[Bug]: NPE when formatting Ballerina code that includes regular expressions

[lnash94]

Description

Occurred this NPE errors[2] while formatting the below ballerina code[1] using bal format command

[1] sample Ballerina code

import ballerina/constraint;

@constraint:String {pattern: re `[A-Z]{1}`}
public type FlightClass string;

@constraint:String {pattern: re `[a-zA-Z0-9]{3}`}
public type Code string;

public function main() {
    Code code = "A380";
    FlightClass flightclass = "A";
}

[2] Error stack

May 30, 2023 8:57:24 PM org.ballerinalang.formatter.core.FormattingTreeModifier formatNode
SEVERE: Error while formatting [kind: RE_SEQUENCE] [line: 3] [column:33]: java.lang.NullPointerException
May 30, 2023 8:57:24 PM org.ballerinalang.formatter.core.FormattingTreeModifier formatNode
SEVERE: Error while formatting [kind: RE_SEQUENCE] [line: 6] [column:33]: java.lang.NullPointerException
modified files:
/Users/hansaninissanka/Documents/Ballerina Projects/pattern_connector/main.bal

format successful.

Steps to Reproduce

No response

Affected Version(s)

2201.5.0
2201.6.0-rc1

OS, DB, other environment details and versions

No response

Related area

-> Compilation

Related issue(s) (optional)

No response

Suggested label(s) (optional)

No response

Suggested assignee(s) (optional)

No response

[pcnfernando]

The issue seems to be at the TreeModifier when we have a single quantifier. The optional mostTimesMatchedDigit is not handled correctly in https://github.com/ballerina-platform/ballerina-lang/blob/master/compiler/ballerina-parser/src/main/java/io/ballerina/compiler/syntax/tree/TreeModifier.java#L3612

_ = re `[a-zA-Z0-9]{3}`;

The below works as expected where the optional nodes are available

_ = re `[a-zA-Z0-9]{3,5}`;

We'll consider this a priority and take this up in the next sprint.

[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.