Dump PostgreSQL primary key with custom function as a default.

For example, if use pgcrypto extension in PostgreSQL 9.4 beta 1, where
uuid-ossp extension isn't available for moment of writing, and thus to
use a gen_random_uuid() method as a primary key default.

In this case schema dumper wasn't able to correctly reconstruct
create_table statement and lost primary key constraint on schema load.

Fixes #16111.

activerecord/CHANGELOG.md

+*   Fix the schema dump generated for tables without constraints and with
+    primary key with default value of custom PostgreSQL function result.
+
+    Fixes #16111
+
+    *Andrey Novikov*
+
 *   Fix the SQL generated when a `delete_all` is run on an association to not
     produce an `IN` statements.
 

activerecord/lib/active_record/schema_dumper.rb

@@ -120,7 +120,8 @@ def table(table, stream)
           # first dump primary key column
           if @connection.respond_to?(:pk_and_sequence_for)
             pk, _ = @connection.pk_and_sequence_for(table)
-          elsif @connection.respond_to?(:primary_key)
+          end
+          if !pk && @connection.respond_to?(:primary_key)
             pk = @connection.primary_key(table)
           end
 

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

@@ -87,10 +87,26 @@ class UUID < ActiveRecord::Base
       t.string 'name'
       t.uuid 'other_uuid', default: 'uuid_generate_v4()'
     end
+
+    # Create custom PostgreSQL function to generate UUIDs
+    # to test dumping tables which columns have defaults with custom functions
+    connection.execute <<-SQL
+    CREATE OR REPLACE FUNCTION my_uuid_generator() RETURNS uuid
+    AS $$ SELECT * FROM uuid_generate_v4() $$
+    LANGUAGE SQL VOLATILE;
+    SQL
+
+    # Create such a table with custom function as default value generator
+    connection.create_table('pg_uuids_2', id: :uuid, default: 'my_uuid_generator()') do |t|
+      t.string 'name'
+      t.uuid 'other_uuid_2', default: 'my_uuid_generator()'
+    end
   end
 
   teardown do
     drop_table "pg_uuids"
+    drop_table 'pg_uuids_2'
+    connection.execute 'DROP FUNCTION IF EXISTS my_uuid_generator();'
   end
 
   if ActiveRecord::Base.connection.supports_extensions?
@@ -122,6 +138,13 @@ def test_schema_dumper_for_uuid_primary_key
       assert_match(/\bcreate_table "pg_uuids", id: :uuid, default: "uuid_generate_v1\(\)"/, schema.string)
       assert_match(/t\.uuid   "other_uuid", default: "uuid_generate_v4\(\)"/, schema.string)
     end
+
+    def test_schema_dumper_for_uuid_primary_key_with_custom_default
+      schema = StringIO.new
+      ActiveRecord::SchemaDumper.dump(connection, schema)
+      assert_match(/\bcreate_table "pg_uuids_2", id: :uuid, default: "my_uuid_generator\(\)"/, schema.string)
+      assert_match(/t\.uuid   "other_uuid_2", default: "my_uuid_generator\(\)"/, schema.string)
+    end
   end
 end