[DO NOT MERGE] Entity proof of concept

Sources/Exporters/OpenTelemetryProtocolCommon/common/ResourceAdapter.swift

@@ -13,6 +13,16 @@ public enum ResourceAdapter {
       let protoAttribute = CommonAdapter.toProtoAttribute(key: $0.key, attributeValue: $0.value)
       outputResource.attributes.append(protoAttribute)
     }
+    resource.entities.forEach {
+      if $0.identifierKeys.isEmpty {
+        return
+      }
+      var entityRef = Opentelemetry_Proto_Common_V1_EntityRef()
+      entityRef.type = $0.type
+      entityRef.idKeys = Array($0.identifierKeys)
+      entityRef.descriptionKeys = Array($0.attributeKeys)
+      outputResource.entityRefs.append(entityRef)
+    }
     return outputResource
   }
 }

Sources/Exporters/OpenTelemetryProtocolCommon/proto/common.pb.swift

@@ -206,6 +206,48 @@ public struct Opentelemetry_Proto_Common_V1_InstrumentationScope: Sendable {
   public init() {}
 }
 
+/// A reference to an Entity.
+/// Entity represents an object of interest associated with produced telemetry: e.g spans, metrics, profiles, or logs.
+///
+/// Status: [Development]
+public struct Opentelemetry_Proto_Common_V1_EntityRef: Sendable {
+  // SwiftProtobuf.Message conformance is added in an extension below. See the
+  // `Message` and `Message+*Additions` files in the SwiftProtobuf library for
+  // methods supported on all messages.
+
+  /// The Schema URL, if known. This is the identifier of the Schema that the entity data
+  /// is recorded in. To learn more about Schema URL see
+  /// https://opentelemetry.io/docs/specs/otel/schemas/#schema-url
+  ///
+  /// This schema_url applies to the data in this message and to the Resource attributes
+  /// referenced by id_keys and description_keys.
+  /// TODO: discuss if we are happy with this somewhat complicated definition of what
+  /// the schema_url applies to.
+  ///
+  /// This field obsoletes the schema_url field in ResourceMetrics/ResourceSpans/ResourceLogs.
+  public var schemaURL: String = String()
+
+  /// Defines the type of the entity. MUST not change during the lifetime of the entity.
+  /// For example: "service" or "host". This field is required and MUST not be empty
+  /// for valid entities.
+  public var type: String = String()
+
+  /// Attribute Keys that identify the entity.
+  /// MUST not change during the lifetime of the entity. The Id must contain at least one attribute.
+  /// These keys MUST exist in the containing {message}.attributes.
+  public var idKeys: [String] = []
+
+  /// Descriptive (non-identifying) attribute keys of the entity.
+  /// MAY change over the lifetime of the entity. MAY be empty.
+  /// These attribute keys are not part of entity's identity.
+  /// These keys MUST exist in the containing {message}.attributes.
+  public var descriptionKeys: [String] = []
+
+  public var unknownFields = SwiftProtobuf.UnknownStorage()
+
+  public init() {}
+}
+
 // MARK: - Code below here is support for the SwiftProtobuf runtime.
 
 fileprivate let _protobuf_package = "opentelemetry.proto.common.v1"
@@ -500,3 +542,53 @@ extension Opentelemetry_Proto_Common_V1_InstrumentationScope: SwiftProtobuf.Mess
     return true
   }
 }
+
+extension Opentelemetry_Proto_Common_V1_EntityRef: SwiftProtobuf.Message, SwiftProtobuf._MessageImplementationBase, SwiftProtobuf._ProtoNameProviding {
+  public static let protoMessageName: String = _protobuf_package + ".EntityRef"
+  public static let _protobuf_nameMap: SwiftProtobuf._NameMap = [
+    1: .standard(proto: "schema_url"),
+    2: .same(proto: "type"),
+    3: .standard(proto: "id_keys"),
+    4: .standard(proto: "description_keys"),
+  ]
+
+  public mutating func decodeMessage<D: SwiftProtobuf.Decoder>(decoder: inout D) throws {
+    while let fieldNumber = try decoder.nextFieldNumber() {
+      // The use of inline closures is to circumvent an issue where the compiler
+      // allocates stack space for every case branch when no optimizations are
+      // enabled. https://github.com/apple/swift-protobuf/issues/1034
+      switch fieldNumber {
+      case 1: try { try decoder.decodeSingularStringField(value: &self.schemaURL) }()
+      case 2: try { try decoder.decodeSingularStringField(value: &self.type) }()
+      case 3: try { try decoder.decodeRepeatedStringField(value: &self.idKeys) }()
+      case 4: try { try decoder.decodeRepeatedStringField(value: &self.descriptionKeys) }()
+      default: break
+      }
+    }
+  }
+
+  public func traverse<V: SwiftProtobuf.Visitor>(visitor: inout V) throws {
+    if !self.schemaURL.isEmpty {
+      try visitor.visitSingularStringField(value: self.schemaURL, fieldNumber: 1)
+    }
+    if !self.type.isEmpty {
+      try visitor.visitSingularStringField(value: self.type, fieldNumber: 2)
+    }
+    if !self.idKeys.isEmpty {
+      try visitor.visitRepeatedStringField(value: self.idKeys, fieldNumber: 3)
+    }
+    if !self.descriptionKeys.isEmpty {
+      try visitor.visitRepeatedStringField(value: self.descriptionKeys, fieldNumber: 4)
+    }
+    try unknownFields.traverse(visitor: &visitor)
+  }
+
+  public static func ==(lhs: Opentelemetry_Proto_Common_V1_EntityRef, rhs: Opentelemetry_Proto_Common_V1_EntityRef) -> Bool {
+    if lhs.schemaURL != rhs.schemaURL {return false}
+    if lhs.type != rhs.type {return false}
+    if lhs.idKeys != rhs.idKeys {return false}
+    if lhs.descriptionKeys != rhs.descriptionKeys {return false}
+    if lhs.unknownFields != rhs.unknownFields {return false}
+    return true
+  }
+}

