engines".equals(this.yarnVersion)) {
+                try {
+                    File packageFile = new File(this.config.getWorkingDirectory(), "package.json");
+                    HashMap<String, Object> data = new ObjectMapper().readValue(packageFile, HashMap.class);
+                    if (data.containsKey("engines")) {
+                        HashMap<String, Object> engines = (HashMap<String, Object>) data.get("engines");
+                        if (engines.containsKey("yarn")) {
+                            this.yarnVersionRequirement = Requirement.buildNPM((String) engines.get("yarn"));
+                        } else {
+                            this.logger.info("Could not read yarn from engines from package.json");
+                        }
+                    } else {
+                        this.logger.info("Could not read engines from package.json");
+                    }
+                } catch (IOException e) {
+                    throw new InstallationException("Could not read yarn engine version from package.json", e);
+                }
+            }
             if (!yarnIsAlreadyInstalled()) {
+                if (this.yarnVersionRequirement != null) {
+                    // download available node versions
+                    try {
+                        String downloadUrl = "https://api.github.com/repos/yarnpkg/yarn/releases";
+
+                        File archive = File.createTempFile("yarn_versions", ".json");
+
+                        downloadFile(downloadUrl, archive, this.userName, this.password);
+
+                        HashMap<String, Object>[] data = new ObjectMapper().readValue(archive, HashMap[].class);
+
+                        List<String> yarnVersions = new LinkedList<>();
+                        for (HashMap<String, Object> d : data) {
+                            if (d.containsKey("name")) {
+                                yarnVersions.add((String) d.get("name"));
+                            }
+                        }
+
+                        // we want the oldest possible version, that satisfies the requirements
+                        Collections.reverse(yarnVersions);
+
+                        logger.debug("Available Yarn versions: {}", yarnVersions);
+                        this.yarnVersion = yarnVersions.stream().filter(version -> yarnVersionRequirement.isSatisfiedBy(new Semver(version, Semver.SemverType.NPM))).findFirst().orElseThrow(() -> new InstallationException("Could not find matching node version satisfying requirement " + this.yarnVersionRequirement));
+                        this.logger.info("Found matching Yarn version {} satisfying requirement {}.", this.yarnVersion, this.yarnVersionRequirement);
+                    } catch (IOException | DownloadException e) {
+                        throw new InstallationException("Could not get available Yarn versions.", e);
+                    }
+                }
                 if (!yarnVersion.startsWith("v")) {
                     throw new InstallationException("Yarn version has to start with prefix 'v'.");
                 }
@@ -81,7 +136,12 @@ private boolean yarnIsAlreadyInstalled() {
                 final String version =
                     new YarnExecutor(executorConfig, Arrays.asList("--version"), null).executeAndGetResult(logger).trim();
 
-                if (version.equals(yarnVersion.replaceFirst("^v", ""))) {
+                if (yarnVersionRequirement != null && yarnVersionRequirement.isSatisfiedBy(new Semver(version, Semver.SemverType.NPM))) {
+                    //update version with installed version
+                    this.yarnVersion = version;
+                    this.logger.info("Yarn {} matches required version range {} installed.", version, yarnVersionRequirement);
+                    return true;
+                } else if (version.equals(yarnVersion.replaceFirst("^v", ""))) {
                     logger.info("Yarn {} is already installed.", version);
                     return true;
                 } else {