fix: support PostgreSQL 18 RETURNING OLD/NEW syntax

The pg_query_go parser already parses RETURNING OLD.* and RETURNING
NEW.* correctly, but sqlc's compiler rejected these queries because
the star expansion and column resolution logic tried to match
"old"/"new" against actual table names and found no match.

This caused star expansion to produce empty column lists (resulting in
invalid SQL like "RETURNING ;") and column refs like OLD.bar to fail
with "column does not exist".

The fix recognizes "old" and "new" as special scope/alias values in
three places and lets them match the target table's columns instead
of being filtered out.

Fixes #3600

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: stepan-romankov

internal/compiler/expand.go

@@ -132,7 +132,8 @@ func (c *Compiler) expandStmt(qc *QueryCatalog, raw *ast.RawStmt, node ast.Node)
 			}
 		}
 		for _, t := range tables {
-			if scope != "" && scope != t.Rel.Name {
+			isOldNew := strings.EqualFold(scope, "old") || strings.EqualFold(scope, "new")
+			if scope != "" && !isOldNew && scope != t.Rel.Name {
 				continue
 			}
 			tableName := c.quoteIdent(t.Rel.Name)

internal/compiler/output_columns.go

@@ -3,6 +3,7 @@ package compiler
 import (
 	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/sqlc-dev/sqlc/internal/sql/ast"
 	"github.com/sqlc-dev/sqlc/internal/sql/astutils"
@@ -269,7 +270,8 @@ func (c *Compiler) outputColumns(qc *QueryCatalog, node ast.Node) ([]*Column, er
 				// TODO: This code is copied in func expand()
 				for _, t := range tables {
 					scope := astutils.Join(n.Fields, ".")
-					if scope != "" && scope != t.Rel.Name {
+					isOldNew := strings.EqualFold(scope, "old") || strings.EqualFold(scope, "new")
+					if scope != "" && !isOldNew && scope != t.Rel.Name {
 						continue
 					}
 					for _, c := range t.Columns {
@@ -669,7 +671,8 @@ func outputColumnRefs(res *ast.ResTarget, tables []*Table, node *ast.ColumnRef)
 		if schema != "" && t.Rel.Schema != schema {
 			continue
 		}
-		if alias != "" && t.Rel.Name != alias {
+		isOldNew := strings.EqualFold(alias, "old") || strings.EqualFold(alias, "new")
+		if alias != "" && !isOldNew && t.Rel.Name != alias {
 			continue
 		}
 		for _, c := range t.Columns {

internal/endtoend/testdata/returning_old_new/postgresql/stdlib/go/db.go

@@ -0,0 +1,11 @@
+-- name: UpdateReturningOldStar :one
+UPDATE foo SET bar = $1 WHERE id = $2 RETURNING OLD.*;
+
+-- name: UpdateReturningNewStar :one
+UPDATE foo SET bar = $1 WHERE id = $2 RETURNING NEW.*;
+
+-- name: UpdateReturningOldNewCols :one
+UPDATE foo SET bar = $1 WHERE id = $2 RETURNING OLD.bar, NEW.bar;
+
+-- name: DeleteReturningOldStar :one
+DELETE FROM foo WHERE id = $1 RETURNING OLD.*;

internal/endtoend/testdata/returning_old_new/postgresql/stdlib/go/models.go

@@ -0,0 +1,5 @@
+CREATE TABLE foo (
+  id serial primary key,
+  bar text not null,
+  baz int not null default 0
+);

internal/endtoend/testdata/returning_old_new/postgresql/stdlib/go/query.sql.go

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "engine": "postgresql",
+      "name": "querytest",
+      "schema": "schema.sql",
+      "queries": "query.sql"
+    }
+  ]
+}