As an alternative to #20725 (which was originally about go vet), let the variables of range loops be implicitly redefined in each iteration like in Dart's for loops. That is,

for k, v := range vals {
  // ...
}

should be equivalent to

for k, v := range vals {
  k := k
  v := v
  // ...
}

This will make it "safe" to take the loop variable's addresses as well as capturing the loop variables in nested functions (see #16520).

The proposal could be expanded to vanilla for loops, although that would make it diverge semantically from other languages.