chore: import upstream snapshot with attribution

server/ast/show_var.go

@@ -0,0 +1,79 @@
+// 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 ast
+
+import (
+	"strings"
+
+	"github.com/cockroachdb/errors"
+	vitess "github.com/dolthub/vitess/go/vt/sqlparser"
+
+	"github.com/dolthub/doltgresql/postgres/parser/sem/tree"
+)
+
+// nodeShowVar handles *tree.ShowVar nodes.
+func nodeShowVar(ctx *Context, node *tree.ShowVar) (vitess.Statement, error) {
+	if node == nil {
+		return nil, nil
+	}
+
+	if strings.ToLower(node.Name) == "is_superuser" {
+		return nil, errors.Errorf("SHOW IS_SUPERUSER is not yet supported")
+	} else if strings.ToLower(node.Name) == "all" {
+		// TODO: need this soon
+		return nil, errors.Errorf("SHOW ALL is not yet supported")
+	}
+
+	// TODO: this is a temporary way to get the param value for the current implementation
+	//   need better way to get these info
+	// We treat namespaced variables (e.g. myvar.myvalue) as user variables.
+	// See set_var.go
+	isUserVar := strings.Index(node.Name, ".") > 0
+	if isUserVar {
+		varName := vitess.NewColIdent(node.Name)
+		return &vitess.Select{
+			SelectExprs: vitess.SelectExprs{
+				&vitess.AliasedExpr{
+					Expr: &vitess.FuncExpr{
+						Name: vitess.NewColIdent("current_setting"),
+						Exprs: []vitess.SelectExpr{
+							&vitess.AliasedExpr{
+								Expr: &vitess.SQLVal{Type: vitess.StrVal, Val: []byte(node.Name)},
+							},
+						},
+					},
+					StartParsePos: 7,
+					EndParsePos:   7 + len(varName.String()),
+					As:            varName,
+				},
+			},
+		}, nil
+	} else {
+		varName := vitess.NewColIdent("@@session." + node.Name)
+		return &vitess.Select{
+			SelectExprs: vitess.SelectExprs{
+				&vitess.AliasedExpr{
+					Expr: &vitess.ColName{
+						Name:      varName,
+						Qualifier: vitess.TableName{},
+					},
+					StartParsePos: 7,
+					EndParsePos:   7 + len(varName.String()),
+					As:            varName,
+				},
+			},
+		}, nil
+	}
+}