`this.blockPath.get("body")` constructs an array of paths corresponding to each node in `blocks.body` so takes O(n) time if n is that length. We were re-constructing that array on each iteration, so the entire loop was O(n^2).
On files with many statements in a single block (such as Rollup-generated bundles), this takes a large portion of time. In particular, this makes transforming react-dom.development.js about 40% faster. Not that you should be transforming our bundle with Babel.
Test Plan:
Make an HTML file with these three lines and watch it in the Chrome Performance tab to see timings (on my machine: 2.9s before, 1.6s after):
```
<!DOCTYPE html>
<script src="https://unpkg.com/babel-standalone@7.0.0-beta.3/babel.js"></script>
<script type="text/babel" src="https://unpkg.com/react-dom@16.2.0/umd/react-dom.development.js"></script>
```
This commit introduces 4 changes:
1) Function declarations are wrapped using function declarations.
This has two advantages:
- We can rely on native hoisting, instead of using _blockHoist
- The function isn't wrapped until it is called. This avoids
problems where `regeneratorRuntime.wrap` was called before
that `babel-polyfill` was imported.
Example:
function fn() {}
// becomes
function fn() { return _fn.apply(this, arguments); }
function _fn() {
_fn = _wrapper(/* Original function ... */);
return _fn.apply(this, arguments);
}
2) Use a single template for both named and anonymous function
expressions. They already had the same behavior, but the one
used for named functions was a bit longer.
3) Use normal functions instead of arrow functions to wrap
function expressions.
4) Generate a name based on the original one for wrapped
functions (e.g. `foo` becomes `_foo` instead of `_ref`).
* Split exportExtensions into two plugins in babylon
* rename proposal-export-default to proposal-export-default-from
* rename proposal-export-namespace to proposal-export-namespace-from
* Consider reexports for bindingKindLookup.
* Update test cases according to reexports change
* Fix order for assign reexports.
* void 0 assignation to module keys only for loose mode.
* Create buildReexportsFromMeta helper.
* Update umd/amd fixtures.
* Refactor reexports build.
* Hoist template for reexports.
* Use map as a second argument of Array.from.
* Remove unnecessary export.
* First implementation sketch and testcase
* Use helper instead of inline IIFE's
* minNodeVersion 6.0.0
* Hoisted visitor for subtraversal and fixed edgest case
* Resolve merge conflicts in helpers
* Remove duplicated helper from messing up Git
