Having difficulty combining sections of the regex to clearly define the operator precedence as intended

I am currently dealing with a regex issue in SonarQube that requires grouping to clarify operator precedence. Despite grouping the regex, it is not functioning as anticipated.

SonarQube Concern: SonarQube indicates that the regex should have grouped components to ensure clear operator precedence.

Existing Regex: /^(\W)|([^a-zA-Z0-9_.]+)|(\W)$/g This regex is designed to validate a string based on specific criteria:

Criteria:

  • If the string begins or ends with dots, an error should be triggered immediately.
  • If the string contains any symbols other than A-Z, a-z, 0-9, underscore, or dot (with dots only permitted in between), an error should be raised.
  • The string should consist solely of A-Z, a-z, 0-9, underscore, or dots (dots cannot start or end but can be present in between).

Note: The current logic is set up to generate an error if the regex matches. Hence, I require a regex that contradicts the mentioned conditions without altering the existing logic, which is integral to a reusable codebase.

I tried using the regex /^(.)|([^a-zA-Z0-9_.]+)|(.*.$)/g, but I am apprehensive about potential SonarQube issues due to operator precedence.

How can I properly format this regex to fulfill these requirements and prevent SonarQube alerts?

Answer №1

Your existing regex pattern is accurate: it will detect a match when the input does not meet the specified requirements.

The SonarQube alert you mentioned is likely related to RSPEC-5850: Group Alternatives in Regular Expressions with Anchors

This rule addresses a common error that occurs when utilizing ^ or $ alongside |. However, your implementation does not exhibit this mistake. To clarify that the ^ should only apply to the first option and the $ should only apply to the last option, it is recommended to enclose them within groups. Your current pattern lacks these groupings.

It's unnecessary to place the middle alternative inside a group since it doesn't involve the use of ^ or $ assertions.

Furthermore, the emphasis is on creating non-capture groups rather than capture groups. Therefore, utilize (?: ) instead of ( ), ensuring to include ^ and $ within them.

Although unrelated, your regex doesn't require the + quantifier as finding just one invalid character suffices. Consider using \w to simplify the character class.

Implementing these adjustments yields:

/(?:^\W)|[^\w.]|(?:\W$)/g

Answer №2

Regular Expression:

/^\.?([^\p{L}_.\r\n]+)\.$|^\.([^\p{L}_.\r\n]+)\.?$/gmu

Breakdown:

  1. Starting and ending anchors ^ and $:

    • ^ at the beginning indicates the pattern starts from the start of the string.
    • $ at the end ensures the pattern matches until the end of the string.
  2. Optional initial dot (^\.?):

    • \.? matches an optional dot at the start, allowing strings to begin with a dot but not requiring it.
  3. Character class in the middle ([^\p{L}_.\r\n]+):

    • ([^\p{L}_.\r\n]+) captures one or more characters not present in the specified set:
      • ^\p{L} excludes non-alphabetic characters, similar to a-zA-Z but also excluding accented characters like é or ä.
      • _ Excludes underscores.
      • . Excludes dots.
      • \r\n Optional (depends on parsing multi-line or single-line strings): excludes newline and carriage return for line break prevention.
  4. Mandatory final dot (\.$):

    • \.$ ensures the string ends with a dot.
  5. Alternation using Pipe |:

    • The regex employs | for alternation, allowing two valid patterns:
      • ^\.?([^\p{L}_.\r\n]+)\.$ Matches strings optionally starting with a dot, having valid characters (excluding dots, underscores, letters), and ending with a dot.
      • ^\.([^\p{L}_.\r\n]+)\.?$ Matches strings beginning with a dot, containing valid characters, and optionally ending with a dot.
  6. Options /gmu:

    • g: Global match for all occurrences, not just the first.
    • m: Allows multi-line matching when input text contains multiple lines.
    • u: Enables unicode support to use \p{L}.

Reasoning Behind Not Capturing 3 Groups as in Your Example:

Opting to capture 3 groups (start, middle, and end dots) is discouraged because the number of capturing groups varies (could be 2 or 3). This variability complicates handling captured groups in subsequent code.

An Alternate Approach to Capture 3 Groups:

/^(\.)?([^\p{L}_.\r\n]+)(\.)$|^(\.)([^\p{L}_.\r\n]+)(\.?)$/gmu

Suggestion:

If only the complete match is required, consider removing the capture groups:

/^\.?[^\p{L}_.\r\n]+\.$|^\.[^\p{L}_.\r\n]+\.?$/gmu

Validation Examples:

Invalid Cases:

a!@#.
.!@_.
abc.def
!!@!
.é*"+.

Valid Instances:

.!@#$.
.!@#$
.@@.
.!#$.

Test Scenarios:

Explore Test Cases

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