Link callsite directly to external function

[fmagin]

I have some analysis that resolves me that at a certain indirect callsite (dynamic dispatch) a function from a different program is called, in this example the method isIOSVersionGreaterThanOrEqual: of the class OSDeviceUtils.

I already have created an external function for this method in the caller program:

Is there any way to directly add the information that this callsite calls that external function?
The underlying API for a local function that I know of is via the ReferenceManager:

val rMgr = program.referenceManager.
val ref = rMgr.addMemoryReference(callsite, targetFunction.entryPoint, RefType.UNCONDITIONAL_CALL, SourceType.USER_DEFINED, 0)
rMgr.setPrimary(ref, true)

But if I use this then I get a weird kind of reference that doesn't seem to work:

If I add a local thunk that has the external function as the thunkedFunction then it works reasonably well:

Is it a hard requirement to add local thunks, and if yes, is there some specific design decision or limitation behind this?

[ghidra1]

There should be a stub/thunk function within memory that the Call instruction refers to either directly or indirectly. You can use the Set Thunked Function GUI action or Function.setThunkedFunction method to set the external function as the function being "thunked". Via the GUI be sure to specify he full namespace path of the external function which includes the Library name (e.g., Library::Namespace::FNName)

[ghidra1]

While you can create external references it is preferred to establish a thunk relationship via a stub/thunk function contained in memory. In some cases with Elf we are forced to create such thunks within an artificial memory block named EXTERNAL to achieve this.

[ghidra1]

We do use external references sometimes when there is a pointer to undefined memory that corresponds to an external function such as with a PE Import Address Table (IAT) or ELF Global Offset Table (GOT).