Fix: Object::from_ref no longer forgetting to increment the strong count #5858
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…unt. Fixes #5851 I haven't been able to produce consistently any program that could exhibit the issue this PR is solving, the only hint I had that this happened was the report of #5851, which I reasoned manually must come from this function that is being skipped. By making it opaque to the compiler, we prevent optimizations that would skip the strong count from increasing. Alternative to this would be to pass &Rc<Self> instead of &Self, which is what https://github.com/dafny-lang/dafny/tree/fix-object-safety-rust does, but &Rc does not make traits object-safe, which means we can't yet use them in the code. I tried also passing a second arguments so that we directly have a `Rc<>` and don't need to recover it from the &T, but `this: Rc<Self>` again makes the trait not object-safe, and `this: Rc<dyn Any>` causes an issue because we can't create this argument when what we have is only the trait, and trait upcast to Any is currently unsound in Rust. This PR is the best workaround I found so far.
ssomayyajula
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MikaelMayer
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…unt (#5858) Fixes #5851 I haven't been able to produce consistently any program that could exhibit the issue this PR is solving, the only hint I had that this happened was the report of #5851, which I reasoned manually must come from this function that is being skipped. By making it opaque to the compiler, we prevent optimizations that would skip the strong count from increasing. Alternative to this would be to pass &Rc<Self> instead of &Self, which is what https://github.com/dafny-lang/dafny/tree/fix-object-safety-rust does, but &Rc does not make traits object-safe, which means we can't yet use them in the code. I tried also passing a second arguments so that we directly have a `Rc<>` and don't need to recover it from the &T, but `this: Rc<Self>` again makes the trait not object-safe, and `this: Rc<dyn Any>` causes an issue because we can't create this argument when what we have is only the trait, and trait upcast to Any is currently unsound in Rust. This PR is the best workaround I found so far. <small>By submitting this pull request, I confirm that my contribution is made under the terms of the [MIT license](https://github.com/dafny-lang/dafny/blob/master/LICENSE.txt).</small>
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Fixes #5851
This PR adds the following safety checks
#[inline(never)]to the function from_ref did fix the soundness issue.&T, it increments the strong count from the pointer obtained by the extractedRc<T>by doing it the normal wayAn alternative to avoid all this hassle would be to pass
self: &Rc<Self>instead ofself: &Self, which is what the branch https://github.com/dafny-lang/dafny/tree/fix-object-safety-rust does, but&Rcdoes not make traits object-safe, which means we can't yet use them in the code. I tried also passing a second arguments so that we directly have aRc<>and don't need to recover it from the &T, butthis: Rc<Self>again makes the trait not object-safe, andthis: Rc<dyn Any>causes an issue because we can't create this argument when what we have is only the trait, and trait upcast to Any is currently unsound in Rust. This PR is the best workaround I found so far.By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.