tests/ui/closures/issue-72408-nested-closures-exponential.rs

   1 // build-pass
   2
   3 // Closures include captured types twice in a type tree.
   4 //
   5 // Wrapping one closure with another leads to doubling
   6 // the amount of types in the type tree.
   7 //
   8 // This test ensures that rust can handle
   9 // deeply nested type trees with a lot
  10 // of duplicated subtrees.
  11
  12 fn dup(f: impl Fn(i32) -> i32) -> impl Fn(i32) -> i32 {
  13     move |a| f(a * 2)
  14 }
  15
  16 fn main() {
  17     let f = |a| a;
  18
  19     let f = dup(f);
  20     let f = dup(f);
  21     let f = dup(f);
  22     let f = dup(f);
  23     let f = dup(f);
  24
  25     let f = dup(f);
  26     let f = dup(f);
  27     let f = dup(f);
  28     let f = dup(f);
  29     let f = dup(f);
  30
  31     let f = dup(f);
  32     let f = dup(f);
  33     let f = dup(f);
  34     let f = dup(f);
  35     let f = dup(f);
  36
  37     let f = dup(f);
  38     let f = dup(f);
  39     let f = dup(f);
  40     let f = dup(f);
  41     let f = dup(f);
  42
  43     // Compiler dies around here if it tries
  44     // to walk the tree exhaustively.
  45
  46     let f = dup(f);
  47     let f = dup(f);
  48     let f = dup(f);
  49     let f = dup(f);
  50     let f = dup(f);
  51
  52     let f = dup(f);
  53     let f = dup(f);
  54     let f = dup(f);
  55     let f = dup(f);
  56     let f = dup(f);
  57
  58     println!("Type size was at least {}", f(1));
  59 }