[EUI i18n token mapping] Long-term approach for complex defStrings

[cee-chen]

Original PR discussion: #109926 (comment)

Summary: EUI has previously not pluralized / passed defaultMessages that translate to complex defStrings. The above PR is the first case of that instance, but it's possible we may pluralize more messages going forward. This leads to defStrings that are essentially stringified functions, and don not pass the defaultMessage is in sync with defString tests.

For the above PR, I went with skipping a single test for now, but I'm opening this issue so y'all can potentially track a better long-term solution for either testing or skipping complex defString cases.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[afharo]

Since the only use-case we've found so far is about Pluralization, I'd vote for a regexp to identify these patterns according to our guidelines and attempt to match the strings with that.

Ideally, we'd be able to call both methods with 0, 1 & 2, and match the results?

What do you think?

[cee-chen]

I agree pluralization is likely the most common case. @chandlerprall, can you think of any other complex i18n scenarios that might come up in the future?

I did a quick grep of EUI's i18ntokens_changelog just to see what other instances we had used functions in defStrings for in the past, and it looks like these are old ones that we eventually removed/refactored:

"({\n  status\n}: {\n  status: EuiTourStepStatus;\n}) => {\n  return `Step ${number} ${status}`;\n};"
// This one is weird and I'm not sure correct, it looks like it should have been a straight pass-through

"({\n  step,\n  title,\n  disabled,\n  isComplete\n}: Pick<EuiStepHorizontalProps, 'step' | 'title' | 'disabled' | 'isComplete'>) => {\n  let titleAppendix = '';\n\n  if (disabled) {\n    titleAppendix = ' is disabled';\n  } else if (isComplete) {\n    titleAppendix = ' is complete';\n  }\n\n  return `Step ${step}: ${title}${titleAppendix}`;\n};"
// This looks like it should have been 2 different strings instead of a conditional

"({\n  status\n}: {\n  status?: EuiStepStatus;\n}) => {\n  if (status === 'incomplete') return 'Incomplete Step';\n  return 'Step';\n};"
// Similar to above, just use 2 different i18n tokens instead of a conditional

"({\n  count,\n  hasActiveFilters\n}) => `${count} ${hasActiveFilters ? 'active' : 'available'} filters`;"
// Similar to above, 2 separate tokens/strings instead of a conditional

If nothing else, identifying functions might help us avoid unnecessary conditional i18n in the future :)

[chandlerprall]

can you think of any other complex i18n scenarios that might come up in the future?

Nothing immediately comes to mind; good to start with the plural case and we can expand that if needed in the future 👍

If nothing else, identifying functions might help us avoid unnecessary conditional i18n in the future :)

🥇