Assertion error from the compiler if no clean build done before compile (i.e. incremental build)

[j-mie6]

I'm getting this error if I don't clean build after editing a specific file in my project:

[error] java.lang.AssertionError: assertion failed: denotation module class assembler invalid in run 1. ValidFor: Period(1..56, run = 2)
[error] 	at dotty.DottyPredef$.assertFail(DottyPredef.scala:16)
[error] 	at dotty.tools.dotc.core.Denotations$SingleDenotation.updateValidity(Denotations.scala:817)
[error] 	at dotty.tools.dotc.core.Denotations$SingleDenotation.bringForward(Denotations.scala:844)
[error] 	at dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:899)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.recomputeDenot(Symbols.scala:486)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.computeDenot(Symbols.scala:481)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.denot(Symbols.scala:475)
[error] 	at dotty.tools.dotc.core.SymDenotations.stillValidInOwner(SymDenotations.scala:62)
[error] 	at dotty.tools.dotc.core.Contexts$Context.stillValidInOwner(Contexts.scala:71)
[error] 	at dotty.tools.dotc.core.SymDenotations.stillValid(SymDenotations.scala:56)
[error] 	at dotty.tools.dotc.core.Contexts$Context.stillValid(Contexts.scala:71)
[error] 	at dotty.tools.dotc.core.Denotations$SingleDenotation.bringForward(Denotations.scala:844)
[error] 	at dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:899)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.recomputeDenot(Symbols.scala:486)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.computeDenot(Symbols.scala:481)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.denot(Symbols.scala:475)
[error] 	at dotty.tools.dotc.core.SymDenotations.stillValidInOwner(SymDenotations.scala:62)
[error] 	at dotty.tools.dotc.core.Contexts$Context.stillValidInOwner(Contexts.scala:71)
[error] 	at dotty.tools.dotc.core.SymDenotations.stillValid(SymDenotations.scala:56)
[error] 	at dotty.tools.dotc.core.Contexts$Context.stillValid(Contexts.scala:71)
[error] 	at dotty.tools.dotc.core.Denotations$SingleDenotation.bringForward(Denotations.scala:844)
[error] 	at dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:899)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.recomputeDenot(Symbols.scala:486)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.computeDenot(Symbols.scala:481)
[error] 	at dotty.tools.dotc.core.Symbols$Symbol.denot(Symbols.scala:475)
[error] 	at dotty.tools.dotc.core.Symbols$.toDenot(Symbols.scala:827)
[error] 	at dotty.tools.dotc.core.MergeError.showSymbol(TypeErrors.scala:170)
[error] 	at dotty.tools.dotc.core.MergeError.toMessage(TypeErrors.scala:191)
[error] 	at dotty.tools.dotc.Driver.doCompile(Driver.scala:42)
[error] 	at dotty.tools.dotc.Driver.process(Driver.scala:172)
[error] 	at dotty.tools.dotc.Main.process(Main.scala)
[error] 	at xsbt.CachedCompilerImpl.run(CachedCompilerImpl.java:69)
[error] 	at xsbt.CompilerInterface.run(CompilerInterface.java:41)
[error] 	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error] 	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[error] 	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error] 	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
[error] 	at sbt.internal.inc.AnalyzingCompiler.call(AnalyzingCompiler.scala:237)
[error] 	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:111)
[error] 	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:90)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$3(MixedAnalyzingCompiler.scala:82)
[error] 	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:133)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:73)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:116)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:307)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:307)
[error] 	at sbt.internal.inc.Incremental$.doCompile(Incremental.scala:106)
[error] 	at sbt.internal.inc.Incremental$.$anonfun$compile$4(Incremental.scala:87)
[error] 	at sbt.internal.inc.IncrementalCommon.recompileClasses(IncrementalCommon.scala:116)
[error] 	at sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:63)
[error] 	at sbt.internal.inc.Incremental$.$anonfun$compile$3(Incremental.scala:89)
[error] 	at sbt.internal.inc.Incremental$.manageClassfiles(Incremental.scala:134)
[error] 	at sbt.internal.inc.Incremental$.compile(Incremental.scala:80)
[error] 	at sbt.internal.inc.IncrementalCompile$.apply(Compile.scala:67)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:311)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:269)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:159)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:238)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:69)
[error] 	at sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:1549)
[error] 	at sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:1523)
[error] 	at scala.Function1.$anonfun$compose$1(Function1.scala:44)
[error] 	at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:40)
[error] 	at sbt.std.Transform$$anon$4.work(System.scala:67)
[error] 	at sbt.Execute.$anonfun$submit$2(Execute.scala:269)
[error] 	at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:16)
[error] 	at sbt.Execute.work(Execute.scala:278)
[error] 	at sbt.Execute.$anonfun$submit$1(Execute.scala:269)
[error] 	at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:178)
[error] 	at sbt.CompletionService$$anon$2.call(CompletionService.scala:37)
[error] 	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] 	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
[error] 	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] 	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
[error] 	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
[error] 	at java.base/java.lang.Thread.run(Thread.java:834)
[error] (Compile / compileIncremental) java.lang.AssertionError: assertion failed: denotation module class assembler invalid in run 1. ValidFor: Period(1..56, run = 2)

Clean compiling fixes the problem. I do not need to clean build if changing any other file, just this specific one. The files makes use of the new trait parameters (with default parameters) and extending multiple of them in each class. There are other things in the file, but they were verbatim taken from the build with Scala 2.12.

[newca12]

This issue and #6643 are probably related (similar stack trace)

[smarter]

@j-mie6 Could you link to a github project where the problem can be reproduced, with the exact steps needed to reproduce it ?

[j-mie6]

Looks like it is something to do with implicit functions, traits, multiple files and who knows what else!
minimal-bug.zip

In order to reproduce, do the following:

bash> sbt
sbt> ;clean;compile

Then edit Bad.scala by introducing a space or something, and finally:

sbt> compile

[newca12]

FWIW even simplier
dotc foo/Oops.scala and then dotc foo/Bad.scala lead to the same stack trace.
while dotc foo/Oops.scala foo/Bad.scala work just fine.

[griggt]

This seems to have been fixed by #8386.