[Bug] A yielded 'fn' from a component is incorrectly rendered as [object Object]

[basz]

🐞 Describe the Bug

A yielded 'fn' from a component is incorrectly rendered as [object Object]

🔬 Minimal Reproduction

Inside a component I have this

{{yield
          (hash
            resourceExtruderCurrentTemperature=(fn ExtruderCurrentTemperature this.printerManager)
          )
        }}

I use the 'fn' helper to be able to add more positional arguments

😕 Actual Behavior

This renders [object Object]

<EmbeddedPrinterComponent @printer={{printer}} as |e|>
{{e.resourceExtruderCurrentTemperature true}}
</EmbeddedPrinterComponent>

🤔 Expected Behavior

Should render 3.5

<EmbeddedPrinterComponent @printer={{printer}} as |e|>
{{e.resourceExtruderCurrentTemperature true}}
</EmbeddedPrinterComponent>

🌍 Environment

ember-cli: 5.4.0
node: 18.18.0
os: darwin arm64
browser: chrome

➕ Additional Context

Using the let helper does render the expected output.

<EmbeddedPrinterComponent @printer={{printer}} as |e|>
{{#let (e.resourceExtruderCurrentTemperature true) as |value|}}{{value}}{{/let}}
</EmbeddedPrinterComponent>

@NullVoxPopuli suggested this might be a bug in 'fn', hence this report.

[NullVoxPopuli]

without digging in to fn, the reason why I think it could be a bug in fn is that these should be equiv:

{{#let (fn someFn 1) as |partiallyApplied|}}

  {{ (partiallyApplied) }}

{{/let}}

and

{{ (someFn 1) }}

as long as fn goes through the helper-manager system, it doesn't matter what someFn is.

[NullVoxPopuli]

Here is a reproduction, showing that this happens with Resources... but even worse: errors with Classic Class and function helpers. With the classic constructs, we get an error saying that call isn't a function, which leads me to believe that we never implemented native helper-manager aware partial application, and only used JavaScript's built in .call behavior.

My hypothesis is that the helper and Helper from @ember/component/helper aren't compatible with fn because neither are functions.

[NullVoxPopuli]

I just remembered!!!

We have (helper) and (modifier) and (component) for partial application of those specific concepts.

Here is the above reproduction, fixed, by using (helper)

[NullVoxPopuli]

So maybe the real question here is -- why do we have 4 ways to partially apply arguments? and can we get that down to 1?