[Enhanced Enums] co19/LanguageFeatures/Enhanced-Enum/semantics_A10_t05 test fails on dartdevk-{strong,weak}-linux-release-chrome

[sgrekhov]

The following co19 test https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Enhanced-Enum/semantics_A10_t05.dart
fails with the following error

/============================================================================================================================================\
| dartdevk-strong-linux-release-chrome:co19/LanguageFeatures/Enhanced-Enum/semantics_A10_t05 is new and failed (RuntimeError, expected Pass) |
\============================================================================================================================================/

--- Command "dartdevc" (took 163ms):
DART_CONFIGURATION=ReleaseX64 CHROME_PATH=/b/s/w/ir/cache/builder/sdk/third_party/browsers/chrome/chrome/google-chrome out/ReleaseX64/dart-sdk/bin/dart out/ReleaseX64/dart-sdk/bin/snapshots/dartdevc.dart.snapshot -Dtest_runner.configuration=dartdevk-strong-linux-release-chrome --enable-experiment=enhanced-enums --sound-null-safety -Dtest_runner.configuration=dartdevk-strong-linux-release-chrome --ignore-unrecognized-flags --no-summarize -o /b/s/w/ir/cache/builder/sdk/out/ReleaseX64/generated_compilations/dartdevk-strong-linux-release-chrome/tests_co19_src_LanguageFeatures_Enhanced-Enum_semantics_A10_t05/semantics_A10_t05.js /b/s/w/ir/cache/builder/sdk/tests/co19/src/LanguageFeatures/Enhanced-Enum/semantics_A10_t05.dart -s /b/s/w/ir/cache/builder/sdk/out/ReleaseX64/gen/utils/dartdevc/pkg_sound/async_helper.dill=async_helper -s /b/s/w/ir/cache/builder/sdk/out/ReleaseX64/gen/utils/dartdevc/pkg_sound/expect.dill=expect -s /b/s/w/ir/cache/builder/sdk/out/ReleaseX64/gen/utils/dartdevc/pkg_sound/js.dill=js -s /b/s/w/ir/cache/builder/sdk/out/ReleaseX64/gen/utils/dartdevc/pkg_sound/meta.dill=meta

exit code:
0

stdout:
Experiment constructor-tearoffs is enabled by default. The use of the flag is deprecated.

--- Command "chrome" (took 638ms):
/b/s/w/ir/cache/builder/sdk/tools/sdks/dart-sdk/bin/dart pkg/test_runner/bin/launch_browser.dart chrome http://127.0.0.1:33939/root_build/generated_tests/dartdevk-strong-linux-release-chrome/tests_co19_src_LanguageFeatures_Enhanced-Enum_semantics_A10_t05/test.html?crossOriginPort=39373

Runtime error:
Error: Expect.isTrue(false) fails.
    at Object.throw_ [as throw] (http://127.0.0.1:33939/root_build/gen/utils/dartdevc/sound/amd/dart_sdk.js:4648:11)
    at Object._fail (http://127.0.0.1:33939/root_dart/out/ReleaseX64/generated_compilations/dartdevk-strong-linux-release-chrome/tests_co19_src_LanguageFeatures_Enhanced-Enum_semantics_A10_t05/semantics_A10_t05.js:755:15)
    at Function.isTrue (http://127.0.0.1:33939/root_dart/out/ReleaseX64/generated_compilations/dartdevk-strong-linux-release-chrome/tests_co19_src_LanguageFeatures_Enhanced-Enum_semantics_A10_t05/semantics_A10_t05.js:232:16)
    at Object.main (http://127.0.0.1:33939/root_dart/out/ReleaseX64/generated_compilations/dartdevk-strong-linux-release-chrome/tests_co19_src_LanguageFeatures_Enhanced-Enum_semantics_A10_t05/semantics_A10_t05.js:208:19)
    at testMainWrapper (http://127.0.0.1:33939/root_build/generated_tests/dartdevk-strong-linux-release-chrome/tests_co19_src_LanguageFeatures_Enhanced-Enum_semantics_A10_t05/test.html?crossOriginPort=39373:86:105)

