fix(shadows): honor opaque(max_size) for report_only(persist) KV buffer - #133
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The generated persist_report_only arm sized its postcard buffer with `<T as MaxSize>::POSTCARD_MAX_SIZE` unconditionally, so a report_only(persist) field required its type to implement MaxSize even when it declared an explicit opaque(max_size = N). Mirror the ValueBuf sizing path, which already prefers opaque_max_size(). This lets report_only(persist) hold types that don't implement MaxSize (e.g. String-carrying enums) as long as the field declares opaque(max_size = N). Adds a compile-guard test whose field type intentionally does not implement MaxSize.
KennethKnudsen97
approved these changes
Jul 3, 2026
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Summary
report_only(persist)fields hardcoded<T as MaxSize>::POSTCARD_MAX_SIZEfor their KV buffer, so the field type had to implementMaxSizeeven when it declared an explicitopaque(max_size = N). The parallel ValueBuf-sizing path already honored the explicit size; this makes thepersist_report_onlycodegen do the same.Effect:
report_only(persist), opaque(max_size = N)now works for types that don't implementMaxSize(e.g.String-carrying enums), which is what lets a device persist a small state-machine field in its shadow across reboots.Includes a compile-guard test (
ReportOnlyPersistOpaqueTest) whose field type intentionally lacksMaxSize.