Improve analyzer error message for an empty enum

[sgrekhov]

enum E { // Analyzer error. The enum must have at least one constant. Try declaring a constant.
  ;
  static const c = 0;
}

I'd say that this enum has one constant. CFE error message in this case is better. It is "An enum declaration can't be empty.".

Dart SDK version: 3.8.0-66.0.dev (dev) (Sun Feb 2 20:05:47 2025 -0800) on "windows_x64"

[bwilkerson]

I agree that the message should be improved, but I don't agree that the CFE message is better. The enum declaration is definitely not empty: there's a static field.

But given that enums can have constants that aren't enum constants, the message should probably be made more specific, perhaps along the lines of "The enum must have at least one enum constant. Try declaring an enum constant."

[eernstg]

[Edit: Upon refresh I discovered that this had already been closed. So there's no need to discuss it further. I'll leave the comment below in place, just in case it comes up again.]

Perhaps the declarations before the first semicolon in an enum declaration (that has a ;, otherwise all of them) can be designated as "the enum values" or "the enumerated values" or just "the values" of that enum declaration? It may not be obvious to every developer that enum E {one, two} declares two constant variables, in spite of the fact that this is true after desugaring, and the example in this issue shows that there's a clash with all other constant variables in the declaration.

So, perhaps?: "An enum declaration must have at least one value, e.g., enum E {one; ...}"?

[bwilkerson]

Yeah. I don't like the term "value" because it feels overly generic, but in the diagnostic documentation we use 'enum value' far more often than 'enum constant'. Using 'value' probably would have been better, but I didn't realize that when I replied above.