T.inputs are evaluated twice

[lolgab]

Reproduction

import mill._

def foo = T.input{ println("bla") }

Current behavior

mill foo
[1/1] foo 
bla
bla

Expected behavior

It should print bla once:

mill foo
[1/1] foo 
bla

[lefou]

Without any investigation of any kind, I remember some strange Scala behavior back from the 2.x times (where x < 10), that resulted in the compiler (?) executing a closure prematurely at definition time to get the actual return type. This is some dark memory, and I may totally reproduce it wrong, but I wanted to mention it at least once. If I find any reference to that issue, I will add it later...