fix(shadows): accept bare-string unit variants in externally-tagged parse_delta#129
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KennethKnudsen97 merged 2 commits intoMay 26, 2026
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…arse_delta
The derive emitted `parse_delta` for an externally-tagged enum with mixed
unit + newtype variants only handled the object form (`{"dhcp": ...}`,
`{"static": {...}}`). Serde, by contrast, serializes unit variants as a
bare string (`"dhcp"`), and AWS echoes that shape back via shadow
desired/delta — causing devices to loop on `InvalidPayload`.
Add a bare-string fast-path before the FieldScanner call: trim ASCII
whitespace, and if the value starts with `"`, match it against each
unit variant's quoted name; fall through to the existing object-form
scanner otherwise. Brings the macro's behaviour into line with what
`serde::Deserialize` already accepts.
MathiasKoch
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May 26, 2026
MathiasKoch
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May 26, 2026
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One minor thing.
Also, could we remove some of the unnecessary comments, and keep the comments to a strict "why we are doing this" on code that is not directly clear or is complex, as opposed to the current "what we are doing" style?
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Summary
For an externally-tagged enum with mixed unit + newtype variants (e.g.
IpSettings { Dhcp, Static(...) }), the derivedparse_deltaonly handled the object form ({"dhcp": ...},{"static": {...}}). Serde itself serializes unit variants as a bare string ("dhcp"), and AWS echoes that shape back via shadow desired/delta — so devices loop onInvalidPayloadwhenever the cloud has the unit variant set.This adds a bare-string fast-path before the
FieldScannercall: trim ASCII whitespace, and if the value starts with", match it against each unit variant's quoted name; fall through to the existing object-form scanner otherwise. Brings the macro's behaviour into line with whatserde::Deserializealready accepts.Found via factbird-mini #667.
Test plan
cargo test --lib --features std,shadows_kv_persist— 177 pass (incl. 4 new insrc/shadows/shadow/tests.rsunder6.4 parse_delta accepts both bare-string and object forms)[patch]— the previously failingparse_known_network_with_bare_string_ip_settingsregression now passes