feat: allow passing context as event hint to sentry (#40)

This allows sentry to extract existing trace information and link
events to their respective traces.

core.go

@@ -160,6 +160,8 @@ func (c *core) Write(ent zapcore.Entry, fs []zapcore.Field) error {
 			}
 		}
 
+		var hint *sentry.EventHint
+
 		event := sentry.NewEvent()
 		event.Message = ent.Message
 		event.Timestamp = ent.Time
@@ -171,8 +173,11 @@ func (c *core) Write(ent zapcore.Entry, fs []zapcore.Field) error {
 		}
 		for _, f := range fs {
 			if f.Type == zapcore.SkipType {
-				if t, ok := f.Interface.(tagField); ok {
+				switch t := f.Interface.(type) {
+				case tagField:
 					event.Tags[t.Key] = t.Value
+				case ctxField:
+					hint = &sentry.EventHint{Context: t.Value}
 				}
 			}
 		}
@@ -186,7 +191,7 @@ func (c *core) Write(ent zapcore.Entry, fs []zapcore.Field) error {
 			}
 		}
 
-		_ = c.client.CaptureEvent(event, nil, c.scope())
+		_ = c.client.CaptureEvent(event, hint, c.scope())
 	}
 
 	// We may be crashing the program, so should flush any buffered events.

field.go

@@ -1,6 +1,8 @@
 package zapsentry
 
 import (
+	"context"
+
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 )
@@ -13,3 +15,15 @@ type tagField struct {
 func Tag(key string, value string) zap.Field {
 	return zap.Field{Key: key, Type: zapcore.SkipType, Interface: tagField{key, value}}
 }
+
+type ctxField struct {
+	Value context.Context
+}
+
+// Context adds a context to the logger.
+// This can be used e.g. to pass trace information to sentry and allow linking events to their respective traces.
+//
+// See also https://docs.sentry.io/platforms/go/performance/instrumentation/opentelemetry/#linking-errors-to-transactions
+func Context(ctx context.Context) zap.Field {
+	return zap.Field{Key: "context", Type: zapcore.SkipType, Interface: ctxField{ctx}}
+}