fix breaking change in MediaType.toString

[fwbrasil]

Problem

#331 changed MediaType.toString to become a lazy val, which is a breaking change. I'm seeing this issue while trying to publish a version of Tapir with the optimizations mentioned in softwaremill/tapir#3552.

Solution

Make the lazy val private and keep the same toString() interface as before.

[adamw]

Oh that's interesting ... what kind of errors do you see? Mima seems happy, but apparently there's more to compatibility ;)

[adamw]

maybe you could add a comment explaining why this particular class has a toStringCache field?

[fwbrasil]

done

[fwbrasil]

Maybe it's binary-compatible because Scala will still generate the overriden toString but it's not source-compatible because it's not possible to call the method with empty parenthesis. The error:

[error] /Users/fwbrasil/workspace/sttp-model/core/src/test/scala/sttp/model/MediaTypeTests.scala:65:16: not enough arguments for method apply: (index: Int)Char in class StringOps.
[error] Unspecified value parameter index.
[error]     mt.toString() shouldBe "application/gzip"
[error]                ^

[adamw]

Ah, makes sense, thanks :) @kciesielski didn't we add a similar optimization elsewhere recently? Maybe we need to add a similar work-around

[adamw]

thx :)

[kciesielski]

@adamw I did this to Uri but didn't publish a PR, just mentioned to you that it would break one toString() call in Tapir and that I didn't see this source incompatibility as a big issue.

[adamw]

@kciesielski ah ... well it would be good to maintain source compat as well, so we'll need the same logic there as well, if you introduce the change