# Version guide

How Saturn Client supports several Minecraft versions, and how to change or add one.

## Layout

- `common/`: all version-independent code (mods, UI, cosmetics, the server client). It has no Minecraft dependency and reaches the game only through the interfaces in `org.saturnclient.common`.
- `versions/<mc>/`: one module per Minecraft version, implementing those interfaces (providers, refs, mixins). Each is a full copy, and they differ only where Minecraft's API differs.
  - `gradle.properties`: the Minecraft, Yarn, Fabric Loader and Fabric API versions.
  - `src/`: the version-specific code and the three mixin configs.

`settings.gradle` includes every folder under `versions/` automatically, as the Gradle project `:mc-<mc>`.

## Porting a change to the other versions

Make the change in one version, usually the newest, then run:

```sh
scripts/port.sh                        # port uncommitted changes to every other version
scripts/port.sh --dry-run              # see what would apply cleanly first
scripts/port.sh --to 1.21.9,1.21.10    # only some versions
scripts/port.sh --commit <rev>         # port what a commit changed instead
```

The script applies the diff under `versions/<from>/src` to each other version with `git apply --3way`:

- **applied**: the files matched, and nothing else is needed.
- **CONFLICTS**: that version's code really differs. The file gets normal conflict markers, with the version's own code in `ours` and the ported change in `theirs`. Adapt the change to that version's API and resolve.
- **already has this change**: nothing to do, which is safe to see when re-running.

Only `src/` is ported. `build.gradle` and `gradle.properties` are version-specific on purpose. Then build everything:

```sh
./gradlew compileJava
```

The **Check** workflow runs the same compile on every pull request, so a version that was missed or mis-ported fails before merging.

## Adding a Minecraft version

1. Copy the closest existing version: `cp -r versions/1.21.11 versions/<new>`. Delete its `build/`, `.gradle/` and `run/` folders if present.
2. In `versions/<new>/gradle.properties`, set `minecraft_version`, `yarn_mappings`, `loader_version` and `fabric_api_version`. The right values are listed at <https://fabricmc.net/develop>.
3. Build it with `./gradlew :mc-<new>:compileJava` and fix what Minecraft changed. Check the mixin configs in `src/main/resources/*.mixins.json` as well: a mixin whose target changed fails at startup, not at compile time, so launch it with `./gradlew :mc-<new>:runClient`.
4. The release workflow builds every folder under `versions/`, and "Publish to Modrinth" takes the game version from each jar's name, so neither needs changing.