feat: add functional unique index

pkg/sqlschema/index.go

@@ -1,6 +1,8 @@
 package sqlschema
 
 import (
+	"fmt"
+	"hash/fnv"
 	"slices"
 	"strings"
 
@@ -49,9 +51,23 @@ type Index interface {
 	ToDropSQL(fmter SQLFormatter) []byte
 }
 
+// UniqueIndex models a unique index on a table.
+//
+// In the common case the index keys on plain columns: set only ColumnNames and
+// the SQL is emitted with each column identifier-quoted by the formatter
+// (`CREATE UNIQUE INDEX uq_t_a_b ON t (a, b)`).
+//
+// For functional indexes (e.g. case-insensitive uniqueness on `LOWER(col)`),
+// set Expressions to the raw SQL parts and use ColumnNames as metadata for
+// "which columns does this index touch". When Expressions is non-empty, it
+// overrides ColumnNames for SQL emission — each entry is written verbatim, so
+// the caller owns well-formedness — and the auto-generated name uses a hash
+// suffix instead of a readable column join because expressions aren't valid
+// identifier fragments.
 type UniqueIndex struct {
 	TableName   TableName
 	ColumnNames []ColumnName
+	Expressions []string
 	name        string
 }
 
@@ -71,16 +87,28 @@ func (index *UniqueIndex) Name() string {
 		}
 		b.WriteString(string(column))
 	}
+
+	if len(index.Expressions) > 0 {
+		if len(index.ColumnNames) > 0 {
+			b.WriteString("_")
+		}
+		hasher := fnv.New32a()
+		_, _ = hasher.Write([]byte(strings.Join(index.Expressions, "\x00")))
+		fmt.Fprintf(&b, "%08x", hasher.Sum32())
+	}
 	return b.String()
 }
 
 func (index *UniqueIndex) Named(name string) Index {
 	copyOfColumnNames := make([]ColumnName, len(index.ColumnNames))
 	copy(copyOfColumnNames, index.ColumnNames)
+	copyOfExpressions := make([]string, len(index.Expressions))
+	copy(copyOfExpressions, index.Expressions)
 
 	return &UniqueIndex{
 		TableName:   index.TableName,
 		ColumnNames: copyOfColumnNames,
+		Expressions: copyOfExpressions,
 		name:        name,
 	}
 }
@@ -101,7 +129,18 @@ func (index *UniqueIndex) Equals(other Index) bool {
 	if other.Type() != IndexTypeUnique {
 		return false
 	}
-
+	otherUnique, ok := other.(*UniqueIndex)
+	if !ok {
+		return false
+	}
+	// Plain and functional indexes produce different SQL even if their column
+	// sets overlap; require both shapes to match.
+	if (len(index.Expressions) == 0) != (len(otherUnique.Expressions) == 0) {
+		return false
+	}
+	if len(index.Expressions) > 0 && !slices.Equal(index.Expressions, otherUnique.Expressions) {
+		return false
+	}
 	return index.Name() == other.Name() && slices.Equal(index.Columns(), other.Columns())
 }
 
@@ -114,12 +153,20 @@ func (index *UniqueIndex) ToCreateSQL(fmter SQLFormatter) []byte {
 	sql = fmter.AppendIdent(sql, string(index.TableName))
 	sql = append(sql, " ("...)
 
-	for i, column := range index.ColumnNames {
-		if i > 0 {
-			sql = append(sql, ", "...)
+	if len(index.Expressions) > 0 {
+		for i, expr := range index.Expressions {
+			if i > 0 {
+				sql = append(sql, ", "...)
+			}
+			sql = append(sql, expr...)
+		}
+	} else {
+		for i, column := range index.ColumnNames {
+			if i > 0 {
+				sql = append(sql, ", "...)
+			}
+			sql = fmter.AppendIdent(sql, string(column))
 		}
-
-		sql = fmter.AppendIdent(sql, string(column))
 	}
 
 	sql = append(sql, ")"...)

