Support Java 22-26 language features

[asm0dey]

Before this PR

palantir-java-format supports Java language features through Java 21. Source code using features finalized in Java 22–26 does not format correctly — several cases crash the formatter outright:

• import module java.base; (module import declarations) throws expected token: 'module'.
• Compact source files / instance main methods crash (the implicit top-level class emits a non-existent class token).
• Unnamed patterns in deconstruction, e.g. case Box(_, _), crash on the AnyPatternTree node.

After this PR

The formatter handles Java language features finalized through Java 26:

• Module import declarations import module M; — JEP 511 (kept as a leading, blank-line-separated import group; never stripped as "unused").
• Compact source files and instance main methods — JEP 512.
• Unnamed patterns in deconstruction, e.g. case Box(_, _) — JEP 456 (fixes the crash above).
• Markdown documentation comments /// — JEP 467 (preserved verbatim, including fenced code blocks and {@snippet} content).
• Flexible constructor bodies — JEP 513.

Dispatch selects Java25InputAstVisitor / Java26InputAstVisitor by runtime major version, with a graceful fallback to the existing Java21InputAstVisitor, so consumers on older JDKs are unaffected. Every javac API newer than Java 17 is reached via reflection / flag-bit detection, so the library still compiles at libraryTarget = 17. Formatter tests run on a JDK 21/22/23/25/26 matrix so each visitor-dispatch tier and each feature's GA boundary is exercised natively; all other modules stay on JDK 21.

Fixes

• Fixes Support for module import #1506 — module import declarations (the JCModuleImport is not an instance of JCImport crash and Expected ; after import).
• Fixes palantir-java-format cannot parse JEP 512 compact source files / instance main on JDK 25 (expected token: 'void') #1701 — compact source files / instance main (expected token: 'void') on JDK 25.
• Fixes Support for Java 21+ features -- unnamed variable #1614 — unnamed patterns in deconstruction, e.g. case Insufficient(_, var source, var reason) (expected token: '_').

==COMMIT_MSG==
Support Java 22–26 language features: module import declarations (JEP 511), compact source files and instance main methods (JEP 512), unnamed patterns in deconstruction (JEP 456), markdown documentation comments (JEP 467), and flexible constructor bodies (JEP 513). Visitors are selected by runtime major version with graceful fallback to Java 21, and post-17 javac APIs are accessed reflectively so the library still targets Java 17. Formatter tests run on a JDK 21/22/23/25/26 matrix.
==COMMIT_MSG==

Possible downsides?

• Formatting Java 25/26-specific syntax requires running the formatter on a matching JDK — an inherent constraint of parsing with javac internals. Earlier syntax, and consumers on JDK 17+, are unaffected.
• ./gradlew build now provisions JDK 22/23/25/26 toolchains for the test matrix, which increases first-run CI provisioning cost.

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Disclosure: this change was prepared with AI assistance (Claude Code). It has been reviewed, and the full test suite passes across the JDK 21/22/23/25/26 matrix.

[palantirtech]

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Description

Support Java 22–26 language features: module import declarations (JEP 511), compact source files and instance main methods (JEP 512), unnamed patterns in deconstruction (JEP 456), markdown documentation comments (JEP 467), and flexible constructor bodies (JEP 513). Visitors are selected by runtime major version with graceful fallback to Java 21, and post-17 javac APIs are accessed reflectively so the library still targets Java 17. Formatter tests run on a JDK 21/22/23/25/26 matrix.

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[abashev]

+1