[enhanced-enums] A value declaration is in a constant context?

[eernstg]

With the upcoming enhanced-enums feature, we can have arguments to constructors in enum value declarations. They are desugared into the right hand side of the declaration of a static const variable, so presumably they'd be in a constant context?

enum E {
    v([]); // Means `v(const [])`?
  const E(_);
}

Currently, the analyzer fails to handle the above declaration because it reports that Enum does not have the required constant constructor (and this means that no enhanced enum declarations will work at all), but the CFE takes the position that it is not a constant context, and hence it is an error to have [] because no implicit addition of const occurs.

I do not see any plausible future development where enum values will accept non-constant constructor arguments, so we might as well make the value declaration terms a constant context.

@lrhn, @munificent, @leafpetersen, @natebosch, @jakemac53, @stereotype441, WDYT?

[lrhn]

Agree. The proposed desugaring makes it a const constructor invocation. The expressions should definitely be in a const context.

It's currently stated as

where args are considered as occurring in a const context, and it’s a compile-time error if they are then not compile-time constants.

[eernstg]

Aha, I hadn't found that bit in the spec, this means that the fact that it is not treated as a constant context is an issue on implementations: dart-lang/sdk#48232.

So I'll close this issue.