feat: expose FTL logger through the Go SDK (#824)

@wesbillman can you let product eng know that a logger is now available
please

.vscode/tasks.json

@@ -45,7 +45,7 @@
 				"kind": "build",
 				"isDefault": true
 			},
-			"detail": "cd /Users/alec/dev/ftl; go build ./..."
+			"detail": "cd ${workspaceFolder}; go build ./..."
 		}
 	]
 }

backend/common/log/logger.go

@@ -41,12 +41,12 @@ func New(level Level, sink Sink) *Logger {
 }
 
 func (l Logger) Scope(scope string) *Logger {
-	return l.Sub(map[string]string{scopeKey: scope})
+	return l.Attrs(map[string]string{scopeKey: scope})
 }
 
-// Sub creates a new logger with the given attributes.
-func (l Logger) Sub(attributes map[string]string) *Logger {
-	attr := map[string]string{}
+// Attrs creates a new logger with the given attributes.
+func (l Logger) Attrs(attributes map[string]string) *Logger {
+	attr := make(map[string]string, len(l.attributes)+len(attributes))
 	maps.Copy(attr, l.attributes)
 	maps.Copy(attr, attributes)
 	l.attributes = attr

backend/controller/controller.go

@@ -1093,7 +1093,7 @@ func (s *Service) getDeploymentLogger(ctx context.Context, deploymentName model.
 		attrs["request"] = requestName.String()
 	}
 
-	return log.FromContext(ctx).AddSink(s.deploymentLogsSink).Sub(attrs)
+	return log.FromContext(ctx).AddSink(s.deploymentLogsSink).Attrs(attrs)
 }
 
 // Periodically sync the routing table from the DB.

backend/runner/runner.go

@@ -60,7 +60,7 @@ func Start(ctx context.Context, config Config) error {
 	client := rpc.Dial(ftlv1connect.NewVerbServiceClient, config.ControllerEndpoint.String(), log.Error)
 	ctx = rpc.ContextWithClient(ctx, client)
 
-	logger := log.FromContext(ctx).Sub(map[string]string{"runner": config.Key.String()})
+	logger := log.FromContext(ctx).Attrs(map[string]string{"runner": config.Key.String()})
 	logger.Infof("Starting FTL Runner")
 	logger.Infof("Deployment directory: %s", config.DeploymentDir)
 	err = os.MkdirAll(config.DeploymentDir, 0700)
@@ -208,7 +208,7 @@ func (s *Service) Deploy(ctx context.Context, req *connect.Request[ftlv1.DeployR
 		return nil, fmt.Errorf("%s: %w", "failed to download artefacts", err)
 	}
 
-	verbCtx := log.ContextWithLogger(ctx, deploymentLogger.Sub(map[string]string{"module": module.Name}))
+	verbCtx := log.ContextWithLogger(ctx, deploymentLogger.Attrs(map[string]string{"module": module.Name}))
 	deployment, cmdCtx, err := plugin.Spawn(
 		unstoppable.Context(verbCtx),
 		log.Info,
@@ -385,5 +385,5 @@ func (s *Service) getDeploymentLogger(ctx context.Context, deploymentName model.
 	}
 
 	sink := newDeploymentLogsSink(s.deploymentLogQueue)
-	return log.FromContext(ctx).AddSink(sink).Sub(attrs)
+	return log.FromContext(ctx).AddSink(sink).Attrs(attrs)
 }

go-runtime/sdk/logging.go

@@ -0,0 +1,16 @@
+package sdk
+
+import (
+	"context"
+
+	"github.com/TBD54566975/ftl/backend/common/log"
+)
+
+// Logger is a levelled printf-style logger with support for structured
+// attributes.
+type Logger = log.Logger
+
+// FromContext retrieves the current logger from the Context.
+func FromContext(ctx context.Context) *Logger {
+	return log.FromContext(ctx)
+}