database/sql: close statement before connection

Fixes #5936

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/11620046

src/pkg/database/sql/sql.go

@@ -759,10 +759,10 @@ func (db *DB) queryConn(dc *driverConn, releaseConn func(error), query string, a
 	ds := driverStmt{dc, si}
 	rowsi, err := rowsiFromStatement(ds, args...)
 	if err != nil {
-		releaseConn(err)
 		dc.Lock()
 		si.Close()
 		dc.Unlock()
+		releaseConn(err)
 		return nil, err
 	}
 

src/pkg/database/sql/sql_test.go

@@ -1046,6 +1046,20 @@ func TestRowsCloseOrder(t *testing.T) {
 	}
 }
 
+func TestStmtCloseOrder(t *testing.T) {
+	db := newTestDB(t, "people")
+	defer closeDB(t, db)
+
+	db.SetMaxIdleConns(0)
+	setStrictFakeConnClose(t)
+	defer setStrictFakeConnClose(nil)
+
+	_, err := db.Query("SELECT|non_existent|name|")
+	if err == nil {
+		t.Fatal("Quering non-existent table should fail")
+	}
+}
+
 func manyConcurrentQueries(t testOrBench) {
 	maxProcs, numReqs := 16, 500
 	if testing.Short() {