Treat cycle errors as bug by default

We should treat unexpected query cycles as bugs, not user-facing errors. Ideally we'd add an attribute to queries to indicate that they are expected to cycle and otherwise ICE on cycles.

Affected queries are crate_variances or effective_visibilities.

original issue:

when fetching effective_visibilities for Adt self types of a local trait while proving a where-clause.

https://github.com/rust-lang/rust/blob/8c32e313cccf7df531e2d49ffb8227bb92304aee/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs#L2871-L2889

This query fetches the hidden type of all opaque types https://github.com/rust-lang/rust/blob/8c32e313cccf7df531e2d49ffb8227bb92304aee/compiler/rustc_privacy/src/lib.rs#L1841-L1846

introduced in #143431, cc @xizheyin @compiler-errors

trait LocalTrait {}
struct SomeType;
fn impls_trait<T: LocalTrait>() {}
fn foo() -> impl Sized {
    impls_trait::<SomeType>();
}

results in

error[E0391]: cycle detected when computing type of `foo::{opaque#0}`
 --> src/lib.rs:4:13
  |
4 | fn foo() -> impl Sized {
  |             ^^^^^^^^^^
  |
note: ...which requires computing type of opaque `foo::{opaque#0}`...
 --> src/lib.rs:4:13
  |
4 | fn foo() -> impl Sized {
  |             ^^^^^^^^^^
note: ...which requires borrow-checking `foo`...
 --> src/lib.rs:4:1
  |
4 | fn foo() -> impl Sized {
  | ^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires promoting constants in MIR for `foo`...
 --> src/lib.rs:4:1
  |
4 | fn foo() -> impl Sized {
  | ^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires checking if `foo` contains FFI-unwind calls...
 --> src/lib.rs:4:1
  |
4 | fn foo() -> impl Sized {
  | ^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires building MIR for `foo`...
 --> src/lib.rs:4:1
  |
4 | fn foo() -> impl Sized {
  | ^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires match-checking `foo`...
 --> src/lib.rs:4:1
  |
4 | fn foo() -> impl Sized {
  | ^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires type-checking `foo`...
 --> src/lib.rs:4:1
  |
4 | fn foo() -> impl Sized {
  | ^^^^^^^^^^^^^^^^^^^^^^
  = note: ...which requires checking effective visibilities...
  = note: ...which again requires computing type of `foo::{opaque#0}`, completing the cycle
note: cycle used when checking that `foo::{opaque#0}` is well-formed
 --> src/lib.rs:4:13
  |
4 | fn foo() -> impl Sized {
  |             ^^^^^^^^^^
  = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information

error[E0277]: the trait bound `SomeType: LocalTrait` is not satisfied
 --> src/lib.rs:5:19
  |
5 |     impls_trait::<SomeType>();
  |                   ^^^^^^^^ the trait `LocalTrait` is not implemented for `SomeType`
  |
help: this trait has no implementations, consider adding one
 --> src/lib.rs:1:1
  |
1 | trait LocalTrait {}
  | ^^^^^^^^^^^^^^^^
note: required by a bound in `impls_trait`
 --> src/lib.rs:3:19
  |
3 | fn impls_trait<T: LocalTrait>() {}
  |                   ^^^^^^^^^^ required by this bound in `impls_trait`

note the query cycle before the actually desired error

Start with the query-cycle handling for crate_variances and effective_visibilities, then inspect the cycle path in compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs and hidden-type lookup in compiler/rustc_privacy/src/lib.rs. Use the reproducer in the issue to verify that unexpected cycles become ICEs while expected cycles retain appropriate handling.