ICE with #[derive(Copy)], missing trait bound, and blanket impl

[sgrif]

I have tested this on both 1.13 and on nightly-2016-12-28. This this is the script to reproduce: https://is.gd/PWV89w

The code is invalid due to missing constraint Col::SqlType: IntoNullable on line 26. The expected error is:

error[E0277]: the trait bound `<Col as Expression>::SqlType: NotNull` is not satisfied
  --> foo.rs:25:1
   |
25 |   pub enum ColumnInsertValue<Col, Expr> where
   |  _^ starting here...
26 | |     Col: Column,
27 | |     Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>,
28 | | {
29 | |     Expression(Col, Expr),
30 | |     Default(Col),
31 | | }
   | |_^ ...ending here: the trait `NotNull` is not implemented for `<Col as Expression>::SqlType`
   |
   = help: consider adding a `where <Col as Expression>::SqlType: NotNull` bound
   = note: required because of the requirements on the impl of `IntoNullable` for `<Col as Expression>::SqlType`

But the compiler instead ICEs. If #[derive(Copy)] is removed, the compiler gives the error message as expected. If the blanket impl<T: NotNull> IntoNullable for T (lines 10-12 in the script) is removed, the compiler gives the error message as expected.

[sgrif]

Slightly simplified repro script: https://is.gd/HXaz0L

[Mark-Simulacrum]

Errors today, which is I think correct. E-needstest.

error[E0277]: the trait bound `<Col as Expression>::SqlType: NotNull` is not satisfied
  --> <anon>:16:10
   |
16 | #[derive(Copy)]
   |          ^^^^ the trait `NotNull` is not implemented for `<Col as Expression>::SqlType`
   |
   = help: consider adding a `where <Col as Expression>::SqlType: NotNull` bound
   = note: required because of the requirements on the impl of `IntoNullable` for `<Col as Expression>::SqlType`

error: aborting due to previous error

[venkatagiri]

@Mark-Simulacrum I want to contribute the test for this issue.
By the example you have provided, my guess would be that we need an UI test in src/test/ui/span/ with issue-38821.rs and issue-38821.stderr files.

Is that correct?

[Mark-Simulacrum]

@venkatagiri I think a compile-fail test would be enough here; we primarily want to just make sure it doesn't ICE. To do that, I'd say that the example code needs to be put into a file in src/test/compile-fail and annotated with the related messages. Let me know if you have any more questions; I'd be happy to help. Please r? me on the pull request when you create it.