[kdroidFilter]

What

A plugin DSL that writes the Flathub repository of any Nucleus app (github.com/flathub/<appId>), for apps that Flathub repackages from their released Linux tar.gz. Flathub builds nothing from source in that setup, which is the path a closed-source app takes. The Lab used a hand-written template and script for this; it now uses the DSL.

linux {
    flathub {
        appId = "com.example.App"
        summary = "Edit example documents"
        projectLicense = "LicenseRef-proprietary"
        archiveUrl = "https://example.com/releases/{version}/app-{version}-linux-{arch}.tar.gz"
        screenshot("https://example.com/shots/main.png", "The main window")
    }
}

./gradlew generateFlathubRepository writes build/flathub/<appId>/:

• the manifest;
• the AppStream metainfo;
• the desktop entry;
• the icon;
• the shared-mime-info XML;
• flathub.json, only when the app targets a subset of architectures.

flathub { } only holds what Flathub alone needs. The other values come from the rest of the DSL:

• name, description, vendor, homepage and categories;
• the icon;
• fileAssociation, which gives the MIME types;
• protocol, which gives x-scheme-handler;
• the version, from packageVersion;
• the executable, from the GraalVM image name (bin/<packageName> for a jpackage build).

This is independent of flatpak { }, which builds a .flatpak bundle that Flathub does not accept.

• Sources: each archive is downloaded once from archiveUrl ({version}, {arch} → x64 / arm64) to compute its sha256. With -Pnucleus.flathub.localArchive=<tar.gz>, the task uses that file instead, for the local repository loop.
• Checks before writing: the task reports every issue Flathub would reject in one go: reverse-DNS app id, a summary of at most 35 characters without a trailing period, description, license, developer, categories, at least one screenshot, #rrggbb branding colors, and a square PNG icon of 256 px or more.

Verification

• The Lab, generated from release v3.0.0-dev-202611011507, gives the same sha256 values as the hand-written script, and its content is identical apart from formatting.
• The generated repository passes flathub-build, flatpak-builder-lint on both manifest and repo, appstreamcli validate and desktop-file-validate.
• FlathubRepositoryTest has 10 tests. ktlint passes. detekt reports nothing in the new code; the plugin's existing detekt findings are unchanged.

docs/internals/flathub.md documents the DSL, the local loop and linting.