fix: support NULLS NOT DISTINCT on unique indexes (#355)

internal/diff/index.go

@@ -121,6 +121,11 @@ func generateIndexSQLWithName(index *ir.Index, indexName string, targetSchema st
 	}
 	builder.WriteString(")")
 
+	// NULLS NOT DISTINCT for unique indexes (PostgreSQL 15+)
+	if index.NullsNotDistinct && index.Type == ir.IndexTypeUnique {
+		builder.WriteString(" NULLS NOT DISTINCT")
+	}
+
 	// WHERE clause for partial indexes
 	if index.IsPartial && index.Where != "" {
 		builder.WriteString(" WHERE ")

internal/diff/table.go

@@ -1414,6 +1414,7 @@ func indexesStructurallyEqual(oldIndex, newIndex *ir.Index) bool {
 		oldIndex.Method != newIndex.Method ||
 		oldIndex.IsPartial != newIndex.IsPartial ||
 		oldIndex.IsExpression != newIndex.IsExpression ||
+		oldIndex.NullsNotDistinct != newIndex.NullsNotDistinct ||
 		oldIndex.Where != newIndex.Where {
 		return false
 	}

internal/plan/rewrite.go

@@ -411,6 +411,10 @@ func generateIndexSQL(index *ir.Index, isConcurrent bool) string {
 	sql.WriteString(joinStrings(columnParts, ", "))
 	sql.WriteString(")")
 
+	if index.NullsNotDistinct && index.Type == ir.IndexTypeUnique {
+		sql.WriteString(" NULLS NOT DISTINCT")
+	}
+
 	if index.Where != "" {
 		sql.WriteString(" WHERE ")
 		sql.WriteString(index.Where)

ir/inspector.go

@@ -757,6 +757,11 @@ func (i *Inspector) buildIndexes(ctx context.Context, schema *IR, targetSchema s
 			Columns:      []*IndexColumn{},
 		}
 
+		// Check for NULLS NOT DISTINCT (PostgreSQL 15+)
+		if indexRow.Indexdef.Valid && strings.Contains(indexRow.Indexdef.String, "NULLS NOT DISTINCT") {
+			index.NullsNotDistinct = true
+		}
+
 		// Set WHERE clause for partial indexes
 		if isPartial && indexRow.PartialPredicate.Valid {
 			// Use the predicate as-is from pg_get_expr, which already has proper formatting

ir/ir.go

@@ -250,10 +250,11 @@ type Index struct {
 	Type         IndexType      `json:"type"`
 	Method       string         `json:"method"` // btree, hash, gin, gist, etc.
 	Columns      []*IndexColumn `json:"columns"`
-	IsPartial    bool           `json:"is_partial"`      // has a WHERE clause
-	IsExpression bool           `json:"is_expression"`   // functional/expression index
-	Where        string         `json:"where,omitempty"` // partial index condition
-	Comment      string         `json:"comment,omitempty"`
+	IsPartial        bool   `json:"is_partial"`                   // has a WHERE clause
+	IsExpression     bool   `json:"is_expression"`                // functional/expression index
+	Where            string `json:"where,omitempty"`              // partial index condition
+	NullsNotDistinct bool   `json:"nulls_not_distinct,omitempty"` // NULLS NOT DISTINCT (PG15+)
+	Comment          string `json:"comment,omitempty"`
 }
 
 // IndexColumn represents a column within an index

testdata/diff/create_index/add_index/diff.sql

@@ -7,6 +7,8 @@ CREATE TABLE IF NOT EXISTS users (
 
 CREATE INDEX IF NOT EXISTS idx_users_email ON users (email varchar_pattern_ops);
 
+CREATE UNIQUE INDEX IF NOT EXISTS idx_users_email_unique ON users (email) NULLS NOT DISTINCT;
+
 CREATE INDEX IF NOT EXISTS idx_users_id ON users (id);
 
