Expressions returning only Just _ : Maybe a -> convert to return a instead

[Janiczek]

What the rule should do:
Check all returned expressions inside if...else and case...of expressions of type Maybe _ for whether they're all Justs.
In that case it should suggest that you change it to instead return the values inside the Justs and (perhaps?) call the Just constructor outside (or refactor the usages of this expression/function to something nicer / more idiomatic).

Example of things the rule would report:

case stuff of
  X -> Just "x"
  Y -> Just "y"
  Z -> 
    if foo then
      Just <| blabla "zzz" 999
    else
      Just <| somethingMoreComplicated "z" 42

⬇️

case stuff of
  X -> "x"
  Y -> "y"
  Z -> 
    if foo then
      blabla "zzz" 999
    else
      somethingMoreComplicated "z" 42

or

if foo then
  Just "x"
else
  Just "y"

⬇️

if foo then
  "x"
else
  "y"

Example of things the rule would not report:

if foo then
  Just "x"
else
  Nothing

When (not) to enable this rule:

Libraries might be bound by their existing API design and so it might not be desirable to refactor such functions to stop exposing Maybe.

I am looking for:

• Feedback
• Someone to implement it with/for me

[MartinSStewart]

If this rule is just checking that all the branches in an expression end with the same custom type variant, maybe it could be generalize to handle other Ok, Err, and user defined custom type variants as well?