Presence of pulumi.DependsOn results in a runtime error

[phillipedwards]

What happened?

Presence of pulumi.DependsOn results in an error: resources.MyComponent.MyEnumProp is typed as *string but must be a type that implements pulumi.Input or pulumi.Output for input with dependencies

Steps to reproduce

Using a go generated MLC, create a simple example that creates a resource and uses pulumi.DependsOn targeting a dependent resource.

Expected Behavior

pulumi up succeeds

Actual Behavior

Program fails with resources.MyComponent.MyEnumProp is typed as *string but must be a type that implements pulumi.Input or pulumi.Output for input with dependencies

Additional context

Internal Slack Thread: https://pulumi.slack.com/archives/C01028X5X3K/p1665508743426729

Contributing

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[justinvp]

When the Go SDK marshals properties, it builds-up a propertyDependencies map of property names to dependencies associated with the property. If a property doesn't have any dependencies, it's not added to the map:

pulumi/sdk/go/pulumi/rpc.go

Lines 146 to 148 in f713611

	if len(allDeps) > 0 {
	pdeps[pname] = allDeps.values()
	}

If none of the properties have any dependencies, then the propertyDependencies will be empty.

This is different from the Node.js and Python SDKs (I need to check the behavior of the other SDKs), where the propertyDependencies map will always be filled with property names, even if a property has an empty set of dependencies.

When the engine receives a RegisterResource call, it has the following code:

pulumi/pkg/resource/deploy/source_eval.go

Lines 1057 to 1062 in f713611

	if len(req.GetPropertyDependencies()) == 0 {
	// If this request did not specify property dependencies, treat each property as depending on every resource
	// in the request's dependency list.
	for pk := range props {
	propertyDependencies[pk] = dependencies
	}

If the propertyDependencies is empty, it treats each property as depending on every resource in the request's dependency list (i.e. the resources specified in pulumi.DependsOn ResourceOption). This was intended for very older clients that didn't have support for propertyDependencies.

So in this particular case, there are no dependencies associated with any of the properties, so the Go SDK is sending an empty propertyDependencies, and when the engine sees that there are no property dependencies, it creates a propertyDependencies map and fills it in with dependencies from pulumi.DependsOn.

There are a few changes we should consider making here to address this:

1. Change the Go SDK to always send a filled-in propertyDependencies, even if the properties have an empty set of dependencies.
2. Fix the engine (CLI) to not back-fill propertyDependencies when the RegisterResource request is for a remote component -- because any SDK that supports that, already supports property dependencies, so no need to backfill.
3. I need to dust-off and get back to this old PR to deprecate propertyDependencies when sending output values to RegisterResource: Deprecate dependency maps when using output values #8410