*
 * If no producer variant is compatible with the requested attributes, this selector will attempt to construct a chain of artifact
 * transforms that can produce a variant compatible with the requested attributes.
 *
 * An instance of {@link ResolutionFailureHandler} is injected in the constructor
 * to allow the caller to handle failures in a consistent manner as during graph variant selection.
 */

[[sec:cpp_unit_test_task_variants]]
=== Variant-dependent Tasks

The {cpp} Unit Test Plugin creates tasks based on the variants of the unit test component.
Read the <<building_cpp_projects.adoc#sec:introducing_build_variants-cpp,introduction to build variants>> for more information.
The following diagrams show the relationship between variant-dependent tasks.

.{cpp} Unit Test Plugin variant-dependent task graph

    }

    @Override
    MavenModule adhocVariants() {
        variants.clear()
        this
    }

    private VariantMetadataSpec createVariant(String variant, Map<String, String> attributes) {
        def variantMetadata = new VariantMetadataSpec(variant, attributes)
        variants.removeAll { it.name == variant }
        variants.add(variantMetadata)
        return variantMetadata
    }

    /**
     * Constructs a complete cacheable variant chain given a root transformed variant and the chain of variants
     * to apply to that root variant.
     *
     * @param stateChain The transform chain from the search state to apply to the root transformed variant.
     * @param root The root variant to apply the chain to.
     *
     * @return A variant chain representing the final transformed variant.
     */

        def childPublication = publication(childComponent, child1)

        def variant = Stub(UsageContext)
        variant.name >> "v1"
        variant.attributes >> attributes(usage: "compile")

        rootComponent.variants >> [childComponent]
        rootComponent.usages >> []
        childComponent.usages >> [variant]

        when:
        writeTo(writer, childPublication, [rootPublication, childPublication])

        failure.assertHasCause("""Multiple incompatible variants of org:test:1.0 were selected:
   - Variant api1 has attributes {custom=c1, org.gradle.status=${MultipleVariantSelectionIntegrationTest.defaultStatus()}}
   - Variant runtime2 has attributes {custom=c2, org.gradle.status=${MultipleVariantSelectionIntegrationTest.defaultStatus()}}""")
    }

The following statements must hold for the variants:

- Variant name must be unique per module
- Each variant must have at least one attribute
- Two variants cannot have the same attributes and capabilities
- If there is at least one dependency in any variant, at least one must carry version information

### `attributes` value

[[sec:cpp_library_task_variants]]
=== Variant-dependent Tasks

The {cpp} Library Plugin creates tasks based on variants of the library component.
Read the <<building_cpp_projects.adoc#sec:introducing_build_variants-cpp,introduction to build variants>> for more information.
The following diagrams show the relationship between variant-dependent tasks.

.{cpp} Library Plugin variant-dependent task graph

- `buildId`: The buildId for the Gradle instance. A string

### `variants` value

This value must contain an array with zero or more elements. Each element must be an object with the following values:

- `name`: The name of the variant. A string. The name must be unique across all variants of the component.
- `attributes`: optional. When missing the variant is assumed to have no attributes.

        List<TestVariant> variants = new ArrayList<TestVariant>();
        variants.add(TestVariant.tapiCurrent(rootId, discoveryRequest));
        variants.add(TestVariant.selected(rootId, discoveryRequest));
        variants.add(TestVariant.tapiTargetLoaded(rootId, discoveryRequest));

        return variants;
    }