Reflection: view-type vtable + dynamic container plumbing#148
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Add the runtime half of vtable-mode reflection: ReflectList/ReflectMap impls for the zero-copy view containers RepeatedView and MapView, so a generated view's reflective get() can return a borrowed list/map without materializing a Vec<Value>. Introduce two helper traits, ReflectElement and ReflectMapKey, with concrete impls for scalars, &str, &[u8], and EnumValue<E>. A trait-bound blanket over ReflectMessage is not possible — it would overlap the scalar impls under Rust's coherence rules — so codegen will emit a one-line ReflectElement impl per generated view and enum in a later change. Map reflection deduplicates duplicate wire entries (last-write-wins) via MapView::iter_unique to match the bridge path's distinct-key semantics, keeping len() and for_each() consistent across both reflection modes. Also record the landed ValueRef::List/Map refactor and the coherence constraint in the vtable design doc.
Generate `impl ReflectMessage for FooView<'a>` directly on view types when both reflection and the internal vtable flag are set. get()/has() read view struct fields through a per-field match — no encode/decode round-trip and no DynamicMessage — covering scalars, string/bytes, enums, nested messages, repeated, map, optional presence, and oneof members. for_each_set walks the descriptor; to_dynamic falls back to a bridge-style snapshot. Also emit `impl ReflectElement` for view types and generated enums so a RepeatedView/MapView of messages or closed enums reflects through the generic container impls. Per-message MessageIndex is memoized via an inherent associated fn (collision-free across sibling views in a shared module). Gated behind a new internal CodeGenConfig flag, exposed experimentally as buffa_build::Config::generate_reflection_vtable. Bridge mode and the reflect() call-site contract are unchanged.
Make the WKT view types (TimestampView, DurationView, AnyView, StructView, ValueView, wrappers, etc.) implement ReflectMessage, so a message that has a WKT field can reflect over it. Previously vtable reflection only worked for protos that did not reference WKTs, because the WKT views lived in buffa-types with no path to ReflectMessage. The reflection surface pulls a buffa-descriptor dependency and requires std (the embedded descriptor pool uses OnceLock), so it is gated behind a new buffa-types `reflect` feature; views and text stay unconditional. This is enabled by a targeted codegen flag, gate_reflect_on_crate_feature, which gates only the reflection impls — unlike gate_impls_on_crate_features, which gates json/views/text/reflect together and would have forced buffa-types consumers to opt into views/text. All seven WKT protos share the google.protobuf package, so one embedded descriptor pool backs every WKT view's reflection.
Add a sixth conformance run that exercises the generated `impl ReflectMessage for FooView`: decode a view, walk its vtable reflection surface (for_each_set/get) to rebuild a DynamicMessage, and serialize that to JSON. This reuses DynamicMessage's JSON serializer — which passes the corpus cleanly under BUFFA_VIA_REFLECT — so any failure isolates a bug in the vtable get/has surface rather than in JSON formatting. Binary and text output are skipped (the reflect rebuild drops unknown fields, which JSON omits anyway). The run passes 1246 binary->JSON conformance tests with zero failures across proto2/proto3/editions, so known_failures_view_vtable.txt is empty. Vtable reflection is enabled on the four view-bearing conformance protos and gated behind the conformance `reflect` feature (via the new buffa_build::Config::gate_reflect_on_crate_feature), so the no_std binary omits it. Also fix a latent needless-return in process_editions surfaced by clippy once the editions protos are present, and correct the stale conformance-run count in CONTRIBUTING (four runs -> six, including the previously undocumented via-reflect run).
Extend the reflection benchmark with the zero-copy view path so the vtable
ReflectMessage work can be measured against the alternatives:
- decode/view — decode_view alone (no reflection), the zero-copy floor.
- reflect/{vtable,bridge,dynamic}_read_{one,all} — from wire bytes, obtain a
reflective handle and read one field / all set fields, comparing the view
vtable path, the bridge round-trip, and pure DynamicMessage reflection.
Enables generate_reflection_vtable on the bench types so the view types
implement ReflectMessage. Measurements: vtable view reflection runs ~6-10x
faster than the bridge round-trip and ~4x faster than pure DynamicMessage
reflection, because it is dominated by decode_view, which is itself cheaper
than owned decode (borrowed strings/bytes, no per-field allocation).
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All contributors have signed the CLA ✍️ ✅ |
This was referenced May 23, 2026
asacamano
previously approved these changes
May 24, 2026
Resolves conflicts from the idiomatic enum aliases (#152) and module collision fix (#145) landing on main while the vtable reflection stack was open: - enumeration.rs: keep both the vtable `ReflectElement` impl for closed enums and the idiomatic-alias doc-note wrapping of `enum_doc`. - codegen lib.rs: keep all three new config fields (generate_reflection_vtable, gate_reflect_on_crate_feature, idiomatic_enum_aliases); move the vtable-config validation into the new generate_with_diagnostics so both entry points enforce it. - buffa-build: keep both new builder methods. - buffa-test/build.rs: keep the new modcollide/modrace build blocks and the vtable-aware proto2 comment. Generated WKT/bootstrap code regenerated; matches the textual merge.
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First of three stacked PRs adding vtable-mode reflection — generated types implement
ReflectMessagedirectly, so reflective field access reads struct fields in place with noDynamicMessageround-trip. This PR lands the view-type path and the shared plumbing.What's here
buffa-descriptor:ReflectElement(element →ValueRef) andReflectMapKey(key →MapKeyRef), with genericReflectList/ReflectMapimpls overRepeatedView/MapView.ValueRef::List/Mapnow carry&dyn ReflectList/&dyn ReflectMap.impl ReflectMessage for FooView<'a>(get/has/for_each_set/to_dynamic) plus a memoized per-messageMessageIndex, behind an internal mode flag.reflectfeature onbuffa-typesso well-known-type views implementReflectMessage(needed by any message that embeds a WKT).BUFFA_VIA_VTABLErun that decodes a view, walks itsReflectMessagesurface to rebuild aDynamicMessage, and serializes that to JSON.Validation
via-vtableconformance suite passes all 1246 binary→JSON cases across proto2/proto3/editions with zero failures (12CONFORMANCE SUITE PASSEDlines total).cargo test --workspace --all-features, clippy-D warnings, and markdownlint all green.Stack
ReflectModepublic API + vtable-by-default (Reflection: owned-message vtable, ReflectMode, vtable by default #149)Owned-type reflection still uses the bridge round-trip after this PR; that flips in PR 2.