SONARJAVA-6196 S1451 should provide a default template for headers

[NoemieBenard]

Add default template for headerFormat in S1451.

[hashicorp-vault-sonar-prod]

SONARJAVA-6196

[sonar-review-alpha]

Summary

This PR adds a meaningful default template for the headerFormat property in rule S1451 (file header check). Previously, the default was an empty string, which meant users had to manually configure the header format from scratch. The new default provides a complete copyright header template with placeholders (<Your-Product-Name>, <Year-From>, <Year-To>, <Your-Company-Name>) and guidance, allowing users to customize it in their SonarCloud/SonarQube quality profile rather than starting from nothing.

What reviewers should know

Review focus: This is a straightforward constant update to the rule's default behavior. The change affects how the rule behaves when enabled without explicit configuration.

Key points:

• The template is a standard Java multi-line copyright comment block with helpful placeholders
• This improves the out-of-the-box experience for users enabling S1451 — they'll see a concrete example to work from
• The rule logic at line 67-69 checks if (headerFormat.isEmpty()) and short-circuits if true. With this change, the rule now runs with the template by default instead of being a no-op
• The template includes a message ("Please configure this header...") to guide users toward customization

Testing to verify: Confirm that rules using this default now flag files that don't match the template pattern (regression test), and that customized headers still work as expected.

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[sonar-review-alpha]

One real test coverage gap needs fixing before merge — the rest of the implementation is correct.

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[sonar-review-alpha]

The test verifies that Class6.java (which contains the default header) is compliant — but there is no negative test asserting that a file without the default header gets flagged.

This gap matters concretely: if DEFAULT_HEADER_FORMAT ever became empty (e.g., due to a text-block indentation accident), the headerFormat.isEmpty() branch would fire, set expectedLines = {}, and matches() would return true for any file. The verifyNoIssues() call would still pass, giving a false sense of correctness.

Add a complementary case that runs the default FileHeaderCheck() against a file that lacks the header and asserts an issue is raised — something like:

check = new FileHeaderCheck();
CheckVerifier.newVerifier()
  .onFile(mainCodeSourcesPath("checks/FileHeaderCheck/Class1.java"))
  .withCheck(check)
  .verifyIssueOnFile("Add or update the header of this file.");

• Mark as noise

[tomasz-tylenda-sonarsource]

Let's use desciprive file names for test samples.

[tomasz-tylenda-sonarsource]

IMO it's a bad practice to do unintentional chages, because they make it hard to understand what is happening, if someone is reading a PR for some reason in the future.

[tomasz-tylenda-sonarsource]

Are these a part of this PR or is it a copied from the other changes?

[tomasz-tylenda-sonarsource]

Let's remove expectedLines.

[tomasz-tylenda-sonarsource]

Let's remove this method.

[tomasz-tylenda-sonarsource]

This should be extracted to checkExpectedLines

[sonarqube-next]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
0 Dependency risks
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarQube

[sonar-review-alpha]

LGTM! ✅

The text block is correct — the 4 spaces of incidental whitespace strip cleanly to produce the expected header, matching ClassDefaultHeader.java exactly. The @RuleProperty(defaultValue = DEFAULT_HEADER_FORMAT) annotation compiles fine since text blocks are compile-time constants. The previously flagged missing negative test has not been addressed.

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[tomasz-tylenda-sonarsource]

LGTM. I think we should take a look at the experience in local SQ to see how changing this rule will affect the users.