feat: Create Flow plugins for webpack (#9295)

Moved stats file handling to a custom plugin.
Added feature for copying custom Flow plugins
for use with webpack.

Fixes #9283

flow-server/README.md

@@ -0,0 +1,79 @@
+## Flow Webpack plugins
+
+Flow now uses webpack plugins to make the `webpack.generated.js` cleaner and easier to extend
+without cluttering the file and making it long and complex.
+
+The files get installed with the task `TaskInstallWebpackPlugins` which reads the `webpack-plugins.json`
+in from `src/main/resources/plugins` and installs the plugins named here e.g.
+
+```json
+{
+  "plugins": [
+    "stats-plugin"
+  ]
+}
+```
+
+The plugin itself should also be contained in `src/main/resources/plugins` with the
+folder name being the same as the plugin name.
+
+For stats-plugin this means it should be located in `src/main/resources/plugins/stats-plugin`.
+
+The plugin folder needs to contain the plugin javascript files plus a package.json with at least the fields
+`version`, `main`, `files` filled where:
+  * `version` is the semver version for the plugin. 
+  (Plugin will not be updated if the same version already exists)
+  * `main` depicts the main js file for the plugin.
+  * `files` contains all files the plugin needs.
+   (only these files will be copied)
+
+The full information would be preferred:
+
+```json
+{
+  "description": "stats-plugin",
+  "keywords": [
+    "plugin"
+  ],
+  "repository": "vaadin/flow",
+  "name": "@vaadin/stats-plugin",
+  "version": "1.0.0",
+  "main": "stats-plugin.js",
+  "author": "Vaadin Ltd",
+  "license": "Apache-2.0",
+  "bugs": {
+    "url": "https://github.com/vaadin/flow/issues"
+  },
+  "files": [
+    "stats-plugin.js"
+  ]
+}
+```
+
+For creating a plugin see [Writing a plugin](https://webpack.js.org/contribute/writing-a-plugin/)
+
+## Using a Flow webpack plugin
+
+The flow plugins get installed to `node_modules/@vaadin` which means that using them we should use the for `@vaadin/${plugin-name}`
+
+As the plugins are meant for internal use the are added to `webpack.generated.js` and
+used from there.
+
+First we need to import the webpack plugin
+
+```js
+const StatsPlugin = require('@vaadin/stats-plugin');
+```
+
+then add the plugin with required options to `plugins` in the generated file
+```js
+  plugins: [
+    new StatsPlugin({
+      devMode: devMode,
+      statsFile: statsFile,
+      setResults: function (statsFile) {
+        stats = statsFile;
+      }
+    }),
+ ]
+```

flow-server/src/main/java/com/vaadin/flow/server/frontend/NodeTasks.java

@@ -31,10 +31,10 @@
 import com.vaadin.flow.server.frontend.scanner.FrontendDependenciesScanner;
 
 import elemental.json.JsonObject;
-
 import static com.vaadin.flow.server.frontend.FrontendUtils.DEFAULT_FRONTEND_DIR;
 import static com.vaadin.flow.server.frontend.FrontendUtils.DEFAULT_GENERATED_DIR;
 import static com.vaadin.flow.server.frontend.FrontendUtils.IMPORTS_NAME;
+import static com.vaadin.flow.server.frontend.FrontendUtils.NODE_MODULES;
 import static com.vaadin.flow.server.frontend.FrontendUtils.PARAM_FRONTEND_DIR;
 import static com.vaadin.flow.server.frontend.FrontendUtils.PARAM_GENERATED_DIR;
 
@@ -465,6 +465,9 @@ private NodeTasks(Builder builder) {
                         classFinder, packageUpdater,
                         builder.enablePnpm, builder.requireHomeNodeExec,
                         builder.nodeVersion, builder.nodeDownloadRoot));
+
+                commands.add(new TaskInstallWebpackPlugins(
+                    new File(builder.npmFolder, NODE_MODULES)));
             }
         }
 

flow-server/src/main/java/com/vaadin/flow/server/frontend/TaskInstallWebpackPlugins.java

