The lexer, parser, AST, serializer, and validator are **no longer embedded here** — they live in the standalone **`logos-lidl`** repo, the language-neutral (Qt-free) common frontend every Logos SDK shares (C++ here, Rust in logos-rust-sdk, …). cpp-generator links it via `find_package(logos-lidl)` and reaches it through `experimental/lidl_compat.h`.
- the **AST**: `TypeExpr` (`Kind`: Primitive/Array/Map/Optional/Named, `name`, `elements`), `ParamDecl`, `FieldDecl`, `MethodDecl` (name, params, returnType, `description`, `jsonReturn`, `resultReturn`), `EventDecl` (name, params, `description`), `TypeDecl`, `ModuleDecl`. (logos-lidl also exposes an AST↔JSON bridge and a C ABI that the Rust SDK consumes over FFI — not used by this generator.)
Validation (in logos-lidl) checks: empty module name, duplicate type/method/event names, builtin type shadowing, unknown named type references, duplicate parameter names. Serialization round-trips `ModuleDecl` back to `.lidl` text (incl. the trailing `description "…"` clause).
| decode, required slot | absent and null are both still errors |
| encode, **named** slot (a record field) | the key is **omitted** |
| encode, **positional** slot (argument, return, event param) | `null` — there is no key to omit, and arity must never change |
A round trip therefore **canonicalises**: a peer that sent `"f": null` gets the key back
omitted. A present-but-wrong-typed value is still an error — optional widens the domain by
exactly one inhabitant, it does not switch type checking off.
Per surface:
| Surface | `?T` | Notes |
|---|---|---|
| cdylib / std (`lidlTypeToStd`, `lidl_gen_cdylib`) | `std::optional<T>` | encoded by logos-protocol's `Codec<std::optional<T>>`; key omission is the record emitter's job (a codec never sees the slot) |
| `?any` / `?{tstr: any}` / `?[any]` | `LogosMap` / `LogosList` | collapses: `nlohmann::json` already carries `null`, so wrapping it would make the slot three-state |
| Qt (`lidlTypeToQt`) | `QVariant` | two-state (an invalid QVariant is Qt's empty inhabitant) but **untyped** — see Known Limitations |
| header-first (`impl_header_parser`) | `std::optional<T>` ↔ `?T` | `std::optional<std::optional<T>>` has no LIDL type; it collapses to `?T` and is reported on stderr |
-`lidlMakeHeader(ModuleDecl)` / `lidlMakeSource(ModuleDecl)` — typed `<Module>` client wrapper; each method (and its `…Async` twin) carries a Doxygen `///` comment generated from the method's `description`
Emits the Qt-free half of a universal C++ cdylib module:
-`lidlCdylibSupported(ModuleDecl)` — gate to the std-convertible (Qt-free) type subset
-`lidlMakeModuleImplExports(...)` — the `logos_module_impl.h` C-ABI export wrapper around the universal impl class (compiled into the module's cdylib; dispatches via nlohmann::json)
-`lidlMakeEventsSourceCdylib(...)` — typed `logos_events:` bodies marshalling into nlohmann::json
The codegen exposes **one** wrapper class per module — `<Module>` — with signatures that match the API style picked at the consumer's build time. The two styles are mutually exclusive (no composite output):
| `lp` | `std::string` / `std::vector<std::string>` / `LogosMap` / `LogosList` / `int64_t` / `StdLogosResult`, over the Qt-free logos-protocol C ABI |
(A third value, `std` — std signatures over a `QVariant` / `LogosAPIClient` body — was retired; the generator now rejects `--api-style=std` instead of aliasing it.)
- A `<Module>` client class with sync method shapes + matching `<method>Async(...)` overloads.
- The std variant additionally inlines Qt↔std conversion in its `.cpp` so the caller's translation unit needs zero Qt headers.
The umbrella `logos_sdk.h` is also generated per-build and aggregates every dep into a flat `LogosModules` struct — no nested view:
```cpp
structLogosModules{
LogosAPI*api;
SomeDepsome_dep;// one accessor per `metadata.json#dependencies` entry
// ...
};
```
Only the modules explicitly listed as dependencies are exposed. The runtime's `core_manager` is intentionally NOT in `LogosModules` — apps that need to manage the core do so via liblogos' C API, not via a typed RPC wrapper.
-`enum class ApiStyle { Qt, Lp }` — passed to every wrapper-emitting function.
- File-local `mapParamTypeStd` / `mapReturnTypeStd` — the std-side type-mapping table the `lp` surface exposes. Hidden from `generator_lib.h` (not part of the public surface).
-`makeHeader(moduleName, className, methods, apiStyle, events)` / `makeSource(moduleName, className, headerBaseName, methods, apiStyle, events)` — single entry points that branch on `apiStyle` internally to emit the right include block, signature shape, and conversion bridges. `events` is loaded from a `<name>.lidl` sidecar via `--events-from`; when non-empty, the wrapper also gets one typed `on<EventName>(callback)` adapter per declared event (callback arg types follow `apiStyle`).
