[PATCH] rust-cpython: add sanity check to PySharedState::decrease_leak_count()

[Raphaël Gomès]

Good idea, thanks!

On 9/15/19 6:29 PM, Yuya Nishihara wrote:
> # HG changeset patch
> # User Yuya Nishihara <yuya at tcha.org>
> # Date 1568555012 -32400
> #      Sun Sep 15 22:43:32 2019 +0900
> # Node ID 071b35e3f7cde53cbf411a536091153741dc4a37
> # Parent  34ed651ba7e4a4b7f0ee79c5a5442b5eed27bbad
> rust-cpython: add sanity check to PySharedState::decrease_leak_count()
>
> If decrease_leak_count() were called unnecessarily, there must be a serious
> bug. It's better to not silently ignore such cases.
>
> diff --git a/rust/hg-cpython/src/ref_sharing.rs b/rust/hg-cpython/src/ref_sharing.rs
> --- a/rust/hg-cpython/src/ref_sharing.rs
> +++ b/rust/hg-cpython/src/ref_sharing.rs
> @@ -85,10 +85,14 @@ impl PySharedState {
>       /// It's unsafe to update the reference count without knowing the
>       /// reference is deleted. Do not call this function directly.
>       pub unsafe fn decrease_leak_count(&self, _py: Python, mutable: bool) {
> -        self.leak_count
> -            .replace(self.leak_count.get().saturating_sub(1));
>           if mutable {
> +            assert_eq!(self.leak_count.get(), 0);
> +            assert!(self.mutably_borrowed.get());
>               self.mutably_borrowed.replace(false);
> +        } else {
> +            let count = self.leak_count.get();
> +            assert!(count > 0);
> +            self.leak_count.replace(count - 1);
>           }
>       }
>   }
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