*!: add JSONB containment predicates usable on postgres and sqlite3

backend/balancer/db.go

@@ -120,6 +120,8 @@ type tx struct {
 	cfn CloseFunc
 }
 
+func (tx *tx) Driver() string { return sql.DriverOf(tx.Tx) }
+
 func (tx *tx) Commit() error {
 	err := tx.Tx.Commit()
 

backend/postgres/db.go

@@ -42,6 +42,7 @@ type tx struct {
 
 func (tx *tx) Commit() error   { return wrapErr(tx.tx.Commit()) }
 func (tx *tx) Rollback() error { return wrapErr(tx.tx.Rollback()) }
+func (tx *tx) Driver() string  { return sql.DriverOf(tx.tx) }
 
 type queryer struct {
 	q sql.Queryer

backend/simple/db.go

@@ -37,8 +37,12 @@ type tx struct {
 
 	q  *queryer
 	tx *stdsql.Tx
+
+	driver string
 }
 
+func (tx *tx) Driver() string { return tx.driver }
+
 func (tx *tx) Commit() error {
 	select {
 	case <-tx.ctx.Done():
@@ -160,9 +164,10 @@ func (d *db) BeginTx(ctx context.Context, opts sql.TxOptions) (sql.Tx, error) {
 	}
 
 	return &tx{
-		ctx: ctx,
-		ch:  make(chan struct{}, 1),
-		q:   &queryer{t},
-		tx:  t,
+		ctx:    ctx,
+		ch:     make(chan struct{}, 1),
+		q:      &queryer{t},
+		tx:     t,
+		driver: d.driver,
 	}, nil
 }

backend/sqlite3/db.go

@@ -46,6 +46,7 @@ type tx struct {
 
 func (tx *tx) Commit() error   { return wrapErr(tx.tx.Commit()) }
 func (tx *tx) Rollback() error { return wrapErr(tx.tx.Rollback()) }
+func (tx *tx) Driver() string  { return sql.DriverOf(tx.tx) }
 
 func (db *db) Driver() string { return db.db.Driver() }
 

backend/static/db.go

@@ -57,6 +57,7 @@ type Tx struct {
 
 func (tx *Tx) Commit() error   { return tx.CommitErr }
 func (tx *Tx) Rollback() error { return tx.RollbackErr }
+func (tx *Tx) Driver() string  { return "sqltest" }
 
 func (db *DB) Driver() string { return "sqltest" }
 

db.go

@@ -40,6 +40,16 @@ type DB interface {
 	Driver() string
 }
 
+// DriverOf returns the driver of q, the DBs and the transactions they
+// begin expose it. It returns an empty string when q does not.
+func DriverOf(q Queryer) string {
+	if d, ok := q.(interface{ Driver() string }); ok {
+		return d.Driver()
+	}
+
+	return ""
+}
+
 type TxOptions struct {
 	Isolation IsolationLevel
 }