ludic/docs/PACKAGES.md

# Ludic packages

Ludic has a package manager built into the task runner (`bin/x`). It fetches,
resolves, stores and links third-party packages with no new infrastructure to
run — it drives plain `git` and rides on the Forgejo host and its release tags.

This is the v1 implementation of the direction decided in issue #63.

## The four decisions

| Axis | Ludic's choice |
| --- | --- |
| Where source comes from | **URL-as-identity, no registry.** The import path *is* the git location — `git.workshopsoft.io/user/pkg`. A `git tag vX.Y.Z` publishes a version. No account, no publish step, no index to run. |
| Version resolution | **Minimum Version Selection (MVS), Go-style.** A `require` is a *minimum*; the resolver picks, per module, the greatest of every required minimum, then keeps the reachable closure at those versions. Deterministic, no SAT solver. |
| Where dependencies live | **A content-addressed global store + per-project links (pnpm-style).** One immutable store keyed by a file-content hash (`~/.ludic/store/<sha256>`); each project gets a light linked view under `ludic_modules/` instead of a full copy. |
| Manifest / lock | **`package.ludic`** (declared deps + provided namespaces + kind + targets) and **`package.lock.ludic`** (resolved versions + content hashes). |

## Commands

```
x add <module>[@version]   add a dependency to package.ludic, then resolve + fetch + link
x get                      resolve every dependency in package.ludic, link them, write the lock
x update [module]          bump a dependency (or all) to its latest published version, then relock
x verify                   check every locked package against the store by content hash
x vendor                   copy the resolved packages into ./vendor for hermetic/offline builds
```

`x add` with no `@version` picks the latest published tag and records it as the
minimum. All the install commands print the resolved build list and write
`package.lock.ludic`.

## The manifest — `package.ludic`

A line-oriented manifest. `#` starts a comment; strings are double-quoted.

```
package "git.workshopsoft.io/orkun/greeter"   # this package's import path
version "1.2.0"                               # the version this checkout publishes
kind    source                                # source | prebuilt
provides "Greet"                              # the Foo.* namespace(s) it registers (repeatable)

require "git.workshopsoft.io/orkun/util" "1.0.0"   # a dependency and its minimum version

# a prebuilt lib also declares the targets it ships:
# kind    prebuilt
# targets "native-arm64" "wasm32"
```

A consumer project's manifest is the same file, usually with only `require`
lines (the `package`/`version` fields describe a *publishable* package and are
optional for a leaf application).

## The lockfile — `package.lock.ludic`

Generated by `x get`; do not edit by hand. One line per resolved module, pinning
its selected version, content hash, kind and provided namespaces:

```
# package.lock.ludic — generated by `x get`. Do not edit by hand.
lock 1
module "git.workshopsoft.io/orkun/greeter" version "1.2.0" hash "sha256:…" kind "source" provides "Greet"
module "git.workshopsoft.io/orkun/util"    version "1.0.0" hash "sha256:…" kind "source" provides "Util"
```

`x verify` rehashes each store entry and confirms the project links to it, so a
tampered or missing dependency is caught before it reaches a build.

## The store and the project view

Fetched packages live once in a global, immutable, content-addressed store:

```
~/.ludic/store/<sha256>/…        the package tree at a version (no .git)
~/.ludic/store/cache/<module>/   a git clone cache used during resolution
```

Each project gets a lightweight view — `ludic_modules/<import-path>` is a symlink
into the store — so many projects share one copy and nothing is duplicated
per-project. Override the store location with `$LUDIC_STORE`.

## Consuming a package — namespace registration

A **source package** ships plain Ludic. The consumer imports the package files by
their import path:

```
program App {
  import "git.workshopsoft.io/orkun/greeter/greet.ludic"
  entry { print(greet_hello()) }
}
```

The compiler resolves an import first relative to the importing file, then — for
a non-absolute path that is not found — under the package module root
(`$LUDIC_MODULES`, default `ludic_modules/`). So a fetched package's code is
spliced into the build and its namespace becomes available exactly the way the
built-in stdlib namespaces (Regex.\*, Grid.\*, …) are.

