Make sure that primitives and inline value classes that are primitives can be packed.

inline popTag -> popTagOrDefault is needed, because packed serializer will use MISSING_TAG for entries, popTag fails on that.

Author: KosmX

formats/protobuf/commonMain/src/kotlinx/serialization/protobuf/internal/Helpers.kt

@@ -68,12 +68,11 @@ internal val ProtoDesc.integerType: ProtoIntegerType
 }
 
 internal val SerialDescriptor.isPackable: Boolean
-    @OptIn(kotlinx.serialization.ExperimentalSerializationApi::class)
     get() = when (kind) {
         PrimitiveKind.STRING,
         !is PrimitiveKind -> false
         else -> true
-    }
+    } || isInline && elementsCount == 1 && getElementDescriptor(0).isPackable
 
 internal val ProtoDesc.isPacked: Boolean
     get() = (this and PACKEDMASK) != 0L

formats/protobuf/commonMain/src/kotlinx/serialization/protobuf/internal/ProtobufTaggedDecoder.kt

@@ -95,7 +95,7 @@ internal abstract class ProtobufTaggedDecoder : ProtobufTaggedBase(), Decoder, C
     }
 
     override fun decodeInline(descriptor: SerialDescriptor): Decoder {
-        return decodeTaggedInline(popTag(), descriptor)
+        return decodeTaggedInline(popTagOrDefault(), descriptor)
     }
 
     override fun decodeInlineElement(

formats/protobuf/commonMain/src/kotlinx/serialization/protobuf/internal/ProtobufTaggedEncoder.kt

@@ -175,7 +175,7 @@ internal abstract class ProtobufTaggedEncoder : ProtobufTaggedBase(), Encoder, C
     }
 
     override fun encodeInline(descriptor: SerialDescriptor): Encoder {
-        return encodeTaggedInline(popTag(), descriptor)
+        return encodeTaggedInline(popTagOrDefault(), descriptor)
     }
 
     override fun encodeInlineElement(descriptor: SerialDescriptor, index: Int): Encoder {