As of this commit, adding the comment `//$ExpectFlowError` in flow-typed
code asserts that the next line must cause a flow error. If it does, no
error or warning is generated. If it does not, then this produces a flow
warning, which is visible to developers running `yarn flow` and
additionally causes travis to fail.
Test plan:
- As committed, `yarn travis` passes.
- I added `//$ExpectFlowError` above some line of flow-checked code which does
not currently throw an error. Afterwards, `yarn travis` failed (and a
helpful message was displayed in console on running `yarn flow`)
- I added the following bad code into one of our files:
```javascript
//$ExpectFlowError
const foo: string = 3;
```
As expected, `yarn flow` and `yarn travis` both passed.
Reorganize the code so that we have a single package.json file, which is at the root.
All source code now lives under `src`, separated into `src/backend` and `src/explorer`.
Test plan:
- run `yarn start` - it works
- run `yarn test` - it finds the tests (all in src/explorer) and they pass
- run `yarn flow` - it works. (tested with an error, that works too)
- run `yarn prettify` - it finds all the js files and writes to them