Conflicting error messages using check inside a type guard

[hasithaa]

Observed with SL-Alpha2 packs.

import ballerina/file;

function test1() returns error? {
    var result = file:remove("somePath");
    if !(result is file:FileNotFoundError) && !(result is ()) {
        check result; 
        // Error 1: variable assignment is required(BCE2526)
        // Error 2: invalid usage of the 'check' expression operator: all expression types are equivalent to error type
    }
}

function test2() returns error? {
    var result = file:remove("somePath");
    if !(result is file:FileNotFoundError) && !(result is ()) {
        var x = check result; // Error: invalid usage of the 'check' expression operator: all expression types are equivalent to error type(BCE3031)
    }

}

[MaryamZi]

The spec currently does not allow using check result as used here even though the implementation allows it.

checking-keyword is allowed in statements only if it is part of a call-stmt.

call-stmt := call-expr ;
call-expr :=
   function-call-expr
   | method-call-expr
   | checking-keyword call-expr

Related spec discussion - ballerina-platform/ballerina-spec#588

As discussed, we may have to fix this deviation first.

However, even when the checking-keyword is used with a function/method call, and the function/method only returns error(s), this compilation error can be observed.

function err() returns error => error("Error!");

public function main() returns error? {
     check err();

     // $ bal run foo.bal 

     // Compiling source
     //      foo.bal
     // ERROR [foo.bal:(4:6,4:18)] variable assignment is required
     // ERROR [foo.bal:(4:12,4:17)] invalid usage of the 'check' expression operator: all expression types are equivalent to error type
}

But the spec does not seem to have such a restriction.