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Write contracts + pre/post conditions for all unsafe methods in duration #136

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Merged
merged 22 commits into from
Dec 11, 2024

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sgpthomas
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Resolves #72

We added invariants for Nanoseconds and Duration to match the safety conditions for those types.

We add safety requirements to the following methods:

  • new, from_secs, from_millis, from_micros, from_nanos, as_secs, as_millis, as_micros, as_nanos, subsec_millis, subsec_micros, subsec_nanos, checked_add, checked_sub, checked_mul, checked_div

We additionally add correctness conditions to the following methods:

  • from_secs, as_secs, subsec_millis, subsec_micros, subsec_nanos, as_millis, as_micros

Support for kani::Invariant depends on #87. For the interim we implemented a proxy trait TempInvariant that exposes the same is_safe method. We will update this once #87 is merged.

While the safety check for Duration::as_nanos() succeeds, we ran into timeouts for Duration::as_nanos() when we tried to use a correctness contract and we're looking for advice on how to speed up that verification time. We were able to prove it for u16::MAX, but hit timeouts for larger numbers.

We are unsure if the pre-conditions for Duration::new() are acceptable because they limit the range of values that you can call Duration::new() with. However, we think it's reasonable since we limit the values to values that don't panic. Let us know if this is a thing that we should change.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

@sgpthomas sgpthomas requested a review from a team as a code owner October 24, 2024 21:32
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@celinval celinval left a comment

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That's awesome! Thank you

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@celinval celinval left a comment

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Awesome! Thanks

@tautschnig tautschnig assigned tautschnig and unassigned feliperodri and celinval Nov 27, 2024
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I don't think we should have anything other than true as a requires clause on safe functions.

@tautschnig tautschnig assigned sgpthomas and unassigned tautschnig Nov 27, 2024
@sgpthomas sgpthomas requested a review from tautschnig December 3, 2024 20:07
@tautschnig tautschnig disabled auto-merge December 10, 2024 20:51
@tautschnig tautschnig added this pull request to the merge queue Dec 10, 2024
Merged via the queue into model-checking:main with commit 8a248d9 Dec 11, 2024
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@sgpthomas sgpthomas deleted the verify_duration_challenge9 branch December 14, 2024 21:45
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Challenge 9: Safe abstractions for core::time::Duration
5 participants