ICE'd during const eval of generic with DST #80742
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C-bug
Category: This is a bug.
F-const_generics
`#![feature(const_generics)]`
F-generic_const_exprs
`#![feature(generic_const_exprs)]`
glacier
ICE tracked in rust-lang/glacier.
I-ICE
Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
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mental32
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C-bug
jonas-schievink
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F-generic_const_exprs
JohnTitor
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Jan 15, 2021
m-ou-se
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Jan 20, 2021
Fix ICE in mir when evaluating SizeOf on unsized type Not quite ready yet. This tries to fix rust-lang#80742 as discussed on [Zulip topic][1], by using `delay_span_bug`. I don't understand what `delay_span_bug` does. It seems like my error message is never used. With this patch, in this program: ```rust #![allow(incomplete_features)] #![feature(const_evaluatable_checked)] #![feature(const_generics)] use std::fmt::Debug; use std::marker::PhantomData; use std::mem::size_of; struct Inline<T> where [u8; size_of::<T>() + 1]: , { _phantom: PhantomData<T>, buf: [u8; size_of::<T>() + 1], } impl<T> Inline<T> where [u8; size_of::<T>() + 1]: , { pub fn new(val: T) -> Inline<T> { todo!() } } fn main() { let dst = Inline::<dyn Debug>::new(0); // line 27 } ``` these errors are printed, both for line 27 (annotated line above): - "no function or associated item named `new` found for struct `Inline<dyn Debug>` in the current scope" - "the size for values of type `dyn Debug` cannot be known at compilation time" Second error makes sense, but I'm not sure about the first one and why it's even printed. Finally, I'm not sure about the span passing in `const_eval`. [1]: https://rust-lang.zulipchat.com/#narrow/stream/269128-miri/topic/Help.20fixing.20.2380742
m-ou-se
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Jan 20, 2021
Fix ICE in mir when evaluating SizeOf on unsized type Not quite ready yet. This tries to fix rust-lang#80742 as discussed on [Zulip topic][1], by using `delay_span_bug`. I don't understand what `delay_span_bug` does. It seems like my error message is never used. With this patch, in this program: ```rust #![allow(incomplete_features)] #![feature(const_evaluatable_checked)] #![feature(const_generics)] use std::fmt::Debug; use std::marker::PhantomData; use std::mem::size_of; struct Inline<T> where [u8; size_of::<T>() + 1]: , { _phantom: PhantomData<T>, buf: [u8; size_of::<T>() + 1], } impl<T> Inline<T> where [u8; size_of::<T>() + 1]: , { pub fn new(val: T) -> Inline<T> { todo!() } } fn main() { let dst = Inline::<dyn Debug>::new(0); // line 27 } ``` these errors are printed, both for line 27 (annotated line above): - "no function or associated item named `new` found for struct `Inline<dyn Debug>` in the current scope" - "the size for values of type `dyn Debug` cannot be known at compilation time" Second error makes sense, but I'm not sure about the first one and why it's even printed. Finally, I'm not sure about the span passing in `const_eval`. [1]: https://rust-lang.zulipchat.com/#narrow/stream/269128-miri/topic/Help.20fixing.20.2380742
JohnTitor
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Jan 21, 2021
Fix ICE in mir when evaluating SizeOf on unsized type Not quite ready yet. This tries to fix rust-lang#80742 as discussed on [Zulip topic][1], by using `delay_span_bug`. I don't understand what `delay_span_bug` does. It seems like my error message is never used. With this patch, in this program: ```rust #![allow(incomplete_features)] #![feature(const_evaluatable_checked)] #![feature(const_generics)] use std::fmt::Debug; use std::marker::PhantomData; use std::mem::size_of; struct Inline<T> where [u8; size_of::<T>() + 1]: , { _phantom: PhantomData<T>, buf: [u8; size_of::<T>() + 1], } impl<T> Inline<T> where [u8; size_of::<T>() + 1]: , { pub fn new(val: T) -> Inline<T> { todo!() } } fn main() { let dst = Inline::<dyn Debug>::new(0); // line 27 } ``` these errors are printed, both for line 27 (annotated line above): - "no function or associated item named `new` found for struct `Inline<dyn Debug>` in the current scope" - "the size for values of type `dyn Debug` cannot be known at compilation time" Second error makes sense, but I'm not sure about the first one and why it's even printed. Finally, I'm not sure about the span passing in `const_eval`. [1]: https://rust-lang.zulipchat.com/#narrow/stream/269128-miri/topic/Help.20fixing.20.2380742
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Reproducible in the playground: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=a7e62bb084b21bc2081c79e320c740a0
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rustc --version --verbose:Error output
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