You can't make the inference you suggest in the bug. It's not always valid. What if you set the variable in the function? This line of type inference is very p

You can't make the inference you suggest in the bug. It's not always valid. What if you set the variable in the function? This line of type inference is very problematic in languages like JavaScript. Your statement that you expected "modern type inference" makes it sound like you only have practical knowledge (maybe you've used ML or Haskell?), not theoretical background. You should review the literature.