Allow multiple outputs for workspace output

`i3 4.16` allows users to list multiple outputs for a workspace and the
first available will be used. The syntax is as follows:
`workspace <workspace> output <outputs...>`

Additionally when the workspace is created, the outputs get added to the
output priority list in the order specified. This ensures that if a higher
output gets connected, the workspace will move to the higher output. This
works the same way as if the user had a workspace on an output, disconnected
the output, and then later reconnected the output.

include/sway/config.h

@@ -183,7 +183,7 @@ struct side_gaps {
  */
 struct workspace_config {
 	char *workspace;
-	char *output;
+	list_t *outputs;
 	int gaps_inner;
 	struct side_gaps gaps_outer;
 };

sway/commands/workspace.c

@@ -21,6 +21,7 @@ static struct workspace_config *workspace_config_find_or_create(char *ws_name) {
 		return NULL;
 	}
 	wsc->workspace = strdup(ws_name);
+	wsc->outputs = create_list();
 	wsc->gaps_inner = INT_MIN;
 	wsc->gaps_outer.top = INT_MIN;
 	wsc->gaps_outer.right = INT_MIN;
@@ -32,7 +33,7 @@ static struct workspace_config *workspace_config_find_or_create(char *ws_name) {
 
 void free_workspace_config(struct workspace_config *wsc) {
 	free(wsc->workspace);
-	free(wsc->output);
+	free_flat_list(wsc->outputs);
 	free(wsc);
 }
 
@@ -141,18 +142,20 @@ struct cmd_results *cmd_workspace(int argc, char **argv) {
 		}
 	}
 	if (output_location >= 0) {
-		if ((error = checkarg(argc, "workspace", EXPECTED_EQUAL_TO, output_location + 2))) {
+		if ((error = checkarg(argc, "workspace", EXPECTED_AT_LEAST,
+						output_location + 2))) {
 			return error;
 		}
-		char *ws_name = join_args(argv, argc - 2);
+		char *ws_name = join_args(argv, output_location);
 		struct workspace_config *wsc = workspace_config_find_or_create(ws_name);
 		free(ws_name);
 		if (!wsc) {
 			return cmd_results_new(CMD_FAILURE, "workspace output",
 					"Unable to allocate workspace output");
 		}
-		free(wsc->output);
-		wsc->output = strdup(argv[output_location + 1]);
+		for (int i = output_location + 1; i < argc; ++i) {
+			list_add(wsc->outputs, strdup(argv[i]));
+		}
 	} else if (gaps_location >= 0) {
 		if ((error = cmd_workspace_gaps(argc, argv, gaps_location))) {
 			return error;

sway/sway.5.scd

@@ -573,8 +573,12 @@ The default colors are:
 	Specifies that workspace _name_ should have the given gaps settings when it
 	is created.
 
-*workspace* <name> output <output>
-	Specifies that workspace _name_ should be shown on the specified _output_.
+*workspace* <name> output <outputs...>
+	Specifies that workspace _name_ should be shown on the specified _outputs_.
+	Multiple outputs can be listed and the first available will be used. If the
+	workspace gets placed on an output further down the list and an output that
+	is higher on the list becomes available, the workspace will be move to the
+	higher priority output.
 
 *workspace\_auto\_back\_and\_forth* yes|no
 	When _yes_, repeating a workspace switch command will switch back to the

sway/tree/output.c

@@ -31,6 +31,13 @@ static void restore_workspaces(struct sway_output *output) {
 				j--;
 			}
 		}
+
+		if (other->workspaces->length == 0) {
+			char *next = workspace_next_name(other->wlr_output->name);
+			struct sway_workspace *ws = workspace_create(other, next);
+			free(next);
+			ipc_event_workspace(NULL, ws, "init");
+		}
 	}
 
