Formatter: append multiple lines seems not to work as expected (prepend works) - resolved: I accidentally have overseen a conflict

[goto40]

I have a Grammar (languim 3.1) as follows (modified hello-world):

entry Model:
    (groups+=Group)+;

Group:
    'group' name=ID '{'
        (persons+=Person | greetings+=Greeting | groups+=Group)*
     '}';

Person:
    'person' name=ID info=STRING;

Greeting:
    'Hello' person=[Person:ID] '!';

with a formatter as follows:

    protected override format(node: AstNode): void {
        if (ast.isGroup(node)) {
            const formatter = this.getNodeFormatter(node);
            const start = formatter.keyword('group');
            const bracesOpen = formatter.keyword('{');
            const bracesClose = formatter.keyword('}');
            start.prepend(Formatting.newLines(3));
            formatter.interior(bracesOpen, bracesClose).prepend(Formatting.indent());
            bracesOpen.prepend(Formatting.newLine());
            bracesClose.prepend(Formatting.newLine());
            formatter.property('name').surround(Formatting.oneSpace());
        } else if (ast.isModel(node)) {
            const formatter = this.getNodeFormatter(node);
            const nodes = formatter.nodes(...node.groups);
            nodes.prepend(Formatting.noIndent());
        }
    }

This works as expected: a model is formatted like in the following example:

group hello
{
  person Tom "not jerry"
  person Jerry "not a cat...a mouse"


  group inner
  {
    person Tim "not a dog"
    person Struppi "not a human...an animal"
  }
}

However, when changing prepend to append (start.append(Formatting.newLines(3));) no empty lines are inserted anywhere... Is this related to some open issue or did I misunderstand the described function call?

[msujew]

Hey @goto40,

at least in this case, you run into conflicting formattings. On one hand you have formatter.property('name').surround(Formatting.oneSpace()), which expects that between group hello there is exactly one space. On the other hand you have start.append(Formatting.newLines(3)), which expects that between group hello there are three new lines. Since the surround(Formatting.oneSpace()) call comes last, it receives precedence.

[goto40]

Thank you for the quick reply!

[msujew]

IIRC you can specify a priority on the formattings (the Formatting functions have an optional parameter for that). A higher priority gets precedence in case of conflicts.

[goto40]

Thanks again. However I probably misused the priority somehow... In the following case the property('name').surround wins in all cases. Only when commenting out the name-formatting I get an effect from start.append:

        if (ast.isGroup(node)) {
            const formatter = this.getNodeFormatter(node);
            const start = formatter.keyword('group');
            const bracesOpen = formatter.keyword('{');
            const bracesClose = formatter.keyword('}');
            start.append(Formatting.newLines(3,{priority: 10})); // this one has no effect (except I comment the line **1**)
            formatter.interior(bracesOpen, bracesClose).prepend(Formatting.indent());
            bracesOpen.prepend(Formatting.newLine());
            bracesClose.prepend(Formatting.newLine());
            formatter.property('name').surround(Formatting.oneSpace({priority: 0})); // this one (**1**) wins
        } ...

[msujew]

Hm, might be that the priority based conflict resolution doesn't work correctly on that case. That another bug/issue I need to track for the formatter improvements I'm planning to do soon (probably for a 4.0 - it's likely minorly API breaking).