Wrong expectation in normalization test.

[crelier]

A new normalization test introduced in this CL does not include requirements to run either in weak or strong mode, therefore, it runs in both modes.

On the VM (a non yet committed version including fixes), this test fails in both modes due to wrong expectations.

Weak mode:

DART_CONFIGURATION=DebugX64 out/DebugX64/dart --enable_asserts --no-null-safety --enable-experiment=non-nullable --ignore-unrecognized-flags --packages=/usr/local/google/home/regis/dart2/sdk/.packages /usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart

exit code:
255

stderr:
Unhandled exception:
Expect.notEquals(unexpected: <<S extends Future<Never>?>() => Never>, actual:<<S extends Future<Never>>() => Never>) fails.
#0      Expect._fail (package:expect/expect.dart:685:5)
#1      Expect.notEquals (package:expect/expect.dart:306:5)
#2      checkNotEquals2 (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/type_builder.dart:134:10)
#3      checkTypeNotEquals2 (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:19:3)
#4      SimpleBoundTests.checkAtBottomType (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:80:7)
#5      SimpleBoundTests.checkBottomTypes (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:88:5)
#6      SimpleBoundTests.check (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:130:5)
#7      main (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:195:20)
#8      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:301:19)
#9      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)

The bounds Future<Never>? and Future<Never> are mutual subtypes, since their nullability is ignored in weak mode.

In strong mode:

DART_CONFIGURATION=DebugX64 out/DebugX64/dart --null-safety --enable-experiment=non-nullable --ignore-unrecognized-flags --packages=/usr/local/google/home/regis/dart2/sdk/.packages /usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart

exit code:
255

stderr:
Unhandled exception:
Expect.notEquals(unexpected: <<S extends FutureOr<Future<Object>>>() => Future<Object>>, actual:<<R extends Future<Object>>() => Future<Object>>) fails.
#0      Expect._fail (package:expect/expect.dart:685:5)
#1      Expect.notEquals (package:expect/expect.dart:306:5)
#2      checkNotEquals2 (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/type_builder.dart:134:10)
#3      checkTypeNotEquals2 (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:19:3)
#4      SimpleBoundTests.checkAtNonNullableType (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:96:5)
#5      SimpleBoundTests.checkNonNullableTypes (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:107:5)
#6      SimpleBoundTests.check (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:131:5)
#7      main (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:195:20)
#8      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:301:19)
#9      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)

Here also, the bounds FutureOr<Future<Object>> and Future<Object> are mutual subtypes.
It is easy to see that Future<Object> is a subtype of FutureOr<Future<Object>>.
The reverse is less obvious. We have to show that Future<Future<Object>> is a subtype of Future<Object> and it is, because Future<Object> is a subtype of Object.

[crelier]

Running the test language/nnbd/normalization/generic_function_type_object_normalization_test.dart in strong mode, the VM encounters two further issues after the one reported above.

The second issue occurs at line 191:
checkTypeNotEquals2(o.i1<Never>(), o.i2<Never>());
where the two types are actually equal. There is a comment near the declaration of i1 and i2 about a CFE issue and what looks like a temporary workaround for this issue, but the workaround is not correct, as the two function types are equal.

The third issue occurs at line 191:

Expect.equals(expected: <<T extends FutureOr<T>?>() => void>, actual: <<S extends FutureOr<S>>() => void>) fails.
#0      Expect._fail (package:expect/expect.dart:685:5)
#1      Expect.equals (package:expect/expect.dart:132:5)
#2      checkEquals2 (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/type_builder.dart:114:10)
#3      checkTypeEquals2 (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:13:3)
#4      fBoundedTests (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:191:3)
#5      main (file:///usr/local/google/home/regis/dart2/sdk/tests/language/nnbd/normalization/generic_function_type_object_normalization_test.dart:197:3)
#6      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:301:19)
#7      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)

Although the source looks like this

  void h1<T extends FutureOr<T?>?>() {}
  void h2<S extends FutureOr<S?>>() {}

  checkTypeEquals2(h1, h2);

the kernel file looks like this

    function h1<T extends asy::FutureOr<T%>? = asy::FutureOr<dynamic>?>() → void {}
    function h2<S extends asy::FutureOr<S%> = asy::FutureOr<dynamic>>() → void {}
    gen::checkTypeEquals2(h1, h2);

which explains the error reported by the VM. The nullability of the type parameters is not correct in the kernel file. Is this a known CFE issue?

[nshahan]

cc @johnniwinther

I'm seeing the same errors from my work in progress change in DDC.

[johnniwinther]

Changed to the issue to a front-end issue for the CFE problem. Will change back if there is more work needed on the test itself after the CFE part has been fixed.

[johnniwinther]

Reopening. The CFE issue has been fixed but none of the mentioned tests were fixed by it so some work seems to be needed on the backend side.

[crelier]

I think that the remaining failures are due to wrong expectations rather than to backend problems. I sent a CL fixing the test: https://dart-review.googlesource.com/c/sdk/+/151440

@johnniwinther The CFE issue #41952 previously mentioned in a comment in the test seems to have been fixed and should probably be closed.