Nested indentation in formatting

[saayv1]

I'm working on a custom language and have a question about the best approach for handling nested indentation in formatters.

My use case:

I have a grammar with nested block structures:

Block:
    'block' name=ID '{' 
         'subBlock' '{' subBlock+=Item+ '}'
    '}';

Item:
    name=ID;

This produces syntax like :

block MyBlock {
subBlock {
item1
item2
}
}

The Challenge:

I need the items inside the 'subBlock' to be double indented(8 spaces with 4-space tabs)- one level for being inside the outer block and another level for being inside subBlock. Like this

block MyBlock {
    subBlock {
        item1
        item2
    }
}

My current solution:

I'm using a custom formatting object with explicit tab counts:

private formatBlock(node: act.Block): void {
    const formatter = this.getNodeFormatter(node);
    
    const doubleIndent = {
        options: {},
        moves: [{
            tabs:2
            lines:1
        }]
    };

    formatter.keyword('block').prepend(Formatting.noIndent());
    formatter.property('name').prepend(Formatting.oneSpace()).append(Formatting.oneSpace());

    const subBlockKeyword = formatter.keyword('subBlock');
    subBlockKeyword.prepend(Formatting.indent()).append(Formatting.oneSpace());

    for (const item of node.subBlock) {
        formatter.node(item).prepend(doubleIndent);
    }
}

My questions:

1. Is this the recommended approach for nested indentation in langium formatters? Or is there a more idiomatic way using the Formatting API?
2. I tried using Formatting.indent{{ allowMore:true }} but it didn't produce double indentation. Should that work differently?

The current solution works but I want to make sure I'm following the best practices. Any guidance would be appreciated.

Thank you!

[cdietrich]

Hi, is there a reason not to move the complete 'subBlock' '{' subBlock+=Item+ '}' into a own rule/ast node.
otherwise you basically have it to do in the way you do it or sth similar

[msujew]

I would recommend to do this as well. I never expected adopters to have multiple levels of indentation in one AST node (it's an anti-pattern, there are multiple reasons for that), so it's reflected as an implementation detail in the formatter.

[saayv1]

@cdietrich & @msujew Thank you for the suggestion. I implemented it as you recommended and that worked for me.