pkg/sqlschema/index_test.go

@@ -38,6 +38,43 @@ func TestIndexToCreateSQL(t *testing.T) {
 			},
 			sql: `CREATE UNIQUE INDEX IF NOT EXISTS "my_index" ON "users" ("id", "name", "email")`,
 		},
+		{
+			name: "Unique_Functional_SingleExpression",
+			index: &UniqueIndex{
+				TableName:   "users",
+				ColumnNames: []ColumnName{"email"},
+				Expressions: []string{"LOWER(email)"},
+			},
+			sql: `CREATE UNIQUE INDEX IF NOT EXISTS "uq_users_email_1e5a87f1" ON "users" (LOWER(email))`,
+		},
+		{
+			name: "Unique_Functional_MixedColumnsAndExpressions",
+			index: &UniqueIndex{
+				TableName:   "tag",
+				ColumnNames: []ColumnName{"org_id", "kind", "key", "value"},
+				Expressions: []string{"org_id", "kind", "LOWER(key)", "LOWER(value)"},
+			},
+			sql: `CREATE UNIQUE INDEX IF NOT EXISTS "uq_tag_org_id_kind_key_value_57e8f81f" ON "tag" (org_id, kind, LOWER(key), LOWER(value))`,
+		},
+		{
+			name: "Unique_Functional_ComplexExpression",
+			index: &UniqueIndex{
+				TableName:   "users",
+				ColumnNames: []ColumnName{"first_name", "last_name"},
+				Expressions: []string{"LOWER(TRIM(first_name) || ' ' || TRIM(last_name))"},
+			},
+			sql: `CREATE UNIQUE INDEX IF NOT EXISTS "uq_users_first_name_last_name_adb1ff53" ON "users" (LOWER(TRIM(first_name) || ' ' || TRIM(last_name)))`,
+		},
+		{
+			name: "Unique_Functional_Named",
+			index: &UniqueIndex{
+				TableName:   "tag",
+				ColumnNames: []ColumnName{"org_id", "kind", "key", "value"},
+				Expressions: []string{"org_id", "kind", "LOWER(key)", "LOWER(value)"},
+				name:        "uq_tag_org_kind_lower_key_lower_value",
+			},
+			sql: `CREATE UNIQUE INDEX IF NOT EXISTS "uq_tag_org_kind_lower_key_lower_value" ON "tag" (org_id, kind, LOWER(key), LOWER(value))`,
+		},
 		{
 			name: "PartialUnique_1Column",
 			index: &PartialUniqueIndex{
@@ -229,6 +266,47 @@ func TestIndexEquals(t *testing.T) {
 			},
 			equals: false,
 		},
+		{
+			name: "Unique_Functional_Same",
+			a: &UniqueIndex{
+				TableName:   "users",
+				ColumnNames: []ColumnName{"email"},
+				Expressions: []string{"LOWER(email)"},
+			},
+			b: &UniqueIndex{
+				TableName:   "users",
+				ColumnNames: []ColumnName{"email"},
+				Expressions: []string{"LOWER(email)"},
+			},
+			equals: true,
+		},
+		{
+			name: "Unique_Functional_DifferentExpressions",
+			a: &UniqueIndex{
+				TableName:   "users",
+				ColumnNames: []ColumnName{"email"},
+				Expressions: []string{"LOWER(email)"},
+			},
+			b: &UniqueIndex{
+				TableName:   "users",
+				ColumnNames: []ColumnName{"email"},
+				Expressions: []string{"UPPER(email)"},
+			},
+			equals: false,
+		},
+		{
+			name: "Unique_Functional_NotEqualToPlainSameColumns",
+			a: &UniqueIndex{
+				TableName:   "users",
+				ColumnNames: []ColumnName{"email"},
+				Expressions: []string{"LOWER(email)"},
+			},
+			b: &UniqueIndex{
+				TableName:   "users",
+				ColumnNames: []ColumnName{"email"},
+			},
+			equals: false,
+		},
 	}
 
 	for _, testCase := range testCases {
@@ -238,6 +316,75 @@ func TestIndexEquals(t *testing.T) {
 	}
 }
 
+func TestUniqueIndexFunctionalName(t *testing.T) {
+	t.Run("autogen uses uq_<table>_<hash>", func(t *testing.T) {
+		idx := &UniqueIndex{
+			TableName:   "tag",
+			ColumnNames: []ColumnName{"org_id", "kind", "key", "value"},
+			Expressions: []string{"org_id", "kind", "LOWER(key)", "LOWER(value)"},
+		}
+		assert.Equal(t, "uq_tag_org_id_kind_key_value_57e8f81f", idx.Name())
+	})
+
+	t.Run("same expressions produce the same name", func(t *testing.T) {
+		a := &UniqueIndex{
+			TableName:   "users",
+			Expressions: []string{"LOWER(email)"},
+		}
+		b := &UniqueIndex{
+			TableName:   "users",
+			Expressions: []string{"LOWER(email)"},
+		}
+		assert.Equal(t, a.Name(), b.Name())
+	})
+
+	t.Run("different expressions produce different names", func(t *testing.T) {
+		a := &UniqueIndex{
+			TableName:   "users",
+			Expressions: []string{"LOWER(email)"},
+		}
+		b := &UniqueIndex{
+			TableName:   "users",
+			Expressions: []string{"UPPER(email)"},
+		}
+		assert.NotEqual(t, a.Name(), b.Name())
+	})
+
+	t.Run("expressions in different order produce different names", func(t *testing.T) {
+		a := &UniqueIndex{
+			TableName:   "tag",
+			Expressions: []string{"org_id", "LOWER(key)"},
+		}
+		b := &UniqueIndex{
+			TableName:   "tag",
+			Expressions: []string{"LOWER(key)", "org_id"},
+		}
+		assert.NotEqual(t, a.Name(), b.Name())
+	})
+
+	t.Run("functional autogen differs from plain autogen for same columns", func(t *testing.T) {
+		plain := &UniqueIndex{
+			TableName:   "users",
+			ColumnNames: []ColumnName{"email"},
+		}
+		functional := &UniqueIndex{
+			TableName:   "users",
+			ColumnNames: []ColumnName{"email"},
+			Expressions: []string{"LOWER(email)"},
+		}
+		assert.Equal(t, "uq_users_email", plain.Name())
+		assert.NotEqual(t, plain.Name(), functional.Name())
+	})
+
+	t.Run("Named() override wins over hash", func(t *testing.T) {
+		idx := (&UniqueIndex{
+			TableName:   "tag",
+			Expressions: []string{"org_id", "LOWER(key)"},
+		}).Named("my_functional_index")
+		assert.Equal(t, "my_functional_index", idx.Name())
+	})
+}
+
 func TestPartialUniqueIndexName(t *testing.T) {
 	a := &PartialUniqueIndex{
 		TableName:   "users",