Added MILL_TEST_FREE_PORT

[albassort]

Made in accordance to #3802

[albassort]

RE: There is some failing tests on HEAD right now. I think

Run Tests / windows (17.0.14, 'integration.bootstrap[no-java-bootstrap].native.server') / run (pull_request)Failing after 9m

Might be related to the PR but im not sure. I will be investigating,

[lefou]

Is this a single port or multiple. The comment is a bit vague. If it is multi, that the variable should be MILL_TEST_FREE_PORTS and we should document here, which separator is used.

[lefou]

Magic number 6! A parameter or a named constant might be better.

[lihaoyi]

This doesn't satisfy the original issue

The end result is that Mill's own example suite can remove all hardcoded ports and replace them with usages of the MILL_TEST_FREE_PORT environment variable

[albassort]

This doesn't satisfy the original issue

The end result is that Mill's own example suite can remove all hardcoded ports and replace them with usages of the MILL_TEST_FREE_PORT environment variable

I misunderstood, I thought that were to be done in a second PR. I will work on this.

[albassort]

@lihaoyi @lefou

So there is numerous limitations with what I have here.

1. The PR uses the PORT environmental variable
2. Ports are ephemeral with no central manager for the following reasons
   1. The desire to have it in a ExternalModule, any build.mill can access the code
   2. The lack of any existing central manager for Tasks as well was UTestManager
   3. The lack of access to the ExecutionContext from the UTestManager
3. Only works for UTESTFramework

I experimented with adding some code in ExecutionImpl, thats where it could be managed if I knew

1. How I can add such env variable from GroupExecute or Execute0. There the ExecutionContext can be modified
2. How to route the ExecutionContext into UTestFramework. From what I can tell, there is no way
3. How I can coordinate from all parts of the code to a specific location easily. This is also an issue in my other PR. I have no way of getting the out/ folder from all parts in the codebase, so I cant move the code to the testkit or server or runner and use a lock to coordinate ports over a JSON port.

Still, you can easily add some code to Task.Command {} (and I did) To allow a centrally managed Port dispatcher for those

---

Regardless, I did manage to replace hard coded ports for most of the TESTS. However, there is still the chance there can be conflicting ports.

[lihaoyi]

I must admit I am having trouble following the code. There's a bunch of random "!" strings, an apparently unused MILL_TEST_FREE_PORT variable, and other things.

As far as I can tell, the current implementation is unique to UTestExampleTestSuite. We should try and make it work with any Task with some kind of ports = true or ports = 1 flag, so it's useful to users as ewll

[albassort]

I must admit I am having trouble following the code. There's a bunch of random "!" strings, an apparently unused MILL_TEST_FREE_PORT variable, and other things.

As far as I can tell, the current implementation is unique to UTestExampleTestSuite. We should try and make it work with any Task with some kind of ports = true or ports = 1 flag, so it's useful to users as ewll

I will mark as WIP until I figure out a way to make it work with all Tasks