[cfe/ffi] Cascading error on wrong types when using `.address`

[dcharkes]

There is 2 errors being thrown for this snippet

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

void main() {
  final typedData = Int8List.fromList([1, 2]);
  myNative(typedData.address);
}

Output of dart <thisfile.dart>:

tests/ffi/static_checks/address_of_cast_test.dart:50:22: Error: The argument type 'Pointer<Int8>' can't be assigned to the parameter type 'Pointer<Void>'.
 - 'Pointer' is from 'dart:ffi'.
 - 'Int8' is from 'dart:ffi'.
 - 'Void' is from 'dart:ffi'.
  myNative(typedData.address);
                     ^
tests/ffi/static_checks/address_of_cast_test.dart:50:22: Error: The '.address' expression can only be used as argument to a leaf native external call.
  myNative(typedData.address);

The second error is not supposed to be thrown, and its not reported by analyzer (confirmed that by running dart analyze and got only one error which is the first one)

I tested this on 3.5.0-292.0.dev, seems this is a existing behavior.

Originally posted by @codesculpture in #55971 (comment)

[codesculpture]

I can take this up, if its okay. @dcharkes

[codesculpture]

@dcharkes i found the root cause of this issue which from above code
myNative(typedData.address) where the typedData.address is not transformed
due to the expression type is InvalidExpression which is skipped for transformation due to this

sdk/pkg/vm/lib/modular/transformations/ffi/use_sites.dart

Lines 1521 to 1527 in 8fa0f56

	if (argument is! StaticInvocation ||
	!addressOfMethods.contains(argument.target)) {
	// The argument has type Pointer, but it's not produced by any of the
	// `.address` getters.
	// Argument must be a Pointer object. Keep unchanged.
	return ('P', parameterType, argument);
	}

Do you think transforming typedData.address even its not the right type make sense ?
am just thinking loud

[codesculpture]

Actually it seems, we don't need to perform the transformation if it isn't the right type, that's just unnecessary

[codesculpture]

Or is it viable to store the context that the given StaticInvocation was part of native leaf call if so we can simply ignore the error reporting

else if (addressOfMethods.contains(target) && !isPartOfNativeLeafCall) {
        diagnosticReporter.report(
            messageFfiAddressPosition, node.fileOffset, 1, node.location?.file);
      }

but storing such isPartOfNativeLeafCall would be overhead it seems.

So i guess all i can think is 2 options:

1. Storing isPartOfNativeLeafCall, but i have no idea how to store and maintain it (which seems complex).
2. We can just transform the .address (even if it is passed for wrong type) which may simple.

Wdyt @dcharkes

[dcharkes]

We can just transform the .address (even if it is passed for wrong type) which may simple.

If we transform, but still report the original error so that the compilation fails, I think that is fine. 👍

Alternatively, we could transform it to a throw 'Invalid code' instead.

[codesculpture]

#56594, Please see here for this

Alternatively, we could transform it to a throw 'Invalid code' instead.

[codesculpture]

This been landed here can be closed https://dart-review.googlesource.com/c/sdk/+/382681