error[E0282]: type annotations needed for `[Foo<_>; 2]`
  --> $DIR/copy-inference-side-effects-are-lazy.rs:17:9
   |
LL |     let x = [Foo(PhantomData); 2];
   |         ^
LL |
LL |     extract(x).max(2);
   |     ---------- type must be known at this point
   |
help: consider giving `x` an explicit type, where the type for type parameter `T` is specified
   |
LL |     let x: [Foo<T>; 2] = [Foo(PhantomData); 2];
   |          +++++++++++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0282`.