* fix: should not remove let binding even it is wrapped in closure
Fixes#10339
* fix: remove bindings defined in blockScope when wrapped in closure
* Move test assertions to the top level to ensure that they run
* Better tdz tests
- Use jest's expect.toThrow/expect.not.toThrow
- Add input/output tests
* Fix basic tdz (a = 2; let a)
Fixes#6848
* Make _guessExecutionStatusRelativeTo more robust
* Add tests
* Return less "unkown" execution status
* "function" execution status does not exist
* Fix recursive functions
* Update helper version
* "finally" blocks are always executed
* Typo
In https://github.com/babel/babel/issues/9511 (and #9495 is another symptom), @PavelKastornyy reported a node crash becaue the JavaScript heap run out of memory. The problem was that their code was adding enumerable properties to `Object.prototype`: it is something that shouldn't be done, but Babel shouldn't make node crash if someone adds them.
I reduced down the problem to `for...in` loops in `@babel/traverse` that grew the memory consumption exponentially because of that unexpected properties.
* rename colliding let bindings with for loop init
* added complex test case to check if loop init collisions were handled correctly
* updated test files
`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>
```
