ICE: cat_expr_errd

[DutchGhost]

The following only ICE's on nightly:

fn main() {
    [(); & { loop { continue } } ]
}

playground: https://play.rust-lang.org/?gist=5301f1ed6aea057aa9f5c921e3ea2f1e&version=nightly&mode=release&edition=2015

Backtrace:

warning: unreachable expression
   --> src\lib.rs:169:14
    |
169 |         [(); & { loop { continue } } ]
    |              ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: #[warn(unreachable_code)] on by default

error: internal compiler error: cat_expr Errd
   --> src\lib.rs:169:9
    |
169 |         [(); & { loop { continue } } ]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

error: Could not compile `test_bugs`.

To learn more, run the command again with --verbose.

Backtrace variable is set, this was all I got. (I also got no backtrace for #52442 when compiling in nightly, perhaps they are related)

[DutchGhost]

Even a slightly smaller example:

fn main() {
    
    [(); loop { break }]
}

With some more brackets, a while loop also ICE's:

fn main() {
    
    [(); {while true {break}; 0}];
}

and for loops as well:

fn main() {
    
    [(); { for _ in 0usize.. {}; 0}];
}

[pnkfelix]

triage: P-high

[oli-obk]

So... there's some very weird stuff going on wrt the ! type and blocks:

DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: >> typechecking: expr=expr(15: [(); ]) expected=NoExpectation
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::collect: explicit_predicates_of(def_id=DefId(0/1:9 ~ issue_52443[317d]::main[0]::{{constant}}[0]))
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: >> typechecking: expr=expr(14: &{ loop  { continue  } }) expected=ExpectHasType(usize)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: >> typechecking: expr=expr(13: { loop  { continue  } }) expected=NoExpectation
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: >> typechecking: expr=expr(12: loop  { continue  }) expected=NoExpectation
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: >> typechecking: expr=expr(11: continue) expected=ExpectHasType(())
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: write_ty(HirId { owner: DefIndex(0:3), local_id: ItemLocalId(3) }, [type error]) in fcx 0x7ffe425f2ea8
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: type of expr continue (id=11) is...
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: ... [type error], expected is ExpectHasType(())
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: write_ty(HirId { owner: DefIndex(0:3), local_id: ItemLocalId(4) }, [type error]) in fcx 0x7ffe425f2ea8
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: write_ty(HirId { owner: DefIndex(0:3), local_id: ItemLocalId(5) }, !) in fcx 0x7ffe425f2ea8
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: type of expr loop  { continue  } (id=12) is...
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: ... !, expected is NoExpectation
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: resolve_type_vars_with_obligations(ty=!)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: resolve_type_vars_with_obligations: ty=!
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check::coercion: coercion::try(expr(12: loop  { continue  }): ! -> _)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check::coercion: Coerce.tys(! => _)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: register_predicate(Obligation(predicate=Binder(SubtypePredicate { a_is_expected: false, a: _, b: _ }),depth=0))
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: apply_adjustments(expr=expr(12: loop  { continue  }), adj=[NeverToAny -> _])
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: write_ty(HirId { owner: DefIndex(0:3), local_id: ItemLocalId(6) }, [type error]) in fcx 0x7ffe425f2ea8
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: write_ty(HirId { owner: DefIndex(0:3), local_id: ItemLocalId(7) }, [type error]) in fcx 0x7ffe425f2ea8
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: type of expr { loop  { continue  } } (id=13) is...
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: ... [type error], expected is NoExpectation
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: warn_if_unreachable: id=NodeId(14) span=/home/oliver/Projects/rust/rust4/src/test/ui/const-eval/issue-52443.rs:12:10: 12:33 kind=expression
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: write_ty(HirId { owner: DefIndex(0:3), local_id: ItemLocalId(8) }, [type error]) in fcx 0x7ffe425f2ea8
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: type of expr &{ loop  { continue  } } (id=14) is...
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: ... [type error], expected is ExpectHasType(usize)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: resolve_type_vars_with_obligations(ty=usize)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: resolve_type_vars_with_obligations: ty=usize
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: resolve_type_vars_with_obligations(ty=[type error])
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: resolve_type_vars_with_obligations: ty=[type error]
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check::coercion: coercion::try(expr(14: &{ loop  { continue  } }): [type error] -> usize)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check::coercion: Coerce.tys([type error] => usize)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: apply_adjustments(expr=expr(14: &{ loop  { continue  } }), adj=[])
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: default_type_parameters: defaulting `_` to `[type error]`
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: default_type_parameters: defaulting `_` to `[type error]`
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: default_type_parameters: defaulting `_` to `[type error]`
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check: select_all_obligations_or_error
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check::regionck: regionck::visit_expr(e=expr(14: &{ loop  { continue  } }), repeating_scope=14)
DEBUG 2018-07-19T16:49:23Z: rustc_typeck::check::regionck: constrain_adjustments(expr=expr(14: &{ loop  { continue  } }))
error: internal compiler error: cat_expr Err ()
  --> /home/oliver/Projects/rust/rust4/src/test/ui/const-eval/issue-52443.rs:12:10
   |
LL |     [(); & { loop { continue } } ];
   |          ^^^^^^^^^^^^^^^^^^^^^^^

It appears that somehow & { loop { continue } } produces an error type, but only if the expression is inside an array length or an enum initializer. Inside a constant that is used for an array length, everything is fine. So I presume this is AnonConst related.

cc @eddyb stable-to-nightly ICE on weird expressions inside AnonConst