OwnedView: remove Deref, add generated FooOwnedView accessor wrappers#154
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The Deref<Target = V> impl exposed the inner view as FooView<'static>, so borrowed fields appeared 'static to the borrow checker and could be held past the point where the OwnedView and its Bytes buffer were dropped. Field access now goes through reborrow(), which ties every borrow to the handle. The Serialize impl forwards via the inner view directly, and a compile_fail doctest pins that field access on the handle no longer compiles.
For each message (when views are generated, excluding map entries), emit a FooOwnedView newtype around OwnedView<FooView<'static>> with one &self-tied accessor method per field, plus decode, decode_with_options, from_owned, view(), to_owned_message, bytes, into_bytes, From conversions to and from the raw OwnedView, and a Serialize forwarding impl when JSON generation is enabled. The wrapper is re-exported at the package root next to Foo and FooView. A field or oneof whose name collides with a reserved wrapper method keeps working through view(); its accessor is skipped with the new CodeGenWarning::OwnedViewAccessorSuppressed. The view type helpers now take the borrow lifetime as a parameter so accessor return types can use the anonymous lifetime. Regenerates checked-in WKT and bootstrap descriptor types.
Rewrite the OwnedView sections of the guide, README, DESIGN, and the prost migration doc around reborrow() and the generated FooOwnedView accessor wrappers, and add CHANGELOG entries for the Deref removal and the new wrapper types.
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rpb-ant
approved these changes
May 28, 2026
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Summary
OwnedView<V>previously implementedDeref<Target = V>. The stored view isFooView<'static>, where the'staticis synthetic — the borrows actually point into the handle'sBytesbuffer. ThroughDeref, safe code could copy borrowed fields (&'static str,&'static [u8]) out of the handle and keep them after the handle dropped, at which point they dangle. Triggering this requires the calling application to deliberately hold a field reference beyond the handle's lifetime, so the practical exposure is limited — but the API should not permit it at all.This PR:
Derefimpl; access goes through the existingreborrow(), which ties every borrow to the handle, with acompile_faildoctest pinning the removal (buffa/src/view.rs);FooOwnedViewwrapper types: a per-message newtype aroundOwnedView<FooView<'static>>with one&self-tied accessor per field (owned.name(),owned.id(), …), plusdecode/decode_with_options/from_owned/view()/to_owned_message/bytes/into_bytes,Fromconversions to and from the rawOwnedView, and JSONSerializeforwarding. The wrapper is re-exported at the package root next toFooandFooView.reborrow()is a pure lifetime coercion, so the accessors compile to the same code as the old direct field access;Breaking change
owned.fieldno longer compiles onOwnedView. Migrate either withowned.reborrow().field(or once per scope:let view = owned.reborrow();), or by switching to the generatedFooOwnedViewand usingowned.field().serde_json::to_string(&owned_view)on the handle is unchanged.Notes
generate_views; there is no separate knob, so generated-code size grows accordingly.bytes,view,decode, …) keeps working throughview(); its accessor is skipped with a build warning (CodeGenWarning::OwnedViewAccessorSuppressed).DerefonOwnedView).