fix: handle Windows UNC paths correctly

org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/edit/LSPEclipseUtilsTest.java

@@ -297,6 +297,20 @@ public void testURICreationUnix() {
 		Assert.assertEquals("file:///test%20with%20space", LSPEclipseUtils.toUri(new File("/test with space")).toString());
 	}
 
+	@Test
+	public void testToUri_WindowsDriveLetter() {
+		Assume.assumeTrue(Platform.OS_WIN32.equals(Platform.getOS()));
+		// Use a synthetic drive path (doesn't need to exist)
+		File drivePath = new File("C:\\Temp\\with space");
+		URI uri = LSPEclipseUtils.toUri(drivePath);
+		// Should be file:///C:/... and percent-encode spaces
+		Assert.assertTrue(uri.toString().startsWith("file:///C:/Temp/"));
+		Assert.assertFalse(uri.toString().contains("  "));
+		Assert.assertTrue(uri.toString().contains("with%20space"));
+		// Should not contain quadruple slashes
+		Assert.assertFalse(uri.toString().startsWith("file:////"));
+	}
+
 	@Test
 	public void testUNCwindowsURI() {
 		Assume.assumeTrue(Platform.OS_WIN32.equals(Platform.getOS()));
@@ -308,6 +322,22 @@ public void testUNCwindowsURI() {
 		Assert.assertEquals(file1, file2);
 	}
 
+    @Test
+    public void testToUri_WindowsUNC() {
+        Assume.assumeTrue(Platform.OS_WIN32.equals(Platform.getOS()));
+        File unc = new File("\\\\localhost\\c$\\Windows");
+        URI uri = LSPEclipseUtils.toUri(unc);
+        System.err.println(uri.toString());
+        Assert.assertTrue(uri.toString().startsWith("file://localhost/c$/Windows"));
+
+		File uncWithSpaces = new File("\\\\server-name\\shared folder\\dir with space");
+		URI uriWithSpaces = LSPEclipseUtils.toUri(uncWithSpaces);
+		Assert.assertTrue(uriWithSpaces.toString().startsWith("file://server-name/shared%20folder/dir%20with%20space"));
+
+		// Ensure there is an authority and no malformed quadruple slashes
+		Assert.assertFalse(uriWithSpaces.toString().startsWith("file:////"));
+	}
+
 	@Test
 	public void testToWorkspaceFolder() {
 		WorkspaceFolder folder = LSPEclipseUtils.toWorkspaceFolder(project);

org.eclipse.lsp4e/src/org/eclipse/lsp4e/LSPEclipseUtils.java

@@ -1332,7 +1332,15 @@ public static URI toUri(IPath absolutePath) {
 	public static URI toUri(File file) {
 		// URI scheme specified by language server protocol and LSP
 		try {
-			return new URI("file", "", file.getAbsoluteFile().toURI().getPath(), null); //$NON-NLS-1$ //$NON-NLS-2$
+			final var path = file.getAbsoluteFile().toURI().getPath();
+			if (path.startsWith("//")) { // UNC path like //localhost/c$/Windows/ //$NON-NLS-1$
+				// split: authority = "localhost", absPath = "/c$/Windows/"
+				final int slash = path.indexOf('/', 2);
+				final String authority = slash > 2 ? path.substring(2, slash) : path.substring(2);
+				final String absPath = slash > 2 ? path.substring(slash) : "/"; //$NON-NLS-1$
+				return new URI(FILE_SCHEME, authority, absPath, null);
+			}
+			return new URI(FILE_SCHEME, "", path, null); //$NON-NLS-1$
 		} catch (URISyntaxException e) {
 			LanguageServerPlugin.logError(e);
 			return file.getAbsoluteFile().toURI();