52985 diagnostics no concrete type behind existential type #53588
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@oli-obk, unrelated, but played around with some use cases for further testing and stumbled across some stuff. Let me know if you want me to move this message elsewhere. I have code snippets and corresponding errors, with expected behavior in comments on the snippets. Please let me know if my understanding is off; I based some assumptions off the documentation at https://github.com/rust-lang/rfcs/blob/master/text/2071-impl-trait-existential-types.md. Would be happy to file issues for and potentially look further into some of these, though some of these issues may already be known. Wanted to just note them because I have a feeling that some of these cases working as described could invalidate or at least affect this PR. |
WRT this PR, does this mean we can revert your previous PR for this error? |
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I think rust-lang/rfcs#2515 is discussing the symmetry between |
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@oli-obk agreed that we can revert the original PR as hitting the inf recursion case in EDIT: I have reverted the relevant code from the original PR in commit a515eee below. |
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Aug 22, 2018
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| let old = self.tables.concrete_existential_types.insert(def_id, definition_ty); | ||
| if let ty::TyAnon(def_id, _substs) = definition_ty.sty { |
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I think we should compare this def_id to the other def_id in scope and only run the type_of query if it is the same. Otherwise we're running it uselessly every time an existential type resolves to an existential type or an impl Trait type
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Worse, it would cause a cycle if you had an existential type that resolved to another TyAnon
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I'll add a test case for this case
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The job Click to expand the log.I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
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The job Click to expand the log.I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
- Original cycle error diagnostics PR'd against this issue caught
panic-causing error while resolving std::mem::transmute calls
- Now, catch invalid use case of not providing a concrete sized type
behind existential type in definining use case.
- Update relevant test to reflect this new error
52985: revert normalize query changes
- PR 53588 invalidates 53316, causing a correct cycle error to occur
with a good span.
- Don't need to revert the whole merge as the test files are
still fine, just need to revert the normalize query changes.
- It should now be correct that infinite recursion detected during
normalize query type folding is a bug, should have been caught earlier
(when resolving the existential type's defining use cases).
52985: code review impl
- Only cause cycle error if anonymous type resolves to anonymous type
that has the same def id (is the same type) as the original (parent)
type.
- Add test case to cover this case for existential types.
52985: remove Ty prefix from TyAnon
- To align with changes per commit 6f637da
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@bors r+ thanks! |
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📌 Commit 7440125 has been approved by |
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…ype_behind_existential_type, r=oli-obk 52985 diagnostics no concrete type behind existential type @oli-obk FYI. See below for new cycle error generated. ```rust error[E0391]: cycle detected when processing `Foo` --> /dev/staging/existential_type_no_concrete_type_nouse_potential.rs:3:1 | 3 | existential type Foo: Copy; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ | note: ...which requires processing `bar`... --> /dev/staging/existential_type_no_concrete_type_nouse_potential.rs:6:23 | 6 | fn bar(x: Foo) -> Foo { | _______________________^ 7 | | x 8 | | } | |_^ = note: ...which again requires processing `Foo`, completing the cycle error: aborting due to previous error For more information about this error, try `rustc --explain E0391`. ```
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☀️ Test successful - status-appveyor, status-travis |
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@oli-obk FYI. See below for new cycle error generated.