dart2js. Strange runtime error in co19 test

[sgrekhov]

The following test fails with a strange runtime error on dart2js https://github.com/dart-lang/co19/blob/master/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_t02.dart

The output is

/=====================================================================================================================================================================\
| dart2js-hostasserts-strong-linux-x64-chrome:co19/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_t02 is new and failed (RuntimeError, expected Pass) |
\=====================================================================================================================================================================/

--- Command "dart2js" (took 06.000855s):
DART_CONFIGURATION=ReleaseX64 sdk/bin/dart2js_developer --enable-experiment=non-nullable --enable-experiment=non-nullable --test-mode --packages=/b/s/w/ir/.packages /b/s/w/ir/tests/co19/src/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_t02.dart --sound-null-safety --libraries-spec=sdk/lib/libraries.json --platform-binaries=out/ReleaseX64/ --out=/b/s/w/ir/out/ReleaseX64/generated_compilations/dart2js/tests_co19_src_Language_Statements_Yield_and_Yield_Each_Yield_execution_async_t02/execution_async_t02.js

exit code:
0

stdout:
Hint: When run on the command-line, the compiled output might require a preamble file located in:
  <sdk>/lib/_internal/js_runtime/lib/preambles.
Compiled 8,069,034 characters Dart to 223,039 characters JavaScript in 6.85 seconds
Dart file /b/s/w/ir/tests/co19/src/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_t02.dart compiled to JavaScript: out/ReleaseX64/generated_compilations/dart2js/tests_co19_src_Language_Statements_Yield_and_Yield_Each_Yield_execution_async_t02/execution_async_t02.js

--- Command "chrome" (took 225ms):
/b/s/w/ir/tools/sdks/dart-sdk/bin/dart pkg/test_runner/bin/launch_browser.dart chrome http://127.0.0.1:38753/root_build/generated_tests/dart2js-chrome/tests_co19_src_Language_Statements_Yield_and_Yield_Each_Yield_execution_async_t02/test.html?crossOriginPort=33223

Runtime window.onerror:
window.onerror called:

http://127.0.0.1:38753/root_build/generated_compilations/dart2js/tests_co19_src_Language_Statements_Yield_and_Yield_Each_Yield_execution_async_t02/execution_async_t02.js:5270:
Uncaught



Deobfuscated error and stack:
<no error message found>
    at window.onerror called:               unparsed
    at _rootHandleUncaughtError.<anonymous> org-dartlang-sdk:///lib/async/zone.dart 1175:21
    at Uncaught                             unparsed


exit code:
0

--- To debug locally, run:
/b/s/w/ir/tools/sdks/dart-sdk/bin/dart /b/s/w/ir/pkg/test_runner/bin/http_server.dart -p 38753 -c 33223 --network 127.0.0.1 --build-directory=/b/s/w/ir/out/ReleaseX64/ --runtime=chrome --packages=/b/s/w/ir/.packages

--- Re-run this test:
python tools/test.py -n dart2js-hostasserts-strong-linux-x64-chrome --dart2js-batch co19/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_t02

[fishythefish]

This seems to be affecting async-related co19 tests on both strong and weak NNBD. For example, LanguageFeatures/nnbd/future_flattening_A01_t12 also fails the same way on dart2js-hostasserts-weak-linux-x64-chrome.

You can get a clearer error message by using the d8 runtime rather than chrome:

tools/test.py -cdart2js -rd8 --enable-experiment="non-nullable" --nnbd=strong --dart2js-options="--sound-null-safety" co19/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_t02

For weak mode, change --nnbd=strong to --nnbd=weak and --sound-null-safety to --no-sound-null-safety.

[fishythefish]

@nshahan @Markzipan Based on the remaining DDC failures, I suspect you might have run into this as well?

/cc @rakudrama @sigmundch

[nshahan]

Originally the future flattening tests were failing due to a lack of an implicit downcast from dynamic in the kernel. That was fixed recently https://dart-review.googlesource.com/c/sdk/+/152150 but I haven't gotten around to fixing the DDC output to make sure the cast is performed (and fails for these tests).

[nshahan]

I just noticed that LanguageFeatures/nnbd/future_flattening_A01_t12 and LanguageFeatures/nnbd/future_flattening_A01_t40 have incorrect expectations for weak mode. They have been updated dart-lang/co19#785 but the changes have not yet been rolled into the SDK.

cc @athomas

[sgrekhov]

Closing as fixed by dart-lang/co19#785