[Bug]: Module-level variables not getting type-narrowed within the function scope

[NipunaRanasinghe]

Description

Refer to the below code, which is a simplified version to reproduce the issue.
This fails with the compilation error operator '+' not defined for '(string|int)' and 'string'.

string|int value = "foo";

function foo() {
    if value is string {
        value += "bar";
    }
}

Steps to Reproduce

No response

Affected Version(s)

2201.8.x

OS, DB, other environment details and versions

No response

Related area

-> Compilation

Related issue(s) (optional)

No response

Suggested label(s) (optional)

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Suggested assignee(s) (optional)

No response

[LakshanWeerasinghe]

The spec currently allow type narrowing for "local variable or parameter" only. Even if make this final this won't work.

[LakshanWeerasinghe]

In this case a work around can be suggested,

string|int value = "foo";

public function main() {
    string|int v = value;
    if v is string {
        v += "bar";
    }
    io:println(v);
    io:println(value);
}

Here we assign the module level variable to a local variable and use it for type narrowing.

[LakshanWeerasinghe]

closing since this is a duplicate of spec issue.

[github-actions]

This issue is NOT closed with a proper Reason/ label. Make sure to add proper reason label before closing. Please add or leave a comment with the proper reason label now.

      - Reason/EngineeringMistake - The issue occurred due to a mistake made in the past.
      - Reason/Regression - The issue has introduced a regression.
      - Reason/MultipleComponentInteraction - Issue occured due to interactions in multiple components.
      - Reason/Complex - Issue occurred due to complex scenario.
      - Reason/Invalid - Issue is invalid.
      - Reason/Other - None of the above cases.