Overly broad error span when function field not assignable to its annotation inside class

[kpdonn]

TypeScript Version: 2.9.0-dev.20180414

Search Terms:
class error span, not assignable to type

Code

type Values = 1 | 2 | 3 | 4 | 5 | 6

type FuncType = (arg: Values) => string

// turn on strictNullChecks
class Example {
  insideClass: FuncType = function(val) { // error span goes from here
    switch (val) {
      case 1:
        return "1";
      case 2:
        return "2";
      case 3:
        return "3"
      case 4:
        return "4"
      case 5:
        return "5"
      // forgot case 6
    }
  } // all the way to here
}

const outsideClass: FuncType = function(val) { // compare to errors only on this line in this case 
    switch (val) {
      case 1:
        return "1";
      case 2:
        return "2";
      case 3:
        return "3"
      case 4:
        return "4"
      case 5:
        return "5"
      // forgot case 6
    }
}

Expected behavior:
Error on insideClass field would look similar to one on outsideClass variable.

Actual behavior:
Error on insideClass spans the entire function implementation.

Playground Link:
Link (Must turn on strictNullChecks to see error)

Related Issues:
Did not notice any duplicates when looking through Domain: Error Messages tag

[DanielRosenwasser]

PRs are welcome! I'd think this should be easy enough to tackle for anyone who wants to help out for the first time.

[mhegazy]

@weswigham we should make sure that all errors on function expression nodes do not extend past the first line (if they are multi-line).