Ballot validation messages

These are the warnings shown while a voter is marking a ballot — "select one more candidate", "shorten your write-in by two characters". They are a different family from the cast-vote failures in Cast Vote Errors, which happen after the voter submits.

Where they come from

The Rust checker in sequent-core reports a problem as a message key plus a message_map. Every value in that map is a string, and the map describes the state of the selection — numSelected, min, max — rather than the number the sentence is actually about.

That distinction is the whole reason this layer exists. "Select 2 more candidates" needs min - numSelected; the checker never sends that number, it sends the two operands.

Rendering them

getBallotErrorOptions bridges the two. Always render these messages through it:

import {getBallotErrorOptions} from "@sequentech/ui-core"

t(error.message || "", getBallotErrorOptions(error.message, error.message_map))

It does two things:

1. Copies every message_map entry into the options, coercing numeric strings to numbers. So if the checker already sends a count, the message pluralises with no further work.
2. Derives count for the keys listed in COUNT_DERIVATIONS, overriding whatever came in the map.

The coercion in step 1 matters: i18next skips pluralisation entirely when count is a string and silently falls back to the unsuffixed key. Passing the raw message_map straight to t() is a bug for exactly that reason.

Adding a new validation message

Adding the key in Rust and translating it is enough when the sentence's number is already in message_map.

Add an entry to COUNT_DERIVATIONS in packages/ui-core/src/services/ballotErrorMessages.ts only when the number has to be computed from the state fields:

message	the sentence is about	derivation
errors.implicit.selectedMin	how many more to pick	min - numSelected
errors.implicit.underVote	how many more are allowed	max - numSelected
errors.implicit.selectedMax	how many to unpick	numSelected - max
errors.implicit.maxSelectionsPerType	how many to unpick from one candidate type	numSelected - max
errors.implicit.overVoteDisabled	the maximum already reached	max, falling back to numSelected when the map carries no max

That is the whole of COUNT_DERIVATIONS. Every other validation message is rendered from the message_map as it arrives.

A derivation always wins over a count that arrived in the map, so do not add one when the checker already sends the right number.

Pluralising them

A derived count is a number like any other, so these messages follow the ordinary plural rules — with one wrinkle worth knowing: the derivations subtract, so they can produce values the checker never sends.

• Give the message the plural forms every target language reports, not just _one and _other. Spanish, Catalan and French also need _many; a missing form falls through to fallbackLng and renders the English sentence rather than the right one. _many is a verbatim copy of _other.
• Adding a suffix to en.ts makes it a required key in every other language file, because they are typed TranslationType = typeof englishTranslation.
• overVoteDisabled is the one message whose count is a bound rather than a difference, so it is the one that can carry a large operator-configured number straight into the sentence.

See Add a New Language for the per-language rules.