How to generate sourcemap from AST transform?

[trusktr]

I see in the Wiki at https://github.com/estools/escodegen/wiki/Source-Map-Usage an example with Esprima, but it doesn't include a transform step:

var ast = esprima.parse('var a = 1', {
  loc: true,
  source: 'my_file.js'
});
var output = escodegen.generate(ast, {
  sourceMap: true, // Settings source in esprima's options gives us
                   // filenames already.
  sourceMapWithCode: true // Get both code and source map
});

var code = output.code; // Generated source code
var map = output.map.toString(); // Generated source map JSON

Is it just as easy with a transform, like the following (haven't tried yet)?

var ast = esprima.parse('var a = 1', {
  loc: true,
  source: 'my_file.js'
});

estraverse.replace(ast, transform); // <-- added this line.

var output = escodegen.generate(ast, {
  sourceMap: true, // Settings source in esprima's options gives us
                   // filenames already.
  sourceMapWithCode: true // Get both code and source map
});

var code = output.code; // Generated source code
var map = output.map.toString(); // Generated source map JSON

If that works, I have another question: what if we have an AST generated from code that was already previously transformed and includes a sourcemap comment at the bottom?