SQLite3 adapter supports expression indexes

activerecord/CHANGELOG.md

@@ -1,3 +1,15 @@
+*   SQLite3 adapter supports expression indexes
+
+    ```
+    create_table :users do |t|
+      t.string :email
+    end
+
+    add_index :users, 'lower(email)', name: 'index_users_on_email', unique: true
+    ```
+
+    *Gray Kemmey*
+
 *   Allow subclasses to redefine autosave callbacks for associated records.
 
     Fixes #33305.

activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb

@@ -21,12 +21,16 @@ module ActiveRecord
               WHERE name = #{quote(row['name'])} AND type = 'index'
             SQL
 
-            /\sWHERE\s+(?<where>.+)$/i =~ index_sql
+            /\sON\s+"(\w+?)"\s+\((?<expressions>.+?)\)(\sWHERE\s+(?<where>.+))?$/i =~ index_sql
 
             columns = exec_query("PRAGMA index_info(#{quote(row['name'])})", "SCHEMA").map do |col|
               col["name"]
             end
 
+            if columns.any?(&:nil?) # index created with an expression
+              columns = expressions.split(", ").map { |e| e.gsub(/^\"|\"?$/, "") }
+            end
+
             # Add info on sort order for columns (only desc order is explicitly specified, asc is
             # the default)
             orders = {}

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

@@ -125,6 +125,10 @@ module ActiveRecord
         true
       end
 
+      def supports_expression_index?
+        sqlite_version >= "3.9.0"
+      end
+
       def requires_reloading?
         true
       end

activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb

@@ -345,6 +345,41 @@ module ActiveRecord
         end
       end
 
+      if ActiveRecord::Base.connection.supports_expression_index?
+        def test_expression_index
+          with_example_table do
+            @conn.add_index "ex", "abs(number)", name: "expression"
+            index = @conn.indexes("ex").find { |idx| idx.name == "expression" }
+            assert_equal %w{ abs(number) }, index.columns
+          end
+        end
+
+        def test_expression_index_with_where
+          with_example_table do
+            @conn.add_index "ex", "id % 10, abs(number)", name: "expression", where: "id > 1000"
+            index = @conn.indexes("ex").find { |idx| idx.name == "expression" }
+            assert_equal ["id % 10", "abs(number)"], index.columns
+            assert_equal "id > 1000", index.where
+          end
+        end
+
+        def test_complicated_expression
+          with_example_table do
+            @conn.add_index "ex", "id % 10, (CASE WHEN number > 0 THEN abs(number) END)", name: "expression"
+            index = @conn.indexes("ex").find { |idx| idx.name == "expression" }
+            assert_equal ["id % 10", "(CASE WHEN number > 0 THEN abs(number) END)"], index.columns
+          end
+        end
+
+        def test_not_everything_an_expression
+          with_example_table do
+            @conn.add_index "ex", %w{ id abs(number) }, name: "expression"
+            index = @conn.indexes("ex").find { |idx| idx.name == "expression" }
+            assert_equal %w{ id abs(number) }.sort, index.columns.sort
+          end
+        end
+      end
+
       def test_primary_key
         with_example_table do
           assert_equal "id", @conn.primary_key("ex")

activerecord/test/cases/schema_dumper_test.rb

@@ -226,6 +226,20 @@ class SchemaDumperTest < ActiveRecord::TestCase
     assert_match %r{t\.float\s+"temperature"$}, output
   end
 
+  if ActiveRecord::Base.connection.supports_expression_index?
+    def test_schema_dump_expression_indices
+      index_definition = dump_table_schema("companies").split(/\n/).grep(/t\.index.*company_expression_index/).first.strip
+
+      if current_adapter?(:PostgreSQLAdapter)
+        assert_match %r{CASE.+lower\(\(name\)::text\)}i, index_definition
+      elsif current_adapter?(:SQLite3Adapter)
+        assert_match %r{CASE.+lower\(name\)}i, index_definition
+      else
+        assert false
+      end
+    end
+  end
+
   if current_adapter?(:Mysql2Adapter)
     def test_schema_dump_includes_length_for_mysql_binary_fields
       output = standard_dump
@@ -278,11 +292,6 @@ class SchemaDumperTest < ActiveRecord::TestCase
       assert_match %r{t\.decimal\s+"decimal_array_default",\s+default: \["1.23", "3.45"\],\s+array: true}, output
     end
 
-    def test_schema_dump_expression_indices
-      index_definition = dump_table_schema("companies").split(/\n/).grep(/t\.index.*company_expression_index/).first.strip
-      assert_match %r{CASE.+lower\(\(name\)::text\)}i, index_definition
-    end
-
     def test_schema_dump_interval_type
       output = dump_table_schema "postgresql_times"
       assert_match %r{t\.interval\s+"time_interval"$}, output