Rename the primary key index when renaming a table in pg

Backport of dcc143cd

Fixes #12856
Closes #14088

activerecord/CHANGELOG.md

+*   Renaming a table in pg also renames the primary key index.
+
+    Fixes #12856
+
+    *Sean Griffin*
+
 *   Make it possible to access fixtures excluded by a `default_scope`.
 
     *Yves Senn*

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

@@ -382,7 +382,10 @@ def rename_table(table_name, new_name)
           pk, seq = pk_and_sequence_for(new_name)
           if seq == "#{table_name}_#{pk}_seq"
             new_seq = "#{new_name}_#{pk}_seq"
+            idx = "#{table_name}_pkey"
+            new_idx = "#{new_name}_pkey"
             execute "ALTER TABLE #{quote_table_name(seq)} RENAME TO #{quote_table_name(new_seq)}"
+            execute "ALTER INDEX #{quote_table_name(idx)} RENAME TO #{quote_table_name(new_idx)}"
           end
 
           rename_table_indexes(table_name, new_name)

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

+require "cases/helper"
+
+class PostgresqlRenameTableTest < ActiveRecord::TestCase
+  def setup
+    @connection = ActiveRecord::Base.connection
+    @connection.create_table :before_rename, force: true
+  end
+
+  def teardown
+    @connection.execute 'DROP TABLE IF EXISTS "before_rename"'
+    @connection.execute 'DROP TABLE IF EXISTS "after_rename"'
+  end
+
+  test "renaming a table also renames the primary key index" do
+    # sanity check
+    assert_equal 1, num_indices_named("before_rename_pkey")
+    assert_equal 0, num_indices_named("after_rename_pkey")
+
+    @connection.rename_table :before_rename, :after_rename
+
+    assert_equal 0, num_indices_named("before_rename_pkey")
+    assert_equal 1, num_indices_named("after_rename_pkey")
+  end
+
+  private
+
+  def num_indices_named(name)
+    @connection.execute(<<-SQL).values.length
+      SELECT 1 FROM "pg_index"
+        JOIN "pg_class" ON "pg_index"."indexrelid" = "pg_class"."oid"
+        WHERE "pg_class"."relname" = '#{name}'
+    SQL
+  end
+end