 CREATE INDEX IF NOT EXISTS idx_users_name ON users (name);

testdata/diff/create_index/add_index/new.sql

@@ -10,3 +10,5 @@ CREATE INDEX idx_users_email ON public.users (email varchar_pattern_ops);
 CREATE INDEX idx_users_id ON public.users (id);
 -- Test index name with dots (issue #196)
 CREATE INDEX "public.idx_users" ON public.users (email, name);
+-- Test NULLS NOT DISTINCT (issue #355)
+CREATE UNIQUE INDEX idx_users_email_unique ON public.users (email) NULLS NOT DISTINCT;

testdata/diff/create_index/add_index/plan.json

@@ -20,6 +20,12 @@
           "operation": "create",
           "path": "public.users.idx_users_email"
         },
+        {
+          "sql": "CREATE UNIQUE INDEX IF NOT EXISTS idx_users_email_unique ON users (email) NULLS NOT DISTINCT;",
+          "type": "table.index",
+          "operation": "create",
+          "path": "public.users.idx_users_email_unique"
+        },
         {
           "sql": "CREATE INDEX IF NOT EXISTS idx_users_id ON users (id);",
           "type": "table.index",

testdata/diff/create_index/add_index/plan.sql

@@ -7,6 +7,8 @@ CREATE TABLE IF NOT EXISTS users (
 
 CREATE INDEX IF NOT EXISTS idx_users_email ON users (email varchar_pattern_ops);
 
+CREATE UNIQUE INDEX IF NOT EXISTS idx_users_email_unique ON users (email) NULLS NOT DISTINCT;
+
 CREATE INDEX IF NOT EXISTS idx_users_id ON users (id);
 
 CREATE INDEX IF NOT EXISTS idx_users_name ON users (name);

testdata/diff/create_index/add_index/plan.txt

@@ -6,6 +6,7 @@ Summary by type:
 Tables:
   + users
     + idx_users_email (index)
+    + idx_users_email_unique (index)
     + idx_users_id (index)
     + idx_users_name (index)
     + public.idx_users (index)
@@ -22,6 +23,8 @@ CREATE TABLE IF NOT EXISTS users (
 
 CREATE INDEX IF NOT EXISTS idx_users_email ON users (email varchar_pattern_ops);
 
+CREATE UNIQUE INDEX IF NOT EXISTS idx_users_email_unique ON users (email) NULLS NOT DISTINCT;
+
 CREATE INDEX IF NOT EXISTS idx_users_id ON users (id);
 
 CREATE INDEX IF NOT EXISTS idx_users_name ON users (name);

testutil/skip_list.go

@@ -61,9 +61,17 @@ var skipListRequiresExtension = []string{
 	"create_table/issue_295_pgvector_typmod",
 }
 
+// skipListPG14 defines test cases that should be skipped for PostgreSQL 14 only.
+//
+// Reason for skipping:
+// These tests use features not available in PostgreSQL 14 (e.g., NULLS NOT DISTINCT is PG15+).
+var skipListPG14 = []string{
+	"create_index/add_index",
+}
+
 // skipListForVersion maps PostgreSQL major versions to their skip lists.
 var skipListForVersion = map[int][]string{
-	14: skipListPG14_15,
+	14: append(append([]string(nil), skipListPG14_15...), skipListPG14...),
 	15: skipListPG14_15,
 }
 
@@ -101,7 +109,7 @@ func ShouldSkipTest(t *testing.T, testName string, majorVersion int) {
 		patternNormalized := strings.ReplaceAll(pattern, "/", "_")
 
 		if testName == patternNormalized || testName == pattern {
-			t.Skipf("Skipping test %q on PostgreSQL %d due to pg_get_viewdef() formatting differences (non-consequential)", testName, majorVersion)
+			t.Skipf("Skipping test %q on PostgreSQL %d (unsupported feature or formatting differences)", testName, majorVersion)
 		}
 	}
 }