Depedency Injection: Diagnostic for handling more than one @Qualifier

[KidoVin01]

Spec

Unchecked Errors:

• When more than one @Qualifier annotation is provided

Potential Solution:

• Remove the last @Qualifier

Related to #153

[kathrynkodama]

Is this diagnostic to warn users when they have a field/method with @Inject and more than one qualifier annotation?

According to https://jakarta.ee/specifications/dependency-injection/2.0/apidocs/jakarta/inject/inject:

A qualifier may annotate an injectable field or parameter and, combined with the type, identify the implementation to inject. Qualifiers are optional, and when used with @Inject in injector-independent classes, no more than one qualifier should annotate a single field or parameter. The qualifiers are bold in the following example:

public class Car {
@Inject private @leather Provider seatProvider;

 @Inject void install(@Tinted Windshield windshield,
     @Big Trunk trunk) { ... }

}
If one injectable method overrides another, the overriding method's parameters do not automatically inherit qualifiers from the overridden method's parameters.

In the example above, how would we determine that @Leather and @Tinted are qualifier annotations if they are in separate classes. We may not have knowledge of those classes.

Also see https://jakarta.ee/specifications/dependency-injection/2.0/apidocs/jakarta/inject/qualifier

[KidoVin01]

Is this diagnostic to warn users

The diagnostic should show an error since it would not compile properly when annotated

when they have a field/method with @Inject and more than one qualifier annotation?

Yes, that is correct.

In the example above, how would we determine that @leather and @TINTED are qualifier annotations if they are in separate classes. We may not have knowledge of those classes.

I guess that does pose a problem.

Maybe if the annotations appear in front of a type or alongside with an @Inject, we can infer it is a @Qualifier? Or we could internally keep track of the declared @Qualifiers (not sure whether that is possible).

[KidoVin01]

According to spec

Any bean may declare multiple qualifier types

Closing this issue until more detailed error can be specified.