Recording an error may carry attributes (#90)

* Recording an error may carry attributes

**Motivation:**
It can be used to attach more information bout the error, like its
stacktrace and similar information.

This is also supported by the otel spec, so we're aligning closer with
it here.

**Modifications:**

Change the recordError to accept optional span attributes

**Result:**

more powerful record error API

* Update Sources/Tracing/Span.swift

Co-authored-by: Moritz Lang <hi@slashmo.codes>

* Update Sources/Tracing/Span.swift

Co-authored-by: Moritz Lang <hi@slashmo.codes>

---------

Co-authored-by: Moritz Lang <hi@slashmo.codes>

Author: ktoso

Sources/Tracing/NoOpTracer.swift

@@ -71,7 +71,7 @@ public struct NoOpTracer: Tracer {
 
         public func addEvent(_ event: SpanEvent) {}
 
-        public func recordError(_ error: Error) {}
+        public func recordError(_ error: Error, attributes: SpanAttributes) {}
 
         public var attributes: SpanAttributes {
             get {

Sources/Tracing/Span.swift

@@ -59,7 +59,8 @@ public protocol Span: AnyObject, _SwiftTracingSendableSpan {
     ///
     /// - Parameters:
     ///   - error: The error to be recorded.
-    func recordError(_ error: Error)
+    ///   - attributes: Additional attributes describing the error.
+    func recordError(_ error: Error, attributes: SpanAttributes)
 
     /// The attributes describing this `Span`.
     var attributes: SpanAttributes { get set }
@@ -114,6 +115,16 @@ extension Span {
     }
 }
 
+extension Span {
+    /// Record a failure described by the given error.
+    ///
+    /// - Parameters:
+    ///   - error: The error to be recorded.
+    public func recordError(_ error: Error) {
+        self.recordError(error, attributes: [:])
+    }
+}
+
 // ==== ----------------------------------------------------------------------------------------------------------------
 // MARK: Span Event
 

Tests/TracingTests/DynamicTracepointTracerTests.swift

@@ -276,7 +276,7 @@ extension DynamicTracepointTestTracer {
             // nothing
         }
 
-        func recordError(_ error: Error) {
+        func recordError(_ error: Error, attributes: SpanAttributes) {
             print("")
         }
 

Tests/TracingTests/TestTracer.swift

@@ -21,7 +21,7 @@ import Tracing
 /// Only intended to be used in single-threaded testing.
 final class TestTracer: Tracer {
     private(set) var spans = [TestSpan]()
-    var onEndSpan: (Span) -> Void = { _ in }
+    var onEndSpan: (TestSpan) -> Void = { _ in }
 
     func startSpan(
         _ operationName: String,
@@ -103,6 +103,8 @@ final class TestSpan: Span {
     private let startTime: DispatchWallTime
     private(set) var endTime: DispatchWallTime?
 
+    private(set) var recordedErrors: [(Error, SpanAttributes)] = []
+
     var operationName: String
     let baggage: Baggage
 
@@ -122,14 +124,14 @@ final class TestSpan: Span {
 
     private(set) var isRecording = false
 
-    let onEnd: (Span) -> Void
+    let onEnd: (TestSpan) -> Void
 
     init(
         operationName: String,
         startTime: DispatchWallTime,
         baggage: Baggage,
         kind: SpanKind,
-        onEnd: @escaping (Span) -> Void
+        onEnd: @escaping (TestSpan) -> Void
     ) {
         self.operationName = operationName
         self.startTime = startTime
@@ -151,7 +153,9 @@ final class TestSpan: Span {
         self.events.append(event)
     }
 
-    func recordError(_ error: Error) {}
+    func recordError(_ error: Error, attributes: SpanAttributes) {
+        self.recordedErrors.append((error, attributes))
+    }
 
     func end(at time: DispatchWallTime) {
         self.endTime = time

Tests/TracingTests/TracedLockTests.swift

@@ -151,7 +151,7 @@ private final class TracedLockPrintlnTracer: Tracer {
             self.events.append(event)
         }
 
-        func recordError(_ error: Error) {}
+        func recordError(_ error: Error, attributes: SpanAttributes) {}
 
         func end(at time: DispatchWallTime) {
             self.endTime = time

Tests/TracingTests/TracerTests+XCTest.swift

@@ -35,6 +35,7 @@ extension TracerTests {
                 ("testWithSpan_automaticBaggagePropagation_async", testWithSpan_automaticBaggagePropagation_async),
                 ("testWithSpan_enterFromNonAsyncCode_passBaggage_asyncOperation", testWithSpan_enterFromNonAsyncCode_passBaggage_asyncOperation),
                 ("testWithSpan_automaticBaggagePropagation_async_throws", testWithSpan_automaticBaggagePropagation_async_throws),
+                ("testWithSpan_recordErrorWithAttributes", testWithSpan_recordErrorWithAttributes),
            ]
    }
 }

Tests/TracingTests/TracerTests.swift

@@ -253,6 +253,37 @@ final class TracerTests: XCTestCase {
         #endif
     }
 
+    func testWithSpan_recordErrorWithAttributes() throws {
+        #if swift(>=5.5) && canImport(_Concurrency)
+        guard #available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *) else {
+            throw XCTSkip("Task locals are not supported on this platform.")
+        }
+
+        let tracer = TestTracer()
+        InstrumentationSystem.bootstrapInternal(tracer)
+        defer {
+            InstrumentationSystem.bootstrapInternal(nil)
+        }
+
+        var endedSpan: TestSpan?
+        tracer.onEndSpan = { span in endedSpan = span }
+
+        let errorToThrow = ExampleSpanError()
+        let attrsForError: SpanAttributes = ["attr": "value"]
+
+        tracer.withSpan("hello") { span in
+            span.recordError(errorToThrow, attributes: attrsForError)
+        }
+
+        XCTAssertTrue(endedSpan != nil)
+        XCTAssertEqual(endedSpan!.recordedErrors.count, 1)
+        let error = endedSpan!.recordedErrors.first!.0
+        XCTAssertEqual(error as! ExampleSpanError, errorToThrow)
+        let attrs = endedSpan!.recordedErrors.first!.1
+        XCTAssertEqual(attrs, attrsForError)
+        #endif
+    }
+
     #if swift(>=5.5) && canImport(_Concurrency)
     @available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
     /// Helper method to execute async operations until we can use async tests (currently incompatible with the generated LinuxMain file).