tapdb: add support for logging migrations

In this commit, we add support for logging migrations as they happen.
This is useful for users to keep track of what happens during a `tapd`
update.

tapdb/migrations.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/btcsuite/btclog"
 	"github.com/golang-migrate/migrate/v4"
 	"github.com/golang-migrate/migrate/v4/database"
 	"github.com/golang-migrate/migrate/v4/source/httpfs"
@@ -33,6 +34,39 @@ var (
 	}
 )
 
+// migrationLogger is a logger that wraps the passed btclog.Logger so it can be
+// used to log migrations.
+type migrationLogger struct {
+	log btclog.Logger
+}
+
+// Printf is like fmt.Printf. We map this to the target logger based on the
+// current log level.
+func (m *migrationLogger) Printf(format string, v ...interface{}) {
+	// Trim trailing newlines from the format.
+	format = strings.TrimRight(format, "\n")
+
+	switch m.log.Level() {
+	case btclog.LevelTrace:
+		m.log.Tracef(format, v...)
+	case btclog.LevelDebug:
+		m.log.Debugf(format, v...)
+	case btclog.LevelInfo:
+		m.log.Infof(format, v...)
+	case btclog.LevelWarn:
+		m.log.Warnf(format, v...)
+	case btclog.LevelError:
+		m.log.Errorf(format, v...)
+	case btclog.LevelCritical:
+		m.log.Criticalf(format, v...)
+	}
+}
+
+// Verbose should return true when verbose logging output is wanted
+func (m *migrationLogger) Verbose() bool {
+	return m.log.Level() <= btclog.LevelDebug
+}
+
 // applyMigrations executes database migration files found in the given file
 // system under the given path, using the passed database driver and database
 // name, up to or down to the given target version.
@@ -58,6 +92,13 @@ func applyMigrations(fs fs.FS, driver database.Driver, path, dbName string,
 		return err
 	}
 
+	migrationVersion, _, _ := sqlMigrate.Version()
+
+	log.Infof("Applying migrations from version=%v", migrationVersion)
+
+	// Apply our local logger to the migration instance.
+	sqlMigrate.Log = &migrationLogger{log}
+
 	// Execute the migration based on the target given.
 	err = targetVersion(sqlMigrate)
 	if err != nil && !errors.Is(err, migrate.ErrNoChange) {