Always provide existing version information in `dotnet workload list --machine-readable`, even if no update is available

Is your feature request related to a problem? Please describe.

From a CI perspective, we need to be able to deterministically check whether a specific version of a given workload is installed. Currently we do this by locating the appropriate WorkloadManifest.json and verifying the version/etc from there. This is not ideal because it depends on implementation details that could change on us down the road.

Describe the solution you’d like

dotnet workload list --machine-readable provides JSON output that could solve this problem, but right now it is focused on updater scenarios. It only shows existingManifestVersion for a workload if there is an update available for it:

{
    "installed": [
        "macos",
        "ios"
    ],
    "updateAvailable": [
        {
            "existingManifestVersion": "12.0.101-preview.10.249",
            "availableUpdateManifestVersion": "12.0.101-preview.10.251",
            "description": ".NET SDK Workload for building macOS applications.",
            "workloadId": "macos"
        },
        {
            "existingManifestVersion": "15.0.101-preview.9.31",
            "availableUpdateManifestVersion": "15.0.101-preview.10.251",
            "description": ".NET SDK Workload for building iOS applications.",
            "workloadId": "ios"
        }
    ]
}

If no update is available, you only see something like this (no version information for macos workload):

{
    "installed": [
        "macos",
        "ios"
    ],
    "updateAvailable": [
        {
            "existingManifestVersion": "15.0.101-preview.9.31",
            "availableUpdateManifestVersion": "15.0.101-preview.10.251",
            "description": ".NET SDK Workload for building iOS applications.",
            "workloadId": "ios"
        }
    ]
}

Ideally, existingManifestVersion would have been in the installed array, regardless of any updates. To avoid changing behavior other tools might depend on, it’s probably necessary to add a new top-level property. Maybe something like this:

{
    "installed": [
        "macos",
        "ios"
    ],
    "updateAvailable": [
        {
            "existingManifestVersion": "15.0.101-preview.9.31",
            "availableUpdateManifestVersion": "15.0.101-preview.10.251",
            "description": ".NET SDK Workload for building iOS applications.",
            "workloadId": "ios"
        }
    ],
    "installedDetails": {
        "macos": {
            "manifestVersion": "12.0.101-preview.10.251"
        },
        "ios": {
            "manifestVersion": "15.0.101-preview.9.31"
        }
    }
}

Additional context

https://github.com/dotnet/sdk/issues/22148 is similar, but for users, not machines.

[sfoslund]

@joeloff @dsplaisted @marcpopMSFT this should be easy to implement, putting it in the 6.0.2xx milestone.

[sandyarmstrong]

Wouldn’t dotnet workload update --print-rollback be better for this?

Playing with this again, it does not actually tell me whether the workloads are installed or not. So I need to either manually check manifests and pack directories to answer my question, or call two commands (workload update --print-rollback and workload list --machine-readable), one of which is slow because it always checks for updates, to get the information I need about what workload versions is installed (if any).

EDIT: Also one command uses the long form workload name and the other uses the short form. It’s very confusing.