Launcher has fallen very far behind the shell script

[headius]

It has been many years since the native launcher had the same feature set as the shell script. A handful of things that are missing:

• The --environment flag which logs the construction of the JRuby command line.

• Proper handling of module flags. When the native launcher is installed, users will see the following warnings and functionality will likely be degraded.

  $ jruby -e 1
  WARNING: Unknown module: org.jruby.dist specified to --add-opens
  WARNING: Unknown module: org.jruby.dist specified to --add-opens
  WARNING: Unknown module: org.jruby.dist specified to --add-opens
  WARNING: Unknown module: org.jruby.dist specified to --add-opens
  

• Any of the CRaC or AppCDS flags jvery recently added. I don't think the native launcher can use appcds at all.

And probably others I've not noticed. I know it's mostly because we don't like maintaining the native launcher.

I have an idea that may solve the issue on Llinux at least.

[headius]

jruby/jruby#8723 (comment)

[headius]

An idea:

int main(int argc, char *argv[]) {
  // argc + sh and null, since we replace argv[0] with jruby.sh
  char **newargs = (char**) valloc((argc + 2) * sizeof(char *));
  memcpy(&newargs[2], &argv[1], (argc - 1) * sizeof(char *));
  newargs[0] = "/bin/sh";
  newargs[1] = "jruby.sh";
  newargs[argc + 1] = NULL;
  int ret = execv(newargs[0], newargs);

  if (ret == -1) {
    perror("execv");
  }
}

[headius]

A fleshed-out version of my idea, by @mrnoname1000: https://gist.github.com/mrnoname1000/f95c72c7866bb9c14e8a52abadf35b21

My current idea would be:

• Use this logic on unix, since we can count on /bin/sh existing and jruby.sh is the place we make launcher updates first.
• Use @enebo's Rust-based launcher on Windows, since it's a fresh new codebase and can compile down to a simple dependency-free executable.

[headius]

#48