[SR-12864] Variables mutated in a nested function incorrectly flagged as not mutated

[sjmadsen]

Previous ID	SR-12864
Radar	None
Original Reporter	@sjmadsen
Type	Bug

Environment

Apple Swift version 5.2.4 (swiftlang-1103.0.32.9 clang-1103.0.32.53)

Target: x86_64-apple-darwin19.4.0

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: a35d2f6707ccac6f1003854766929f98

Issue Description:

This code produces an incorrect compiler diagnostic:

func outer() {
  func inner() {
    mutable = false
  }
  var mutable = true
  inner()
}

warning.swift:6:9: warning: initialization of variable 'mutable' was never used; consider replacing with assignment to '_' or removing it
    var mutable = true
    ~~~~^~~~~~~