If an index can't be found by column, use the index name.

schema_statements uses the column name by default to construct the index name, and then raises an exception if it doesn't exist, even if the name option is specified, which causes rails#8858.  this commit makes index_name_for_remove fall back to constructing the index name to remove based on the name option.

Author: heartpunk

activerecord/CHANGELOG.md

@@ -1,5 +1,15 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   When `:name` option is provided to `remove_index`, use it if there is no index by the conventional name.
+
+    For example, previously if an index was removed like so
+    `remove_index :values, column: :value, name: 'a_different_name'`
+    the generated SQL would not contain the specified index name,
+    and hence the migration would fail.
+    Fixes #8858.
+
+    *Ezekiel Smithburg*
+
 *   Expand `#cache_key` to consult all relevant updated timestamps.
 
     Previously only `updated_at` column was checked, now it will

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

@@ -687,6 +687,12 @@ def index_name_for_remove(table_name, options = {})
           index_name = index_name(table_name, options)
 
           unless index_name_exists?(table_name, index_name, true)
+            if options.has_key? :name
+              options_without_column = options.dup
+              options_without_column.delete :column
+              index_name_without_column = index_name(table_name, options_without_column)
+              return index_name_without_column if index_name_exists?(table_name, index_name_without_column, false)
+            end
             raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' does not exist"
           end
 

activerecord/test/cases/migration_test.rb

@@ -462,6 +462,22 @@ def test_drop_index_from_table_named_values
   end
 end
 
+class ExplicitlyNamedIndexMigrationTest < ActiveRecord::TestCase
+  def test_drop_index_by_name
+    connection = Person.connection
+    connection.create_table :values, force: true do |t|
+      t.integer :value
+    end
+
+    assert_nothing_raised ArgumentError do
+      connection.add_index :values, :value, name: 'a_different_name'
+      connection.remove_index :values, column: :value, name: 'a_different_name'
+    end
+
+    connection.drop_table :values rescue nil
+  end
+end
+
 if ActiveRecord::Base.connection.supports_bulk_alter?
   class BulkAlterTableMigrationsTest < ActiveRecord::TestCase
     def setup