What problem does this feature solve?

With @12.1.0 it was possible (though not officially documented) to set pug doctype like below

{
    test: /\.vue$/,
    loader: 'vue-loader',
    options: {
        template: { doctype: 'html' }
    }
}

Upgrading to @12.2.0, the doctype setting is no longer processed, result in symptoms like below:

div(v-my-directive) ==>

which generates tons of warnings like v, my, directive not defined since Vue tries to interpret "v-my-directive" as JS expression at runtime

I respect the changes in @12.2.0 to "simplify template preprocessor", but I'd like to see an "official" approach to set doctype, or I'll have to settle with @12.1.0

What does the proposed API look like?

The old settings like above or explicit pug rule block alongside vue:

{
  test: /\.pug$/,
  loader: 'pug'
}