Type parameter related false positive error messages.

I encountered some error messages on my code that can be correctly compiled and run, meaning that these errors could be false positives. After simplifying the code, I found that these false positives could be caused by incorrect name shadowing for type parameters.

Environment

• Operating System: Linux
• JDK version: 21
• Visual Studio Code version: 1.94.2
• Java extension version: 1.35.1

Steps To Reproduce

1. Create an empty java project and open it with vscode.
2. Create a package demo and a App.java file in this package.
3. Paste the code below into App.java:

package demo;

interface BinaryExpr {
    interface Op { }

    Op getOperator();
}

abstract class AbstractBinaryExpr<Op extends BinaryExpr.Op> implements BinaryExpr {
    private final Op op;

    public AbstractBinaryExpr(Op op) { this.op = op; }

    @Override
    public Op getOperator() {
        return op;
    }
}

final class ArithExpr extends AbstractBinaryExpr<ArithExpr.Op> {
    enum Op implements BinaryExpr.Op {
        ADD, SUB
    }

    public ArithExpr(Op op) { super(op); }
}

public class App {
    
    public static void main(String[] args) {
        var e = new ArithExpr(ArithExpr.Op.ADD);
        System.out.println(toStr(e));
    }

    public static String toStr(ArithExpr e) {
        return switch(e.getOperator()) {
            case ADD -> "+";
            case SUB -> "-";
        };
    }
}

Current Result

You will see the following three error messages:

// ...
public static String toStr(ArithExpr e) {
    return switch(e.getOperator()) { // Error 1: A switch expression should have a default case
        case ADD -> "+"; // Error 2: ADD cannot be resolved to a variable
        case SUB -> "-"; // Error 3: SUB cannot be resolved to a variable
    };
}

Expected Result

No error messages are expected because java compiler can handle it correctly.

Additional Informations

If you rename the type parameter Op and its following occurrances in class AbstractBinaryExpr into O, the error messages will disappear. This hints that the return type Op of AbstractBinaryExpr.getOperator() may be resolved to the Op in the superclass BinaryExpr rather than the type parameter.

Riproducete il report nel progetto Java vuoto usando il codice fornito di demo/App.java, quindi confrontate la diagnostica di VS Code con il comportamento del compilatore Java. Tracciate la risoluzione dei nomi dei parametri di tipo coinvolta in AbstractBinaryExpr e verificate che l’espressione switch e i relativi casi ADD e SUB non producano più errori falsi positivi.