config: allow setting stdout/err for exec

Introduces the exec_output command, which sets the file to use for
stdout and stderr in the exec and exec_always commands.

include/sway/commands.h

@@ -127,6 +127,7 @@ sway_cmd cmd_default_floating_border;
 sway_cmd cmd_default_orientation;
 sway_cmd cmd_exec;
 sway_cmd cmd_exec_always;
+sway_cmd cmd_exec_output;
 sway_cmd cmd_exit;
 sway_cmd cmd_floating;
 sway_cmd cmd_floating_maximum_size;

include/sway/config.h

@@ -521,6 +521,7 @@ struct sway_config {
 	enum sway_fowa focus_on_window_activation;
 	enum sway_popup_during_fullscreen popup_during_fullscreen;
 	enum xwayland_mode xwayland;
+	int exec_out;
 
 	// swaybg
 	char *swaybg_command;

sway/commands.c

@@ -59,6 +59,7 @@ static const struct cmd_handler handlers[] = {
 	{ "default_floating_border", cmd_default_floating_border },
 	{ "exec", cmd_exec },
 	{ "exec_always", cmd_exec_always },
+	{ "exec_output", cmd_exec_output },
 	{ "floating_maximum_size", cmd_floating_maximum_size },
 	{ "floating_minimum_size", cmd_floating_minimum_size },
 	{ "floating_modifier", cmd_floating_modifier },

sway/commands/exec_always.c

@@ -3,6 +3,7 @@
 #include <string.h>
 #include <sys/wait.h>
 #include <unistd.h>
+#include <fcntl.h>
 #include <signal.h>
 #include "sway/commands.h"
 #include "sway/config.h"
@@ -81,7 +82,23 @@ struct cmd_results *cmd_exec_process(int argc, char **argv) {
 			if (ctx && !no_startup_id) {
 				export_startup_id(ctx);
 			}
+			int errfd = -1;
+			if (config->exec_out >= 0) {
+				errfd = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC); // save for logging
+				if (dup2(config->exec_out, STDOUT_FILENO) < 0) {
+					sway_log_errno(SWAY_ERROR, "dup2(exec_out, stdout) failed");
+					close(STDOUT_FILENO);
+				}
+				if (dup2(config->exec_out, STDERR_FILENO) < 0) {
+					sway_log_errno(SWAY_ERROR, "dup2(exec_out, stderr) failed");
+					close(STDERR_FILENO);
+				}
+				close(config->exec_out);
+			}
 			execlp("sh", "sh", "-c", cmd, (void *)NULL);
+			if (errfd >= 0) {
+				dup2(errfd, STDERR_FILENO);
+			}
 			sway_log_errno(SWAY_ERROR, "execlp failed");
 			_exit(1);
 		}

sway/commands/exec_output.c

@@ -0,0 +1,33 @@
+#include <fcntl.h>
+#include <unistd.h>
+#include "sway/commands.h"
+
+struct cmd_results *cmd_exec_output(int argc, char **argv) {
+	struct cmd_results *error =
+		checkarg(argc, "exec_output", EXPECTED_AT_MOST, 1);
+	if (error) {
+		return error;
+	}
+
+	if (config->exec_out >= 0) {
+		if (close(config->exec_out) < 0) {
+			return cmd_results_new(
+				CMD_FAILURE,
+				"Failed to close existing fd %d",
+				config->exec_out
+			);
+		};
+		config->exec_out = -1;
+	}
+
+	if (argc == 0) {
+		return cmd_results_new(CMD_SUCCESS, NULL);
+	}
+
+	int out = open(argv[0], O_RDWR | O_APPEND | O_CREAT, 0600); // u=rw
+	if (out < 0) {
+		return cmd_results_new(CMD_FAILURE, "Could not open file %s", argv[0]);
+	}
+	config->exec_out = out;
+	return cmd_results_new(CMD_SUCCESS, NULL);
+}

sway/config.c

@@ -257,6 +257,7 @@ static void config_defaults(struct sway_config *config) {
 	config->focus_on_window_activation = FOWA_URGENT;
 	config->popup_during_fullscreen = POPUP_SMART;
 	config->xwayland = XWAYLAND_MODE_LAZY;
+	config->exec_out = -1;
 
 	config->titlebar_border_thickness = 1;
 	config->titlebar_h_padding = 5;

sway/meson.build

@@ -55,6 +55,7 @@ sway_sources = files(
 	'commands/exit.c',
 	'commands/exec.c',
 	'commands/exec_always.c',
+	'commands/exec_output.c',
 	'commands/floating.c',
 	'commands/floating_minmax_size.c',
 	'commands/floating_modifier.c',