dockerfile-gradle-dependencies-without-cache-mount

Warnings require a CI-discovered build with a recognized persistent builder path: Depot, configured Blacksmith, or repository-visible Buildkite local Docker state persistence. Unknown/disposable builders are not flagged for missing cache mounts.

Detects Java Dockerfiles that run Gradle dependency resolution without a visible BuildKit cache mount on the same instruction.

This rule looks for:

• a qualifying persistent Docker build discovered from GitHub Actions or Buildkite
• build.gradle, build.gradle.kts, settings.gradle, or settings.gradle.kts in the build context
• RUN gradle dependencies, RUN gradlew dependencies, or RUN ./gradlew dependencies
• no --mount=type=cache on that Dockerfile instruction

Why it matters:

• Gradle dependency resolution populates Gradle user home with dependency and plugin cache data.
• Without a BuildKit cache mount such as /cache/.gradle or /root/.gradle, Docker rebuilds can repeatedly download dependencies and plugin artifacts.
• Depot’s optimized Gradle Dockerfile mounts Gradle user home during dependency resolution.

What to do:

• Add a BuildKit cache mount for Gradle user home.
• If GRADLE_USER_HOME points to /cache/.gradle, mount /cache/.gradle.
• Otherwise, /root/.gradle is a common default in root-based build stages.

This rule focuses on the dependency resolution step and does not require a specific Gradle distribution strategy.