macOS: Add an entry point to use that works even if run via a symlink

Fixes #1539

setup.py

@@ -744,6 +744,10 @@ Categories=System;TerminalEmulator;
         os.rename('../lib', 'Frameworks')
         if not os.path.exists(logo_dir):
             raise SystemExit('The kitty logo has not been generated, you need to run logo/make.py')
+        cmd = [env.cc] + ['-Wall', '-Werror'] + [
+                'symlink-deref.c', '-o', os.path.join('MacOS', 'kitty-deref-symlink')]
+        run_tool(cmd)
+
         subprocess.check_call([
             'iconutil', '-c', 'icns', logo_dir, '-o',
             os.path.join('Resources', os.path.basename(logo_dir).partition('.')[0] + '.icns')

symlink-deref.c

@@ -0,0 +1,47 @@
+/*
+ * symlink-deref.c
+ * Copyright (C) 2019 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+
+#include <unistd.h>
+#include <sys/stat.h>
+#include <mach-o/dyld.h>
+#include <sys/syslimits.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <libgen.h>
+#include <unistd.h>
+
+static inline bool
+safe_realpath(const char* src, char *buf, size_t buf_sz) {
+    char* ans = realpath(src, NULL);
+    if (ans == NULL) return false;
+    snprintf(buf, buf_sz, "%s", ans);
+    free(ans);
+    return true;
+}
+
+static inline bool
+read_exe_path(char *exe, size_t buf_sz) {
+    (void)buf_sz;
+    uint32_t size = PATH_MAX;
+    char apple[PATH_MAX+1] = {0};
+    if (_NSGetExecutablePath(apple, &size) != 0) { fprintf(stderr, "Failed to get path to executable\n"); return false; }
+    if (!safe_realpath(apple, exe, buf_sz)) { fprintf(stderr, "realpath() failed on the executable's path\n"); return false; }
+    return true;
+}
+
+
+int
+main(int argc, char *argv[]) {
+    char exe[PATH_MAX+1] = {0};
+    char real_exe[PATH_MAX+1] = {0};
+    if (!read_exe_path(exe, sizeof(exe))) return 1;
+    snprintf(real_exe, sizeof(real_exe), "%s/kitty", dirname(exe));
+    return execv(real_exe, argv);
+}