Deprecate allowed_index_name_length in DatabaseLimits

`allowed_index_name_length` was used for internal temporary operations
in SQLite3, since index name in SQLite3 must be globally unique and
SQLite3 doesn't have ALTER TABLE feature (so it is emulated by creating
temporary table with prefix).

`allowed_index_name_length` was to reserve the margin for the prefix,
but actually SQLite3 doesn't have a limitation for identifier name
length, so the margin has removed at 36901e6.

Now `allowed_index_name_length` is no longer relied on by any adapter,
so I'd like to remove the internal specific method which is no longer
used.

Author: kamipo

activerecord/CHANGELOG.md

@@ -1,4 +1,4 @@
-*   Deprecate `in_clause_length` in `DatabaseLimits`.
+*   Deprecate `in_clause_length` and `allowed_index_name_length` in `DatabaseLimits`.
 
     *Ryuta Kamizono*
 

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

@@ -32,6 +32,7 @@ def table_name_length
       def allowed_index_name_length
         index_name_length
       end
+      deprecate :allowed_index_name_length
 
       # Returns the maximum length of an index name.
       def index_name_length

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

@@ -1441,10 +1441,8 @@ def extract_foreign_key_action(specifier)
         end
 
         def validate_index_length!(table_name, new_name, internal = false)
-          max_index_length = internal ? index_name_length : allowed_index_name_length
-
-          if new_name.length > max_index_length
-            raise ArgumentError, "Index name '#{new_name}' on table '#{table_name}' is too long; the limit is #{allowed_index_name_length} characters"
+          if new_name.length > index_name_length
+            raise ArgumentError, "Index name '#{new_name}' on table '#{table_name}' is too long; the limit is #{index_name_length} characters"
           end
         end
 

activerecord/test/cases/adapter_test.rb

@@ -411,6 +411,10 @@ def test_joins_per_query_is_deprecated
       assert_deprecated { @connection.joins_per_query }
     end
 
+    def test_allowed_index_name_length_is_deprecated
+      assert_deprecated { @connection.allowed_index_name_length }
+    end
+
     unless current_adapter?(:OracleAdapter)
       def test_in_clause_length_is_deprecated
         assert_deprecated { @connection.in_clause_length }

activerecord/test/cases/migration/columns_test.rb

@@ -254,7 +254,7 @@ def test_change_column_with_custom_index_name
 
       def test_change_column_with_long_index_name
         table_name_prefix = "test_models_"
-        long_index_name = table_name_prefix + ("x" * (connection.allowed_index_name_length - table_name_prefix.length))
+        long_index_name = table_name_prefix + ("x" * (connection.index_name_length - table_name_prefix.length))
         add_column "test_models", "category", :string
         add_index :test_models, :category, name: long_index_name
 

activerecord/test/cases/migration/index_test.rb

@@ -44,7 +44,7 @@ def test_rename_index_too_long
         e = assert_raises(ArgumentError) {
           connection.rename_index(table_name, "old_idx", too_long_index_name)
         }
-        assert_match(/too long; the limit is #{connection.allowed_index_name_length} characters/, e.message)
+        assert_match(/too long; the limit is #{connection.index_name_length} characters/, e.message)
 
         assert connection.index_name_exists?(table_name, "old_idx")
       end
@@ -66,7 +66,7 @@ def test_add_index_does_not_accept_too_long_index_names
         e = assert_raises(ArgumentError) {
           connection.add_index(table_name, "foo", name: too_long_index_name)
         }
-        assert_match(/too long; the limit is #{connection.allowed_index_name_length} characters/, e.message)
+        assert_match(/too long; the limit is #{connection.index_name_length} characters/, e.message)
 
         assert_not connection.index_name_exists?(table_name, too_long_index_name)
         connection.add_index(table_name, "foo", name: good_index_name)
@@ -229,7 +229,7 @@ def test_add_partial_index
 
       private
         def good_index_name
-          "x" * connection.allowed_index_name_length
+          "x" * connection.index_name_length
         end
     end
   end