Gradle Sync task is not incremental

While this may seem obvious to some it came as a surprise to learn that Gradle’s Sync task will copy the entire source even if only one file has changed.

For example, with this task in our build.gradle

task syncToTarget(type: Sync) {
  from "sourceDir"
  into new File("targetSync/destDir")
  eachFile { details ->
    println "Syncing file: ${details.name}"
  }
}

and the following project layout

.
├── build.gradle
├── sourceDir
│   ├── file1.txt
│   ├── file2.txt
│   └── file3.txt
└── targetSync

running the first Sync task produces the following output

:syncToTarget
Syncing file: file1.txt
Syncing file: file2.txt
Syncing file: file3.txt

BUILD SUCCESSFUL

Total time: 2.531 secs

and then the next sync with no changes works as expected

:syncToTarget UP-TO-DATE

BUILD SUCCESSFUL

Total time: 2.119 secs

If we then add a single file to the source directory

$ echo $RANDOM > sourceDir/file4.txt

And re-run the Sync task we’ll see that all files are copied again

:syncToTarget
Syncing file: file1.txt
Syncing file: file2.txt
Syncing file: file3.txt
Syncing file: file4.txt

BUILD SUCCESSFUL

Total time: 2.927 secs

Checking the time stamps confirms that all files have been copied again. Thus, in conclusion, the Gradle Sync task is not an rsync replacement.