FFI doesn't sign-extend 32-bit integer results from C

[sjindel-google]

typedef NativeNullaryOpSigned = ffi.Int32 Function();

void testExtension() {
  ffi.Pointer fn = ffiTestFunctions.lookup("TestExtension");
  int Function() signedOp = fn
      .cast<ffi.Pointer<ffi.NativeFunction<NativeNullaryOpSigned>>>()
      .asFunction();
  Expect.equals(signedOp(), 0xffffffff80000000);
}

DART_EXPORT int32_t TestExtension() {
  return 1UL << 31;
}

@dcharkes @mraleph

[dcharkes]

We already have a test for this:

DART_EXPORT int32_t ReturnMinInt32() {
  return 0x80000000;
}

void testExtension() {
  Expect.equals(returnMaxUint8(), 0xff);
  Expect.equals(returnMaxUint16(), 0xffff);
  Expect.equals(returnMaxUint32(), 0xffffffff);
  Expect.equals(returnMinInt8(), -0x80);
  Expect.equals(returnMinInt16(), -0x8000);
  Expect.equals(returnMinInt32(), -0x80000000); // here is our test.

  Expect.equals(takeMaxUint8(0xff), 1);
  Expect.equals(takeMaxUint16(0xffff), 1);
  Expect.equals(takeMaxUint32(0xffffffff), 1);
  Expect.equals(takeMinInt8(0x80), 1);
  Expect.equals(takeMinInt16(0x8000), 1);
  Expect.equals(takeMinInt32(0x80000000), 1);
}

And

Expect.equals(-0x80000000, 0xffffffff80000000);