Build bug: process PID reuse with non-cleaned-up tmp directory

[chriskrycho]

The Bug

We use the process.pid for building the output directory:

ember-cli-typescript/ts/lib/incremental-typescript-compiler/index.js

Line 119 in 1228ff0

let outDir = path.join(tmpdir(), `e-c-ts-${process.pid}`);

This can cause different builds (even from different apps) to end up with the same directory in the build tree. Here's the scenario where we triggered it:

• running on CI, so reusing the same local directory for various apps (because it's just getting checked out to some default checkout directory)
• the system temp directory we created doesn't get deleted for some reason (we don't delete it in e-c-ts at all as far I can see)
• the PID happens to get recycled

When this happens, the actual same folder on disk gets reused, and you can end up with build artifacts from a previous build – including from totally separate applications! – in the build pipeline, causing runtime require resolution errors or similarly weird behaviors.

1. We should generate a UUID or some such for those to make sure that this kind of collision isn't possible.
2. We should be good citizens and clear the directory when we're done.

[chriskrycho]

Suggestion: replace use of pid with an actual uuid.