 	// Saved workspaces

sway/tree/workspace.c

@@ -33,14 +33,15 @@ struct workspace_config *workspace_find_config(const char *ws_name) {
 struct sway_output *workspace_get_initial_output(const char *name) {
 	// Check workspace configs for a workspace<->output pair
 	struct workspace_config *wsc = workspace_find_config(name);
-	if (wsc && wsc->output) {
-		struct sway_output *output = output_by_name(wsc->output);
-		if (!output) {
-			output = output_by_identifier(wsc->output);
-		}
-		
-		if (output) {
-			return output;
+	if (wsc) {
+		for (int i = 0; i < wsc->outputs->length; i++) {
+			struct sway_output *output = output_by_name(wsc->outputs->items[i]);
+			if (!output) {
+				output = output_by_identifier(wsc->outputs->items[i]);
+			}
+			if (output) {
+				return output;
+			}
 		}
 	}
 	// Otherwise put it on the focused output
@@ -85,7 +86,6 @@ struct sway_workspace *workspace_create(struct sway_output *output,
 	ws->floating = create_list();
 	ws->tiling = create_list();
 	ws->output_priority = create_list();
-	workspace_output_add_priority(ws, output);
 
 	ws->gaps_outer = config->gaps_outer;
 	ws->gaps_inner = config->gaps_inner;
@@ -110,9 +110,17 @@ struct sway_workspace *workspace_create(struct sway_output *output,
 			// Since default outer gaps can be smaller than the negation of
 			// workspace specific inner gaps, check outer gaps again
 			prevent_invalid_outer_gaps(ws);
+
+			// Add output priorities
+			for (int i = 0; i < wsc->outputs->length; ++i) {
+				list_add(ws->output_priority, strdup(wsc->outputs->items[i]));
+			}
 		}
 	}
 
+	// If not already added, add the output to the lowest priority
+	workspace_output_add_priority(ws, output);
+
 	output_add_workspace(output, ws);
 	output_sort_workspaces(output);
 
@@ -134,8 +142,7 @@ void workspace_destroy(struct sway_workspace *workspace) {
 
 	free(workspace->name);
 	free(workspace->representation);
-	list_foreach(workspace->output_priority, free);
-	list_free(workspace->output_priority);
+	free_flat_list(workspace->output_priority);
 	list_free(workspace->floating);
 	list_free(workspace->tiling);
 	list_free(workspace->current.floating);
@@ -178,7 +185,18 @@ static bool workspace_valid_on_output(const char *output_name,
 	struct sway_output *output = output_by_name(output_name);
 	output_get_identifier(identifier, sizeof(identifier), output);
 
-	return !wsc || !wsc->output || strcmp(wsc->output, output_name) == 0 || strcasecmp(identifier, output_name) == 0;
+	if (!wsc) {
+		return true;
+	}
+
+	for (int i = 0; i < wsc->outputs->length; i++) {
+		if (strcmp(wsc->outputs->items[i], output_name) == 0 ||
+				strcmp(wsc->outputs->items[i], identifier) == 0) {
+			return true;
+		}
+	}
+
+	return false;
 }
 
 static void workspace_name_from_binding(const struct sway_binding * binding,
@@ -281,10 +299,19 @@ char *workspace_next_name(const char *output_name) {
 	for (int i = 0; i < config->workspace_configs->length; ++i) {
 		// Unlike with bindings, this does not guarantee order
 		const struct workspace_config *wsc = config->workspace_configs->items[i];
-		if (wsc->output && strcmp(wsc->output, output_name) == 0
-				&& workspace_by_name(wsc->workspace) == NULL) {
-			free(target);
-			target = strdup(wsc->workspace);
+		if (workspace_by_name(wsc->workspace)) {
+			continue;
+		}
+		bool found = false;
+		for (int j = 0; j < wsc->outputs->length; ++j) {
+			if (strcmp(wsc->outputs->items[j], output_name) == 0) {
+				found = true;
+				free(target);
+				target = strdup(wsc->workspace);
+				break;
+			}
+		}
+		if (found) {
 			break;
 		}
 	}