chore: import upstream snapshot with attribution

utils/alias.go

@@ -0,0 +1,45 @@
+// Copyright 2023 Dolthub, Inc.
+//
+// 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 utils
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"sync/atomic"
+)
+
+// uniqueAliasCounter is used to create unique aliases. Aliases are required by GMS when some expressions are contained
+// within an AliasedTableExpr. Postgres does not have this restriction, so we must do this for compatibility.
+var uniqueAliasCounter atomic.Uint64
+
+// uniqueAliasPrefix is the prefix given to aliases that have been generated by GenerateUniqueAlias.
+var uniqueAliasPrefix = "doltgres!|!alias!|_"
+
+// GenerateUniqueAlias generates a unique alias. This is thread-safe.
+func GenerateUniqueAlias() string {
+	return fmt.Sprintf("%s%d", uniqueAliasPrefix, uniqueAliasCounter.Add(1))
+}
+
+// IsGeneratedAlias returns whether the given alias was generated using GenerateUniqueAlias.
+func IsGeneratedAlias(alias string) bool {
+	if strings.HasPrefix(alias, uniqueAliasPrefix) && len(alias) > len(uniqueAliasPrefix) {
+		aliasDigits := alias[len(uniqueAliasPrefix):]
+		if _, err := strconv.ParseUint(aliasDigits, 10, 64); err == nil {
+			return true
+		}
+	}
+	return false
+}