Consider more forgiving DX about ember-intl HOT 2 OPEN

In regards to ICU Message syntax what would you expect The number is: {nonexistent} to look like?

That said I did a little research and found that per the ECMAScript specs that the value is anything as it will be coerced to a number (defaulting with undefined).

I didn't look up the other formats. But it seems to me that it is safe to assume value is not a required parameter. It may be weird to have the format convert to NaN or something but I presume that is what is expected?

from ember-intl.

I did a little more research:

Since format-message uses the above internal implementations their expectations should be the same (i.e. do not assert). Also since lists are the only one I found that does need an assertion and that the ICU message syntax does not provide for lists it is reasonable that the format-message also should not assert values.

I am uncertain about the utility of allowing dynamic messages for format-message in app code instead perhaps using some alternative pattern that guarantees the existence of the value passed in (like hard coded strings or constants).

As for format-list the ICU guides recommend its use outside the message formatting:

Format the parameters separately (recommended)
You can format the parameter as you need before calling MessageFormat, and then passing the resulting string as a parameter to MessageFormat.
This offers maximum control, and is preferred to using custom format objects (see below).
~ https://unicode-org.github.io/icu/userguide/format_parse/messages/index#format-the-parameters-separately-recommended

Which I interpret that we should to the following with lists:

{{t "…" items=(format-list items)}}

from ember-intl.