1.`metadata.json#interface == "universal"` (or `"cdylib"`) → `mkLogosModule.nix` adds `-DLOGOS_API_STYLE=lp` to `extraCmakeFlags`. Anything else (`"legacy"`, `"provider"`, absent) leaves the default `qt`.
2.`LogosModule.cmake` reads `${LOGOS_API_STYLE}` (default `qt`) and forwards `--api-style=${LOGOS_API_STYLE}` to the `logos-cpp-generator --general-only` invocation that writes the umbrella. Each module's Nix build emits **two** header derivations (`<name>.headers-qt` and `<name>.headers-lp`) via `buildHeaders.nix` — one `logos-cpp-generator --api-style=…` run per style, at the dep's build time. A consumer's `buildPlugin.nix` picks `dep.headers-${apiStyle}` and copies its `include/` straight into the build sandbox; no codegen runs at consume time. Nix's laziness means only the variant a downstream actually depends on is realised.
3.`legacy/main.cpp` parses `--api-style` once (rejecting the retired `std`) and threads the resulting `ApiStyle` through `generateFromPlugin`, `writeUmbrellaHeader{,FromDeps}`. No per-style filenames are ever emitted; each module gets a single `<name>_api.h` + `<name>_api.cpp` pair regardless of style.
> The Qt provider glue (`lidl_gen_provider.{h,cpp}`) is emitted by **logos-qt-sdk's `logos-qt-generator`**, not this binary — it consumes the same `logos-lidl` frontend (+ the shared `lidl_emit_common` / `impl_header_parser` / `lidl_compat.h` helpers, distributed under `share/lidl-frontend`). Documented here for reference.
- Always emits an `onInit(LogosAPI*) override` that, via SFINAE'd helpers in `logos_module_context.h`, (a) copies the three runtime-injected properties (`modulePath`, `instanceId`, `instancePersistencePath`) into the impl, (b) constructs a per-module `LogosModules` aggregate and threads its pointer through the same base, and (c) installs the typed-event callback (`maybeSetEmitEvent`) consumed by `<name>_events.cpp` method bodies. Impls that don't inherit `LogosModuleContext` compile unchanged — the helper overloads collapse to no-ops. The full `LogosAPI` is never exposed past the provider boundary.
- Always emits `#include "logos_sdk.h"` and a `std::unique_ptr<LogosModules> m_logosModules` member; ownership lives on the provider, the context base sees only a non-owning `void*` reinterpreted in `LogosModuleContext::modules()` (which depends on the impl's TU having included `logos_sdk.h`).
-`lidlMakeProviderDispatch(ModuleDecl)` — generates callMethod/getMethods dispatch. `getMethods()` emits the full interface: each method tagged `type: "method"`, then each `module.events` entry tagged `type: "event"` (name, signature, parameters, escaped `description`; no returnType/isInvokable). There is no separate `getEvents()` — folding events into `getMethods()` keeps the provider vtable ABI-stable.
-`lidlMakeEventsSource(ModuleDecl, implClass, implHeader)` — generates `<name>_events.cpp`: Qt-MOC-style method bodies for prototypes declared in the impl's `logos_events:` block. Each body marshals typed args into a `QVariantList` and calls `this->emitEventImpl_("<name>", &args)` on the LogosModuleContext base.
-`lidlGenerateProviderGlue(lidlPath, ...)` — full pipeline from .lidl file. Also emits `<name>_events.cpp` and a `<name>.lidl` sidecar (via `lidlSerialize`) when the module has any events; both ride the dep's `headers-*` outputs to power consumer-side typed `on<X>()` accessors.
- The literal `logos_events:` token (defined in `logos_module_context.h` as `#define logos_events public`) opens an events section; bare prototypes inside become `EventDecl{name, params, description}` entries appended to `ModuleDecl.events` (the `description` is the doc comment immediately above the declaration, captured via `joinDocLines` exactly as for methods)
- Recognizes `std::optional<T>` → `?T` (see Optionality). Anything it does *not* recognize still falls back to the opaque `any`, silently — that fallback is why an optional was unexpressible header-first until it was named explicitly
The `--events-from <path>` flag points the legacy `<plugin>.dylib --module-only` codegen at a LIDL sidecar shipped alongside the dep's pre-built headers. When set, the generated `<name>_api.{h,cpp}` gains one typed `on<EventName>(callback)` accessor per declared event (callback arg types match `--api-style`):
In Nix builds this is wired automatically: `buildHeaders.nix` looks for `<pluginLib>/share/logos/<name>.lidl` (which `buildPlugin.nix`'s installPhase placed there) and threads it through.
The frontend tests (lexer/parser/validator/serializer) moved to the **logos-lidl** repo along with the code; only the C++/Qt-specific backends are tested here:
-`--from-header` emits the **cdylib** backend here (the `qt` glue backend moved to logos-qt-generator); the **Rust** backend lives in logos-rust-sdk's `lidl-gen`, generating over logos-lidl's C ABI
