fix(postgresql): DROP TABLE ... CASCADE drops dependent views (#4416)

sqlc's in-memory catalog dropped the table but left views that depended
on it, so a later CREATE VIEW reusing the name failed with
'relation "..." already exists' even though the SQL is valid Postgres.

- ast: carry DROP behavior (RESTRICT/CASCADE) into DropTableStmt; add
  named DropBehavior constants matching the pg_query enum.
- postgresql parser: thread n.Behavior into the DropTableStmt.
- catalog: record each view's referenced tables (DependsOn) at create
  time, and on DROP TABLE ... CASCADE evict dependent views transitively.
- RESTRICT / unspecified behavior is unchanged (views are kept).
- tests: catalog unit tests covering cascade eviction (incl. views on
  views) and the restrict/default keep-path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: luongs3

internal/engine/postgresql/parse.go

@@ -579,6 +579,7 @@ func translate(node *nodes.Node) (ast.Node, error) {
 		case nodes.ObjectType_OBJECT_TABLE, nodes.ObjectType_OBJECT_VIEW, nodes.ObjectType_OBJECT_MATVIEW:
 			drop := &ast.DropTableStmt{
 				IfExists: n.MissingOk,
+				Behavior: ast.DropBehavior(n.Behavior),
 			}
 			for _, obj := range n.Objects {
 				name, err := parseRelation(obj)

internal/sql/ast/drop_behavior.go

@@ -2,6 +2,14 @@ package ast
 
 type DropBehavior uint
 
+// Matches pganalyze/pg_query_go DropBehavior enum:
+// DropBehavior_UNDEFINED = 0, DROP_RESTRICT = 1, DROP_CASCADE = 2.
+const (
+	DropBehaviorUndefined DropBehavior = 0
+	DropBehaviorRestrict  DropBehavior = 1
+	DropBehaviorCascade   DropBehavior = 2
+)
+
 func (n *DropBehavior) Pos() int {
 	return 0
 }

internal/sql/ast/drop_table_stmt.go

@@ -3,6 +3,7 @@ package ast
 type DropTableStmt struct {
 	IfExists bool
 	Tables   []*TableName
+	Behavior DropBehavior
 }
 
 func (n *DropTableStmt) Pos() int {

internal/sql/catalog/table.go

@@ -13,9 +13,10 @@ import (
 // A database table is a collection of related data held in a table format within a database.
 // It consists of columns and rows.
 type Table struct {
-	Rel     *ast.TableName
-	Columns []*Column
-	Comment string
+	Rel       *ast.TableName
+	Columns   []*Column
+	Comment   string
+	DependsOn []*ast.TableName // for views: tables/views referenced by the view query
 }
 
 func checkMissing(err error, missingOK bool) error {
@@ -384,11 +385,43 @@ func (c *Catalog) dropTable(stmt *ast.DropTableStmt) error {
 			return err
 		}
 
+		droppedName := schema.Tables[idx].Rel.Name
 		schema.Tables = append(schema.Tables[:idx], schema.Tables[idx+1:]...)
+
+		if stmt.Behavior == ast.DropBehaviorCascade {
+			c.dropDependentViews(schema, droppedName)
+		}
 	}
 	return nil
 }
 
+// dropDependentViews removes every view in schema whose DependsOn references
+// name, recursing so views-on-views are also evicted. Cascade-only.
+func (c *Catalog) dropDependentViews(schema *Schema, name string) {
+	for {
+		removed := false
+		for i, t := range schema.Tables {
+			depends := false
+			for _, d := range t.DependsOn {
+				if d.Name == name {
+					depends = true
+					break
+				}
+			}
+			if depends {
+				victim := schema.Tables[i].Rel.Name
+				schema.Tables = append(schema.Tables[:i], schema.Tables[i+1:]...)
+				c.dropDependentViews(schema, victim)
+				removed = true
+				break
+			}
+		}
+		if !removed {
+			return
+		}
+	}
+}
+
 func (c *Catalog) renameColumn(stmt *ast.RenameColumnStmt) error {
 	_, tbl, err := c.getTable(stmt.Table)
 	if err != nil {

