Update PostgreSQLAdapter#extensions to include schema name

This allows the schema dumper's generated `enable_extension` statements
to include the schema name, if different from `current_schema`.

[Fix #52312]

activerecord/CHANGELOG.md

@@ -1,3 +1,24 @@
+*   Include schema name in `enable_extension` statements in `db/schema.rb`.
+
+    The schema dumper will now include the schema name in generated
+    `enable_extension` statements if they differ from the current schema.
+
+    For example, if you have a migration:
+
+    ```ruby
+    enable_extension "heroku_ext.pgcrypto"
+    enable_extension "pg_stat_statements"
+    ```
+
+    then the generated schema dump will also contain:
+
+    ```ruby
+    enable_extension "heroku_ext.pgcrypto"
+    enable_extension "pg_stat_statements"
+    ```
+
+    *Tony Novak*
+
 *   Fix `ActiveRecord::Encryption::EncryptedAttributeType#type` to return
     actual cast type.
 

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -494,7 +494,19 @@ module ActiveRecord
       end
 
       def extensions
-        internal_exec_query("SELECT extname FROM pg_extension", "SCHEMA", allow_retry: true, materialize_transactions: false).cast_values
+        query = <<~SQL
+          SELECT
+            pg_extension.extname,
+            n.nspname AS schema
+          FROM pg_extension
+          JOIN pg_namespace n ON pg_extension.extnamespace = n.oid
+        SQL
+
+        internal_exec_query(query, "SCHEMA", allow_retry: true, materialize_transactions: false).cast_values.map do |row|
+          name, schema = row[0], row[1]
+          schema = nil if schema == current_schema
+          [schema, name].compact.join(".")
+        end
       end
 
       # Returns a list of defined enum types, and their values.

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

@@ -561,6 +561,24 @@ module ActiveRecord
         @connection.execute("DROP DOMAIN example_type")
       end
 
+      def test_extensions_omits_current_schema_name
+        @connection.execute("DROP EXTENSION IF EXISTS hstore")
+        @connection.execute("CREATE SCHEMA customschema")
+        @connection.execute("CREATE EXTENSION hstore SCHEMA customschema")
+        assert_includes @connection.extensions, "customschema.hstore"
+      ensure
+        @connection.execute("DROP SCHEMA IF EXISTS customschema CASCADE")
+        @connection.execute("DROP EXTENSION IF EXISTS hstore")
+      end
+
+      def test_extensions_includes_non_current_schema_name
+        @connection.execute("DROP EXTENSION IF EXISTS hstore")
+        @connection.execute("CREATE EXTENSION hstore")
+        assert_includes @connection.extensions, "hstore"
+      ensure
+        @connection.execute("DROP EXTENSION IF EXISTS hstore")
+      end
+
       def test_ignores_warnings_when_behaviour_ignore
         with_db_warnings_action(:ignore) do
           # libpq prints a warning to stderr from C, so we need to stub