Dotty: Fuzzing test succeeds even though the compiler crashes

[smarter]

cp tests/pending/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala

> testCompilation tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala

[warn] Multiple main classes detected.  Run show discoveredMainClasses to see the list
[info] Test run started
[info] Test dotty.tools.dotc.CompilationTests.negAll started
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
[info] Test dotty.tools.dotc.CompilationTests.runAll started
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
[info] Test dotty.tools.dotc.CompilationTests.pickling started
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
[info] Test dotty.tools.dotc.CompilationTests.pos started
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
[info] Test dotty.tools.dotc.CompilationTests.tastyBootstrap started
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
[info] Test dotty.tools.dotc.CompilationTests.posTwice started
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test
[info] Test dotty.tools.dotc.CompilationTests.fuzzyAll started
java.lang.StackOverflowError            ] completed (0/1, 0 failed, 3s)
        at java.util.IdentityHashMap.remove(IdentityHashMap.java:520)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.recur$1(SymDenotations.scala:1860)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.baseTypeOf(SymDenotations.scala:1867)
        at dotty.tools.dotc.core.Types$Type.baseType(Types.scala:925)
        at dotty.tools.dotc.core.Types$NamedType.argForParam(Types.scala:2060)
        at dotty.tools.dotc.core.Types$NamedType.derivedSelect(Types.scala:2112)
        at dotty.tools.dotc.core.Types$TypeMap.derivedSelect(Types.scala:4345)
        at dotty.tools.dotc.core.Types$ApproximatingTypeMap.derivedSelect(Types.scala:4637)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:63)
        at dotty.tools.dotc.core.Types$TypeMap.mapArgs$1(Types.scala:4407)
        at dotty.tools.dotc.core.Types$TypeMap.mapOver(Types.scala:4415)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:69)
        at dotty.tools.dotc.core.Types$TypeMap.mapOver(Types.scala:4437)
        at dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:69)
        at dotty.tools.dotc.core.TypeOps.asSeenFrom(TypeOps.scala:30)
        at dotty.tools.dotc.core.Contexts$Context.asSeenFrom(Contexts.scala:71)
        at dotty.tools.dotc.core.Types$Type.asSeenFrom(Types.scala:832)
        at dotty.tools.dotc.core.Types$Type.memberInfo(Types.scala:825)
        at dotty.tools.dotc.transform.GenericSignatures$.jsig$1(GenericSignatures.scala:219)
        at dotty.tools.dotc.transform.GenericSignatures$.boxedSig$1(GenericSignatures.scala:64)
        at dotty.tools.dotc.transform.GenericSignatures$.argSig$1(GenericSignatures.scala:145)
        at dotty.tools.dotc.transform.GenericSignatures$.classSig$1$$anonfun$1(GenericSignatures.scala:174)
        at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:392)
        at dotty.tools.dotc.transform.GenericSignatures$.classSig$2(GenericSignatures.scala:174)
        at dotty.tools.dotc.transform.GenericSignatures$.jsig$1(GenericSignatures.scala:228)
        at dotty.tools.dotc.transform.GenericSignatures$.boxedSig$1(GenericSignatures.scala:64)
        at dotty.tools.dotc.transform.GenericSignatures$.argSig$1(GenericSignatures.scala:145)
        at dotty.tools.dotc.transform.GenericSignatures$.classSig$1$$anonfun$1(GenericSignatures.scala:174)
        at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)

[...]
[=======================================] completed (1/1, 0 failed, 4s)
[info] Test dotty.tools.dotc.CompilationTests.genericJavaSignatures started
No files matched "tests/fuzzy/SOE-9cb9025fd025d2e548933c770ce32877f4e21b50.scala" in test

================================================================================
Test Report
================================================================================

1 suites passed, 0 failed, 1 total

[info] Test run finished: 0 failed, 0 ignored, 8 total, 5.452s
[info] Test run started
[info] Test run finished: 0 failed, 0 ignored, 0 total, 0.0s
[info] Passed: Total 8, Failed 0, Errors 0, Passed 8
[success] Total time: 8 s, completed 30 avr. 2019 15:54:00

[nicolasstucki]

The test framework is doing the correct. That stack trace is caught, printed and an error is emitted https://github.com/lampepfl/dotty/blob/master/compiler/src/dotty/tools/backend/jvm/GenBCode.scala#L184. Hence the compiler does not actually crash.

[smarter]

OK we shouldn't catch the exception then, that's not a proper way to report any kind of error.

[nicolasstucki]

Agreed. I already opened #6408 with this fix.

[alexknvl]

This makes me very very happy. @nicolasstucki I used to modify the compiler as described in the https://github.com/lampepfl/dotty/issues/5006#issuecomment-415870060

I believe there might still be other places where exceptions are ignored.

[nicolasstucki]

@alexknvl thanks for the link to your diff. I would have missed someone of those crashes.