fix: use Path.toUri() to handle WSL paths correctly

build.gradle.kts

@@ -104,6 +104,7 @@ dependencies {
 
     testImplementation(libs.junit)
     testImplementation(libs.junit.jupiter.api)
+    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine")
 }
 
 // Set the JVM language level used to build the project.
@@ -206,6 +207,7 @@ changelog {
 }
 
 tasks.withType<Test> {
+    useJUnitPlatform()
     environment("GRADLE_RELEASE_REPOSITORY","https://services.gradle.org/distributions")
     systemProperty("idea.log.leaked.projects.in.tests", "false")
     systemProperty( "idea.maven.test.mirror", "https://repo1.maven.org/maven2")

src/main/java/com/redhat/devtools/lsp4ij/LSPIJUtils.java

@@ -490,13 +490,7 @@ private static Language doGetFileLanguage(@NotNull VirtualFile file, @NotNull Pr
     }
 
     public static @NotNull URI toUri(@NotNull File file) {
-        // URI scheme specified by language server protocol and LSP
-        try {
-            return new URI("file", "", file.getAbsoluteFile().toURI().getPath(), null); //$NON-NLS-1$ //$NON-NLS-2$
-        } catch (URISyntaxException e) {
-            LOGGER.warn(e.getLocalizedMessage(), e);
-            return file.getAbsoluteFile().toURI();
-        }
+        return file.toPath().toUri();
     }
 
     public static @Nullable URI toUri(@NotNull PsiFile psiFile) {

src/main/java/com/redhat/devtools/lsp4ij/features/formatting/AbstractLSPFormattingService.java

@@ -43,7 +43,7 @@ protected FormattingTask createFormattingTask(@NotNull AsyncFormattingRequest fo
         if (ioFile == null) {
             return null;
         }
-        VirtualFile file = LSPIJUtils.findResourceFor(ioFile.toURI());
+        VirtualFile file = LSPIJUtils.findResourceFor(LSPIJUtils.toUri(ioFile).toString());
         if (file == null) {
             return null;
         }

src/test/java/com/redhat/devtools/lsp4ij/LSPIJUtils_toUriTest.java

@@ -0,0 +1,64 @@
+package com.redhat.devtools.lsp4ij;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledOnOs;
+import org.junit.jupiter.api.condition.OS;
+
+import java.io.File;
+import java.net.URI;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.fail;
+
+public class LSPIJUtils_toUriTest {
+
+    @Test
+    @EnabledOnOs(OS.WINDOWS)
+    void testToUriWithWslPath() {
+        // Given: Create a File object from a UNC path string
+        // Note: File object may normalize the path, so we test with the actual behavior
+        String wslPath = "\\\\wsl$\\Ubuntu\\home\\user\\project\\file.txt";
+        File wslFile = new File(wslPath);
+
+        // When
+        URI resultUri = LSPIJUtils.toUri(wslFile);
+
+        // Then
+        assertNotNull(resultUri);
+        assertEquals("file", resultUri.getScheme());
+
+        // The URI should either:
+        // 1. Have authority="wsl$" and path="/Ubuntu/home/user/project/file.txt" (correct UNC handling)
+        // 2. Or at minimum, not produce the old broken format with 4 slashes
+        String uriString = resultUri.toString();
+        assertNotNull(uriString);
+
+        // Verify it doesn't have the broken 4-slash format
+        if (uriString.contains("file:////")) {
+            fail("URI should not contain file://// (broken UNC format): " + uriString);
+        }
+    }
+
+    @Test
+    void testToUriWithLocalPath() {
+        // Given
+        File localFile = new File("/home/user/project/file.txt");
+        if (System.getProperty("os.name").toLowerCase().contains("win")) {
+            localFile = new File("C:\\Users\\user\\project\\file.txt");
+        }
+
+
+        // When
+        URI resultUri = LSPIJUtils.toUri(localFile);
+
+        // Then
+        assertNotNull(resultUri);
+        assertEquals("file", resultUri.getScheme());
+        if (System.getProperty("os.name").toLowerCase().contains("win")) {
+            assertEquals("/C:/Users/user/project/file.txt", resultUri.getPath());
+        } else {
+            assertEquals("/home/user/project/file.txt", resultUri.getPath());
+        }
+    }
+}