Sources/Exporters/OpenTelemetryProtocolCommon/proto/logs.pb.swift

@@ -407,8 +407,6 @@ public struct Opentelemetry_Proto_Logs_V1_LogRecord: @unchecked Sendable {
   /// as an event.
   ///
   /// [Optional].
-  ///
-  /// Status: [Development]
   public var eventName: String = String()
 
   public var unknownFields = SwiftProtobuf.UnknownStorage()

Sources/Exporters/OpenTelemetryProtocolCommon/proto/metrics.pb.swift

@@ -397,7 +397,7 @@ public struct Opentelemetry_Proto_Metrics_V1_Metric: Sendable {
   public var description_p: String = String()
 
   /// unit in which the metric value is reported. Follows the format
-  /// described by http://unitsofmeasure.org/ucum.html.
+  /// described by https://unitsofmeasure.org/ucum.html.
   public var unit: String = String()
 
   /// Data determines the aggregation type (if any) of the metric, what is the
@@ -551,7 +551,7 @@ public struct Opentelemetry_Proto_Metrics_V1_ExponentialHistogram: Sendable {
 
 /// Summary metric data are used to convey quantile summaries,
 /// a Prometheus (see: https://prometheus.io/docs/concepts/metric_types/#summary)
-/// and OpenMetrics (see: https://github.com/OpenObservability/OpenMetrics/blob/4dbf6075567ab43296eed941037c12951faafb92/protos/prometheus.proto#L45)
+/// and OpenMetrics (see: https://github.com/prometheus/OpenMetrics/blob/4dbf6075567ab43296eed941037c12951faafb92/protos/prometheus.proto#L45)
 /// data type. These data points cannot always be merged in a meaningful way.
 /// While they can be useful in some applications, histogram data points are
 /// recommended for new applications.
@@ -699,7 +699,9 @@ public struct Opentelemetry_Proto_Metrics_V1_HistogramDataPoint: Sendable {
   /// The sum of the bucket_counts must equal the value in the count field.
   ///
   /// The number of elements in bucket_counts array must be by one greater than
-  /// the number of elements in explicit_bounds array.
+  /// the number of elements in explicit_bounds array. The exception to this rule
+  /// is when the length of bucket_counts is 0, then the length of explicit_bounds
+  /// must also be 0.
   public var bucketCounts: [UInt64] = []
 
   /// explicit_bounds specifies buckets with explicitly defined bounds for values.
@@ -715,6 +717,9 @@ public struct Opentelemetry_Proto_Metrics_V1_HistogramDataPoint: Sendable {
   /// Histogram buckets are inclusive of their upper boundary, except the last
   /// bucket where the boundary is at infinity. This format is intentionally
   /// compatible with the OpenMetrics histogram definition.
+  ///
+  /// If bucket_counts length is 0 then explicit_bounds length must also be 0,
+  /// otherwise the data point is invalid.
   public var explicitBounds: [Double] = []
 
   /// (Optional) List of exemplars collected from
@@ -897,7 +902,7 @@ public struct Opentelemetry_Proto_Metrics_V1_ExponentialHistogramDataPoint: Send
     // methods supported on all messages.
 
     /// Offset is the bucket index of the first entry in the bucket_counts array.
-    /// 
+    ///
     /// Note: This uses a varint encoding as a simple form of compression.
     public var offset: Int32 = 0