Fix Rails generated index name being too long

This updates the index name generation to always create a valid index name if one is not passed by the user.

Set the limit to 62 bytes to ensure it works for the default configurations of Sqlite, mysql & postgres.

MySQL: 64
Postgres: 63
Sqlite: 62

When over the limit, we fallback to a "short format" that includes a hash to guarantee uniqueness in the generated index name.

activerecord/CHANGELOG.md

@@ -1,3 +1,24 @@
+*   Limit max length of auto generated index names
+
+    Auto generated index names are now limited to 62 bytes, which fits within
+    the default index name length limits for MySQL, Postgres and SQLite.
+
+    Any index name over the limit will fallback to the new short format.
+
+    Before (too long):
+    ```
+    index_testings_on_foo_and_bar_and_first_name_and_last_name_and_administrator
+    ```
+
+    After (short format):
+    ```
+    ix_on_foo_bar_first_name_last_name_administrator_5939248142
+    ```
+
+    The short format includes a hash to ensure the name is unique database-wide.
+
+    *Mike Coutermarsh*
+
 *   Introduce a more stable and optimized Marshal serializer for Active Record models.
 
     Can be enabled with `config.active_record.marshalling_format_version = 7.1`.

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

@@ -962,7 +962,7 @@ def rename_index(table_name, old_name, new_name)
       def index_name(table_name, options) # :nodoc:
         if Hash === options
           if options[:column]
-            "index_#{table_name}_on_#{Array(options[:column]) * '_and_'}"
+            generate_index_name(table_name, options[:column])
           elsif options[:name]
             options[:name]
           else
@@ -1509,7 +1509,26 @@ def valid_primary_key_options # :nodoc:
         [:limit, :default, :precision]
       end
 
+      # Returns the maximum length of an index name in bytes.
+      def max_index_name_size
+        62
+      end
+
       private
+        def generate_index_name(table_name, column)
+          name = "index_#{table_name}_on_#{Array(column) * '_and_'}"
+          return name if name.bytesize <= max_index_name_size
+
+          # Fallback to short version, add hash to ensure uniqueness
+          hashed_identifier = "_" + OpenSSL::Digest::SHA256.hexdigest(name).first(10)
+          name = "ix_on_#{Array(column) * '_'}"
+
+          short_limit = max_index_name_size - hashed_identifier.bytesize
+          short_name = name.mb_chars.limit(short_limit).to_s
+
+          "#{short_name}#{hashed_identifier}"
+        end
+
         def validate_change_column_null_argument!(value)
           unless value == true || value == false
             raise ArgumentError, "change_column_null expects a boolean value (true for NULL, false for NOT NULL). Got: #{value.inspect}"

activerecord/lib/active_record/migration/compatibility.rb

@@ -54,6 +54,10 @@ def add_column(table_name, column_name, type, **options)
           super
         end
 
+        def add_index(table_name, column_name, **options)
+          options[:name] = legacy_index_name(table_name, column_name) if options[:name].nil?
+          super
+        end
 
         def create_table(table_name, **options)
           options[:_uses_legacy_table_name] = true
@@ -105,6 +109,32 @@ class << t
             end
             super
           end
+
+          def legacy_index_name(table_name, options)
+            if Hash === options
+              if options[:column]
+                "index_#{table_name}_on_#{Array(options[:column]) * '_and_'}"
+              elsif options[:name]
+                options[:name]
+              else
+                raise ArgumentError, "You must specify the index name"
+              end
+            else
+              legacy_index_name(table_name, index_name_options(options))
+            end
+          end
+
+          def index_name_options(column_names)
+            if expression_column_name?(column_names)
+              column_names = column_names.scan(/\w+/).join("_")
+            end
+
+            { column: column_names }
+          end
+
+          def expression_column_name?(column_name)
+            column_name.is_a?(String) && /\W/.match?(column_name)
+          end
       end
 
       class V6_1 < V7_0

activerecord/test/cases/migration/compatibility_test.rb

@@ -550,6 +550,22 @@ def migrate(x)
         connection.drop_table :more_testings rescue nil
       end
 
+      def test_add_index_errors_on_too_long_name_7_0
+        migration = Class.new(ActiveRecord::Migration[7.0]) {
+          def migrate(x)
+            add_column :testings, :very_long_column_name_to_test_with, :string
+            add_index :testings, [:foo, :bar, :very_long_column_name_to_test_with]
+          end
+        }.new
+
+        error = assert_raises(StandardError) do
+          ActiveRecord::Migrator.new(:up, [migration], @schema_migration, @internal_metadata).migrate
+        end
+
+        assert_match(/index_testings_on_foo_and_bar_and_very_long_column_name_to_test_with/i, error.message)
+        assert_match(/is too long/i, error.message)
+      end
+
       def test_add_reference_on_6_0
         create_migration = Class.new(ActiveRecord::Migration[6.0]) {
           def version; 100 end

activerecord/test/cases/migration/index_test.rb

@@ -103,6 +103,11 @@ def test_add_index_with_if_not_exists_matches_exact_index
         assert connection.index_name_exists?(table_name, "index_testings_on_foo_and_bar")
       end
 
+      def test_add_index_fallback_to_short_name
+        connection.add_index(table_name, [:foo, :bar, :first_name, :last_name, :administrator])
+        assert connection.index_name_exists?(table_name, "ix_on_foo_bar_first_name_last_name_administrator_5939248142")
+      end
+
       def test_remove_index_which_does_not_exist_doesnt_raise_with_option
         connection.add_index(table_name, "foo")