libnm: rework compare_property() implementation for NMSetting

NMSetting's compare_property() has and had two callers:
nm_setting_compare() and nm_setting_diff().

compare_property() accepts a NMSettingCompareFlags argument, but
at the same time, both callers have another complex (and
inconsistent!) set of pre-checks for shortcuting the call of
compare_property(): should_compare_prop().

Merge should_compare_prop() into compare_property(). This way,
nm_setting_compare() and nm_setting_diff() has less additional
code, and are simpler to follow. Especially nm_setting_compare()
is now trivial. And nm_setting_diff() is still complicated, but
not related to the question how the property compares or whether
it should be compared at all.

If you want to know whether it should be compared, all you need to do
now is follow NMSettingClass.compare_property().

This changes function pointer NMSettingClass.compare_property(),
which is public API. However, no user can actually use this (and shall
not!), because _nm_setting_class_commit_full() etc. is private API. A
user outside of libnm-core cannot create his/her own subclasses of
NMSetting, and never could in the past. So, this API/ABI change doesn't
matter.

1 files changed, 13 insertions, 5 deletions

diff --git a/libnm-core/nm-setting.h b/libnm-core/nm-setting.h
index 3576bdc663..326b533f12 100644
--- a/libnm-core/nm-setting.h
+++ b/libnm-core/nm-setting.h
@@ -169,6 +169,7 @@ typedef gboolean (*NMSettingClearSecretsWithFlagsFn) (NMSetting *setting,
                                                       gpointer user_data);
 
 struct _NMMetaSettingInfo;
+struct _NMSettInfoSetting;
 
 typedef struct {
 	GObjectClass parent;
@@ -204,11 +205,18 @@ typedef struct {
 	                                         NMSettingClearSecretsWithFlagsFn func,
 	                                         gpointer user_data);
 
-	/* Returns TRUE if the given property contains the same value in both settings */
-	gboolean    (*compare_property)  (NMSetting *setting,
-	                                  NMSetting *other,
-	                                  const GParamSpec *prop_spec,
-	                                  NMSettingCompareFlags flags);
+	/* compare_property() returns a ternary, where DEFAULT means that the property should not
+	 * be compared due to the compare @flags. A TRUE/FALSE result means that the property is
+	 * equal/not-equal.
+	 *
+	 * @other may be %NULL, in which case the function only determines whether
+	 * the setting should be compared (TRUE) or not (DEFAULT). */
+	/*< private >*/
+	NMTernary  (*compare_property)  (const struct _NMSettInfoSetting *sett_info,
+	                                 guint property_idx,
+	                                 NMSetting *setting,
+	                                 NMSetting *other,
+	                                 NMSettingCompareFlags flags);
 
 	/*< private >*/
 	const struct _NMMetaSettingInfo *setting_info;