[Bug]: var _ wildcard binding pattern in match statement never matches when match expression type contains error

[senuriwick]

Description

When a match statement's subject expression has a type that includes error (e.g. JSON field access j.kind which produces json|error), the var _ wildcard binding pattern never matches at runtime even when it should.

Steps to Reproduce

1. Create a Ballerina file with the following code:

import ballerina/io;

function getKind(json j) returns string {
    match j.kind {
        "a" => {
            return "A";
        }
        error(var _) => {
            return "E";
        }
        var _ => {
            return "B";
        }
    }
}

public function main() {
    json myData = {kind: "b"};
    string result = getKind(myData);
    io:println("Returned value: ", result);
}

2. Observe the output:

Returned value:

Expected: Returned value: B
The var _ clause should match "b" since it is a non-error json value.

Affected Version(s)

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OS, DB, other environment details and versions

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Related area

-> Compilation

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