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Playbook — Add a new C++ library as a cppjs-package

Persona 3 — Package author. The user wants to wrap an existing C++ library so it can be pnpm add @cpp.js/package-<name> consumed.

Goal​

Produce a cppjs-package-<name> family that:

  • Builds for wasm, android, ios with one command.
  • Exposes the library to JavaScript through Embind / SWIG bridges.
  • Ships with README.md, LICENSE, .npmignore, and a nativeVersion-pinned package.json.

When to use​

  • The user says "I want to use library X (e.g. libsodium, FreeType, …) from JS".
  • The user is contributing a new package to the cpp.js ecosystem.
  • A cppjs-package-X already exists but the user is creating a new arch sub-package (e.g. only -wasm exists, they need -ios).

Decision: where does the new package live?​

Does this package extend or affect GDAL (or another package already in
this monorepo's transitive dep graph)?
│
├─ YES → Add directly to this repo under cppjs-packages/cppjs-package-<name>/
│         Use the @cpp.js/* npm scope.
│
└─ NO  → Author it outside this repo:
          1. Strongly encourage the user to create it under the
             cppjs-community GitHub org and PR upstream once it works.
          2. They can also keep it in their own org. In that case the npm
             package name MUST stay unscoped: `cppjs-package-<name>`
             (NOT `@user/cppjs-package-X`, NOT `@cpp.js/...`).

The @cpp.js/* scope is reserved for packages reviewed and adopted into this repo. Unscoped cppjs-package-<name> is the convention for community-authored packages in user orgs; this lets cpp.js's plugin discovery find them by name pattern.

Files involved​

Mirror the canonical cppjs-packages/cppjs-package-zlib/ skeleton:

cppjs-package-<name>/
├── cppjs-package-<name>/                 ← meta package
│   ├── package.json                      ← name, version 0.1.0, deps to sub-arch packages
│   ├── cppjs.config.js                   ← re-export sub-arch configs
│   ├── README.md
│   ├── LICENSE
│   └── .npmignore
├── cppjs-package-<name>-wasm/
│   ├── package.json                      ← nativeVersion, workspace deps to other -wasm packages
│   ├── cppjs.config.js                   ← env, data, libName, build params
│   ├── cppjs.build.js                    ← source acquisition + cmake/configure invocation
│   ├── assets/CMakeLists.txt             ← (only if upstream needs an override)
│   ├── README.md
│   ├── LICENSE
│   └── .npmignore
├── cppjs-package-<name>-android/         ← same shape as -wasm
└── cppjs-package-<name>-ios/             ← same shape + cppjs-package-<name>.podspec

Required content per file​

  • package.json (each sub-arch):
    • "version": "0.1.0" for fresh packages.
    • "nativeVersion": "<upstream version>" — pinned via pnpm run check:native.
    • "dependencies": workspace refs to other @cpp.js/package-*-<arch> (or unscoped cppjs-package-*-<arch> for community) the library needs to link against. pnpm derives topological build order from this.
  • cppjs.config.js: exported targetSpecs array with env, data, libName, optional cmake.compileOptions. Function-typed env values receive (state, target) and resolve at build time.
  • cppjs.build.js: getSource() (download/copy/patch upstream), prepare() (cmake configure step), build() (cmake build / make install). Uses getCppJsScript, run, etc. from cpp.js exports.
  • cppjs-package-<name>.podspec (ios only): CocoaPods manifest. Always include s.user_target_xcconfig = { 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'x86_64' } to keep consumer apps from linking arm64-only iOS simulator slices.
  • README.md: one paragraph intent, nativeVersion, license note, install snippet.
  • LICENSE: copy upstream library's license file. cpp.js's package wrapper itself can use a permissive license (MIT) but the bundled native binary's license governs distribution.
  • .npmignore: exclude .cppjs/, dist/<...>/source/, build intermediates. Keep dist/prebuilt/ (consumers need the prebuilt artifacts).

Native version sourcing​

Always use the latest stable upstream version. Resolution order:

  1. GitHub releases API (https://api.github.com/repos/<owner>/<repo>/releases). Filter out prereleases unless the library only ships prereleases.
  2. GitHub tags API (/tags) — fallback when the project doesn't use Releases.
  3. Project HTML page / download index — last resort (autotools projects often ship tarballs with no GitHub releases).

