[Bug]: Creation of nested character classes in regex patterns at runtime

[LakshanWeerasinghe]

Description

According to our spec nested character class defining should not be allowed. Following program execution should result in runtime error.

import ballerina/lang.regexp;

public function main() returns error? {
    string:RegExp pattern = check regexp:fromString("[a-z[a-z]]");
}

Steps to Reproduce

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Affected Version(s)

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OS, DB, other environment details and versions

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Related area

-> Compilation

Related issue(s) (optional)

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[github-actions]

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      - 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.