Support traverse of comments

[mamacdon]

Esprima can include source code comments in its AST. For example, when parsing this code with the comment:true flag:

function f(){
    /*hello*/
    //world
}

Esprima returns this AST:

{
    "type": "Program",
    "body": [ /* omitted to save space */ ],
    "comments": [
        {
            "type": "Block",
            "value": "hello"
        },
        {
            "type": "Line",
            "value": "world"
        },
    ]
}

It would be helpful for estraverse to visit the comment nodes. Currently it does not.

(I believe comments are an Esprima extension to the Spidermonkey API, so this may be non-standard. But it would be really useful for downstream projects. For example, I'm currently trying to write a linting rule for ESLint that deals with comments, and fixing this issue is a prerequisite.)

[michaelficarra]

Just use escodegen's attachComments and access the leadingComments member of the nodes as you visit them in a regular traversal. In your PR (#10), they are treated as regular nodes (not desirable) and just stuck on the end of the traversal (also not desirable).

[mamacdon]

OK