[SR-5744] Refactoring action to convert if-let to guard-let and vice versa

[Regno]

Implement action to convert from:

func foo(idxOpt: Int?) {
  if let idx = idxOpt {
    print(idx)
  }
}

to

func foo(idxOpt: Int?) {
  guard let idx = idxOpt else {
    return
  }
  print(idx)
}

and vice-versa

Resolves new feature request SR-5744.
Refactoring action to convert if-let to guard-let and vice versa

Feedback is very much appreciated!

[Regno]

@swift-ci test

[theblixguy]

You can't invoke CI yourself, you need commit access for it.

[theblixguy]

cc @akyrtzi

[nkcsgexi]

The implementation looks great overall👍! I have only several nitpicks inline.

[nkcsgexi]

We should always use 2-spaces indentation. Could you fix other indentation issues as well in this change?

[Regno]

Fixed.

[nkcsgexi]

We can assume performChange() is called only when isApplicable returns true. So it seems the above logics are unnecessary.

[Regno]

Removed.

[nkcsgexi]

Could you move the ThenStmt check to the isApplicable function too? so we don't need to check it here and surprising the users by aborting.

[Regno]

Moved to the isApplicable.

[nkcsgexi]

These two statements can be merged as if (auto *ElseBody = dyn_cast_or_null<BraceStmt>(If->getElseStmt())) {}

[Regno]

Fixed.

[nkcsgexi]

Similarly, can we move these condition checkings into isApplicable function and only check it there?

[Regno]

Moved.

[nkcsgexi]

Indentation issue here and all other places.

[Regno]

Fixed.

[nkcsgexi]

@swift-ci please smoke test

[nkcsgexi]

@swift-ci please stress test

[Regno]

Also I fixed similar issues at this PR: Refactoring action to convert to computed property.

[nkcsgexi]

All tests passed. Congratulations for your first Swift contribution!🚢