Dump index options to pretty format

```ruby
  # Before
  t.index ["firm_id", "type", "rating"], name: "company_index", order: {"rating"=>:desc}, using: :btree

  # After
  t.index ["firm_id", "type", "rating"], name: "company_index", order: { rating: :desc }, using: :btree
```

5 files changed, 10 insertions, 12 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 51819f7980..0f1a83324b 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -1192,7 +1192,7 @@ module ActiveRecord
         def quoted_columns_for_index(column_names, **options)
           return [column_names] if column_names.is_a?(String)
 
-          quoted_columns = Hash[column_names.map { |name| [name, quote_column_name(name).dup] }]
+          quoted_columns = Hash[column_names.map { |name| [name.to_sym, quote_column_name(name).dup] }]
           add_options_for_index_columns(quoted_columns, options).values
         end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 5923136df8..003ba6eff5 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -384,11 +384,11 @@ module ActiveRecord
               mysql_index_type = row[:Index_type].downcase.to_sym
               index_type  = INDEX_TYPES.include?(mysql_index_type)  ? mysql_index_type : nil
               index_using = INDEX_USINGS.include?(mysql_index_type) ? mysql_index_type : nil
-              indexes << IndexDefinition.new(row[:Table], row[:Key_name], row[:Non_unique].to_i == 0, [], [], nil, nil, index_type, index_using, row[:Index_comment].presence)
+              indexes << IndexDefinition.new(row[:Table], row[:Key_name], row[:Non_unique].to_i == 0, [], {}, nil, nil, index_type, index_using, row[:Index_comment].presence)
             end
 
             indexes.last.columns << row[:Column_name]
-            indexes.last.lengths << row[:Sub_part]
+            indexes.last.lengths.merge!(row[:Column_name] => row[:Sub_part]) if row[:Sub_part]
           end
         end
 
diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index 41fed004a0..fc28ac7cb0 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -192,12 +192,8 @@ HEADER
           "name: #{index.name.inspect}",
         ]
         index_parts << "unique: true" if index.unique
-
-        index_lengths = (index.lengths || []).compact
-        index_parts << "length: #{Hash[index.columns.zip(index.lengths)].inspect}" if index_lengths.any?
-
-        index_orders = index.orders || {}
-        index_parts << "order: #{index.orders.inspect}" if index_orders.any?
+        index_parts << "length: { #{format_options(index.lengths)} }" if index.lengths.present?
+        index_parts << "order: { #{format_options(index.orders)} }" if index.orders.present?
         index_parts << "where: #{index.where.inspect}" if index.where
         index_parts << "using: #{index.using.inspect}" if index.using
         index_parts << "type: #{index.type.inspect}" if index.type
diff --git a/activerecord/test/cases/schema_dumper_test.rb b/activerecord/test/cases/schema_dumper_test.rb
index 8b604ba930..7f9a5798dd 100644
--- a/activerecord/test/cases/schema_dumper_test.rb
+++ b/activerecord/test/cases/schema_dumper_test.rb
@@ -183,8 +183,10 @@ class SchemaDumperTest < ActiveRecord::TestCase
 
   def test_schema_dumps_index_columns_in_right_order
     index_definition = standard_dump.split(/\n/).grep(/t\.index.*company_index/).first.strip
-    if current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter)
-      assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index", using: :btree', index_definition
+    if current_adapter?(:PostgreSQLAdapter)
+      assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index", order: { rating: :desc }, using: :btree', index_definition
+    elsif current_adapter?(:Mysql2Adapter)
+      assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index", length: { type: 10 }, using: :btree', index_definition
     else
       assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index"', index_definition
     end
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index a4756ec75a..d2fb090118 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -197,7 +197,7 @@ ActiveRecord::Schema.define do
     t.integer :rating, default: 1
     t.integer :account_id
     t.string :description, default: ""
-    t.index [:firm_id, :type, :rating], name: "company_index"
+    t.index [:firm_id, :type, :rating], name: "company_index", length: { type: 10 }, order: { rating: :desc }
     t.index [:firm_id, :type], name: "company_partial_index", where: "rating > 10"
     t.index :name, name: "company_name_index", using: :btree
     t.index "lower(name)", name: "company_expression_index" if supports_expression_index?