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.

    }

----
<1> *Register Output*: The `process` task writes its output to a log file.
<2> *Modify Output*: The task writes to its output file as it executes.
<3> *Task Failure*: The task throws a `VerificationException` and fails at this point.
<4> *Continue to Modify Output*: This line never runs due to the exception stopping the task.

      location, concat_dim_type, concat_dimension_attr);

  // Correctly set output shapes of concat op output if output shape is
  // statically known. Since the shape of TPUExecute op must be the same
  // across logical devices, we refer to the shape of 0th logical device
  // computation output.
  mlir::Type output_type;
  auto input_type = mlir::cast<mlir::TensorType>(inputs[0].getType());

[[sec:task_output_caching_details]]
== Cacheable tasks

Since a task describes all of its inputs and outputs, Gradle can compute a _build cache key_ that uniquely defines the task's outputs based on its inputs.
That build cache key is used to request previous outputs from a build cache or store new outputs in the build cache.