Package PostProject in a Flatpak

A Flatpak application links PostProject the same way as any other native consumer: through the installed CMake package. PostProject is built from the release source archive as one more module of the application’s manifest. The build is offline, as Flathub requires, and the application’s own build never invokes Cargo.

Each release since 0.4.0-alpha.1 publishes two files for this next to its source archive:

• postproject-VERSION-flatpak.json, the module, pinned to that release’s source archive and its SHA-256 checksum;

• postproject-VERSION-cargo-sources.json, the Rust crates the build needs, generated from Cargo.lock with the Flatpak project’s flatpak-cargo-generator.

Copy both next to your manifest and list the module before the modules that use PostProject. The example names use 0.9.0-alpha.1; if matching release assets are not yet available, render a local module with the command below:

{
    "sdk-extensions": [
        "org.freedesktop.Sdk.Extension.rust-stable"
    ],
    "modules": [
        "postproject-0.9.0-alpha.1-flatpak.json",
        {
            "name": "my-application",
            "buildsystem": "cmake-ninja"
        }
    ]
}

The Rust SDK extension is needed only while building PostProject. It is not added to the finished application. The module is this template, with the release version and checksum filled in:

{
    "name": "postproject",
    "buildsystem": "simple",
    "build-options": {
        "append-path": "/usr/lib/sdk/rust-stable/bin",
        "env": {
            "CARGO_HOME": "/run/build/postproject/cargo"
        }
    },
    "build-commands": [
        "cargo --offline build --release --locked -p postproject-ffi",
        "cmake -S . -B target/package -DPOSTPROJECT_LIBRARY=\"$PWD/target/release/libpostproject.so\" -DCMAKE_INSTALL_PREFIX=\"$FLATPAK_DEST\"",
        "cmake --install target/package"
    ],
    "sources": [
        {
            "type": "archive",
            "url": "https://github.com/postproject-org/postproject/releases/download/v@VERSION@/postproject-@VERSION@-source.tar.gz",
            "sha256": "@SHA256@"
        },
        "postproject-@VERSION@-cargo-sources.json"
    ]
}

It installs the shared library, the C header, the C++ wrapper, and the CMake and pkg-config metadata into /app, so find_package(PostProject) works in later modules without further configuration. Manifests that clean up /include and /lib/cmake after the build, as KDE application manifests do, still ship the library.

What is tested

The Flatpak module workflow renders the module for a source archive of the revision under test. It builds the module on the KDE 6.10 SDK that Kdenlive’s manifest uses, then builds and runs the C and C++ smoke programs from tests/abi against /app. Pull requests that change the module, the lockfile, or the CMake package run it, and it also runs weekly. The quality checks verify on every change that postproject-cargo-sources.json lists exactly the crates in Cargo.lock.

When Cargo.lock changes, regenerate the Cargo sources with flatpak-builder-tools:

python3 flatpak-builder-tools/cargo/flatpak-cargo-generator.py Cargo.lock \
  -o packaging/flatpak/postproject-cargo-sources.json
python3 tools/flatpak_module.py check

To try a revision that has not been released, render the module for a local archive. The command also writes a small check application that builds it:

git archive --format=tar.gz --prefix=postproject-0.9.0-alpha.1/ \
  --output=target/flatpak/postproject-0.9.0-alpha.1-source.tar.gz HEAD
python3 tools/flatpak_module.py render --version 0.9.0-alpha.1 \
  --archive target/flatpak/postproject-0.9.0-alpha.1-source.tar.gz \
  --output target/flatpak
flatpak-builder --user --install-deps-from=flathub --force-clean \
  target/flatpak/app target/flatpak/org.postproject.FlatpakCheck.json

The Kdenlive pilot is the application this module was made for.