Issue a PR to GH from extension

[rvantonder]

An extension for issuing a GitHub pull request on the client side (given a changeset and commit/PR metadata).

Doing this as a PR because I want feedback on TypeScript things :)

Exposes a top-level function issuePullRequestWithToken which kicks off the following sequence:

• get the commit of the branch we will PR, or create it if it does not exist
• create a git tree from the file(s) and content changes passed to the extension, and attach it to the PR branch
• push the commit to the PR branch
• create the pull request against a destination branch

All of the PR logic lives in pull-request-core.ts. I pulled this out of the extension due to sourcegraph/sourcegraph#733, so I could set up testing.

The extension entry point exposes the main command as pr.issuePullRequest.

Some simplifying assumptions for now:

• One shot commit-and-PR, meaning
  • One commit attached to PR
  • No support to add multiple commits to an existing PR, or remove/close PR

See other comments inline.

[rvantonder]

cc @felixfbecker teach me things about TS :))

[felixfbecker]

Suggested change

	"extends": "./node_modules/@sourcegraph/tsconfig/tsconfig.json",
	"extends": "@sourcegraph/tsconfig",

[rvantonder]

I don't think I touched this file (I ran the Sourcegraph script to set up extensions). Unsure, but thanks for catching.

[felixfbecker]

You almost never need the Promise constructor, unless you need to convert some other callback API to Promises. When you do need to use it, you should minimize the code inside it. Here you already have a Promise at hand so you can just return and chain that (or use async/await).

If you were looking for a way to reject the Promise, you just need to throw inside a handler or async function.

[rvantonder]

Makes sense. Is throw new Error(...) a reasonable thing or are there better conventions for error handling?

[felixfbecker]

throw new Error() is the way to go for errors.

[felixfbecker]

Here ya go :)

[rvantonder]

That was really helpful thanks Felix!