@@ -0,0 +1,179 @@
+/*
+ * Copyright 2000-2020 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.flow.server.frontend;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.UncheckedIOException;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.apache.commons.io.FileUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import elemental.json.Json;
+import elemental.json.JsonArray;
+import elemental.json.JsonObject;
+import static com.vaadin.flow.server.Constants.PACKAGE_JSON;
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+/**
+ * Task that installs any Flow webpack plugins into node_modules/@vaadin for
+ * use with webpack compilation.
+ * <p>
+ * This should preferably be executed after npm installation to not make it skip
+ * or have the plugins deleted by {@link TaskRunNpmInstall}.
+ *
+ * @since
+ */
+public class TaskInstallWebpackPlugins implements FallibleCommand {
+
+    private File nodeModulesFolder;
+
+    /**
+     * Copy Flow webpack plugins into the given nodeModulesFolder.
+     *
+     * @param nodeModulesFolder
+     *     node_modules folder to copy files to
+     */
+    public TaskInstallWebpackPlugins(File nodeModulesFolder) {
+        this.nodeModulesFolder = nodeModulesFolder;
+    }
+
+    @Override
+    public void execute() {
+        getPlugins().forEach(plugin -> {
+            try {
+                generatePluginFiles(plugin);
+            } catch (IOException ioe) {
+                throw new UncheckedIOException(
+                    "Installation of Flow webpack plugin '" + plugin
+                        + "' failed", ioe);
+            }
+        });
+    }
+
+    /**
+     * Get names for plugins to install into node_modules.
+     *
+     * @return names of plugins to install
+     */
+    protected List<String> getPlugins() {
+        try {
+            final JsonObject jsonFile = getJsonFile(
+                "plugins/webpack-plugins.json");
+            if (jsonFile == null) {
+                log().error(
+                    "Couldn't locate plugins/webpack-plugins.json, no Webpack plugins for Flow will be installed."
+                        + "If webpack build fails validate flow-server jar content.");
+                return Collections.emptyList();
+            }
+
+            final JsonArray plugins = jsonFile.getArray("plugins");
+            List<String> pluginsToInstall = new ArrayList<>(plugins.length());
+            for (int i = 0; i < plugins.length(); i++) {
+                pluginsToInstall.add(plugins.getString(i));
+            }
+            return pluginsToInstall;
+        } catch (IOException ioe) {
+            throw new UncheckedIOException(
+                "Couldn't load webpack-plugins.json file", ioe);
+        }
+    }
+
+    private void generatePluginFiles(String pluginName) throws IOException {
+        // Get the target folder where the plugin should be installed to
+        File pluginTargetFile = new File(nodeModulesFolder,
+            "@vaadin/" + pluginName);
+
+        final String pluginFolderName = "plugins/" + pluginName + "/";
+        final JsonObject packageJson = getJsonFile(
+            pluginFolderName + PACKAGE_JSON);
+        if (packageJson == null) {
+            log().error(
+                "Couldn't locate '{}' for plugin '{}'. Plugin will not be installed.",
+                PACKAGE_JSON, pluginName);
+            return;
+        }
+
+        // Validate installed version and don't override if same
+        if (pluginTargetFile.exists() && new File(pluginTargetFile,
+            PACKAGE_JSON).exists()) {
+            String packageFile = FileUtils
+                .readFileToString(new File(pluginTargetFile, PACKAGE_JSON),
+                    StandardCharsets.UTF_8);
+            final FrontendVersion packageVersion = new FrontendVersion(
+                Json.parse(packageFile).getString("version"));
+            FrontendVersion pluginVersion = new FrontendVersion(
+                packageJson.getString("version"));
+            if (packageVersion.isEqualTo(pluginVersion)) {
+                log().debug(
+                    "Skipping install of {} for version {} already installed",
+                    pluginName, pluginVersion.getFullVersion());
+                return;
+            }
+        }
+
+        // Create target folder if necessary
+        FileUtils.forceMkdir(pluginTargetFile);
+
+        // copy only files named in package.json { files }
+        final JsonArray files = packageJson.getArray("files");
+        for (int i = 0; i < files.length(); i++) {
+            final String file = files.getString(i);
+            FileUtils.copyURLToFile(getResourceUrl(pluginFolderName + file),
+                new File(pluginTargetFile, file));
+        }
+        // copy package.json to plugin directory
+        FileUtils.copyURLToFile(getResourceUrl(pluginFolderName + PACKAGE_JSON),
+            new File(pluginTargetFile, PACKAGE_JSON));
+    }
+
+    private JsonObject getJsonFile(String jsonFilePath) throws IOException {
+        final URL urlResource = getResourceUrl(jsonFilePath);
+        if (urlResource == null) {
+            return null;
+        }
+        File jsonFile = new File(urlResource.getFile());
+        String jsonString;
+        if (!jsonFile.exists()) {
+            try (InputStream resourceAsStream = this.getClass().getClassLoader()
+                .getResourceAsStream(jsonFilePath)) {
+                if (resourceAsStream != null) {
+                    jsonString = FrontendUtils.streamToString(resourceAsStream);
+                } else {
+                    return null;
+                }
+            }
+        } else {
+            jsonString = FileUtils.readFileToString(jsonFile, UTF_8);
+        }
+        return Json.parse(jsonString);
+    }
+
+    private URL getResourceUrl(String resource) {
+        return this.getClass().getClassLoader().getResource(resource);
+    }
+
+    private Logger log() {
+        return LoggerFactory.getLogger(this.getClass());
+    }
+}

flow-server/src/main/resources/plugins/stats-plugin/package.json

@@ -0,0 +1,18 @@
+{
+  "description": "stats-plugin",
+  "keywords": [
+    "plugin"
+  ],
+  "repository": "vaadin/flow",
+  "name": "@vaadin/stats-plugin",
+  "version": "1.0.0",
+  "main": "stats-plugin.js",
+  "author": "Vaadin Ltd",
+  "license": "Apache-2.0",
+  "bugs": {
+    "url": "https://github.com/vaadin/flow/issues"
+  },
+  "files": [
+    "stats-plugin.js"
+  ]
+}