gradle/gradle · error · IllegalStateException

Unexpected convention-supporting type %s used in property %s

Error message

Unexpected convention-supporting type %s used in property %s.%s

What it means

Gradle throws this error when the following condition is violated: Unexpected convention-supporting type <value> used in property <value>.<value>

Source

Thrown at platforms/core-configuration/model-core/src/main/java/org/gradle/internal/extensibility/ConventionAwareHelper.java:94

        String renamedProperty = ProviderApiMigrationConventionHelper.findRenamedProperty(sourceType, propertyName);
        if (renamedProperty != null) {
            propertyName = renamedProperty;
        }

        if (_ineligiblePropertyNames.contains(propertyName)) {
            Method getter = JavaPropertyReflectionUtil.findGetterMethod(sourceType, propertyName);
            // When there's a convention-supporting object, use its `.convention()` method instead
            // This is something we added to support properties migrated in the future from
            // Java bean to Property where old code uses ConventionMapping to set conventions.
            if (getter != null && SupportsConvention.class.isAssignableFrom(getter.getReturnType())) {
                SupportsConvention target;
                try {
                    target = Cast.uncheckedNonnullCast(getter.invoke(_source));
                } catch (IllegalAccessException | InvocationTargetException e) {
                    throw new IllegalStateException(String.format("Could not access property %s.%s", sourceType.getSimpleName(), propertyName), e);
                }
                if (!mapConventionOn(target, mapping)) {
                    throw new IllegalStateException(String.format(
                        "Unexpected convention-supporting type %s used in property %s.%s", getter.getReturnType().getName(), sourceType.getSimpleName(), propertyName));
                }
            } else {
                throw DocumentedFailure.builder()
                    .withSummary("Using internal convention mapping with a Provider backed property.")
                    .withUpgradeGuideSection(7, "convention_mapping")
                    .build();
            }
        } else {
            _mappings.put(propertyName, mapping);
        }
        return mapping;
    }

    private boolean mapConventionOn(SupportsConvention target, MappedPropertyImpl mapping) {
        if (target instanceof FileSystemLocationProperty) {
            FileSystemLocationPropertyInternal<?> asFileSystemLocationProperty = Cast.uncheckedNonnullCast(target);
            asFileSystemLocationProperty.conventionFromAnyFile(new DefaultProvider<>(() -> mapping.getValue()));

View on GitHub (pinned to 534f27719b)

Solutions

1. Review the values passed to this API and correct the invalid input described in the error message.

When it happens

Trigger: Thrown at platforms/core-configuration/model-core/src/main/java/org/gradle/internal/extensibility/ConventionAwareHelper.java:94 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of gradle/gradle@534f27719b (2026-08-22). Data as JSON: /api/errors/0cbdd94c61334ac8. Report an issue: GitHub.