pg, change_column_default accepts []. Closes #11586.

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   `change_column_default` allows `[]` as argument to `change_column_default`.
+
+    Fixes #11586.
+
+    *Yves Senn*
+
 *   Handle `name` and `"char"` column types in the PostgreSQL adapter.
 
     `name` and `"char"` are special character types used internally by

activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb

@@ -187,8 +187,8 @@ module ActiveRecord
         def quote_default_value(value, column) #:nodoc:
           if column.type == :uuid && value =~ /\(\)/
             value
-          else 
-            quote(value)
+          else
+            quote(value, column)
           end
         end
       end

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

@@ -405,6 +405,7 @@ module ActiveRecord
         def change_column_default(table_name, column_name, default)
           clear_cache!
           column = column_for(table_name, column_name)
+
           execute "ALTER TABLE #{quote_table_name(table_name)} ALTER COLUMN #{quote_column_name(column_name)} SET DEFAULT #{quote_default_value(default, column)}" if column
         end
 

activerecord/test/cases/adapters/postgresql/array_test.rb

@@ -61,7 +61,7 @@ class PostgresqlArrayTest < ActiveRecord::TestCase
 
   def test_change_column_with_array
     @connection.add_column :pg_arrays, :snippets, :string, array: true, default: []
-    @connection.change_column :pg_arrays, :snippets, :text, array: true, default: "{}"
+    @connection.change_column :pg_arrays, :snippets, :text, array: true, default: []
 
     PgArray.reset_column_information
     column = PgArray.columns.find { |c| c.name == 'snippets' }
@@ -80,6 +80,14 @@ class PostgresqlArrayTest < ActiveRecord::TestCase
     end
   end
 
+  def test_change_column_default_with_array
+    @connection.change_column_default :pg_arrays, :tags, []
+
+    PgArray.reset_column_information
+    column = PgArray.columns_hash['tags']
+    assert_equal [], column.default
+  end
+
   def test_type_cast_array
     data = '{1,2,3}'
     oid_type  = @column.instance_variable_get('@oid_type').subtype