Fix dollar sign escaping for json key names.

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/AdapterGenerator.kt

@@ -303,7 +303,7 @@ internal class AdapterGenerator(
 
     result.addStatement("%N.beginObject()", writerParam)
     propertyList.forEach { property ->
-      result.addStatement("%N.name(%S)", writerParam, property.jsonName)
+      result.addStatement("%N.name(\"${property.jsonName}\")", writerParam)
       result.addStatement("%N.toJson(%N, %N.%L)",
           nameAllocator.get(property.delegateKey), writerParam, valueParam, property.name)
     }

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/TargetProperty.kt

@@ -128,7 +128,7 @@ internal data class TargetProperty(
   private val Element?.jsonName: String?
     get() {
       if (this == null) return null
-      return getAnnotation(Json::class.java)?.name
+      return getAnnotation(Json::class.java)?.name?.replace("$", "\\$")
     }
 
   override fun toString() = name

kotlin/tests/src/test/kotlin/com/squareup/moshi/kotlin/codgen/GeneratedAdaptersTest.kt

@@ -55,6 +55,27 @@ class GeneratedAdaptersTest {
   @JsonClass(generateAdapter = true)
   data class JsonAnnotation(@Json(name = "foo") val bar: String)
 
+  @Test
+  fun jsonAnnotationWithDollarSign() {
+    val adapter = moshi.adapter(JsonAnnotationWithDollarSign::class.java)
+
+    // Read
+    @Language("JSON")
+    val json = "{\"\$foo\": \"bar\"}"
+
+    val instance = adapter.fromJson(json)!!
+    assertThat(instance.bar).isEqualTo("bar")
+
+    // Write
+    @Language("JSON")
+    val expectedJson = "{\"\$foo\":\"baz\"}"
+
+    assertThat(adapter.toJson(JsonAnnotationWithDollarSign("baz"))).isEqualTo(expectedJson)
+  }
+
+  @JsonClass(generateAdapter = true)
+  data class JsonAnnotationWithDollarSign(@Json(name = "\$foo") val bar: String)
+
   @Test
   fun defaultValues() {
     val adapter = moshi.adapter(DefaultValues::class.java)