cmd_workspace: Don't fill up config->workspace_outputs with duplicates.

This also fixes a bug where issuing a new "workspace a output b" command
for an already assigned workspace would not work (the old config would
be found first and used instead).

common/list.c

@@ -54,10 +54,10 @@ void list_sort(list_t *list, int compare(const void *left, const void *right)) {
 	qsort(list->items, list->length, sizeof(void *), compare);
 }
 
-int list_seq_find(list_t *list, int (*cmp)(const void *item, const void *data), const void *data) {
+int list_seq_find(list_t *list, int compare(const void *item, const void *data), const void *data) {
 	for (int i = 0; i < list->length; i++) {
 		void *item = list->items[i];
-		if ((cmp)(item, data) == 0) {
+		if (compare(item, data) == 0) {
 			return i;
 		}
 	}

include/config.h

@@ -102,6 +102,8 @@ char *do_var_replacement(char *str);
 void apply_output_config(struct output_config *oc, swayc_t *output);
 void free_output_config(struct output_config *oc);
 
+int workspace_output_cmp_workspace(const void *a, const void *b);
+
 /**
  * Global config singleton.
  */

sway/commands.c

@@ -1318,9 +1318,15 @@ static struct cmd_results *cmd_workspace(int argc, char **argv) {
 				return error;
 			}
 			struct workspace_output *wso = calloc(1, sizeof(struct workspace_output));
-			sway_log(L_DEBUG, "Assigning workspace %s to output %s", argv[0], argv[2]);
 			wso->workspace = strdup(argv[0]);
 			wso->output = strdup(argv[2]);
+			int i = -1;
+			if ((i = list_seq_find(config->workspace_outputs, workspace_output_cmp_workspace, wso)) != -1) {
+				struct workspace_output *old = config->workspace_outputs->items[i];
+				free(old); // workspaces can only be assigned to a single output
+				list_del(config->workspace_outputs, i);
+			}
+			sway_log(L_DEBUG, "Assigning workspace %s to output %s", argv[0], argv[2]);
 			list_add(config->workspace_outputs, wso);
 			if (!config->reading) {
 				// TODO: Move workspace to output. (dont do so when reloading)

sway/config.c

@@ -375,3 +375,11 @@ char *do_var_replacement(char *str) {
 	}
 	return str;
 }
+
+// the naming is intentional (albeit long): a workspace_output_cmp function
+// would compare two structs in full, while this method only compares the
+// workspace.
+int workspace_output_cmp_workspace(const void *a, const void *b) {
+	const struct workspace_output *wsa = a, *wsb = b;
+	return lenient_strcmp(wsa->workspace, wsb->workspace);
+}