feat: add compat.godot-cpp 4.5.0 - #143

What

Adds compat.godot-cpp 4.5.0 (upstream tag godot-4.5-stable) — the C++ bindings for Godot's GDExtension API, consumable as an ordinary mcpp source package: #include <godot_cpp/...>, no SCons, no CMake, no Python.

Shape: upstream codegen frozen into the mirror archive

godot-cpp's tag archives are half a source tree. The other half — ~1000 engine classes and every builtin Variant type, i.e. gen/include/ and gen/src/ — is emitted by upstream's own binding_generator.py from gdextension/extension_api.json at build time, and ships in no upstream archive or release:

upstream archive:  include/ 67 .hpp    src/ 32 .cpp
after generation:  +1010 .hpp          +990 .cpp     (18 MB)

Three ways to get it, and why this one:

So the download is a repack, in the same spirit as the asio symlink repack: upstream's tree byte-for-byte, plus gen/.

tools/godot-cpp/repack.sh is the archive's only source and its verifier — it re-extracts the upstream archive, diff -rs it against the generated tree and refuses to publish if any upstream file differs, then packs deterministically (--sort=name, fixed mtime, gzip -n). Two independent runs hash identically.

Mirrors

Both re-downloaded and hashed: b0c36e77f02c4181352cdd7547b209b93a833be1ad6197f8c650d92987221a00, identical to the local build. Upstream godot-4.5-stable archive is ac78539c0042554c494ea419549d2de88758d448721aeb0e5d41129aa87e339c; both are recorded in the mirror repo's README together with the reproduction recipe.

One OS-neutral archive for all three platforms — godot-cpp is portable C++ with no per-platform source selection; the platform split lives in Godot itself, behind the gdextension_interface.h C ABI.

Defines / features

GDEXTENSION is upstream's PUBLIC compile definition (cmake puts it on the target's INTERFACE), so library and consumer TUs must agree — it rides on default = { implies = { "gdextension" } }, the same shape as CURL_STATICLIB in compat.curl.

Deliberately not features:

• DEBUG_ENABLED / DEV_ENABLED — extra checks, off in upstream's release default.
• HOT_RELOAD_ENABLED — changes the Wrapped layout; that is ABI, not a switch.
• REAL_T_IS_DOUBLE — needs a gen/ tree generated with precision=double, which is not in this archive. It could only ever be a separate version/package, never a feature over these bytes.

Shared reason for the first two: each re-keys the store into a second full 1022-TU build of the same library.

Test member

tests/examples/godot-cpp/ (inherits the workspace-root compat redirect). Both halves are asserted, and either can fail:

• linking — Vector2::length(), Basis::orthonormalized(), Color::to_rgba32(), AABB::get_volume() are declared in headers but defined in src/variant/*.cpp, so a pass proves the 1022 TUs really compiled and linked in.
• generated bindings — <godot_cpp/classes/node.hpp>, Node::PROCESS_MODE_*, godot::OK, godot::ERR_FILE_NOT_FOUND, Variant::OBJECT exist only under gen/.

Out of scope by nature: anything routed through the gdextension_interface_* function pointers (String, Array, class registration) needs a Godot process that has loaded the extension. The pure-math half does not, so that is where the assertions live.

Verification

Cold run with the CI-pinned mcpp (MCPP_VERSION = 2026.8.3.3):

$ mcpp test -p godot-cpp
   Compiling compat.godot-cpp v4.5.0
     Running bin/godot_cpp
vec2=1 vec3=1 basis=1 color=1 aabb=1 gen=1
godot_cpp ... ok (0.12s)
 test result ok. 1 passed; 0 failed; finished in 106.54s (build 55.60s + run 0.02s)

Local lint mirrors validate.yml (syntax, required fields, no leading v, mirror table, package name, cross-package refs, mcpp xpkg parse) — all clean, and the CN url returns 200.

Separately, all 1022 TUs were built once with gcc 13 at -std=c++23 and every object linked eagerly against the test's main to confirm no unresolved symbols under whole-object dependency linking (no -ldl/-lpthread needed). ~16 CPU-minutes, so ~4–5 min on a 4-core runner.

Note src/core/object.cpp and gen/src/classes/object.cpp share a basename — covered by mcpp's obj-path disambiguation (mcpp#233/#240), well below this index's client floor, and verified by the passing link.

Follow-up (separate PR)

The C++23 module layer stays out of this index: it will be the external Form-A package mcpplibs/godot-cpp-m, depending on compat.godot-cpp and exposing import godot_cpp;, registered here as pkgs/g/godotengine.godot-cpp.lua.

That has to come after this one merges and publish-artifact republishes: a module test member can declare only one [indices] redirect (godotengine), so its transitive compat.godot-cpp resolves from the published index — the same constraint tests/examples/ffmpeg-module documents.

Design notes: .agents/docs/2026-08-04-add-godot-cpp-plan.md.