gradle/gradle · warning

Could not read annotation processor declarations from {}. Gr

Error message

Could not read annotation processor declarations from {}. Gradle will assume that this directory contains no annotation processors.

What it means

While scanning a classes directory for annotation processors, Gradle first reads META-INF/services/javax.annotation.processing.Processor (PROCESSOR_DECLARATION). If that read fails (getProcessorClassNames throws - I/O error, unreadable/corrupt declaration), Gradle assumes the directory contains NO annotation processors and returns an empty list. javac still discovers processors itself at execution time, but Gradle's incremental-processing bookkeeping for this directory is lost.

Source

Thrown at platforms/jvm/language-java/src/main/java/org/gradle/api/internal/tasks/compile/processing/AnnotationProcessorDetector.java:109

                return detectProcessorsInClassesDir(file);
            } else if (FileUtils.hasExtensionIgnoresCase(file.getName(), ".jar")) {
                return detectProcessorsInJar(file);
            }
            return Collections.emptyList();
        }

        private List<AnnotationProcessorDeclaration> detectProcessorsInClassesDir(File classesDir) {
            try {
                List<String> processorClassNames = getProcessorClassNames(classesDir);
                try {
                    Map<String, IncrementalAnnotationProcessorType> processorTypes = getProcessorTypes(classesDir);
                    return toProcessorDeclarations(processorClassNames, processorTypes);
                } catch (Exception e) {
                    logger.warn("Could not read annotation processor declarations from " + classesDir + ". Gradle will assume that all processors in this directory are non-incremental.", logStackTraces ? e : null);
                    return toProcessorDeclarations(processorClassNames, Collections.emptyMap());
                }
            } catch (Exception e) {
                logger.warn("Could not read annotation processor declarations from " + classesDir + ". Gradle will assume that this directory contains no annotation processors.", logStackTraces ? e : null);
                return Collections.emptyList();
            }
        }

        private List<String> getProcessorClassNames(File classesDir) throws IOException {
            File processorDeclaration = new File(classesDir, PROCESSOR_DECLARATION);
            if (!processorDeclaration.isFile()) {
                return Collections.emptyList();
            }
            return readLines(processorDeclaration);
        }

        private Map<String, IncrementalAnnotationProcessorType> getProcessorTypes(File classesDir) throws IOException {
            File incrementalProcessorDeclaration = new File(classesDir, INCREMENTAL_PROCESSOR_DECLARATION);
            if (!incrementalProcessorDeclaration.isFile()) {
                return Collections.emptyMap();
            }
            List<String> lines = readLines(incrementalProcessorDeclaration);

View on GitHub (pinned to 534f27719b)

Solutions

1. Run with --stacktrace to see the underlying exception and identify the failing file
2. Clean and rebuild the project that produces the classes directory
3. Check filesystem permissions and antivirus exclusions on the build output directory
4. If the dir comes from another build tool, package the processor as a jar instead of shipping an exploded dir

Example fix

# before: unreadable declaration file -> directory assumed processor-free
ls libs/processor-classes/META-INF/services/javax.annotation.processing.Processor
# file exists but is locked/corrupt

# after: rebuild restores a readable declaration
./gradlew :processor:clean :processor:compileJava

// guard: every processor classes dir must expose a readable, non-empty declaration
def dir = file('libs/processor-classes')
def decl = new File(dir, 'META-INF/services/javax.annotation.processing.Processor')
assert decl.isFile() && decl.canRead() : "unreadable processor declaration in ${dir}"
assert decl.readLines().any { it.trim() && !it.startsWith('#') } : "empty processor declaration in ${dir}"

When it happens

Trigger: The outer catch fires because reading the processor declaration from the classes dir throws: permission problems, concurrent truncation of the directory while Gradle scans it, or a malformed/encoding-broken declaration file.

Common situations: Classes dirs mutated by a concurrent build or file sync (Docker/rsync) during scanning; antivirus or permissions blocking reads on Windows; corrupted build outputs after a killed daemon or interrupted build.

Related errors

• Could not read annotation processor declarations from {}. Gr
• Could not read annotation processor declarations from {}. Gr
• Annotation processor '{}' not found
• Could not instantiate annotation processor '{}'
• Cannot specify -processorpath or --processor-path via `Compi

AI-assisted analysis of gradle/gradle@534f27719b (2026-08-22). Data as JSON: /api/errors/fdbbce03f8083c68. Report an issue: GitHub.