New checks:

• AlmostExhaustiveTestParameter: Prefer an exhaustive @TestParameter with an assumption to filter out specific enum values, so newly added enum values are automatically tested (disabled by default).
• SingleTestParameter: Suggest @TestParameter on the parameter instead of @TestParameters when there is only one test parameter, replacing PreferTestParameter (disabled by default).
• SingleValueTestParameter: Suggest replacing a @TestParameter that has only a single value with a local variable in the test method (disabled by default).
• ValueClassEquals: Require non-record concrete value classes to explicitly override equals and hashCode.

Other changes:

• LoopToTestParameter: Changed severity to SUGGESTION (disabled by default).
• DistinctVarargsChecker: Allow duplicate arguments to Iterables.concat (#6239) and Mockito argument matchers such as any() (#6240).
• UnusedVariable: Treat fields accessed via MethodHandles.Lookup (VarHandle/getter/setter lookups) or Atomic*FieldUpdater.newUpdater as used.
• StringBuilderInitWithChar / StringBuffer refactoring: Refactor StringBuffer to StringBuilder even when used with Matcher.appendReplacement and appendTail (when supported by the target JDK or Android minSdkVersion).
• CompileTimeConstant: Treat record and interface fields and field accesses on compile-time constants (compileTimeConstant.compileTimeConstantField) as compile-time constants.
• ValueClassIdentity / ReferenceEquality: Handle JEP 401 value classes.
• FieldCanBeFinal / ThreadSafety: Improve compile-time performance on large classes and deep type hierarchies, and update SafeRE to 1.1.0 (#6230).
• Added ClassName for caching resolved ClassSymbol, Type, and binary Name lookups across a compilation.

Closed issues: #5964, #6165, #6230, #6239, #6240, #6275

Full changelog: v2.51.0...v2.52.0

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

Full changelog: v2.50.0...v2.51.0

New checks:

• BoxingComparator: Detect implicitly-boxing Comparator.comparing key extractors
• ExposedPrivateType: Discourage references to private member classes from non-private APIs
• JUnitMethodInvoked: Discourage directly invoking JUnit test methods
• ListRemoveAmbiguous: Detect ambiguous calls to List.remove(int|Integer)
• PreferTestParameter: suggests using @TestParameter instead of @TestParameters for exhaustive boolean and enum parameters on single-element parameterized tests
• RecordComponentAccessorAnnotationConflict: Detect conflicts between record components and explicit accessor methods
• RecordComponentOverride: Discourage @Override on record component declarations that don't override
  anything
• ThrowableEqualsHashCode: Discourage overriding Throwable.equals() and hashCode()

Closed issues: #5553, #5649, #5778

Full changelog: v2.49.0...v2.50.0

This release includes several changes to Matcher APIs, and removed some deprecated or problematic APIs:

• Remove deprecated MethodMatchers.withSignature API, which relies on fragile toString behaviour. Alternatives for matching on method signatures with varargs and type parameters were added in a98a1c5.
• Removed variableType(Matcher) API. Matchers.variableType(Matcher) uses VariableTree#getType to match variable types, which own't work for lambda parameters with inferred types after JDK-8268850. The recommended replacement is variableType(TypePredicate).
• Make enclosingPackage return an optional. Module elements are not enclosed by a package, checks using enclosingPackage shouldn't assume an enclosing package exists when processing arbitrary elements.
• New FieldMatchers API, similar to MethodMatchers (1dd9c3a).

New checks:

• AssertThrowsBlockToExpression: Discourage unnecessary block lambdas in assertThrows.
• AssertThrowsMinimizer: Suggest minimizing the amount of logic in assertThrows.
• MemorySegmentReferenceEquality: Discourage using reference equality for MemorySegments.
• PreferThrowsTag: Recommends using @throws instead of the legacy @exception javadoc tag.
• RecordAccessorInCompactConstructor: detect record accessors inside the compact canonical ctors, which read uninitialized fields.

Closed issues: #2283, #3503, #5210, #5289, #5548, #5548, #5554, #5609, #5614, #5656

Full changelog: v2.48.0...v2.49.0

Changes:

• Added support for passing flags with command-line argument files (@-files) (8e84edf)

New checks:

• AvoidValueSetter
• UnnecessarySemicolon

Closed issues: #5529, #5537, #5522, #5521

Full changelog: v2.47.0...v2.48.0

New checks:

• InterruptedInCatchBlock: Detect accidental calls to Thread.interrupted() inside of catch(InterruptedException e) blocks.
• RefactorSwitch: Refactorings to simplify arrow switches
• UnnamedVariable: Rename unused variables to _

Closed issues: #1811, #4168, #5459, #5460

Full changelog: v2.46.0...v2.47.0

Changes:

• The javac flag -XDaddTypeAnnotationsToSymbol=true is now required for Error Prone invocations on JDK 21, to enable the javac fix for JDK-8225377: type annotations are not visible to javac plugins across compilation boundaries. See #5426 for details.
• Remove deprecated value attribute from @IncompatibleModifiers and @RequiredModifiers (#2122)
• Error Prone API changes to encapsulate references to internal javac APIs for end position handling (EndPosTable, DiagnosticPosition) (5440bb4, 06c2905, f3915ec)

New checks:

• DuplicateAssertion: detect duplicated assertion lines where the argument to assertThat is pure
• IfChainToSwitch: suggest converting chains of if-statements into arrow switches
• ScannerUseDelimiter: discourage Scanner.useDelimiter("\\A")
• AddNullMarkedToClass: refactoring to add @NullMarked annotation to top level classes

Full changelog: v2.45.0...v2.46.0

Changes:

• Improved compatibility with latest JDK 26 EA builds.

New checks:

• AssertSameIncompatible: Detect calls to assertSame and similar assertions, where the calls are guaranteed to either succeed or fail.
• FormatStringShouldUsePlaceholders: Suggests using a format string instead of string concatenation operations on format methods

Closed issues: #5335

Full changelog: v2.44.0...v2.45.0

Changes

• The default severity for LabelledBreakTarget is now an error
• Update dependency on Guava (#5108)

Closed issues: #5218, #5278

Full changelog: v2.43.0...v2.44.0

The minimum supported JDK version to run Error Prone is now JDK 21 (#4867).

Changes:

• -XepPatchChecks now skips disabled checks (#4943)
• AndroidJdkLibsChecker has been removed, the recommended replacement for Android code is Android Lint's NewApi check

New checks:

• NullNeedsCastForVarargs: Detect calls that incorrectly passes a null array instead of a null element.
• RedundantNullCheck: detect checks on expressions that are non-null.

Closed issues: #4943, #5102, #5107, #5121, #5158, #5217, #5239

Full changelog: v2.42.0...v2.43.0