Added codegen support for inline classes (#923)

* Added codegen support for inline classes

* moved to DualKotlinTest

* added test class consuming inline class

kotlin/tests/pom.xml

@@ -117,6 +117,7 @@
           <args>
             <arg>-Werror</arg>
             <arg>-Xuse-experimental=kotlin.ExperimentalStdlibApi</arg>
+              <arg>-XXLanguage:+InlineClasses</arg>
           </args>
         </configuration>
       </plugin>

kotlin/tests/src/test/kotlin/com/squareup/moshi/kotlin/DualKotlinTest.kt

@@ -252,4 +252,36 @@ class DualKotlinTest(useReflection: Boolean) {
     assertThat(decoded.a).isEqualTo(null)
   }
 
+  @Test fun inlineClass() {
+    val adapter = moshi.adapter<InlineClass>()
+
+    val inline = InlineClass(5)
+
+    val expectedJson = """{"i":5}"""
+    assertThat(adapter.toJson(inline)).isEqualTo(expectedJson)
+
+    val testJson = """{"i":6}"""
+    val result = adapter.fromJson(testJson)!!
+    assertThat(result.i).isEqualTo(6)
+  }
+
+  @JsonClass(generateAdapter = true)
+  data class InlineConsumer(val inline: InlineClass)
+
+  @Test fun inlineClassConsumer() {
+    val adapter = moshi.adapter<InlineConsumer>()
+
+    val consumer = InlineConsumer(InlineClass(23))
+
+    val expectedJson= """{"inline":{"i":23}}"""
+    assertThat(adapter.toJson(consumer)).isEqualTo(expectedJson)
+
+    val testJson = """{"inline":{"i":42}}"""
+    val result = adapter.fromJson(testJson)!!
+    assertThat(result.inline.i).isEqualTo(42)
+  }
 }
+
+// Has to be outside since inline classes are only allowed on top level
+@JsonClass(generateAdapter = true)
+inline class InlineClass(val i: Int)