[chore] Update interactionPolicy sub-policy parsing in line with documented defaults (#4229)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
> If this is a documentation change, please briefly describe what you've changed and why.

Brings our parsing of unset sub-policies in line with the defaults documented here: https://docs.gotosocial.org/en/v0.19.1/federation/interaction_policy/#defaults-per-sub-policy

Closes https://codeberg.org/superseriousbusiness/gotosocial/issues/4146

Part of https://codeberg.org/superseriousbusiness/gotosocial/issues/4026

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4229
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/internal/typeutils/internaltoas.go b/internal/typeutils/internaltoas.go
index cef48e194..4762e3c8b 100644
--- a/internal/typeutils/internaltoas.go
+++ b/internal/typeutils/internaltoas.go
@@ -1939,6 +1939,19 @@ func (c *Converter) InteractionPolicyToASInteractionPolicy(
 	policy := streams.NewGoToSocialInteractionPolicy()
 
 	/*
+		Implementation note for the below:
+		While it's possible for remote instances to set
+		sub-policies like canLike, canReply, etc to null
+		values, or omit them entirely, GtS always falls
+		back to default non-nil sub-policies when storing
+		policies created for local statuses. Therefore,
+		since we only ever serialize our *own* statuses
+		to AS format using this function, it's safe to
+		assume that the values will always be set, rather
+		than checking for nil ptrs.
+	*/
+
+	/*
 		CAN LIKE
 	*/