[docs/ffi] `.address` position should mention `.cast()`

[codesculpture]

TODO

• The dartdoc comment of .address should mention or show an example of using .cast().
• The published ADDRESS_POSITION documentation should mention .cast().

---

Original bug report:

While trying to fix this,
I found the below code is

@Native<Void Function(Pointer<Void>)>(isLeaf: true)
external void myNative(Pointer<Void> buff);

void main() {
  final buff = Int8List.fromList([2]);
  myNative(buff.address.cc);
}

throws 2 errors by the analyzer

1. ERROR|COMPILE_TIME_ERROR|ADDRESS_POSITION|9|17|7|The '.address' expression can only be used as argument to a leaf native external call.
2. ERROR|COMPILE_TIME_ERROR|UNDEFINED_GETTER|9|25|2|The getter 'cc' isn't defined for the type 'Pointer<Int8>'.

But expected is only one error

1. ERROR|COMPILE_TIME_ERROR|UNDEFINED_GETTER|9|25|2|The getter 'cc' isn't defined for the type 'Pointer<Int8>'.

FYI @dcharkes

[dart-github-bot]

Summary: The analyzer incorrectly throws an .address position error when a native call is made with an undefined getter, even though the getter error should be the only one reported. This issue was discovered while trying to fix a related issue.

[codesculpture]

I found the root cause of this issue and i actually tried to fix this, but i planned to fix this seperately once i landed this

#56462

[codesculpture]

(am not good at writing issue title, feel free to edit)

[codesculpture]

I had a thought while reasoning about this issue, we recently "supported" .cast() on Pointers here

But i think thats a existing "bug" which we just fixed (i.e its not something we added to support, it should have worked before)

Because as far as i understand "Address Position" Error, We are only allowing .address on leaf native call.

From the above statement, .address.cast() should have worked before since still the .address is called on native leaf call.

Also we should allow .address.a.b.c these on native leaf call, if such a,b,c exists.
The cfe is now allowing such expression, this been landed while fixing this #56462
So now analyzer should do the same.

If we dont allow such these expression address.a.b.c, then the definition of error should be different from what we have already "Address Position", it should be more like "Address member access is prohibited except cast"
But i dont think this is what we intended to.

Feel free to correct me. @dcharkes

[codesculpture]

Requested CL (this is my first direct cl which was created through git cl upload, previously copybara helped me) here,
based on this below statement

Also we should allow .address.a.b.c these on native leaf call.

[dcharkes]

If we dont allow such these expression address.a.b.c, then the definition of error should be different from what we have already "Address Position", it should be more like "Address member access is prohibited except cast"

It should be like this. .address is not a real expression, it changes how the FFI call works.