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We won't support trait object constants in type level constants for the forseeable future

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This commit is contained in:
Oli Scherer 2021-03-12 13:00:16 +00:00
parent 6ca1d87194
commit c51749af6e
1 changed files with 5 additions and 3 deletions
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8
compiler/rustc_mir/src/const_eval/mod.rs
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@ -87,9 +87,11 @@ fn const_to_valtree_inner<'tcx>(
ty::FnPtr(_) | ty::RawPtr(_) => None,
ty::Ref(..) => unimplemented!("need to use deref_const"),
ty::Dynamic(..) => unimplemented!(
"for trait objects we must look at the vtable and figure out the real type"
),
// Trait objects are not allowed in type level constants, as we have no concept for
// resolving their backing type, even if we can do that at const eval time. We may want to consider
// adding a `ValTree::DownCast(Ty<'tcx>, Box<ValTree>)` in the future, but I don't even know the
// questions such a concept would open up, so an RFC would probably be good for this.
ty::Dynamic(..) => None,
ty::Slice(_) | ty::Str => {
unimplemented!("need to find the backing data of the slice/str and recurse on that")