387. A resource directory is a package

Date: 2026-09-18

Status

Accepted. Fixes the start-up failure ADR-0384 shipped, and adds the check that would have caught it.

Context

goldberry-emoji put its face where the asset step had always put faces:

io/github/digitalsmile/goldberry/assets/fonts/OpenMoji-black.ttf

goldberry-core still ships four faces and an icon table in that same directory. A resource directory is a package to the module system, exactly as a directory of classes is — so two modules contained io.github.digitalsmile.goldberry.assets.fonts, and the showcase died before its first frame:

java.lang.LayerInstantiationException: Package io.github.digitalsmile.goldberry.assets.fonts
    in both module io.github.digitalsmile.goldberry.emoji and module …core

Every test passed, and that is the part worth writing down. Tests run on a class path, where a split package is two directories and nobody objects; ./gradlew :example:run puts the modules on a module path, which is where the rule lives. A green suite and an application that will not open is the exact shape of failure this repository has tests for — and the module graph, which docs/ARCHITECTURE.md §3.1 calls load-bearing, had no test at all.

Decision

A module’s resources live under that module’s own package, and a test walks the artifacts to say so.

• PrepareAssets takes --root=, so a build script says where inside the jar its assets land. :core keeps io/github/digitalsmile/goldberry/assets; :emoji writes io/github/digitalsmile/goldberry/emoji, and its face is …/emoji/fonts/OpenMoji-black.ttf.
• SplitPackageTest is :example’s, because :example is the one module that depends on every other. It walks each Goldberry artifact on the class path — directory or jar — collects the directories that hold files, and fails when a package is in two modules.
• It asks the question the JVM asks, rather than reading ModuleDescriptor.packages(): that set comes from the ModulePackages attribute javac wrote about the classes it compiled, and what the runtime objected to came from the jar’s contents.

Consequences

• The showcase runs again, and the run is part of what was verified rather than assumed: ./gradlew :example:run painting three frames on the dummy driver.
• The test is discovery-based, so a module added later is covered without anybody remembering to add it — and it refuses to pass if it finds almost nothing, which is how a discovery test says it has stopped discovering.
• The rule now has a name to cite: assets belong under the module that ships them. :html already obeyed it by accident, having no resources outside its own package.