Gradle Incremental Builds
External
- https://docs.gradle.org/current/userguide/more_about_tasks.html#sec:up_to_date_checks
- https://docs.gradle.org/current/userguide/custom_tasks.html#incremental_tasks
- https://docs.gradle.org/current/userguide/build_cache.html
Internal
Overview
An incremental build is a build that does not execute one or more tasks if it does not need to. Gradle determines whether it needs to execute a task or not by analyzing its inputs and outputs.
Incremental Build
Task Inputs and Outputs
Gradle determines whether a task is up to date if the task's inputs and outputs have not changed since the last execution, by comparing their values with those preserved in the build cache. Does the build cache need to be enabled for inputs and outputs to be relevant?
If the input and output snapshots are identical to the previous ones, the task is not executed. An input can be a property, a directory or one or more files. An output is a directory or one or more files. Inputs and outputs are fields of the DefaultTask class. Task inputs and outputs are obtained with Task.getInputs() and Task.getOutputs(), which return TaskInputs and TaskOutputs instances, respectively.
Task inputs and outputs are evaluated during the configuration phase to wire up the task dependencies. That is why they need to be defined in a configuration block. To avoid unexpected behavior, make sure that the value you assign to inputs and outputs is accessible at configuration time. If you need to implement programmatic output evaluation, the method upToDateWhen(Closure) on TaskOutputs comes in handy. In contrast to regular inputs/outputs evaluation, this method is evaluated at execution time. If the closure returns true, the task is considered up to date.
Debug a Java compilation task to see how input/output works.
Annotations
@Input
⚠️ Note that in Java, the annotation must be attached to the getter method. Annotations on setters or just the field in Java are ignored.