Unexpected E0271 while using Pointee trait #91446
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A-inference
Area: Type inference
A-traits
Area: Trait system
C-bug
Category: This is a bug.
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
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inquisitivecrystal
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A-inference
matthiaskrgr
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Jan 6, 2022
…pointee, r=jackh726 Normalize struct tail type when checking Pointee trait Let's go ahead and implement the FIXMEs by properly normalizing the struct-tail type when satisfying a Pointee obligation. This should fix the ICE when we try to calculate a layout depending on `<Ty as Pointee>::Metadata` later. Fixes rust-lang#92128 Additionally, mark the obligation as ambiguous if there are any infer types in that struct-tail type. This has the effect of causing `<_ as Pointee>::Metadata` to be properly replaced with an infer variable ([here](https://github.com/rust-lang/rust/blob/master/compiler/rustc_trait_selection/src/traits/project.rs#L813)) and registered as an obligation... this turns out to be very important in unifying function parameters with formals that are assoc types. Fixes rust-lang#91446 Fixes rust-lang#92248
matthiaskrgr
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Jan 9, 2022
…pointee, r=jackh726 Normalize struct tail type when checking Pointee trait Let's go ahead and implement the FIXMEs by properly normalizing the struct-tail type when satisfying a Pointee obligation. This should fix the ICE when we try to calculate a layout depending on `<Ty as Pointee>::Metadata` later. Fixes rust-lang#92128 Fixes rust-lang#92577 Additionally, mark the obligation as ambiguous if there are any infer types in that struct-tail type. This has the effect of causing `<_ as Pointee>::Metadata` to be properly replaced with an infer variable ([here](https://github.com/rust-lang/rust/blob/master/compiler/rustc_trait_selection/src/traits/project.rs#L813)) and registered as an obligation... this turns out to be very important in unifying function parameters with formals that are assoc types. Fixes rust-lang#91446
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I tried this code:
https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=53652794c179fb2128d73e2f11888a8a
I expected to see this happen:
The code compiles successfully
Instead, this happened:
There are two errors, despite the error sites apparently being no different from the successfully compiled ones, aside from the presence of generic type inference.
I couldn't get this to happen with a user-defined trait, so it may be related to
Pointee's magic implementations. On the other hand, it may be possible to trigger via user code and I just couldn't find an example.Meta
Playground Nightly Version Used:
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