[analyzer/ffi] Inline array const lengths

[dcharkes]

The following code is accepted by the dart runtime, but rejected by the analyzer.

const EIGHT = 8;

class Struct8BytesInlineArrayInt extends Struct {
  @Array(EIGHT)
  external Array<Uint8> a0;
}

The ffi_verifier expects an int or int list expression here. Instead, we should evaluate the annotation to a const, so that referenced consts are inlined.

@timsneath thanks for reporting.

[dcharkes]

  void _validateSizeOfAnnotation(AstNode errorNode,
      NodeList<Annotation> annotations, int arrayDimensions) {

    // ...
    final x = annotation.elementAnnotation?.computeConstantValue();
    print(x?.hasKnownValue); // false.

@bwilkerson Contrary to the implementation of @Packed(1) in _validatePackedAnnotation, the annotations found in _validateSizeOfAnnotation do not have a known value. Is this due to using redirecting const factory constructors (from Array to _ArraySize)?

edit: We could consider moving the _ArraySize and forwarding constructors from Array out of the patch file to dart:ffi itself. That way the analyzer could pick it up. (The analyzer does not include patch files because it would not know whether to include the VM ones or the JS ones in general.)

sdk/sdk/lib/_internal/vm/lib/ffi_patch.dart

Lines 136 to 166 in 77dc74b

	@patch
	const factory Array(int dimension1,
	[int dimension2,
	int dimension3,
	int dimension4,
	int dimension5]) = _ArraySize<T>;
	@patch
	const factory Array.multi(List<int> dimensions) = _ArraySize<T>.multi;
	}
	class _ArraySize<T extends NativeType> implements Array<T> {
	final int? dimension1;
	final int? dimension2;
	final int? dimension3;
	final int? dimension4;
	final int? dimension5;
	final List<int>? dimensions;
	const _ArraySize(this.dimension1,
	[this.dimension2, this.dimension3, this.dimension4, this.dimension5])
	: dimensions = null;
	const _ArraySize.multi(this.dimensions)
	: dimension1 = null,
	dimension2 = null,
	dimension3 = null,
	dimension4 = null,
	dimension5 = null;
	}

[bwilkerson]

Based on off-thread discussions, it sounds like analyzer can't compute an actual value because some of the values it needs are in patch files, and it doesn't know how to read patch files. (There might also be a bug around external declarations, but that has yet to be confirmed.)