sql: add a test for the validity of values produced by RETURNING

As detected in issue #22304, a mutation with RETURNING could let
values go through to the client that would violate constraints. This
was fixed in a combination of previous patches; this commit adds the
corresponding regression test.

Release note: None

pkg/sql/mutation_test.go

@@ -0,0 +1,97 @@
+// Copyright 2018 The Cockroach Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+package sql_test
+
+import (
+	"context"
+	gosql "database/sql"
+	"testing"
+
+	"github.com/cockroachdb/cockroach/pkg/sql/tests"
+	"github.com/cockroachdb/cockroach/pkg/testutils"
+	"github.com/cockroachdb/cockroach/pkg/testutils/serverutils"
+	"github.com/cockroachdb/cockroach/pkg/util/leaktest"
+)
+
+// Regression tests for #22304.
+// Checks that a mutation with RETURNING checks low-level constraints
+// before returning anything -- or that at least no constraint-violating
+// values are visible to the client.
+func TestConstraintValidationBeforeBuffering(t *testing.T) {
+	defer leaktest.AfterTest(t)()
+
+	params, _ := tests.CreateTestServerParams()
+	s, db, _ := serverutils.StartServer(t, params)
+	defer s.Stopper().Stop(context.TODO())
+
+	if _, err := db.Exec(`
+CREATE DATABASE d;
+CREATE TABLE d.a(a INT PRIMARY KEY);
+INSERT INTO d.a(a) VALUES (1);
+	`); err != nil {
+		t.Fatal(err)
+	}
+
+	step1 := func() (*gosql.Rows, error) {
+		return db.Query("INSERT INTO d.a(a) TABLE generate_series(1,3000) RETURNING a")
+	}
+	step2 := func() (*gosql.Rows, error) {
+		if _, err := db.Exec(`INSERT INTO d.a(a) TABLE generate_series(2, 3000)`); err != nil {
+			return nil, err
+		}
+		return db.Query("UPDATE d.a SET a = a - 1 WHERE a > 1 RETURNING a")
+	}
+	for i, step := range []func() (*gosql.Rows, error){step1, step2} {
+		rows, err := step()
+		if err != nil {
+			if !testutils.IsError(err, `duplicate key value \(a\)=\(1\)`) {
+				t.Errorf("%d: %v", i, err)
+			}
+		} else {
+			defer rows.Close()
+
+			hasNext := rows.Next()
+			if !hasNext {
+				t.Errorf("%d: returning claims to return no error, yet returns no rows either", i)
+			} else {
+				var val int
+				err := rows.Scan(&val)
+
+				if err != nil {
+					if !testutils.IsError(err, `duplicate key value \(a\)=\(1\)`) {
+						t.Errorf("%d: %v", i, err)
+					}
+				} else {
+					// No error. Maybe it'll come later.
+					if val == 1 {
+						t.Errorf("%d: returning returns rows, including an invalid duplicate", i)
+					}
+
+					for rows.Next() {
+						err := rows.Scan(&val)
+						if err != nil {
+							if !testutils.IsError(err, `duplicate key value \(a\)=\(1\)`) {
+								t.Errorf("%d: %v", i, err)
+							}
+						}
+						if val == 1 {
+							t.Errorf("%d returning returns rows, including an invalid duplicate", i)
+						}
+					}
+				}
+			}
+		}
+	}
+}