Enable Hierarchical Projects (HMPP) support

[twyatt]

Similar to touchlab/Stately#46, HMPP is needed in order for downstream consumers of this library to enable HMPP.

See JuulLabs/kable#63 as an example (failed) attempt to enable HMPP downstream of this library.

[benasher44]

My understanding was that this doesn't work for user-defined libraries yet: https://youtrack.jetbrains.com/issue/KT-40975. Though, JuulLabs/kable's test PR seems to prove otherwise. Will this break non-HMPP consumers of 1.4+?

[benasher44]

Regardless, given how close we are to 1.4.30 release, I think I'll include support for this in the 1.4.30 release

[twyatt]

Will this break non-HMPP consumers of 1.4+

My understanding is that it is backwards compatible (or at least there is another flag that can make it backwards compatible). If I can find the time, I'll try to look into this to confirm and see if I can find the flag that I'm thinking of.

[benasher44]

I asked Kotlin folks, and the "compatibility variant" needs to be enabled to support non-HMPP clients. Here's an example:

https://github.com/ktorio/ktor/blob/master/gradle.properties#L80-L81

They're working on correcting the docs for this.

[twyatt]

I asked Kotlin folks, and the "compatibility variant" needs to be enabled to support non-HMPP clients.

Nice! You beat me to it. I found a kotlinlang Slack thread that also discusses the enableCompatibilityMetadataVariant flag, and reaffirms your findings.

[russhwolf]

FYI I currently don't have any of this stuff enabled in Multiplatform Settings largely because the 1.4.20 release blog mentioned better compatibility with people on older Kotlin versions or who don't enable hmpp themselves if it's disabled in the library https://blog.jetbrains.com/kotlin/2020/11/kotlin-1-4-20-released/#updated-structure-of-multiplatform-library-publications

Because I never had a reply in that Slack thread, I don't know whether kotlin.mpp.enableCompatibilityMetadataVariant=true alleviates that.

[benasher44]

kotlin.mpp.enableCompatibilityMetadataVariant=true should alleviate it. The issue is that the newer model has a different metadata format that's incompatible. That flag will additionally publish the old format, as I understand it.

[benasher44]

Should be fixed in 0.2.4