Fix nrepl port race condition

[clyfe]

What has Changed?

• Race is: the get-port-from-file code overwrites the port-from-regex with nothing when the nrepl-port file is not yet present at the time is read.
• Fix: don't get-port-from-file when port already present.

Fixes #901

My Calva PR Checklist

I have:

• Read How to Contribute.
• Directed this pull request at the dev branch. (Or have specific reasons to target some other branch.)
• Made sure I have changed the PR base branch, so that it is not published. (Sorry for the nagging.)
• Updated the [Unreleased] entry in CHANGELOG.md, linking the issue(s) that the PR is addressing.
• Figured if anything about the fix warrants tests on Mac/Linux/Windows/Remote/Whatever, and either tested it there if so, or mentioned it in the PR.
• Tested the VSIX built locally from the PR (so, after you've submitted the PR).
  • Tested the particular change
  • Figured if the change might have some side effects and tested those as well.
  • Smoke tested the extension as such.
• Referenced the issue I am fixing/addressing in a commit message for the pull request.
  • If I am fixing the issue, I have used GitHub's fixes/closes syntax

The Calva Team PR Checklist:

Before merging we (at least one of us) have:

• Made sure the PR is directed at the dev branch (unless reasons).
• Figured if anything about the fix warrants tests on Mac/Linux/Windows/Remote/Whatever, and tested it there if so.
• Read the source changes.
• Given feedback and guidance on source changes, if needed. (Please consider noting extra nice stuff as well.)
• Tested the VSIX built from the PR (well, if this is a PR that changes the source code.)
  • Tested the particular change
  • Figured if the change might have some side effects and tested those as well.
  • Smoke tested the extension as such.
• If need be, had a chat within the team about particular changes.

Ping @PEZ, @kstehn, @cfehse, @bpringe

[PEZ]

Ah, great that you found where this happens! It's consistent with the behaviour that this just happens now and then.

However, we can't delete that code. It is used for the Calva Connect command. What you'll need to do is to only execute it conditionally. So if we already have a port, this should not be done, otherwise it should.

[clyfe]

Tested the VSIX built from the PR locally, but not the one off circleci, nor will I do so.

[PEZ]

Tested the VSIX built from the PR locally, but not the one off circleci

That's perfectly OK. The point is to make sure the release build works in the sense that the tree shaking and munging hasn't broken things. It is tested just as well with your locally built VSIX:

[clyfe]

Let's merge.

[PEZ]

This needs to be addressed before merge.

[PEZ]

Thanks. We're getting there. 😄

Generally (and we should add this to the contribution guidelines) we want fixes like this to be quite surgical. You've found the place for the race condition, you've fixed it. If you see other changes that should be made, better send them in a separate PR.

[PEZ]

Thanks. Totally appreciate that you helped fix this and followed through.