Remove duplicate violations in WhitespaceAfter and WhitespaceAround in sun_checks.xml

[vivek-0509]

Following the discussion at #17265 (comment)

I have read check documentation: https://checkstyle.org/checks/whitespace/whitespaceafter.html
I have read check documentation: https://checkstyle.org/checks/whitespace/whitespacearound.html
I have downloaded the latest cli from: https://checkstyle.org/cmdline.html#Download_and_Run
I have executed the cli and showed it below, as cli describes the problem better than 1,000 words

How it works Now:

 cat > /tmp/DuplicateError.java << 'EOF'
/** some data. */
class DuplicateError {
  /** method. */
  void test(Object o) {
    switch (o) {
      case String s when (
          s.equals("a"))->{
      }
      default -> {}
    }
  }
}
EOF

java -jar target/checkstyle-*-all.jar -c src/main/resources/sun_checks.xml /tmp/DuplicateError.java

Starting audit...
[ERROR] /tmp/DuplicateError.java:7:25: '->' is not followed by whitespace. [WhitespaceAfter]
[ERROR] /tmp/DuplicateError.java:7:25: '->' is not followed by whitespace. [WhitespaceAround]
[ERROR] /tmp/DuplicateError.java:7:25: '->' is not preceded with whitespace. [WhitespaceAround]
Audit done.

The first and second violations are duplicates (same message from different checks).

Is your feature request related to a problem? Please describe.

sun_checks.xml uses default tokens for both WhitespaceAfter and WhitespaceAround checks. These default tokens overlap, causing duplicate violations for the same issue at the same code location.

In the example above, line 7 column 25 shows:

'->' is not followed by whitespace. [WhitespaceAfter]
'->' is not followed by whitespace. [WhitespaceAround]

This is the same violation reported twice by two different checks.

Describe the solution you'd like

Add explicit tokens to WhitespaceAfter in sun_checks.xml to remove overlapping tokens that are already covered by WhitespaceAround.

# Expected output (no duplicate):
[ERROR] DuplicateError.java:7:25: '->' is not followed by whitespace. [WhitespaceAround]
[ERROR] DuplicateError.java:7:25: '->' is not preceded with whitespace. [WhitespaceAround]

[vivek-0509]

i am on it after approval

[Atharv3221]

@vivek-0509 I feel both checks are doing there work well
if any one wants they can configure them as per their requirements
https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/sun_checks.xml#L25C1-L30C50

[Brijeshthummar02]

@vivek-0509 I feel both checks are doing there work well if any one wants they can configure them as per their requirements https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/sun_checks.xml#L25C1-L30C50

Agree to this

[vivek-0509]

@Atharv3221
The issue here is about user experience with the default configuration.

When a user runs sun_checks.xml out of the box, they see this:

[ERROR] DuplicateError.java:7:25: '->' is not followed by whitespace. [WhitespaceAfter]
[ERROR] DuplicateError.java:7:25: '->' is not followed by whitespace. [WhitespaceAround]

This is the exact same message at the same location reported by two different checks. While technically correct, this is confusing and unhelpful for users who expect the standard configuration to be well-tuned.

The purpose of sun_checks.xml is to provide a sensible default configuration. Users shouldn't need to customize it just to avoid seeing duplicate violations. This change simply removes the redundancy from the default, making the output cleaner and more actionable.