const std::vector<Output>& outputs,
                            const std::vector<Output>& inputs,
                            std::vector<Output>* grad_outputs) {
  std::vector<Output> grad_inputs;
  grad_inputs.reserve(outputs.size());
  for (const Output& output : outputs) {
    grad_inputs.emplace_back(ops::OnesLike(scope, output));
  }

For the aforementioned reasons, task output caching is automatically disabled for tasks whose output directories overlap with another task.

Build scans show tasks where caching was disabled due to overlapping outputs in the timeline:

[.screenshot]
image::build-cache/overlapping-outputs-timeline.png[]

== Reuse of outputs between different tasks

        output.contains "Task 'b' file 'output.txt' with 'output-file'"
        output.contains "Task 'b2' file 'output.txt' with 'output-file'"

        when:
        succeeds "b", "b2"

        then:
        result.assertTasksSkipped(':a')
        result.assertTasksNotSkipped(':b', ':b2')
        output.contains "Task 'b' file 'output.txt' with 'output-file'"

                void transform(TransformOutputs outputs) {
                    def input = inputArtifact.get().asFile
                    println "processing \${input.name} using \${parameters.someFiles*.name}"
                    def output = outputs.file(input.name + ".green")
                    def paramContent = parameters.someFiles.collect { it.file ? it.text : it.list().length }.join("")
                    output.text = input.text + paramContent + ".green"

public class OutputSnapshotUtil {

    /**
     * Finds outputs that are still present since the last execution when overlapping outputs are present.
     *
     * Note: when there are no overlapping outputs, all outputs currently existing in the output locations
     * are considered outputs of the work.
     *
     * If a property did not exist after the previous execution then all the outputs for it will be ignored.
     *

        withBuildCache().run "compileJava", "--info"

        then:
        noneSkipped()
        output.contains("Build cache key for task ':compileJava' is ")
        !output.contains("Appending implementation to build cache key:")
        !output.contains("Appending input value fingerprint for")
        !output.contains("Appending input file fingerprints for 'classpath'")
    }

For the very same reason using `outputs.upToDateWhen` is discouraged and should be replaced by properly declaring the task's inputs.

=== Overlapping outputs

You already saw that <<build_cache_concepts.adoc#concepts_overlapping_outputs,overlapping outputs are a problem for task output caching>>.
When you add new tasks to your build or re-configure built-in tasks make sure you do not create overlapping outputs for cacheable tasks.

    }

    }

    def "does not clean up stale outputs for untracked tasks"() {
        def untrackedStaleFile = file("build/untracked/stale-output-file").createFile()
        def untrackedOutputFile = file("build/untracked/output.txt")
        def trackedStaleFile = file("build/tracked/stale-output-file").createFile()
        def trackedOutputFile = file("build/tracked/output.txt")

        buildFile("""

        inputDir = project.mkdir('inputs')
        outputDir = project.mkdir('outputs')
        prop = 'foo'
    }
"""
        file('inputs/file0.txt') << "inputFile0"
        file('inputs/file1.txt') << "inputFile1"
        file('inputs/file2.txt') << "inputFile2"

        file('outputs/file1.txt') << "outputFile1"
        file('outputs/file2.txt') << "outputFile2"
    }