Devolutions/UniGetUI · warning · InvalidOperationException

Flatpak does not support installing arbitrary versions

Error message

Flatpak does not support installing arbitrary versions

What it means

Flatpak's GetInstallableVersions_UnSafe unconditionally throws InvalidOperationException. Flatpak installs one commit per branch and has no arbitrary-version catalog, so requesting installable versions is unsupported.

Source

Thrown at src/UniGetUI.PackageEngine.Managers.Flatpak/Helpers/FlatpakPkgDetailsHelper.cs:101

        // System-wide installs live under /var/lib/flatpak, per-user installs under
        // ~/.local/share/flatpak. Return whichever actually contains the app.
        foreach (var baseDir in new[]
        {
            "/var/lib/flatpak",
            Path.Join(
                Environment.GetFolderPath(Environment.SpecialFolder.UserProfile),
                ".local", "share", "flatpak"),
        })
        {
            var path = Path.Join(baseDir, "app", package.Id);
            if (Directory.Exists(path))
                return path;
        }
        return null;
    }

    protected override IReadOnlyList<string> GetInstallableVersions_UnSafe(IPackage package)
        => throw new InvalidOperationException("Flatpak does not support installing arbitrary versions");
}

View on GitHub (pinned to 9b1d7d0eab)

Solutions

  1. Disable the version picker for Flatpak via the capability check.
  2. Install the default Flatpak branch/commit without a version pin.
  3. Catch InvalidOperationException and surface only the current/default version.

Example fix

// before
var versions = await pkg.GetInstallableVersionsAsync(); // throws for flatpak
// after
if (pkg.Manager.Capabilities.SupportsArbitraryVersions)
    versions = await pkg.GetInstallableVersionsAsync();
else
    versions = [pkg.Version];
Defensive patterns

Strategy: validation

Validate before calling

if (package.Manager.Capabilities.SupportsArbitraryVersions)
    versions = package.GetInstallableVersionsAsync();
else
    versions = new[] { package.Version };

Type guard

static bool CanListVersions(IPackage pkg) =>
    pkg.Manager.Capabilities.SupportsArbitraryVersions;

Prevention

When it happens

Trigger: Any code path that calls GetInstallableVersions on a Flatpak package (version picker, pre-install resolution).

Common situations: UI version dropdown for a Flatpak app; automation assuming a version list exists.

Related errors

AI-assisted analysis of Devolutions/UniGetUI@9b1d7d0eab (2026-08-13). Data as JSON: /api/errors/24593fdf239f77bf. Report an issue: GitHub.