error[E0560]: union `U` has no field named `principle`
  --> $DIR/union-suggest-field.rs:20:17
   |
20 |     let u = U { principle: 0 };
   |                 ^^^^^^^^^ field does not exist - did you mean `principal`?

error[E0609]: no field `principial` on type `U`
  --> $DIR/union-suggest-field.rs:22:15
   |
LL |     let w = u.principial; //~ ERROR no field `principial` on type `U`
   |               ^^^^^^^^^^ did you mean `principal`?

error[E0615]: attempted to take value of method `calculate` on type `U`
  --> $DIR/union-suggest-field.rs:25:15
   |
LL |     let y = u.calculate; //~ ERROR attempted to take value of method `calculate` on type `U`
   |               ^^^^^^^^^
   |
   = help: maybe a `()` to call it is missing?

error: aborting due to 3 previous errors

You've got a few errors: E0560, E0609, E0615
If you want more information on an error, try using "rustc --explain E0560"