scripts: add a XML preprocessor script

gdbus-codegen doesn't support conditions or pre-processing.

Rather than duplicating D-Bus interfaces for win32 adaptation, let's
have a preprocess step, so we can have platform-specific interfaces.

The python script is based on
https://github.com/peitaosu/XML-Preprocessor, with bug fixes, some
testing and replacing lxml dependency with the built-in xml module.

This preprocessing syntax style is not very common, but is similar to
the one provided by WiX (https://wixtoolset.org/docs/v3/overview/preprocessor/)
or wixl, that we adopted in QEMU for packaging the guest agent.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230606115658.677673-5-marcandre.lureau@redhat.com>

MAINTAINERS

@@ -3202,6 +3202,7 @@ F: docs/interop/dbus*
 F: docs/sphinx/dbus*
 F: docs/sphinx/fakedbusdoc.py
 F: tests/qtest/dbus*
+F: scripts/xml-preprocess*
 
 Seccomp
 M: Daniel P. Berrange <berrange@redhat.com>

scripts/meson.build

@@ -1,3 +1,5 @@
 if stap.found()
   install_data('qemu-trace-stap', install_dir: get_option('bindir'))
 endif
+
+test('xml-preprocess', files('xml-preprocess-test.py'), suite: ['unit'])

scripts/xml-preprocess-test.py

@@ -0,0 +1,136 @@
+#!/usr/bin/env python3
+#
+# Copyright (c) 2023 Red Hat, Inc.
+#
+# SPDX-License-Identifier: MIT
+"""Unit tests for xml-preprocess"""
+
+import contextlib
+import importlib
+import os
+import platform
+import subprocess
+import tempfile
+import unittest
+from io import StringIO
+
+xmlpp = importlib.import_module("xml-preprocess")
+
+
+class TestXmlPreprocess(unittest.TestCase):
+    """Tests for xml-preprocess.Preprocessor"""
+
+    def test_preprocess_xml(self):
+        with tempfile.NamedTemporaryFile(mode="w", delete=False) as temp_file:
+            temp_file.write("<root></root>")
+            temp_file_name = temp_file.name
+        result = xmlpp.preprocess_xml(temp_file_name)
+        self.assertEqual(result, "<root></root>")
+        os.remove(temp_file_name)
+
+    def test_save_xml(self):
+        with tempfile.NamedTemporaryFile(mode="w", delete=False) as temp_file:
+            temp_file_name = temp_file.name
+            xmlpp.save_xml("<root></root>", temp_file_name)
+        self.assertTrue(os.path.isfile(temp_file_name))
+        os.remove(temp_file_name)
+
+    def test_include(self):
+        with tempfile.NamedTemporaryFile(mode="w", delete=False) as inc_file:
+            inc_file.write("<included>Content from included file</included>")
+            inc_file_name = inc_file.name
+        xml_str = f"<?include {inc_file_name} ?>"
+        expected = "<included>Content from included file</included>"
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess(xml_str)
+        self.assertEqual(result, expected)
+        os.remove(inc_file_name)
+        self.assertRaises(FileNotFoundError, xpp.preprocess, xml_str)
+
+    def test_envvar(self):
+        os.environ["TEST_ENV_VAR"] = "TestValue"
+        xml_str = "<root>$(env.TEST_ENV_VAR)</root>"
+        expected = "<root>TestValue</root>"
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess(xml_str)
+        self.assertEqual(result, expected)
+        self.assertRaises(KeyError, xpp.preprocess, "$(env.UNKNOWN)")
+
+    def test_sys_var(self):
+        xml_str = "<root>$(sys.ARCH)</root>"
+        expected = f"<root>{platform.architecture()[0]}</root>"
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess(xml_str)
+        self.assertEqual(result, expected)
+        self.assertRaises(KeyError, xpp.preprocess, "$(sys.UNKNOWN)")
+
+    def test_cus_var(self):
+        xml_str = "<root>$(var.USER)</root>"
+        expected = "<root></root>"
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess(xml_str)
+        self.assertEqual(result, expected)
+        xml_str = "<?define USER=FOO?><root>$(var.USER)</root>"
+        expected = "<root>FOO</root>"
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess(xml_str)
+        self.assertEqual(result, expected)
+
+    def test_error_warning(self):
+        xml_str = "<root><?warning \"test warn\"?></root>"
+        expected = "<root></root>"
+        xpp = xmlpp.Preprocessor()
+        out = StringIO()
+        with contextlib.redirect_stdout(out):
+            result = xpp.preprocess(xml_str)
+        self.assertEqual(result, expected)
+        self.assertEqual(out.getvalue(), "[Warning]: test warn\n")
+        self.assertRaises(RuntimeError, xpp.preprocess, "<?error \"test\"?>")
+
+    def test_cmd(self):
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess('<root><?cmd "echo hello world"?></root>')
+        self.assertEqual(result, "<root>hello world</root>")
+        self.assertRaises(
+            subprocess.CalledProcessError,
+            xpp.preprocess, '<?cmd "test-unknown-cmd"?>'
+        )
+
+    def test_foreach(self):
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess(
+            '<root><?foreach x in a;b;c?>$(var.x)<?endforeach?></root>'
+        )
+        self.assertEqual(result, "<root>abc</root>")
+
+    def test_if_elseif(self):
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess('<root><?if True?>ok<?endif?></root>')
+        self.assertEqual(result, "<root>ok</root>")
+        result = xpp.preprocess('<root><?if False?>ok<?endif?></root>')
+        self.assertEqual(result, "<root></root>")
+        result = xpp.preprocess('<root><?if True?>ok<?else?>ko<?endif?></root>')
+        self.assertEqual(result, "<root>ok</root>")
+        result = xpp.preprocess('<root><?if False?>ok<?else?>ko<?endif?></root>')
+        self.assertEqual(result, "<root>ko</root>")
+        result = xpp.preprocess(
+            '<root><?if False?>ok<?elseif True?>ok2<?else?>ko<?endif?></root>'
+        )
+        self.assertEqual(result, "<root>ok2</root>")
+        result = xpp.preprocess(
+            '<root><?if False?>ok<?elseif False?>ok<?else?>ko<?endif?></root>'
+        )
+        self.assertEqual(result, "<root>ko</root>")
+
+    def test_ifdef(self):
+        xpp = xmlpp.Preprocessor()
+        result = xpp.preprocess('<root><?ifdef USER?>ok<?else?>ko<?endif?></root>')
+        self.assertEqual(result, "<root>ko</root>")
+        result = xpp.preprocess(
+            '<?define USER=FOO?><root><?ifdef USER?>ok<?else?>ko<?endif?></root>'
+        )
+        self.assertEqual(result, "<root>ok</root>")
+
+
+if __name__ == "__main__":
+    unittest.main()