Add rewrite HtmlImports step (#6109)

* Rename the goal

* Flatten frontend directory

* Correct the logic to search for themed files inside node_modules

* Add IT test for client side imported components theming

* Revert "Add IT test for client side imported components theming"

This reverts commit 0cfb723.

* Revert "Correct the logic to search for themed files inside node_modules"

This reverts commit 8e65792.

* Rewrite HtmlImports to JsModules

Fixes #6092

* Rewrite the content of the file even if it doesn't match the declaration
pattern.

* Add parameter for html import rewrite strategy

* Add unit tests for rewrite HtmlImports step.

* Fix code review comments

* Add javadocs and fix minor things in code

* Apply better replacement suggestion by code review

flow-maven-plugin/pom.xml

@@ -1,4 +1,5 @@
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+<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/maven-v4_0_0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <parent>
@@ -108,5 +109,28 @@
                 </plugin>
             </plugins>
         </pluginManagement>
+
+        <plugins>
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>build-helper-maven-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <id>add-resource</id>
+                        <phase>generate-resources</phase>
+                        <goals>
+                            <goal>add-test-resource</goal>
+                        </goals>
+                        <configuration>
+                            <resources>
+                                <resource>
+                                    <directory>src/test/java</directory>
+                                </resource>
+                            </resources>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
     </build>
 </project>

flow-maven-plugin/src/main/java/com/vaadin/flow/plugin/maven/MigrateMojo.java

@@ -37,11 +37,15 @@
 import org.apache.maven.plugins.annotations.LifecyclePhase;
 import org.apache.maven.plugins.annotations.Mojo;
 import org.apache.maven.plugins.annotations.Parameter;
+import org.apache.maven.plugins.annotations.ResolutionScope;
 import org.apache.maven.project.MavenProject;
 
+import com.vaadin.flow.component.dependency.HtmlImport;
+import com.vaadin.flow.plugin.common.FlowPluginFrontendUtils;
 import com.vaadin.flow.plugin.migration.CopyMigratedResourcesStep;
 import com.vaadin.flow.plugin.migration.CopyResourcesStep;
 import com.vaadin.flow.plugin.migration.CreateMigrationJsonsStep;
+import com.vaadin.flow.plugin.migration.RewriteHtmlImportsStep;
 import com.vaadin.flow.server.frontend.FrontendUtils;
 
 import elemental.json.Json;
@@ -54,11 +58,19 @@
  * @author Vaadin Ltd
  *
  */
-@Mojo(name = "migrate", defaultPhase = LifecyclePhase.PROCESS_RESOURCES)
+@Mojo(name = "migrate-to-p3", requiresDependencyResolution = ResolutionScope.COMPILE, defaultPhase = LifecyclePhase.PROCESS_CLASSES)
 public class MigrateMojo extends AbstractMojo {
 
     private static final String DEPENDENCIES = "dependencies";
 
+    /**
+     * The strategy to rewrite {@link HtmlImport} annotations.
+     *
+     */
+    public static enum HtmlImportsRewriteStrategy {
+        ALWAYS, SKIP, SKIP_ON_ERROR;
+    }
+
     /**
      * A list of directories with files to migrate.
      */
@@ -96,6 +108,24 @@ public class MigrateMojo extends AbstractMojo {
     @Parameter(defaultValue = "true")
     private boolean ignoreModulizerErrors;
 
+    /**
+     * Allows to specify the strategy to use to rewrite {@link HtmlImport}
+     * annotations in Java files.
+     * <p>
+     * Three values are available:
+     * <ul>
+     * <li>ALWAYS : if chosen then {@link HtmlImport} will be always rewritten
+     * regardless of migration of the import files content
+     * <li>SKIP : if chosen then neither {@link HtmlImport} annotation will be
+     * rewritten
+     * <li>SKIP_ON_ERROR : if chosen then {@link HtmlImport} annotations will be
+     * rewritten only if there are no errors during migration of imported files
+     * content
+     * </ul>
+     */
+    @Parameter(defaultValue = "ALWAYS")
+    private HtmlImportsRewriteStrategy htmlImportsRewrite;
+
     @Override
     public void execute() throws MojoExecutionException, MojoFailureException {
         prepareMigrationDirectory();
@@ -195,6 +225,20 @@ public void execute() throws MojoExecutionException, MojoFailureException {
         if (!modulizerHasErrors && !keepOriginal) {
             removeOriginalResources(paths);
         }
+
+        switch (htmlImportsRewrite) {
+        case SKIP:
+            break;
+        case ALWAYS:
+            rewrite();
+            break;
+        case SKIP_ON_ERROR:
+            if (!modulizerHasErrors) {
+                rewrite();
+            }
+            break;
+        }
+
     }
 
     private void prepareMigrationDirectory() {
@@ -371,14 +415,18 @@ private void cleanUp(File dir) throws IOException {
     private String[] getResources() {
         if (resources == null) {
             File webApp = new File(project.getBasedir(), "src/main/webapp");
-            File frontend = new File(webApp, "frontend");
-            if (frontend.exists() && webApp.listFiles().length == 1) {
-                resources = new String[] { frontend.getPath() };
-            } else {
-                resources = new String[] { webApp.getPath() };
-            }
+            resources = new String[] { webApp.getPath() };
         }
         return resources;
     }
 
+    private void rewrite() {
+        RewriteHtmlImportsStep step = new RewriteHtmlImportsStep(
+                new File(project.getBuild().getOutputDirectory()),
+                FlowPluginFrontendUtils.getClassFinder(project),
+                project.getCompileSourceRoots().stream().map(File::new)
+                        .collect(Collectors.toList()));
+        step.rewrite();
+    }
+
 }

flow-maven-plugin/src/main/java/com/vaadin/flow/plugin/migration/AbstractCopyResourcesStep.java

@@ -116,6 +116,14 @@ List<String> getVisitedPaths() {
 
         private Path getTarget(Path source) {
             Path relativePath = sourceRoot.relativize(source);
+            String topLevel = relativePath.getName(0).toString();
+            if ("frontend".equals(topLevel)) {
+                if (relativePath.getNameCount() == 1) {
+                    return targetRoot;
+                }
+                relativePath = relativePath.subpath(1,
+                        relativePath.getNameCount());
+            }
             return targetRoot.resolve(relativePath);
         }
     }