grpc-pb: Fix lowercase name of oneof field

Signed-off-by: Johannes Zottele <[email protected]>

Author: Jozott00

protoc-gen/src/main/kotlin/kotlinx/rpc/protobuf/ModelToKotlinCommonGenerator.kt

@@ -439,7 +439,7 @@ class ModelToKotlinCommonGenerator(
 
     private fun FieldDeclaration.wireSizeCall(variable: String): String {
         val sizeFunc =
-            "$PB_PKG.WireSize.${type.decodeEncodeFuncName()!!.replaceFirstChar { it.lowercase() }}($variable)"
+            "$PB_PKG.WireSize.${type.decodeEncodeFuncName()!!.decapitalize()}($variable)"
         return when (val fieldType = type) {
             is FieldType.IntegralType -> when {
                 fieldType.wireType == WireType.FIXED32 -> "32"

protoc-gen/src/main/kotlin/kotlinx/rpc/protobuf/codeRequestToModel.kt

@@ -125,7 +125,7 @@ private fun Descriptors.Descriptor.toModel(): MessageDeclaration = cached {
     regularFields = regularFields + oneOfs.map {
         FieldDeclaration(
             // TODO: Proper handling of this field name
-            it.name.simpleName.lowercase(),
+            it.name.simpleName.decapitalize(),
             FieldType.OneOf(it),
             doc = null,
             dec = it.variants.first().dec,

protoc-gen/src/main/kotlin/kotlinx/rpc/protobuf/utils.kt

@@ -0,0 +1,9 @@
+/*
+ * Copyright 2023-2025 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.rpc.protobuf
+
+internal fun String.decapitalize(): String {
+    return this.replaceFirstChar { it.lowercase() }
+}