Devolutions/UniGetUI · warning · InvalidOperationException

Pacman does not support installing arbitrary versions

Error message

Pacman does not support installing arbitrary versions

What it means

Pacman's GetInstallableVersions_UnSafe unconditionally throws InvalidOperationException. Pacman resolves versions from synced repositories and does not provide an arbitrary installable-version list.

Source

Thrown at src/UniGetUI.PackageEngine.Managers.Pacman/Helpers/PacmanPkgDetailsHelper.cs:166

        string? result = null;
        string? line;
        while ((line = p.StandardOutput.ReadLine()) is not null)
        {
            if (result is not null) continue;
            var spaceIdx = line.IndexOf(' ');
            if (spaceIdx < 0) continue;
            var path = line[(spaceIdx + 1)..].Trim();
            if (Directory.Exists(path))
                result = path;
        }

        p.StandardError.ReadToEnd();
        p.WaitForExit();
        return result;
    }

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

    private static long ParsePacmanSize(string value)
    {
        // Format: "2.34 MiB", "234.56 KiB", "1.20 GiB"
        var parts = value.Split(' ');
        if (parts.Length < 2 || !double.TryParse(parts[0],
                System.Globalization.NumberStyles.Any,
                System.Globalization.CultureInfo.InvariantCulture, out var num))
            return 0;

        return parts[1] switch
        {
            "KiB" or "kB" => (long)(num * 1024),
            "MiB" or "MB" => (long)(num * 1024 * 1024),
            "GiB" or "GB" => (long)(num * 1024 * 1024 * 1024),
            _ => (long)num,
        };
    }

View on GitHub (pinned to 9b1d7d0eab)

Solutions

  1. Gate version requests on the capability flag for Pacman.
  2. Install via the repository version without a version pin.
  3. Catch InvalidOperationException and surface only the current version.

Example fix

// before
var versions = await pkg.GetInstallableVersionsAsync(); // throws for pacman
// 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 requesting installable versions for a Pacman package (version picker, pre-install resolution).

Common situations: UI version dropdown for an Arch/pacman package; automation expecting a version list.

Related errors

AI-assisted analysis of Devolutions/UniGetUI@9b1d7d0eab (2026-08-13). Data as JSON: /api/errors/111e2054fa18607f. Report an issue: GitHub.