"watch" mode

[benjie]

V5 is split into these phases, effectively:

1. read/resolve the config
2. build the inflectors
3. perform the data gathering
4. generate the schema

Step 3 pulls data typically from external sources (e.g. a PostgreSQL database), and changes to that should trigger step 3 and 4 to run again. This is what V4 did and it's what V5 should do.

However, it'd be really nice if watch mode also applied to configuration/plugins/etc. To achieve that, however, is incredibly complex - we need to negotiate things like require.cache and asynchronous import without caches - and we need to do so without causing memory leaks.

We have similar concerns when doing watch mode in graphile-worker, and there's known bugs in the implementation we have for that.

For now, we're going to have watch mode just watch the PostgreSQL database I think - any changes to code (configuration, plugins, etc) should be handled by restarting the Node process via nodemon or similar.

If you have ideas on how to improve this situation, please detail them below!

[benjie]

Initial watch mode in #15

[ab-pm]

Hot module reloading doesn't appear to be very popular yet in node.js. There are a few projects though:

• https://github.com/fgnass/node-dev
• https://github.com/palmerhq/backpack
• https://github.com/jaredpalmer/razzle
• https://github.com/jlongster/backend-with-webpack
• https://hackernoon.com/hot-reload-all-the-things-ec0fed8ab0