The **engine runtime is the exception** (issue #75): the compiler auto-splices
`runtime/native/*` for any ECS game, and that runtime ships with the *toolchain*,
not the project. A `runtime/...` import that is not found relative to the build is
resolved from the install root **`$LUDIC_HOME`** (default: the compiler binary's
directory — the same place the platform `.ll` files come from), *before* the
package module root. So an external game does not have to copy or symlink the
engine runtime into its `ludic_modules/`; that directory holds only third-party
packages. In-repo builds are unaffected — the runtime resolves locally there. Because Ludic compiles
ahead-of-time, a source package is compiled *into* the consumer's binary — no
ABI seam, and the whole-program guarantees (determinism, replay, `world_save`)
still hold.

Two packages may not register the same `Foo.*` namespace — a collision is a hard
error naming both modules.

## Package-declarable namespaces and engine systems (issue #62)

A package can register two things that used to be compiler-hardcoded — a `Foo.*`
namespace and an engine-owned system — with **no compiler edit**, via two
keyword-free annotations. This is what lets gameplay-controller libraries ship as
ordinary packages instead of living in the compiler's stdlib.

- `@Namespace(Name)` on a function opens a `Name.method(…)` namespace that
  dispatches to the bare `name_method(…)` (the same generic path the built-in
  namespaces use, applied only after them so it never shadows a core one):

  ```
  @Namespace(Coach) function coach_bonus() -> int { return 99 }
  # a consumer then writes  Coach.bonus()
  ```

- `@EngineSystem(Component, Phase)` registers an engine-owned system: the frame
  loop calls it every `Phase` (after the game's own handlers) whenever the named
  `Component` is present — the package-declarable form of the built-in
  `SpriteAnim`/`Motion`/`Light2D` systems. It reads and writes components by name
  through the reflection ABI, so an unused registration is byte-identical:

  ```
  @EngineSystem(Score, Update) function esys_score() -> void { … }
  ```

The core stdlib namespaces and engine systems keep their own optimized codegen;
packages flow through the generic registry alongside them. (For a *prebuilt*
binary module, the runtime counterpart of `@EngineSystem` is `@System(Phase)` —
see below.)

## Prebuilt binary packages (issue #64)

A `kind prebuilt` package ships a **compiled artifact** (a native dylib per
target it lists in `targets`) instead of source. A consumer uses its exported
**functions, systems and components** without ever seeing the source. This is
the escape hatch for closed-source or other-language code; source packages stay
the default because they keep cross-compilation (including wasm) and the
compile-time ECS first-class. Prebuilt packages are **native-only** and ride the
stable reflection C-ABI — second-class ECS (dynamic, by-name components; one
indirect call per registered system), not part of the deterministic/replay core.

**How a binary module works.** The module is compiled with `--emit-module`: no
`main`, no world table (the consumer owns the single world). It carries a
load-time constructor that, when the dylib loads, registers its pieces against
the host through the C-ABI:

- **Components** — `world_register_prop(name, nfields)` in a `module_init`
  function; the host owns storage, the module reads/writes by name with
  `world_get`/`world_set`/`world_has`/`world_attach_dyn`.
- **Systems** — a function marked `@System(Phase)` is registered with
  `ludic_register_system`; the host's frame loop calls it every frame in that
  phase, after its own handlers. Phases: `Input`, `FixedUpdate`, `Update`,
  `LateUpdate`, `Render`, `Start`, `OnQuit`.
- **Functions** — plain functions become dylib symbols; a consumer binds them
  with `extern function name(...) -> T = "fn_name"`.

A module registers its `ludic_*` calls as undefined and binds them back to the
host image at load (`-undefined dynamic_lookup`); the host exports its ABI
(`-export_dynamic`). Every Ludic game is a capable host — the reflection ABI is
always emitted (unused parts dead-strip).

**Publishing.** In the package repo:

```
x build-lib module.ludic     # -> lib/<target>/lib<name>.dylib
# add `kind prebuilt` and `targets "<target>"` to package.ludic, commit lib/, git tag
```

**Consuming.** In the game project:

```
x add git.host/user/module   # kind prebuilt is resolved + the dylib linked into the view
x get                         # links the artifact for the build target (hard error if the target is missing)
```

then link the module dylibs into the game build. `x link-flags` prints the exact
clang flags (the dylib, an rpath to the store, `-export_dynamic`) for any build
system to splice into its link step:

```
clang -O2 game.ll $(x link-flags) -o game
```

(`x app` links them automatically when building in-repo.) If the package does
not ship the build target, `x get` fails — build from source instead where the
package offers it.

## Offline / hermetic builds

`x vendor` copies the resolved packages out of the store into `./vendor`. Build
against the copy with `LUDIC_MODULES=vendor`, so the build needs neither the
network nor the global store.