Failed marshaling of arguments with nested structs of input types

[MMartyn]

What happened?

I am not sure if this error is expected and is the same as referenced here https://github.com/pulumi/pulumi-go-provider/blob/main/examples/random-login/main.go#L41, but essentially we have component arguments that contain a nested struct that has a pulumi.StringInput. The provider compiles successfully, but when you use it it throws a error: an unhandled error occurred: waiting for RPCs: rpc error: code = Unknown desc = waiting for RPCs: cannot marshal an input of type pulumi.StringOutput with element type string as a value of type pulumi.StringInput

Example

The following will throw the marshal error:

type CustomComponent struct{}

type NestedThing struct {
	Bar string             `pulumi:"bar"`
	Baz Pulumi.StringInput `pulumi:"baz"`
}

type CustomComponentArgs struct {
	Foo         string      `pulumi:"foo"`
	NestedThing NestedThing `pulumi:"nestedThing"`
}

type CustomComponentState struct {
	pulumi.ResourceState
	CustomComponentArgs
	// Outputs
	// None at this time
}

func (k *CustomComponent) Construct(ctx *pulumi.Context, name, typ string, args CustomComponentArgs, opts pulumi.ResourceOption) (*CustomComponentState, error) {
	comp := &CustomComponentState{CustomComponentArgs: args}
    .....
}

If we remove the CustomComponentArgs from the CustomComponentState struct and make the comp just comp := &CustomComponentState{} it will run without error. I am unsure of any errors that will result from removing this from the state as in the example this is how I see it working.

Output of pulumi about

CLI
Version 3.131.0
Go Version go1.23.0
Go Compiler gc

Additional context

No response

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[mjeffryes]

I'm not 100% sure on this, but I wonder if that error isn't coming from the fact that baz in NestedThing is a Pulumi.StringInput and we can't coerce the output values to a StringInput. Does it work if baz is a plain string?

[MMartyn]

Yeah plain values are fine but Input/Output types don't work in nested structs. Unfortunately the value I am passing in is in reality is a Pulumi.StringOutput that is not known until a dependent resource is created.

[iwahbe]

@MMartyn The error message looks like the marshaling code is having issues with inputs vs outputs. Can you try marking baz as an output:

 type NestedThing struct {
 	bar string             `pulumi:"bar"`
-	baz Pulumi.StringInput `pulumi:"baz"`
+	baz Pulumi.StringOutput `pulumi:"baz"`
 }

Do you see the same error message?

---

Also, I'm pretty sure that nothing will work right for un-exported fields (baz vs Baz).

[MMartyn]

My bad, I messed up the capitalization when writing the example for the ticket. But know that the fields are properly capitalized in the real code.

[MMartyn]

Edited example to show proper capitalization to match the real world