Add swayrun command to run sway using a login shell

When running Sway from a display manager, a user's login shell is
not used. Because of this, profile scripts are not run and the
environment may not be configured. As suggested in #3109, this can
be solved by a wrapper that runs sway via the user's configured
shell. This is similar to the approach taken by GNOME to source
the standard set of profile scripts.

This could be accomplished with a shell script, but a dedicated
binary avoids dependencies on specific shells.

The sway.desktop wayland session file is also updated to call the
swayrun wrapper.

meson.build

@@ -107,6 +107,7 @@ if scdoc.found()
 		'swaymsg/swaymsg.1.scd',
 		'swaynag/swaynag.1.scd',
 		'swaynag/swaynag.5.scd',
+		'swayrun/swayrun.1.scd'
 	]
 	foreach filename : man_files
 		topic = filename.split('.')[-3].split('/')[-1]
@@ -149,6 +150,7 @@ subdir('client')
 subdir('swaybg')
 subdir('swaybar')
 subdir('swaynag')
+subdir('swayrun')
 
 config = configuration_data()
 config.set('datadir', join_paths(prefix, datadir))

sway.desktop

@@ -1,5 +1,5 @@
 [Desktop Entry]
 Name=Sway
 Comment=SirCmpwn's Wayland window manager
-Exec=sway
+Exec=swayrun
 Type=Application

swayrun/main.c

@@ -0,0 +1,71 @@
+#define _POSIX_C_SOURCE 200809L // for getline
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "stringop.h"
+
+#define SWAY_COMMAND "sway"
+
+char allowed_shell(char *shell) {
+	FILE *fp;
+	char *line = NULL;
+	size_t len = 0;
+	char allowed = false;
+
+	if (strstr(shell, "false") != NULL || strstr(shell, "nologin") != NULL) {
+		return false;
+	}
+
+	fp = fopen("/etc/shells", "r");
+	if (fp == NULL) {
+		return true;
+	}
+
+	while (getline(&line, &len, fp) != -1) {
+		strip_whitespace(line);
+		if (strcmp(shell, line) == 0) {
+			allowed = true;
+			break;
+		}
+	}
+
+	fclose(fp);
+	if (line) {
+		free(line);
+	}
+	return allowed;
+}
+
+int main(int argc, char **argv) {
+	char *shell = getenv("SHELL");
+
+	if (shell && allowed_shell(shell)) {
+		// 3 exec arguments + argc + argv[argc] NULL pointer
+		int exec_argc = 4 + argc;
+		char **exec_argv = malloc(exec_argc * sizeof(char*));
+
+		// Prefix - to shell path to indicate login shell
+		char *login_shell = malloc(strlen(shell) + 2);
+		strcpy(login_shell, "-");
+		strcat(login_shell, shell);
+
+		// Build the argumrnts to exec
+		memcpy(exec_argv + 3, argv, (argc + 1) * sizeof(argv));
+		exec_argv[0] = login_shell;
+		exec_argv[1] = "-c";
+		exec_argv[2] = "exec " SWAY_COMMAND " \"$@\"";
+		exec_argv[3] = shell;
+
+		execvp(shell, exec_argv);
+		fprintf(stderr, "Could not run %s using login shell: %s\n", SWAY_COMMAND, shell);
+	} else {
+		argv[0] = SWAY_COMMAND;
+		execvp(SWAY_COMMAND, argv);
+		fprintf(stderr, "Could not run %s\n", SWAY_COMMAND);
+	}
+
+	return errno;
+}

swayrun/meson.build

@@ -0,0 +1,7 @@
+executable(
+  'swayrun',
+  'main.c',
+  include_directories: [sway_inc],
+  link_with: [lib_sway_common],
+  install: true
+)

swayrun/swayrun.1.scd

@@ -0,0 +1,34 @@
+swayrun(1)
+
+# NAME
+
+swayrun - Run Sway from a login shell
+
+# SYNOPSIS
+
+_swayrun_ [options...] [command]
+
+# DESCRIPTION
+
+Attempts to run *sway*(1) via the user's login shell. This allows environment
+configuration and other login actions, for example when run via a login manager.
+
+All arguments to swayrun will be passed through unaltered to sway.
+
+If a valid login shell cannot be determined, sway will be executed normally.
+
+# CONFIGURATION
+
+swayrun will consult */etc/shells* if it exists for a list of valid login
+shells. In addition, *false* and *nologin* will be considered invalid shells.
+
+# ENVIRONMENT
+
+The following environment variables have an effect on swayrun:
+
+_SHELL_
+	Holds the path to the login shell.
+
+# SEE
+
+*sway*(1) *shells*(5)