Error Prone 2.51.0

New checks:

• HashCodeInObjectsHash: Detect redundant hashCode() or Objects.hash() calls inside Objects.hash(...), and simplify single-argument Objects.hash(x) calls to Objects.hashCode(x).
• LoopToTestParameter: Suggest migrating loops in unit tests to TestParameterInjector.
• MissingJavadoc: Flag public types that are missing Javadoc comments (disabled by default).
• PreferCharsetOverload: Prefer calling method and constructor overloads that accept a Charset over those that accept a String encoding name.
• PreferPreconditions: Suggest using Guava's Preconditions instead of explicit if-throw statements for parameter validation (disabled by default).
• RequireNonNullRefactoring: Refactor explicit if (x == null) { throw new NullPointerException(...); } checks to Objects.requireNonNull (disabled by default).
• SimplifyTestParameter: Remove redundant explicit value lists on @TestParameter annotations for boolean and Enum types when all values are specified (disabled by default).
• TraditionalJavadocToMarkdown: Convert traditional /** ... */ Javadoc comments into /// Markdown Javadoc comments (disabled by default).
• ValueClassIdentity: Flag reliance on identity semantics (such as synchronization, WeakReference, IdentityHashMap, or System.identityHashCode) of value-based classes (disabled by default).

Other changes:

• CompareToZero: Upgraded from warning to error, and expanded to flag non-relational operations, unary negation, and switch statements/expressions on compareTo and compare results without Integer.signum.
• IfChainToSwitch: Enabled by default as a warning.
• UndefinedEquals: Merged ArrayAsKeyOfSetOrMap and CollectionUndefinedEquality into UndefinedEquals (retaining their names as altNames), and generalized detection of types without well-defined equals or hashCode across direct equality, collection containment, and hash-based containers.
• EqualsIncompatibleType / TruthIncompatibleType: Flag equality comparisons between distinct record types (#6107).
• ReferenceEquality: Allow == comparisons on private classes whose type hierarchy does not override Object.equals (#5865), private static final sentinel fields, Thread (#5900), and com.sun.source.tree.Tree.
• PatternMatchingInstanceof: Support while and for loops, parenthesized expressions (#5843), and replacing additional redundant casts when the instanceof already introduces a pattern variable.
• DistinctVarargsChecker: Expanded to check Objects.hash, CompletableFuture.allOf/anyOf, EnumSet.of, Sets.union/intersection/difference, Stream.concat, Math.min/max, and additional JDK, Guava, Protobuf, Truth, and Mockito methods.
• MustBeClosedChecker: Require java.lang.foreign.Arena.ofConfined and Arena.ofShared to be closed.
• ImpossibleNullComparison: Flag null checks on the return value of Class.forName.
• RestrictedApi / RestrictedInheritance: Added an allowedPaths attribute to allow calls or inheritance from matching file paths without a regular expression.
• InlineMeInliner: Support substituting type arguments at call sites when inlining generic @InlineMe methods.
• WellKnownKeep: Recognize Apache Beam DoFn annotations and retain open-source library annotations (Gson, Mockito, Guice, Objectify, TestParameterInjector, AutoFactory).
• Per-check timing collection is now disabled by default, reducing Error Prone compile-time overhead by ~3–5%; pass -XepPrintTimings to print a timing report after compilation or -XepRecordTimings to record timings programmatically (#6079).
• CompilationTestHelper now reports all lines with mismatched diagnostic expectations in a single test run rather than failing on the first mismatch (#6116).
• Replaced the RE2/J dependency with SafeRE.

Closed issues: #4914, #5182, #5843, #5857, #5865, #5878, #5900, #6029, #6079, #6107, #6116, #6133