Deobfuscated error and stack:
Error: Expect.isTrue(false) fails.
    at Object.throw_   out/ReleaseX64/gen/utils/dartdevc/sound/amd/dart_sdk.js 4648:11
    at Object._fail    ../../../../../tests/co19/src/Utils/expect.dart 18:5
    at Function.isTrue ../../../../../tests/co19/src/Utils/expect_common.dart 24:7
    at Object.main     ../../../../../tests/co19/src/LanguageFeatures/Enhanced-Enum/semantics_A10_t05.dart 55:10
    at testMainWrapper out/ReleaseX64/generated_tests/dartdevk-strong-linux-release-chrome/tests_co19_src_LanguageFeatures_Enhanced-Enum_semantics_A10_t05/test.html 86:105


exit code:
0

--- To debug locally, run:
/b/s/w/ir/cache/builder/sdk/tools/sdks/dart-sdk/bin/dart /b/s/w/ir/cache/builder/sdk/pkg/test_runner/bin/http_server.dart -p 33939 -c 39373 --network 127.0.0.1 --build-directory=/b/s/w/ir/cache/builder/sdk/out/ReleaseX64/ --runtime=chrome --packages=/b/s/w/ir/cache/builder/sdk/.packages

--- Re-run this test:
python3 tools/test.py -n dartdevk-strong-linux-release-chrome co19/LanguageFeatures/Enhanced-Enum/semantics_A10_t05

This is a dartdevk issue. Wrong semantics in evaluation of operator== of E1

[Markzipan]

As a heads up, the language team has decided to disallow overriding of == for enhanced enums (it's not in the spec yet though). Updating the test should resolve this failure.

[eernstg]

the language team has decided to disallow overriding of == for enhanced enums

We did discuss operator == recently, but I'm not aware of a decision to make it an error to override it with enhanced enums.

One thing which is relevant to operator == (but which is not new) is that the enum does not 'have a primitive operator ==' if there is a concrete declaration of operator == in the enum or a superclass that overrides the one which is inherited from Object. And if an enum (or a class) does not have a primitive operator == then its instances cannot be elements in a constant set, or keys in a constant map, or cases in a switch. So you can override operator ==, but it carries a cost.

(And there's a separate discussion about hashCode, cf. dart-lang/language#2108.)

[Markzipan]

Thanks for the clarification, @eernstg! I have a change out that resolves this bug, but I may let it sit until there's resolution here. Pinging @nshahan on this point as well.

[nshahan]

@eernstg I cc'd you in the doc comment thread where this topic came up.

@rakudrama Do you recall the details about this? I thought we were asking to disallow overriding equality so that enums can still be used in native javascript switch statements.

[eernstg]

@nshahan wrote:

disallow overriding equality so that enums can still be used in native javascript switch statements

I would assume that the ability to override operator == in an enum declaration, or in a superclass thereof, would make it an error for that particular enum's values to occur as case values in a switch, to be a member of a constant set, or to be a key of a constant map; but all other enum declarations would not be affected. This corresponds to the description I gave, a la "it is possible, but that particular enum is then less usable".

(hashCode might be treated the same as operator ==, dart-lang/language#2108.)

But we could of course make it an error, based on the assumption that this trade-off is never going to work well in practice.

[lrhn]

If your enum overrides operator==, you can't use that enum type in Dart switches, so there should be no need to use them in JavaScript switches either (at least not while worrying about matching any Dart equality semantics).

I'm not aware of any currently open issues on operator== of enhanced enums, so I'm not sure there is any resolution to wait for.

If we end up changing the rules about "primitive hashCode", or constant equality, it will have effects beyond enhanced enums, and will likely require a dedicated change unrelated to enhanced enums.

[eernstg]

The language team just decided that it is an error for an enum declaration to have an implementation of operator == or hashCode that overrides the one which is inherited from Object. The spec will be updated accordingly.