Autoharness: do not synthesize Arbitrary for structs with reference fields - #4694
Open
tautschnig wants to merge 1 commit into
Open
Autoharness: do not synthesize Arbitrary for structs with reference fields#4694tautschnig wants to merge 1 commit into
tautschnig wants to merge 1 commit into
Conversation
…ields
can_derive_arbitrary recursed into reference field types (reachable for
'static references; reference fields with a lifetime parameter were already
rejected via the ADT's generic arguments), so a struct like
struct HasStaticRef { r: &'static u32 }
was deemed derivable. The synthesized any() then created the referent's
storage inside its own body and returned a dangling reference, producing
spurious 'dereference failure: dead object' verification failures in the
generated harness.
Reject reference fields in the derivability check. Note the asymmetry with
top-level argument references, which remain supported: for those, the
generated harness itself owns the referent's storage, which therefore
outlives the call.
Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>
github-actions
Bot
added
Z-EndToEndBenchCI
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Description
can_derive_arbitraryrecursed into reference field types, so a struct with a&'staticreference field (reference fields with lifetime parameters were already rejected via the ADT's generic arguments) was deemed derivable. The compiler-synthesizedany()then created the referent's storage inside its own body and returned a dangling reference, so the generated harness failed spuriously with "dereference failure: dead object" — a false alarm the user can do nothing about.Reject reference fields in the derivability check; such functions are now skipped with the usual "Missing Arbitrary implementation" reason. Top-level reference arguments are unaffected: for those the generated harness itself owns the referent's storage, which outlives the call.
Found while implementing #4691 (the storage-lifetime asymmetry between argument position and field position is exactly what that PR documents for slices).
Testing
New script-based test
cargo_autoharness_ref_field: asserts the struct-with-reference-field function is skipped (previously: spurious dead-object failure) while a plain&u32argument remains supported. Formatting and the compiler unit tests pass.By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.