feat: Add instrumentation for MetricKit.

OpenTelemetry-Swift-Instrumentation-MetricKit.podspec

@@ -0,0 +1,25 @@
+Pod::Spec.new do |spec|
+  spec.name = "OpenTelemetry-Swift-Instrumentation-MetricKit"
+  spec.version = "2.2.0"
+  spec.summary = "Swift OpenTelemetry MetricKit Instrumentation"
+
+  spec.homepage = "https://github.com/open-telemetry/opentelemetry-swift"
+  spec.documentation_url = "https://opentelemetry.io/docs/languages/swift"
+  spec.license = { :type => "Apache 2.0", :file => "LICENSE" }
+  spec.authors = "OpenTelemetry Authors"
+
+  spec.source = { :git => "https://github.com/open-telemetry/opentelemetry-swift.git", :tag => spec.version.to_s }
+  spec.source_files = "Sources/Instrumentation/MetricKit/*.swift"
+  spec.exclude_files = "Sources/Instrumentation/MetricKit/README.md"
+
+  spec.swift_version = "5.10"
+  spec.ios.deployment_target = "13.0"
+  spec.osx.deployment_target = "12.0"
+  spec.watchos.deployment_target = "6.0"
+  spec.visionos.deployment_target = "1.0"
+  spec.module_name = "MetricKitInstrumentation"
+
+  spec.dependency 'OpenTelemetry-Swift-Sdk', '~> 2.1.1'
+  spec.pod_target_xcconfig = { "OTHER_SWIFT_FLAGS" => "-module-name MetricKitInstrumentation -package-name opentelemetry_swift_metrickit_instrumentation" }
+
+end

Package.swift

@@ -253,7 +253,8 @@ extension Package {
         .executable(name: "OTLPExporter", targets: ["OTLPExporter"]),
         .executable(name: "OTLPHTTPExporter", targets: ["OTLPHTTPExporter"]),
         .library(name: "SignPostIntegration", targets: ["SignPostIntegration"]),
-        .library(name: "ResourceExtension", targets: ["ResourceExtension"])
+        .library(name: "ResourceExtension", targets: ["ResourceExtension"]),
+        .library(name: "MetricKitInstrumentation", targets: ["MetricKitInstrumentation"])
       ])
       targets.append(contentsOf: [
         .target(
@@ -381,6 +382,23 @@ extension Package {
           ],
           path: "Tests/InstrumentationTests/SDKResourceExtensionTests"
         ),
+        .target(
+          name: "MetricKitInstrumentation",
+          dependencies: [
+            .product(name: "OpenTelemetrySdk", package: "opentelemetry-swift-core")
+          ],
+          path: "Sources/Instrumentation/MetricKit",
+          exclude: ["README.md"]
+        ),
+        .testTarget(
+          name: "MetricKitInstrumentationTests",
+          dependencies: [
+            "MetricKitInstrumentation",
+            "InMemoryExporter",
+            .product(name: "OpenTelemetrySdk", package: "opentelemetry-swift-core")
+          ],
+          path: "Tests/InstrumentationTests/MetricKitTests"
+        ),
         .executableTarget(
           name: "PrometheusSample",
           dependencies: [

Sources/Instrumentation/MetricKit/AttributeValueExtensions.swift

@@ -0,0 +1,52 @@
+#if canImport(MetricKit) && !os(tvOS) && !os(macOS)
+import Foundation
+import OpenTelemetryApi
+
+/// A protocol to make it easier to write generic functions for AttributeValues.
+protocol AttributeValueConvertable {
+    func attributeValue() -> AttributeValue
+}
+
+extension Int: AttributeValueConvertable {
+    func attributeValue() -> AttributeValue {
+        AttributeValue.int(self)
+    }
+}
+extension Bool: AttributeValueConvertable {
+    func attributeValue() -> AttributeValue {
+        AttributeValue.bool(self)
+    }
+}
+extension String: AttributeValueConvertable {
+    func attributeValue() -> AttributeValue {
+        AttributeValue.string(self)
+    }
+}
+
+extension [String]: AttributeValueConvertable {
+    func attributeValue() -> AttributeValue {
+        AttributeValue.array(AttributeArray(values: self.map { AttributeValue.string($0) }))
+    }
+}
+
+extension TimeInterval: AttributeValueConvertable {
+    func attributeValue() -> AttributeValue {
+        // The OTel standard for time durations is seconds, which is also what TimeInterval is.
+        // https://opentelemetry.io/docs/specs/semconv/general/metrics/
+        AttributeValue.double(self)
+    }
+}
+
+extension Measurement: AttributeValueConvertable {
+    func attributeValue() -> AttributeValue {
+        // Convert to the "base unit", such as seconds or bytes.
+        let value =
+            if let unit = self.unit as? Dimension {
+                unit.converter.baseUnitValue(fromValue: self.value)
+            } else {
+                self.value
+            }
+        return AttributeValue.double(value)
+    }
+}
+#endif