Original PR: https://github.com/babel/babel/pull/2469. Seems this got
lost in the v6 changes.
- - -
Without this, the only way to replace the arrow function is to either
manually override its `node.body`, or duplicate the arrow:
```js
// Old
ArrowFunctionExpression: function (node) {
node.body = t.blockStatement(...);
// Or
return t.ArrowFunctionExpression(
node.params,
t.blockStatement(...),
node.async
);
}
// New
ArrowFunctionExpression: function() {
this.get("body").replaceWith(t.blockStatement(...));
}
```
This introduces "pass per preset" feature, spawting a new traversal for each preset in case if the `passPerPreset` is `true` (default is `false`). This gives opportunity to define "before" and "after" presets, mimicking a similar feature from Babel 5. A rationally for this is to make plugins as short as possible, and handled only needed nodes, not afrading potential collisions in case if presets are merged.
Rather than repeating the original location when we exit a node, we need to restore the previous parent’s original line location, since the source map format denotes the start location.
As a follow up from #3145 we agreed to add a new format that is a
superset of the compact format option. Do things that are considered
dangerous. e.g. not printing semicolons, or print literal values
as opposed to raw values.
`generatedPositionFor` accepts a position in one of the sourcemap's *input* source files. Therefore the `source` path
should be one of the sourcemap's input `sources`, not the output `file`.
- Drops input mappings that cannot be mapped through Babel's sourcemap
- For example, Babel's sourcemap does not have mappings for leading comments, so any mapping from an input sourcemap for those leading comments must be dropped from the merged sourcemap
