Fix env in kernel.json serialized as array instead of JSON object (issue #1499)

[Copilot]

Summary

Fixes #1499.

Since v0.14.0-RC15, installing the Almond kernel would produce a broken kernel.json where the env field was a JSON array of pairs instead of a JSON object:

"env": [["COURSIER_REPOSITORIES", "repo-dummy"]]   ← broken (RC15+)
"env": {"COURSIER_REPOSITORIES": "repo-dummy"}     ← correct (RC14)

Jupyter rejects the broken format with:

TraitError: The 'env' trait of a KernelSpec instance expected a dict, not the list

Root Cause

The regression was introduced with the Scala 3 toolchain update between RC14 and RC15. In jsoniter-scala 2.13.5 under Scala 3, the macro does not recognise Map[String, String] as a JSON-object type and instead falls back to treating it as an Iterable[(String, String)], which is serialised as a JSON array of pairs.

Fix

Introduce a new ActualMap[T](map: Map[String, T]) wrapper class with a general implicit def codec[T: JsonValueCodec]: JsonValueCodec[ActualMap[T]] that always serialises and deserialises as a JSON object. The KernelSpec.env field is changed from Map[String, String] to ActualMap[String], allowing KernelSpec.codec to remain a simple JsonCodecMaker.make-derived codec — the macro picks up the ActualMap codec from its companion object, the same pattern used by RawJson elsewhere in the codebase.

• Sorts map entries alphabetically for deterministic output.

A regression test is added to ProtocolTests that asserts env serialises as {"KEY":"VALUE"} and round-trips correctly.

[alexarchambault]

Fix the CI errors

[Copilot]

Fix the CI errors

Fixed in 6f41165. The compilation errors were caused by a do-while loop, which was removed from Scala 3. Converted it to an equivalent while loop with a hasMore boolean flag.

[alexarchambault]

Can't you instead introduce a custom case class ActualMap[T](map: Map[String, T]), define a codec for it, and use it in KernelSpec? So that we can keep using the jsoniter-scala macro when defining the KernelSpec codec

[Copilot]

Can't you instead introduce a custom case class ActualMap[T](map: Map[String, T]), define a codec for it, and use it in KernelSpec? So that we can keep using the jsoniter-scala macro when defining the...

Done in 18f05dd. Introduced ActualMap[T](map: Map[String, T]) in ActualMap.scala with a custom implicit val stringCodec: JsonValueCodec[ActualMap[String]] that always serializes as a JSON object. KernelSpec.env is now typed as ActualMap[String] and KernelSpec.codec is back to JsonCodecMaker.make — the macro picks up ActualMap.stringCodec from the companion object, same pattern as RawJson.

[alexarchambault]

Can't you define a more general implicit def codec[T: JsonValueCodec]: JsonValueCodec[ActualMap[T]] = ... here?

[Copilot]

Done in cb3654e. Replaced implicit val stringCodec with implicit def codec[T: JsonValueCodec]: JsonValueCodec[ActualMap[T]], using tCodec.decodeValue/tCodec.encodeValue for the value type instead of the String-specific methods.