customizable subsystem loggers

subsystem.go

@@ -1,8 +1,14 @@
 package app
 
+import (
+	"fmt"
+	"log/slog"
+)
+
 // Subsystem represents a sub-system of the application, with its setup and
 // teardown functions and dependencies.
 type Subsystem struct {
+	logger   *slog.Logger
 	name     string
 	setup    setupFn
 	teardown teardownFn
@@ -28,3 +34,11 @@ func NewSubsystem(name string, opts SubsystemOpts) *Subsystem {
 		depends:  opts.Depends,
 	}
 }
+
+// Logger returns the logger for the subsystem.
+func (s *Subsystem) Logger() *slog.Logger {
+	if s.logger == nil {
+		panic(fmt.Sprintf("subsytem %s used before logger was initialized", s.name))
+	}
+	return s.logger
+}