Relax NG schema validation not working when DOCTYPE declaration missing with file association

[AidanRandtoul]

The following error message appears above the root tag in the xml file:

Document root element must match DOCTYPE root "null"

With this error the validation based on the schema sometimes works however the completion and hover does not work at all. It cannot either complete based on exisiting tags in the file, which is something the extension supports when schema validation is switched off.

I am using Relax NG compact schema and the issue still occurs when using the non-compact schema.

[fbricon]

can you please provide a sample xml file and its schema, reproducing the issue?

[dngulin]

I confirm the bug.

A sample schema:

element foo {
    element bar { text }
}

An xml-file with error:

<?xml version="1.0" encoding="UTF-8"?>
<foo><bar>baz</bar></foo>

An xml-file without error:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo>
<foo><bar>baz</bar></foo>

The schema is associated to the file using an xml.fileAssociations setting.

[angelozerr]

File association is not a standard association (it belongs to vscode-xml) . If you use xml-model association it should work.

I started to create a PR eclipse-lemminx/lemminx#1393 to fix this issue.