Assume .tablet files shadow any ones with the same name

Commit 2dc213c introduced a duplicate resolution to fix #379 so
that we could have a tablet file in /etc/libwacom that had a DeviceMatch
that partially overlapped with a DeviceMatch in /usr/share/libwacom,
e.g. in this setup:
  DeviceMatch=usb|1234|abcd;bluetooth|1234|abcd
  DeviceMatch=usb|1234|abcd

This triggered a bug: during the duplicate resolution the device match
was removed from the currently parsed file, leading to the file having
no device matches which triggered a g_warn_if_reached().

This approach is too complicated and likely unnecessary, use a more
conventional approach where a named file hides the same file in any
other datadir, i.e. /etc/libwacom/foo-bar.tablet will hide
/usr/share/libwacom/foo-bar.tablet, the latter of which will not be
parsed at all.

This matches how e.g. system handles service files and many other
components in the stack work with a similar approach.

Reverts commit 2dc213c ("libwacom: allow for duplicates across data directories")

.github/workflows/main.yml

@@ -183,19 +183,19 @@ jobs:
         # the multiple matches of the Intuos Pro L.
       - name: copy and modify tablet files to override another one
         run: |
-          sed -e 's/27QHD/27QHD MODIFIED/' data/wacom-cintiq-27hd.tablet | sudo tee /etc/libwacom/modified-cintiq.tablet
-          sed -e 's/Pro L/Pro L MODIFIED/' -e 's/usb|056a|0358;//' data/wacom-intuos-pro-2-l.tablet | sudo tee /etc/libwacom/modified-intuos.tablet
+          sed -e 's/27QHD/27QHD MODIFIED/' data/wacom-cintiq-27hd.tablet | sudo tee /etc/libwacom/wacom-cintiq-27hd.tablet
+          sed -e 's/Pro L/Pro L MODIFIED/' -e 's/usb|056a|0358;//' data/wacom-intuos-pro-2-l.tablet | sudo tee /etc/libwacom/wacom-intuos-pro-2-l.tablet
       - name: list all devices for debugging
         run: libwacom-list-devices --format=yaml
 
       # We expect the modified tablets to be listed
-      # We expect the remaining match for a modified tablet to be listed
+      # We expect the remaining match for a modified tablet to not be listed
       # We expect the overridden match *not* to be listed
       - name: check for the expected devices to be present (or not present)
         run: |
           test "$(libwacom-list-devices --format=yaml | yq -r '.devices[] | select(.bus == "usb") | select(.vid == "0x056a") | select(.pid == "0x032a") | .name')" == "Wacom Cintiq 27QHD MODIFIED"
           test "$(libwacom-list-devices --format=yaml | yq -r '.devices[] | select(.bus == "bluetooth") | select(.vid == "0x056a") | select(.pid == "0x0361") | .name')" == "Wacom Intuos Pro L MODIFIED"
-          test $(libwacom-list-devices --format=yaml | yq -r '.devices[] | select(.bus == "usb") | select(.vid == "0x056a") | select(.pid == "0x0358") | .name' | wc -l) -eq 1
+          test $(libwacom-list-devices --format=yaml | yq -r '.devices[] | select(.bus == "usb") | select(.vid == "0x056a") | select(.pid == "0x0358") | .name' | wc -l) -eq 0
           test $(libwacom-list-devices --format=yaml | yq -r '.devices[] | select(.bus == "usb") | select(.vid == "0x056a") | select(.pid == "0x032a") | .name' | wc -l) -eq 1
 
   ####

libwacom/libwacom-database.c

@@ -1017,32 +1017,28 @@ is_stylus_file(const struct dirent *entry)
 }
 
 static bool
-load_tablet_files(WacomDeviceDatabase *db, const char *datadir)
+load_tablet_files(WacomDeviceDatabase *db, GHashTable *parsed_filenames, const char *datadir)
 {
 	DIR *dir;
 	struct dirent *file;
 	bool success = false;
-	GHashTable *keyset = NULL;
 
 	dir = opendir(datadir);
 	if (!dir)
 		return errno == ENOENT; /* non-existing directory is ok */
 
-	/* A set of all matches for duplicate detection. We allow duplicates
-	 * across data directories, but we don't allow for duplicates
-	 * within the same data directory.
-	 */
-	keyset = g_hash_table_new_full (g_str_hash, g_str_equal, free, NULL);
-	if (!keyset)
-		goto out;
-
 	while ((file = readdir(dir))) {
 		WacomDevice *d;
 		guint idx = 0;
 
 		if (!is_tablet_file(file))
 			continue;
 
+		if (g_hash_table_lookup(parsed_filenames, file->d_name))
+			continue;
+
+		g_hash_table_add(parsed_filenames, g_strdup(file->d_name));
+
 		d = libwacom_parse_tablet_keyfile(db, datadir, file->d_name);
 		if (!d)
 			continue;
@@ -1059,28 +1055,13 @@ load_tablet_files(WacomDeviceDatabase *db, const char *datadir)
 			const char *matchstr;
 
 			matchstr = libwacom_match_get_match_string(match);
-			/* no duplicate matches allowed within the same
-			 * directory */
-			if (g_hash_table_contains(keyset, matchstr)) {
+			/* no duplicate matches allowed */
+			if (g_hash_table_contains(db->device_ht, matchstr)) {
 				g_critical("Duplicate match of '%s' on device '%s'.",
 					   matchstr, libwacom_get_name(d));
 				goto out;
 			}
-			g_hash_table_add(keyset, g_strdup(matchstr));
-
-			/* We already have an entry for this match in the database,
-			 * that takes precedence. Remove the current match
-			 * from the new tablet - that's fine because we
-			 * haven't exposed the tablet yet.
-			 */
-			if (g_hash_table_lookup(db->device_ht, matchstr)) {
-				libwacom_remove_match(d, match);
-				continue;
-			}
-
-			g_hash_table_insert(db->device_ht,
-					    g_strdup (matchstr),
-					    d);
+			g_hash_table_insert(db->device_ht, g_strdup (matchstr), d);
 			libwacom_ref(d);
 			idx++;
 		}
@@ -1090,8 +1071,6 @@ load_tablet_files(WacomDeviceDatabase *db, const char *datadir)
 	success = true;
 
 out:
-	if (keyset)
-		g_hash_table_destroy(keyset);
 	closedir(dir);
 	return success;
 }
@@ -1146,6 +1125,11 @@ database_new_for_paths (char * const *datadirs)
 {
 	WacomDeviceDatabase *db;
 	char * const *datadir;
+	GHashTable *parsed_filenames;
+
+	parsed_filenames = g_hash_table_new_full (g_str_hash, g_str_equal, free, NULL);
+	if (!parsed_filenames)
+		return NULL;
 
 	db = g_new0 (WacomDeviceDatabase, 1);
 	db->device_ht = g_hash_table_new_full (g_str_hash,
@@ -1163,10 +1147,12 @@ database_new_for_paths (char * const *datadirs)
 	}
 
 	for (datadir = datadirs; *datadir;  datadir++) {
-		if (!load_tablet_files(db, *datadir))
+		if (!load_tablet_files(db, parsed_filenames, *datadir))
 			goto error;
 	}
 
+	g_hash_table_unref(parsed_filenames);
+
 	/* If we couldn't load _anything_ then something's wrong */
 	if (g_hash_table_size (db->stylus_ht) == 0 ||
 	    g_hash_table_size (db->device_ht) == 0) {