Peg.js mode doesn't support JavaScript embeds

[jcubic]

Just found that CodeMirror PEG.js mode doesn't work properly if you use JavaScript prefix in the grammar.

PEG.js (and Peggy maintained fork) supports code like this that break the mode:

{

    var heredoc_begin = null;
    var $$__m; // result of match
    var variable_prefix = '$_';
    var match_identifer = make_identifier('$$__m');
    var match_method = make_identifier('match');

    function make_if(test, body, alternative) {
        return {
            "type": "IfStatement",
            "test": test,
            "consequent": make_block(body),
            "alternate": alternative
        };
    }
}

Start = statements:(!"end" _ statement* / _) {
    return {
        "type": "Program",
        "body": [{
            "type": "ExpressionStatement",
            "expression": {
                "type": "CallExpression",
                "callee": {
                    "type": "FunctionExpression",
                    "id": null,
                    "async": true,
                    "params": [],
                    "body": {
                        "type": "BlockStatement",
                        "body": statements[2].filter(Boolean)
                    }
                },
                "arguments": []
            }
        }]
    };
}

Peggy also supports {{ <JavaScript> }} not sure if it's also supported by PEG.js.

This copy/pasted part of my parser. As you can see, GitHub supports JavaScript code snippets like this.

I think that this should be easy to fix because adding:

start = '' 

in front fix the issue.

I can check the mode file and see if I can fix it.

[jcubic]

It may be something more complex. When PegJS mode initially loaded with JavaScript mode, it looks correct. But after editing it the colors are broken. I may create Video to show this.

Also found this code problematic:

function_definition = _ "def" _ name:variable _ "(" args:(variable _ ","? _)* ")" _  body:statement* _ "end" _ {
    const fn_name = name.name.replace(/\$_/, '');
    if (available_commands.includes(fn_name)) {
        const error = new Error(`invalid function name, '${fn_name}' is a command`);
        error.location = move_location(location(), 4, fn_name.length + 4);
        throw error;
    }
    var args = args.map(function(arg) { return arg[0]; });
    return {
        "type": "FunctionDeclaration",
        "id": name,
        "params": args,
        "async": true,
        "body": {
            "type": "BlockStatement",
            "body": body
        }
    };
}