internal/sql/catalog/table_test.go

@@ -0,0 +1,105 @@
+package catalog_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/sqlc-dev/sqlc/internal/engine/postgresql"
+	"github.com/sqlc-dev/sqlc/internal/sql/ast"
+	"github.com/sqlc-dev/sqlc/internal/sql/catalog"
+)
+
+// stubColumnGenerator satisfies the catalog's column generator dependency
+// without pulling in the full compiler. CREATE VIEW only needs a column set
+// to store; these tests assert on relation presence and dependency tracking,
+// not on the view's column types.
+type stubColumnGenerator struct{}
+
+func (stubColumnGenerator) OutputColumns(ast.Node) ([]*catalog.Column, error) {
+	return []*catalog.Column{
+		{Name: "id", Type: ast.TypeName{Name: "int4"}},
+	}, nil
+}
+
+func update(t *testing.T, c *catalog.Catalog, sql string) {
+	t.Helper()
+	stmts, err := postgresql.NewParser().Parse(strings.NewReader(sql))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, stmt := range stmts {
+		if err := c.Update(stmt, stubColumnGenerator{}); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+func publicSchema(t *testing.T, c *catalog.Catalog) *catalog.Schema {
+	t.Helper()
+	for _, s := range c.Schemas {
+		if s.Name == "public" {
+			return s
+		}
+	}
+	t.Fatal(`schema "public" not found`)
+	return nil
+}
+
+func tableNames(schema *catalog.Schema) []string {
+	names := make([]string, 0, len(schema.Tables))
+	for _, tbl := range schema.Tables {
+		names = append(names, tbl.Rel.Name)
+	}
+	return names
+}
+
+func TestDropTableCascadeEvictsDependentViews(t *testing.T) {
+	c := catalog.New("public")
+	update(t, c, `
+CREATE TABLE base (id int);
+CREATE VIEW child AS SELECT id FROM base;
+CREATE VIEW grandchild AS SELECT id FROM child;
+`)
+
+	schema := publicSchema(t, c)
+	if got := tableNames(schema); len(got) != 3 {
+		t.Fatalf("expected 3 relations before drop, got %v", got)
+	}
+
+	update(t, c, `DROP TABLE base CASCADE;`)
+
+	// base is dropped; child depends on base and grandchild depends on child,
+	// so CASCADE must transitively evict both views.
+	if got := tableNames(schema); len(got) != 0 {
+		t.Fatalf("expected cascade drop to remove base and dependent views, got %v", got)
+	}
+}
+
+func TestDropTableWithoutCascadeKeepsDependentViews(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		sql  string
+	}{
+		{name: "restrict", sql: `DROP TABLE base RESTRICT;`},
+		{name: "default", sql: `DROP TABLE base;`},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			c := catalog.New("public")
+			update(t, c, `
+CREATE TABLE base (id int);
+CREATE VIEW child AS SELECT id FROM base;
+`)
+
+			schema := publicSchema(t, c)
+			update(t, c, tc.sql)
+
+			got := tableNames(schema)
+			if len(got) != 1 || got[0] != "child" {
+				t.Fatalf("expected dependent view to remain after %s, got %v", tc.name, got)
+			}
+			if len(schema.Tables[0].DependsOn) != 1 || schema.Tables[0].DependsOn[0].Name != "base" {
+				t.Fatalf("expected remaining view dependency to be preserved, got %#v", schema.Tables[0].DependsOn)
+			}
+		})
+	}
+}

internal/sql/catalog/view.go

@@ -2,6 +2,7 @@ package catalog
 
 import (
 	"github.com/sqlc-dev/sqlc/internal/sql/ast"
+	"github.com/sqlc-dev/sqlc/internal/sql/astutils"
 	"github.com/sqlc-dev/sqlc/internal/sql/sqlerr"
 )
 
@@ -20,13 +21,32 @@ func (c *Catalog) createView(stmt *ast.ViewStmt, colGen columnGenerator) error {
 		schemaName = *stmt.View.Schemaname
 	}
 
+	var dependsOn []*ast.TableName
+	list := astutils.Search(stmt.Query, func(node ast.Node) bool {
+		_, ok := node.(*ast.RangeVar)
+		return ok
+	})
+	for _, item := range list.Items {
+		if rv, ok := item.(*ast.RangeVar); ok && rv.Relname != nil {
+			tn := &ast.TableName{Name: *rv.Relname}
+			if rv.Schemaname != nil {
+				tn.Schema = *rv.Schemaname
+			}
+			if rv.Catalogname != nil {
+				tn.Catalog = *rv.Catalogname
+			}
+			dependsOn = append(dependsOn, tn)
+		}
+	}
+
 	tbl := Table{
 		Rel: &ast.TableName{
 			Catalog: catName,
 			Schema:  schemaName,
 			Name:    *stmt.View.Relname,
 		},
-		Columns: cols,
+		Columns:   cols,
+		DependsOn: dependsOn,
 	}
 
 	ns := tbl.Rel.Schema