fix: Remove read-only flag on copy

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

@@ -18,7 +18,11 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.UncheckedIOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.Objects;
+import java.util.stream.Stream;
 
 import org.apache.commons.io.FileUtils;
 import org.slf4j.Logger;
@@ -72,6 +76,12 @@ static void copyLocalResources(File source, File target) {
         }
         try {
             FileUtils.copyDirectory(source, target);
+            try (Stream<Path> fileStream = Files
+                    .walk(Paths.get(target.getPath()))) {
+                // used with try-with-resources as defined in walk API note
+                fileStream.filter(file -> !Files.isWritable(file)).forEach(
+                        filePath -> filePath.toFile().setWritable(true));
+            }
         } catch (IOException e) {
             throw new UncheckedIOException(String.format(
                     "Failed to copy project frontend resources from '%s' to '%s'",

flow-server/src/test/java/com/vaadin/flow/server/frontend/TaskCopyLocalFrontendFilesTest.java

@@ -0,0 +1,53 @@
+package com.vaadin.flow.server.frontend;
+
+import java.io.File;
+import java.io.IOException;
+
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+public class TaskCopyLocalFrontendFilesTest {
+
+    @Rule
+    public final TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+    @Test
+    public void directoryWithReadOnlyFile_copyIsNotReadOnly()
+            throws IOException {
+        final File sourceFolder = createReadOnlySource();
+
+        final File outFolder = temporaryFolder.newFolder("out");
+
+        TaskCopyLocalFrontendFiles.copyLocalResources(sourceFolder, outFolder);
+
+        final File copiedReadOnly = new File(outFolder, "readOnly.txt");
+        Assert.assertTrue(
+                "Copied files should be writable even when source is readOnly",
+                copiedReadOnly.canWrite());
+
+    }
+
+    @Test
+    public void directoryWithReadOnlyFile_canCopyMultipleTimesToSource()
+            throws IOException {
+        final File sourceFolder = createReadOnlySource();
+
+        final File outFolder = temporaryFolder.newFolder("out");
+
+        TaskCopyLocalFrontendFiles.copyLocalResources(sourceFolder, outFolder);
+
+        TaskCopyLocalFrontendFiles.copyLocalResources(sourceFolder, outFolder);
+    }
+
+    private File createReadOnlySource() throws IOException {
+        final File sourceFolder = temporaryFolder.newFolder("source");
+        File readOnly = new File(sourceFolder, "readOnly.txt");
+        readOnly.createNewFile();
+        Assert.assertTrue("Could not make file read-only",
+                readOnly.setReadOnly());
+
+        return sourceFolder;
+    }
+}