Existing helper: scripts/check-native-versions.js already implements this resolution chain. Run pnpm run check:native -- --update after adding the package to auto-bump (or to write the initial nativeVersion).

Build system preference​

  1. CMake first. If upstream has a CMakeLists.txt, use it. Easiest cross-platform story — the cpp.js build pipeline is CMake-native.
  2. autotools (./configure && make) fallback. Use when upstream has no CMake support and porting is too invasive. Requires state.config.build.buildType = 'configure' in cppjs.config.js. See cppjs-package-openssl-* for a reference.
  3. Custom Make / scons / etc. Last resort; usually means writing a thin CMake wrapper or using getDependFilePath + manual shell-out.

Commands​

# 1. Scaffold (Sprint 4 will add scripts/scaffold-package.js to automate this).
#    For now: copy cppjs-packages/cppjs-package-zlib/ as a starting point.
cp -r cppjs-packages/cppjs-package-zlib cppjs-packages/cppjs-package-<name>
# Then rename every "zlib" reference inside.

# 2. Resolve and write nativeVersion
pnpm run check:native -- --update
# (Manually verify the picked version is sane.)

# 3. Build all arches
pnpm --filter='@cpp.js/package-<name>*' run build
# Or one arch at a time during development:
pnpm --filter=@cpp.js/package-<name>-wasm run build

# 4. (Only if integrating into THIS repo) Add an e2e exercise to a sample
#    that consumes the new package, e.g. cppjs-sample-lib-prebuilt-matrix.

Validation​

Required:

  • pnpm --filter='@cpp.js/package-<name>*' run build succeeds for wasm, android (Linux/macOS), iOS (macOS only).
  • pnpm run check:dist shows the new package as built.
  • Each sub-arch has README + LICENSE + .npmignore + correct podspec (iOS).
  • nativeVersion matches latest upstream stable.
  • All transitive C++ deps appear in each sub-arch's package.json dependencies.

When integrating into this repo (not a community fork):

  • An e2e test exists in a sample that exercises the new package (mirror an existing test in cppjs-samples/cppjs-playground-*).
  • pnpm run e2e:dev && pnpm run e2e:prod pass.

When the user is keeping the package outside this repo:

  • Skip the e2e step. Their own project tests it.
  • Verify the package builds standalone via pnpm cppjs build in their package directory.

Common pitfalls​

  • Forgetting EXCLUDED_ARCHS[sdk=iphonesimulator*] = x86_64 in the iOS podspec. Without it, consumer apps fail to link on Apple Silicon Macs running iOS simulator.
  • Missing workspace deps. If package-<name>-wasm doesn't list package-zlib-wasm in dependencies, pnpm may build them in the wrong order; the linker then fails to find symbols.
  • Mixing scoped and unscoped names. Stick to one: @cpp.js/* for in-repo, plain cppjs-package-* for community/user-org. Don't mix.
  • Not pinning nativeVersion. Without a pin, check:native --update later overwrites silently and reproducible builds break.
  • bin/ artifacts in .npmignore — make sure dist/prebuilt/<target>/lib/lib<name>.a (and .so for android, .xcframework for ios) is not ignored, or consumers can't link.
  • Wrong upstream license. The cpp.js wrapper README is permissive but the native binary's license governs distribution. If the upstream is GPL-only, surface this prominently in README and ask the user to confirm intent.
  • Naming collisions in user orgs. A user can't publish @cpp.js/package-foo. They need cppjs-package-foo (unscoped, on npm). cpp.js's plugin discovery finds packages matching *cppjs-package-* regardless of scope.
  • Recommend over enforce. The user always picks where to host (their org / cppjs-community / direct PR here). Surface the decision tree, don't force.

Reference​

  • Canonical small example: cppjs-packages/cppjs-package-zlib/
  • CMake-heavy example: cppjs-packages/cppjs-package-tiff/ (transitive deps: zlib, jpegturbo, zstd, lerc)
  • autotools example: cppjs-packages/cppjs-package-openssl/
  • Big aggregator example: cppjs-packages/cppjs-package-gdal/ (depends on ~13 other packages)
  • Native version checker: scripts/check-native-versions.js
  • Distribution CMake template: cppjs-core/cpp.js/src/assets/cmake/dist.cmake