github-lines-to-issue.scpt.js

function run() {
  xcode = Application('Xcode')
  var app = Application.currentApplication()
  app.includeStandardAdditions = true;
  docs = xcode.sourceDocuments()
  for (var i = docs.length-1; i >= 0; i--) {
    var doc = docs[i];
    var range = doc.selectedParagraphRange();
    if (!range) {
      continue;
    }
    var start = range[0];
    var end = range[1];
    if (start > end) {
      var tmp = start;
      start = end;
      end = tmp;
    }
    var path = doc.path();
    var basename = path.substring(path.lastIndexOf('/')+1);
    var gitinfo = app.doShellScript(
      `cd \`dirname '${path}'\`\n` +
      `git remote -v | head -1\n` + 
      `git rev-parse --show-toplevel\n` + 
      `git rev-parse HEAD\n`
    ).split('\r');
    var remote = gitinfo[0];
    var gitroot = gitinfo[1];
    var branch = gitinfo[2];
    var relativePath = path.substring(gitroot.length+1);
    var m = remote.match(/.*github.com\/(.*?)\/(.*?)\.git.*/);
    if (m) {
      var owner = m[1];
      var repo = m[2];
    
      var lineAnchor = `L${start}`;
      if (end != start) {
        lineAnchor += `-L${end}`;
      }

      var url = `https://github.com/${owner}/${repo}/blob/${branch}/${relativePath}#${lineAnchor}`;
      app.openLocation(`ship+github://newissue/${owner}/${repo}?title=${escape(basename+":"+start)}&body=${escape(url)}`);
    }
    break;
  }
}

Put at ~/Library/Scripts/Applications/Xcode and use with Script Menu (turn on via Script Editor.app's preferences)