Fix for crash when methods with default private type params in remote packages are called

[stefandd]

This attempts to fix the compiler crash reported in #4130

The crash happens upon attempting to call a methods from a different package that uses a package-private type as default parameter. Since it has been decided to treat this as a bug instead of a missing error, this PR implements the fix suggested by @ergl (#4130 (comment)) , namely using lookup_try() instead of lookup() in call.c's check_partial_function_call() since the former can be configured to permit private types.

With this PR, the two examples below that crashed the compiler now both compile:

Original example:

// inside the "useful" package

primitive _PrivateDefault

actor Useful[A: Any val]
  fun tag config(value: (A | _PrivateDefault) = _PrivateDefault): Useful[A] => this

// inside "main"

use "useful"

primitive This
primitive That

type Stuff is (This | That)

actor Main
  new create(env: Env) =>
    let u = Useful[Stuff].config()

Minimal example:

// In the "lib" pacakge

primitive _Private

primitive Public
  fun apply[T](v: (T | _Private) = _Private): None => None

// In main
use lib = "lib"

actor Main
  new create(env: Env) =>
    let p = lib.Public.apply[U8]()
    env.out.print(p.string())

Co-authored-by: Borja o'Cook [email protected]

[ergl]

@stefandd Can you add the minimal example as a runner test so that we can ensure that this doesn't break in the future?

[ponylang-main]

Hi @stefandd,

The changelog - fixed label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 4167.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.

[stefandd]

@stefandd Can you add the minimal example as a runner test so that we can ensure that this doesn't break in the future?

@ergl Will do. I am not familiar with the folder naming in libponyc-run but it is clearly meant to be problem-related and discernable. For this issue I have longish names like "out-of-package calls to methods with private-type default parameters".
Is this too much - do you have a suggestion how to call the folder, or does it truly not matter?

[ergl]

@stefandd Having long names is not a deal breaker. Perhaps something along the lines of private-type-as-default-argument-in-public-function ?

[stefandd]

@ergl Since both the direction for the fix and the minimal example that is now a test runner came from you, it'd be very appropriate for you to be added to this PR. How can I do this?

[ergl]

@stefandd I'm not aware of a way to do that, but don't worry about it. If you insist, you can add my github info to the commit message like this: https://stackoverflow.com/questions/7442112/how-to-attribute-a-single-commit-to-multiple-developers

[stefandd]

@stefandd I'm not aware of a way to do that, but don't worry about it. If you insist, you can add my github info to the commit message like this: https://stackoverflow.com/questions/7442112/how-to-attribute-a-single-commit-to-multiple-developers

Thanks. Looks like you were added with the last commit.

[ergl]

Apart from some nits with the release notes, I think this looks good