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# Field Annotations
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Annotations for marking generated message fields with encoding metadata and serialization behavior. These annotations control how Wire generates code and how fields are handled during encoding and decoding.
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## Capabilities
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### WireField Annotation
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Primary annotation for protocol buffer field metadata used by Wire's code generator.
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```kotlin { .api }
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/**
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 * Annotates generated Message fields with metadata for serialization and deserialization
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 */
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@Target(AnnotationTarget.FIELD)
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@Retention(AnnotationRetention.RUNTIME)
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annotation class WireField(
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    /** The tag number used to store the field's value */
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    val tag: Int,
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    /** Reference to ProtoAdapter for keys (maps only) */
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    val keyAdapter: String = "",
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    /** Reference to ProtoAdapter for values */
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    val adapter: String,
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    /** Field label (OPTIONAL, REQUIRED, REPEATED, etc.) */
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    val label: Label = Label.OPTIONAL,
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    /** Redacted fields omitted from toString() */
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    val redacted: Boolean = false,
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    /** Original proto field name if different from generated */
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    val declaredName: String = "",
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    /** JSON field name if different from proto name */
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    val jsonName: String = "",
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    /** Oneof group name if field is part of oneof */
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    val oneofName: String = "",
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    /** Declaration order in proto schema */
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    val schemaIndex: Int = -1
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)
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```
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### Field Labels
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Enum defining the protocol buffer field behavior and encoding rules.
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```kotlin { .api }
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enum class Label {
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    /** Required field (proto2 only) */
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    REQUIRED,
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    /** Optional field (default) */
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    OPTIONAL,
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    /** Repeated field */
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    REPEATED,
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    /** Oneof field */
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    ONE_OF,
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    /** Packed repeated field (more efficient for primitives) */
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    PACKED,
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    /** Proto3 field omitted if identity value */
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    OMIT_IDENTITY;
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    /** True if field is repeated */
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    val isRepeated: Boolean
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    /** True if field uses packed encoding */
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    val isPacked: Boolean
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    /** True if field is part of oneof */
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    val isOneOf: Boolean
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}
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```
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**Usage Examples:**
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```kotlin
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// Generated message class with field annotations
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class Person(
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    @field:WireField(
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        tag = 1,
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        adapter = "com.squareup.wire.ProtoAdapter#STRING"
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    )
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    val name: String,
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    @field:WireField(
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        tag = 2,
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        adapter = "com.squareup.wire.ProtoAdapter#INT32",
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        label = WireField.Label.OPTIONAL
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    )
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    val age: Int,
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    @field:WireField(
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        tag = 3,
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        adapter = "com.squareup.wire.ProtoAdapter#STRING",
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        label = WireField.Label.REPEATED
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    )
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    val emails: List<String>,
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    @field:WireField(
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        tag = 4,
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        adapter = "com.example.AddressAdapter#ADAPTER"
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    )
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    val address: Address?,
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    unknownFields: ByteString = ByteString.EMPTY
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) : Message<Person, Person.Builder>(ADAPTER, unknownFields)
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```
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### Other Annotations
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Additional annotations for specialized use cases.
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```kotlin { .api }
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/** Annotation for enum constants */
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@Target(AnnotationTarget.FIELD)
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@Retention(AnnotationRetention.RUNTIME)
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annotation class WireEnumConstant(
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    val declaredName: String = ""
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)
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/** Annotation for RPC methods */
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@Target(AnnotationTarget.FUNCTION)
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@Retention(AnnotationRetention.RUNTIME) 
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annotation class WireRpc(
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    val path: String,
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    val requestAdapter: String,
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    val responseAdapter: String
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)
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```