dconf: Check for changes properly despite style of quotes used by user

changelogs/fragments/6049-dconf-strings.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - dconf - parse GVariants for equality comparison when the Python module ``gi.repository`` is available (https://github.com/ansible-collections/community.general/pull/6049).

plugins/modules/dconf.py

@@ -21,11 +21,23 @@
   - Since C(dconf) requires a running D-Bus session to change values, the module
     will try to detect an existing session and reuse it, or run the tool via
     C(dbus-run-session).
+requirements:
+  - Optionally the C(gi.repository) Python library (usually included in the OS
+    on hosts which have C(dconf)); this will become a non-optional requirement
+    in a future major release of community.general.
 notes:
   - This module depends on C(psutil) Python library (version 4.0.0 and upwards),
     C(dconf), C(dbus-send), and C(dbus-run-session) binaries. Depending on
     distribution you are using, you may need to install additional packages to
     have these available.
+  - This module uses the C(gi.repository) Python library when available for
+    accurate comparison of values in C(dconf) to values specified in Ansible
+    code. C(gi.repository) is likely to be present on most systems which have
+    C(dconf) but may not be present everywhere. When it is missing, a simple
+    string comparison between values is used, and there may be false positives,
+    that is, Ansible may think that a value is being changed when it is not.
+    This fallback will be removed in a future version of this module, at which
+    point the module will stop working on hosts without C(gi.repository).
   - Detection of existing, running D-Bus session, required to change settings
     via C(dconf), is not 100% reliable due to implementation details of D-Bus
     daemon itself. This might lead to running applications not picking-up
@@ -128,6 +140,12 @@
 import os
 import traceback
 
+try:
+    from gi.repository.GLib import Variant, GError
+except ImportError:
+    Variant = None
+    GError = AttributeError
+
 PSUTIL_IMP_ERR = None
 try:
     import psutil
@@ -258,6 +276,25 @@ def __init__(self, module, check_mode=False):
         # Check if dconf binary exists
         self.dconf_bin = self.module.get_bin_path('dconf', required=True)
 
+    @staticmethod
+    def variants_are_equal(canonical_value, user_value):
+        """Compare two string GVariant representations for equality.
+
+        Assumes `canonical_value` is "canonical" in the sense that the type of
+        the variant is specified explicitly if it cannot be inferred; this is
+        true for textual representations of variants generated by the `dconf`
+        command. The type of `canonical_value` is used to parse `user_value`,
+        so the latter does not need to be explicitly typed.
+
+        Returns True if the two values are equal.
+        """
+        try:
+            variant1 = Variant.parse(None, canonical_value)
+            variant2 = Variant.parse(variant1.get_type(), user_value)
+            return variant1 == variant2
+        except GError:
+            return canonical_value == user_value
+
     def read(self, key):
         """
         Retrieves current value associated with the dconf key.
@@ -298,7 +335,7 @@ def write(self, key, value):
         """
         # If no change is needed (or won't be done due to check_mode), notify
         # caller straight away.
-        if value == self.read(key):
+        if self.variants_are_equal(self.read(key), value):
             return False
         elif self.check_mode:
             return True
@@ -369,6 +406,12 @@ def main():
         supports_check_mode=True
     )
 
+    if Variant is None:
+        module.warn(
+            'WARNING: The gi.repository Python library is not available; '
+            'using string comparison to check value equality. This fallback '
+            'will be deprecated in a future version of community.general.')
+
     if not HAS_PSUTIL:
         module.fail_json(msg=missing_required_lib("psutil"), exception=PSUTIL_IMP_ERR)
 

tests/unit/plugins/modules/test_dconf.py

@@ -0,0 +1,44 @@
+# Copyright (c) 2023 Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or
+# https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import pytest
+
+from ansible_collections.community.general.plugins.modules import dconf
+
+try:
+    from gi.repository.GLib import Variant
+except ImportError:
+    Variant = None
+
+DconfPreference = dconf.DconfPreference
+
+
+@pytest.mark.parametrize(
+    "v1,v2,expected,fallback_expected",
+    (("'foo'", "'foo'", True, True),
+     ('"foo"', "'foo'", True, False),
+     ("'foo'", '"foo"', True, False),
+     ("'foo'", '"bar"', False, False),
+     ("[1, 2, 3]", "[1, 2, 3]", True, True),
+     ("[1, 2, 3]", "[3, 2, 1]", False, False),
+     ('1234', '1234', True, True),
+     ('1234', '1235', False, False),
+     ('1.0', '1.0', True, True),
+     ('1.000', '1.0', True, False),
+     ('2.0', '4.0', False, False),
+     # GVariants with different types aren't equal!
+     ('1', '1.0', False, False),
+     # Explicit types
+     ('@as []', '[]', True, False),
+     ))
+def test_gvariant_equality(mocker, v1, v2, expected, fallback_expected):
+    assert DconfPreference.variants_are_equal(v1, v2) is \
+        (expected if Variant else fallback_expected)
+    mocker.patch.object(dconf, 'Variant', None)
+    mocker.patch.object(dconf, "GError", AttributeError)
+    assert DconfPreference.variants_are_equal(v1, v2) is fallback_expected