title: Qt Creator 4.3.1 code highlighting for custom files not working
body: <p>I am using Qt Creator and opening TypeScript files using it but the code highlighting is not working. I used the "Import existing project" option to open a project that contains some .ts files, opened one of the files and the "a highlight definition was not found" error. Then I added *.ts to the patterns of the application/javascript MIME type but this didn't make the highlighting work. Then I tried renaming the file from filename.ts to filename.js but this also didn't make the highlighting work. How do I get the IDE to highlight my ts files?</p>
  
  <p>Update: it seems that the IDE is highlighting ts files as html files.</p>