Blank line preservation

[aleclarson]

When moving a block of code, you can use toString on each node and "paste" the result by using the appropriate method. There needs to be a way to preserve blank lines between nodes, so we can preserve the author's style.

The first idea that comes to mind is a method that returns a string containing only newlines (and maybe indentation?) corresponding to the number of blank lines before or after the node (so two variants). This string can then be "pasted" just like the toString result.

As an example:

foo()

// comment 1
bar()

// comment 2
foo()

Assume the bar() expression is represented by node:

node.spaceBefore() // => "\n\n// comment 1\n"
node.toString()    // => "bar()"
node.spaceAfter()  // => "\n\n\n// comment 2\n"

In the above example, the \n that begins bar()'s line is included in the spaceBefore result. And the \n that begins the line after that is included in the spaceAfter result. I'm not certain, but I think that's the expected behavior.

I'm also undecided if indentation should be included or not. I'm leaning towards no, because toString currently strips indentation and we should match that behavior.

Another thing: maybe toString(true) can include the result of spaceAfter (and even the result of spaceBefore if we're the first sibling of a BlockStatement) to make things easier?

These decisions could easily be a source of many bugs if we aren't careful.