Sam's Blog

This is part 2 of [many?] posts about creating an ANTLR-based language service for Visual Studio.

Since this is a near-trivial feature to add based on the code in my previous post, I’ll go ahead and get it in tonight. We want to fold from the opening { to the closing } of a function, so the first thing to do is find that in the grammar.

declaration_
    :   class1? type? IDENTIFIER paren_params block
    |   simple_declaration
    ;

The first alternative in the declaration_ rule is a function: clearly you have return type, name, parameters, and then the definition block. Since the block rule starts with { and ends with }, it’s exactly what we want to fold. We’ll make this work just like the braces; change the rule to add an action to mark the folding region:

declaration_
    :   class1? type? IDENTIFIER paren_params block
        { Region( $block.start, $block.stop ); }
    |   simple_declaration
    ;

Then open up your MyCParserHelper.cs file and add these two Region helper functions immediately above the DefineRegion function already there:

1
2
3
4
5
6
7
8

public void Region( IToken lh, IToken rh )
{
    DefineRegion( TextSpanHelper.Merge( ToTextSpan( lh ), ToTextSpan( rh ) ) );
}
public void Region( IToken token )
{
    DefineRegion( ToTextSpan( token ) );
}

Finally, you need to make sure the AuthoringSink knows that you are making changes to the document’s hidden region markers by adding a line to DefineRegion:

1
2
3
4
5

public void DefineRegion( TextSpan span )
{
    Sink.ProcessHiddenRegions = true;
    Sink.AddHiddenRegion( span );
}