invalid_annotation

Annotation must be either a const variable reference or const constructor invocation.

The analyzer produces this diagnostic when an annotation without arguments references something that is neither a variable marked as const nor a constructor. An annotation with arguments, such as @f(), is an invocation of a const constructor, so when f isn't a class it's reported like any other constant constructor invocation, as creation_with_non_type.

Getters can't be used as annotations.

The following code produces this diagnostic because the variable v isn't a const variable:

var v = 0;
​
@v
void f() {}

The following code produces this diagnostic because f isn't a variable:

@f
void f() {}

The following code produces this diagnostic because g is a getter:

@g
int get g => 0;

If the annotation is referencing a variable that isn't a const constructor, add the keyword const to the variable's declaration:

const v = 0;
​
@v
void f() {}

If the annotation isn't referencing a variable, then remove it:

int v = 0;
​
void f() {}