feat: implement extension detection and management in schema diff

Author: William-W-Chen

internal/diff/diff.go

@@ -42,6 +42,7 @@ const (
 	DiffTypePrivilege
 	DiffTypeRevokedDefaultPrivilege
 	DiffTypeColumnPrivilege
+	DiffTypeExtension
 )
 
 // String returns the string representation of DiffType
@@ -103,6 +104,8 @@ func (d DiffType) String() string {
 		return "revoked_default_privilege"
 	case DiffTypeColumnPrivilege:
 		return "column_privilege"
+	case DiffTypeExtension:
+		return "extension"
 	default:
 		return "unknown"
 	}
@@ -177,6 +180,8 @@ func (d *DiffType) UnmarshalJSON(data []byte) error {
 		*d = DiffTypeRevokedDefaultPrivilege
 	case "column_privilege":
 		*d = DiffTypeColumnPrivilege
+	case "extension":
+		*d = DiffTypeExtension
 	default:
 		return fmt.Errorf("unknown diff type: %s", s)
 	}
@@ -260,6 +265,8 @@ type Diff struct {
 }
 
 type ddlDiff struct {
+	addedExtensions   []string
+	droppedExtensions []string
 	addedSchemas              []*ir.Schema
 	droppedSchemas            []*ir.Schema
 	modifiedSchemas           []*schemaDiff
@@ -462,6 +469,26 @@ func GenerateMigration(oldIR, newIR *ir.IR, targetSchema string) []Diff {
 		modifiedColumnPrivileges:   []*columnPrivilegeDiff{},
 	}
 
+	// Compare extensions
+	oldExtSet := make(map[string]bool)
+	for _, ext := range oldIR.Extensions {
+		oldExtSet[ext] = true
+	}
+	for _, ext := range newIR.Extensions {
+		if !oldExtSet[ext] {
+			diff.addedExtensions = append(diff.addedExtensions, ext)
+		}
+	}
+	newExtSet := make(map[string]bool)
+	for _, ext := range newIR.Extensions {
+		newExtSet[ext] = true
+	}
+	for _, ext := range oldIR.Extensions {
+		if !newExtSet[ext] {
+			diff.droppedExtensions = append(diff.droppedExtensions, ext)
+		}
+	}
+
 	// Compare schemas first in deterministic order
 	schemaNames := sortedKeys(newIR.Schemas)
 	for _, name := range schemaNames {
@@ -1497,6 +1524,18 @@ func (d *ddlDiff) generatePreDropMaterializedViewsSQL(targetSchema string, colle
 
 // generateCreateSQL generates CREATE statements in dependency order
 func (d *ddlDiff) generateCreateSQL(targetSchema string, collector *diffCollector) {
+	// Create extensions first - must be installed before any schema objects that depend on them
+	for _, ext := range d.addedExtensions {
+		context := &diffContext{
+			Type:                DiffTypeExtension,
+			Operation:           DiffOperationCreate,
+			Path:                ext,
+			Source:              &ir.Extension{Name: ext},
+			CanRunInTransaction: true,
+		}
+		collector.collect(context, fmt.Sprintf("CREATE EXTENSION IF NOT EXISTS %s;", ir.QuoteIdentifier(ext)))
+	}
+
 	// Note: Schema creation is out of scope for schema-level comparisons
 
 	// Build function lookup early - needed for both domain and table dependency checks

internal/dump/formatter.go

@@ -116,7 +116,7 @@ func (f *DumpFormatter) FormatMultiFile(diffs []diff.Diff, outputPath string) er
 	}
 
 	// Create files in dependency order
-	orderedDirs := []string{"types", "domains", "sequences", "functions", "procedures", "tables", "views", "materialized_views", "default_privileges", "privileges"}
+	orderedDirs := []string{"extensions", "types", "domains", "sequences", "functions", "procedures", "tables", "views", "materialized_views", "default_privileges", "privileges"}
 
 	for _, dir := range orderedDirs {
 		if objects, exists := filesByType[dir]; exists {
@@ -235,6 +235,8 @@ func (f *DumpFormatter) writeObjectFile(filePath string, diffs []diff.Diff) erro
 // getObjectDirectory returns the directory name for an object type
 func (f *DumpFormatter) getObjectDirectory(objectType string) string {
 	switch objectType {
+	case "extension":
+		return "extensions"
 	case "type":
 		return "types"
 	case "domain":