foot/footclient: use a custom exit code when foot/footclient fail to run

Normally, foot and footclient uses the exit code from the client
application (i.e. the shell).

However, foot (or footclient) itself may fail to run; if run outside
of a Wayland session, or no fonts are installed, or the client
application/shell cannot be found (“foot lsdjfldsjf”) etc.

Up until now, there has been no way to differentiate these kind of
failures from the client application exiting with code 1.

This patch changes foot’s failure exit code to -27/229, and
footclient’s to -28/228. Note that footclient will exit with foot’s
-27/229 if footclient ran successfully, but the foot server failed to
instantiate a new window.

Closes #466.

client.c

@@ -69,7 +69,10 @@ print_usage(const char *prog_name)
 int
 main(int argc, char *const *argv)
 {
-    int ret = EXIT_FAILURE;
+    /* Custom exit code, to enable users to differentiate between foot
+     * itself failing, and the client application failiing */
+    static const int foot_exit_failure = -28;
+    int ret = foot_exit_failure;
 
     const char *const prog_name = argv[0];
 
@@ -135,7 +138,7 @@ main(int argc, char *const *argv)
             struct stat st;
             if (stat(optarg, &st) < 0 || !(st.st_mode & S_IFDIR)) {
                 fprintf(stderr, "error: %s: not a directory\n", optarg);
-                return EXIT_FAILURE;
+                return ret;
             }
             custom_cwd = optarg;
             break;
@@ -144,7 +147,7 @@ main(int argc, char *const *argv)
         case 'w':
             if (sscanf(optarg, "%ux%u", &width, &height) != 2 || width == 0 || height == 0) {
                 fprintf(stderr, "error: invalid window-size-pixels: %s\n", optarg);
-                return EXIT_FAILURE;
+                return ret;
             }
             size_type = 0; // CONF_SIZE_PX
             break;
@@ -152,7 +155,7 @@ main(int argc, char *const *argv)
         case 'W':
             if (sscanf(optarg, "%ux%u", &width, &height) != 2 || width == 0 || height == 0) {
                 fprintf(stderr, "error: invalid window-size-chars: %s\n", optarg);
-                return EXIT_FAILURE;
+                return ret;
             }
             size_type = 1; // CONF_SIZE_CELLS
             break;
@@ -187,7 +190,7 @@ main(int argc, char *const *argv)
                     "-d,--log-level: %s: argument must be one of %s\n",
                     optarg,
                     log_level_string_hint());
-                return EXIT_FAILURE;
+                return ret;
             }
             log_level = lvl;
             break;
@@ -202,7 +205,7 @@ main(int argc, char *const *argv)
                 log_colorize = LOG_COLORIZE_ALWAYS;
             else {
                 fprintf(stderr, "%s: argument must be one of 'never', 'always' or 'auto'\n", optarg);
-                return EXIT_FAILURE;
+                return ret;
             }
             break;
 
@@ -215,7 +218,7 @@ main(int argc, char *const *argv)
             return EXIT_SUCCESS;
 
         case '?':
-            return EXIT_FAILURE;
+            return ret;
         }
     }
 
@@ -373,6 +376,8 @@ main(int argc, char *const *argv)
     int exit_code;
     ssize_t rcvd = recv(fd, &exit_code, sizeof(exit_code), 0);
 
+    LOG_INFO("exit-code=%d", exit_code);
+
     if (rcvd == -1 && errno == EINTR)
         xassert(aborted);
     else if (rcvd != sizeof(exit_code))