Autocomplete in XML using XSD

To get Intellisense (aka autocomplete) in VSCode, you need to:

1. Install the XML extension by Red Hat
2. Have an XSD file for the XML
3. Reference the XSD from the XML, or configure the extension with a mapping.

Generate an XSD from an XML

If you don't have the XSD (or it doesn't exist)

1. Use an online tool such as FreeFormatter to use an example XML as basis for the XSD.
2. Save the XSD content in a .xsd file in the same folder as the XML (preferably), e.g. example.xsd.

What happens next is dependent on the content of the XML file. What I'm about to describe below is based on a single XML file I experimented with. YMMV.

In the example XML file I looked at, the XML elements did not have a namespace prefix. The root element had an xmlns attribute that contained a URI to some metadata, but that URI didn't exist. The presence of the xmlns attribute in the XML manifests as a targetNamespace attribute in the root element of the generated XSD. This may cause the following warning by the XML VSCode extension:

Expecting no namespace, but the schema document has a target namespace ...

To avoid this (temporarily at least), remove the targetNamespace attribute from the XSD and the xmlns attribute from the top element.

Activating Autocomplete

When you activate autocomplete for XML in VSCode (such as when you type < inside an element), you should get additional suggestions in the menu that pops up. There should be choices other than <!-- and <![CDATA[>. For this to work, the XML file must be associated with the XSD file. There are several ways to do this:

1. Using xml-model

This is probably the easiest. Simply add a new line (below the top <?xml) like in this example:

<?xml version="1.0" encoding="UTF-8" ?>
<?xml-model href="example.xsd"?>

Remove any xsi attributes (see option 3) if you have them.

2. Using XMLSchema-instance

Configure your top XML element by adding the attributes shown in the example below:

<TopLevelElement xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  xsi:noNamespaceSchemaLocation="example.xsd">
    <!-- ... -->
</TopLevelElement>

Notice the use of the noNamespaceSchemaLocation attribute instead of the schemaLocation attribute.

3. Using a local configuration

In VSCode, while the XML file is the active tab, bring up the command palette and select XML: Bind to grammar/schema file. If you're using a local file for the XSD, select File Association next. Select the XSD file in the file dialog. You may need to massage the filename a little bit before it accepts it. (Decode URL-encoded characters and remove the double asterisk.) The extension will save this configuration into your Workspace Settings under xml.fileAssociations, which you can later edit.

If you're trying this option first, make sure to clear those settings before you try other options.

Relaxing the XSD

The generated XSD may assume that the elements may have to come in a certain order, so it describes child elements using <xs:sequence>. You can replace this with <xs:choice minOccurs="0" maxOccurs="unbounded">.