Refactor Pattern.compile calls to static final fields

[Copilot]

Pattern.compile() was called inside methods and constructors throughout the codebase, recompiling identical regex patterns on every invocation. These should be compiled once as private static final Pattern fields.

Changes

• Extracted to static fields (previously compiled in methods/constructors):

  • IacrEprint → IACR_EPRINT_PATTERN
  • ArXivIdentifier → OLD_IDENTIFIER_PATTERN
  • FollowUpQuestionGenerator → NUMBERED_PATTERN
  • StringUtil → SPLIT_TEXT_PATTERN
  • CSLFormatUtils → BIBLIOGRAPHY_NUMBER_PATTERN
  • CSLReferenceMarkManager → CITATION_NUMBER_PATTERN
  • CSLCitationOOAdapter → CITATION_NUMBER_PATTERN
  • ExtractReferencesAction → COMMENT_NUMBER_PATTERN
  • PreviewTabViewModel → XML_TAG_PATTERN, XML_ATTRIBUTES_PATTERN
  • MarkdownDefinitionProvider → CITATION_COMMAND_PATTERN, CITATION_KEY_INSIDE_PATTERN
  • ImporterTest → WHITESPACE_PATTERN

• Promoted instance fields to static (were private final, now private static final):

  • CoinsParser — 9 pattern fields (DOI, TITLE, JOURNAL, etc.)
  • MSBibEntry — ADDRESS_PATTERN

• Extracted constructor-time compilations to static predicates (PagesChecker):

  // Before: compiled on every PagesChecker instantiation
  isValidPageNumber = Pattern.compile(PAGES_EXP_BIBLATEX).asPredicate();
  
  // After: compiled once
  private static final Predicate<String> IS_VALID_PAGE_NUMBER_BIBLATEX =
      Pattern.compile(PAGES_EXP_BIBLATEX).asPredicate();

• Added Checkstyle rule (PatternCompileToStaticField) in config/checkstyle/checkstyle.xml to detect future violations. The rule flags any Pattern.compile() call where the argument is a self-contained string literal but the declaration is not static. Dynamic patterns (where the argument is a variable, concatenation with a variable, or a method call like .formatted()) are intentionally excluded.

Dynamic patterns that are built from method parameters (e.g., RegexKeywordGroup, BibTeXConverter, RegExpBasedFileFinder) are intentionally left unchanged, as they cannot be made static.

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[InAnYan]

Okay nice. Two things:

1. Can you check for other patterns in the code and double check that you moved all of them?
2. Is it possible to make an open rewrite rule or check style rule to keep track when a pattern compiled in a non static code but could be compiled in static? Or something to analyze the code and signal an error?
3. There might be cases where a pattern is constructed dynamically using some value of a variable - which is NOT a mistake. This shouldn’t be triggered as error, idk how to write this in open rewrite. Maybe open rewrite rule will target only of the argument of pattern compile is a string

[Copilot]

Okay nice. Two things:

1. Can you check for other patterns in the code and double check that you moved all of them?...

Done in commit c19bdbb. Here's a summary of the three points:

1. Scan for remaining violations — Scanned the full codebase. One true remaining violation was found: ImporterTest.java:57 used Pattern.compile("\\s") inside a parameterized test method. Fixed by extracting it to private static final WHITESPACE_PATTERN. The remaining non-static Pattern.compile calls are all legitimately dynamic (argument uses a variable or string concatenation with a variable), so they can't be made static.

2. Checkstyle rule added — Added PatternCompileToStaticField to config/checkstyle/checkstyle.xml. It flags any line containing Pattern.compile( where the first argument is a self-contained string literal (not a variable).

3. Dynamic patterns are excluded — The rule uses the regex Pattern\.compile\s*\(\s*"(?:[^"\\]|\\.)*"\s*[,)] which only matches when the argument is a complete string literal (closed ") immediately followed by , or ). This means Pattern.compile("prefix" + variable), Pattern.compile(variable), and Pattern.compile("str".formatted(x)) are all safely excluded. Verified against the full codebase — zero false positives.

[InAnYan]

TODO: Run the check without refactor and see what would be shown