Using 'lambda' in a method name triggers an assertion failure in the compiler

[LPTK]

The bug looks very arcane, and I did not manage to reduce it to a simple self-contained example. Here is a permanent link to the place where the problematic method is defined, in my code base.

Try renaming lamImpl to lambdaImpl. When compiling such code (with sbt compile), an assertion is raised with the following message:

$ sbt compile
[info] Loading global plugins from user/.sbt/0.13/plugins
[info] Loading project definition from squid/project
[info] Set current project to squid (in build file:squid/)
[info] Executing in batch mode. For better performance use sbt's shell
[info] Compiling 1 Scala source to squid/core/target/scala-2.12/classes...
java.lang.AssertionError: assertion failed:
  MetaBases$MirrorBase$$anonfun$lambdaImpl$2
     while compiling: squid/core/src/main/scala/squid/quasi/MetaBases.scala
        during phase: jvm
     library version: version 2.12.5
    compiler version: version 2.12.5
  reconstructed args: -deprecation -Xplugin:user/.ivy2/cache/org.scalamacros/paradise_2.12.5/jars/paradise_2.12.5-2.1.0.jar -feature -language:postfixOps -language:implicitConversions -language:higherKinds -classpath squid/core/target/scala-2.12/classes:squid/core_macros/target/scala-2.12/classes:user/.ivy2/cache/org.scala-lang/scala-compiler/jars/scala-compiler-2.12.5.jar:user/.ivy2/cache/org.scala-lang/scala-reflect/jars/scala-reflect-2.12.5.jar:user/.ivy2/cache/org.scala-lang.modules/scala-xml_2.12/bundles/scala-xml_2.12-1.0.6.jar:user/.ivy2/cache/org.scalactic/scalactic_2.12/bundles/scalactic_2.12-3.0.5.jar -unchecked -bootclasspath /Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/sunrsasign.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/classes:user/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.12.5.jar

  last tree to typer: TypeTree(class Universe)
       tree position: line 406 of squid/core/src/main/scala/squid/quasi/MetaBases.scala
            tree tpe: scala.reflect.api.Universe
              symbol: abstract class Universe in package api
   symbol definition: abstract class Universe extends Symbols with Types with FlagSets with Scopes with Names with Trees with Constants with Annotations with Positions with Exprs with TypeTags with ImplicitTags with StandardDefinitions with StandardNames with StandardLiftables with Mirrors with Printers with Liftables with Quasiquotes with Internals (a ClassSymbol)
      symbol package: scala.reflect.api
       symbol owners: class Universe
           call site: constructor MetaBases$Runtime$ScalaReflectionBase in object MetaBases$Runtime$ScalaReflectionBase in package quasi

== Source file context for tree position ==

   403
   404 object MetaBases {
   405
   406   object Runtime extends MetaBases {
   407     val u: sru.type = sru
   408
   409     private var varCount = 0
	at scala.reflect.internal.SymbolTable.throwAssertionError(SymbolTable.scala:163)
	at scala.tools.nsc.backend.jvm.BCodeHelpers.isAnonymousOrLocalClass(BCodeHelpers.scala:77)
	at scala.tools.nsc.backend.jvm.BCodeHelpers.enclosingMethodAttribute(BCodeHelpers.scala:199)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.initJClass(BCodeSkelBuilder.scala:140)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:95)
	at scala.tools.nsc.backend.jvm.CodeGen.genClass(CodeGen.scala:69)
	at scala.tools.nsc.backend.jvm.CodeGen.genClassDef$1(CodeGen.scala:31)
	at scala.tools.nsc.backend.jvm.CodeGen.$anonfun$genUnit$3(CodeGen.scala:54)
	at scala.tools.nsc.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:54)
	at scala.tools.nsc.backend.jvm.CodeGen.$anonfun$genUnit$2(CodeGen.scala:53)
	at scala.tools.nsc.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:53)
	at scala.tools.nsc.backend.jvm.CodeGen.$anonfun$genUnit$2(CodeGen.scala:53)
	at scala.tools.nsc.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:53)
	at scala.tools.nsc.backend.jvm.CodeGen.$anonfun$genUnit$4(CodeGen.scala:58)
	at scala.tools.nsc.backend.jvm.CodeGen.genUnit(CodeGen.scala:58)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.apply(GenBCode.scala:67)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$applyPhase$1(Global.scala:426)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:419)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1(Global.scala:390)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1$adapted(Global.scala:390)
	at scala.collection.Iterator.foreach(Iterator.scala:944)
	at scala.collection.Iterator.foreach$(Iterator.scala:944)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1432)
	at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:390)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.super$run(GenBCode.scala:73)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.$anonfun$run$1(GenBCode.scala:73)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:71)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1446)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1430)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1423)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1539)
	at xsbt.CachedCompiler0.run(CompilerInterface.scala:116)
	at xsbt.CachedCompiler0.run(CompilerInterface.scala:95)
	at xsbt.CompilerInterface.run(CompilerInterface.scala:26)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:107)
	at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:53)
	at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:47)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply$mcV$sp(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:74)
	at sbt.compiler.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:49)
	at sbt.compiler.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:64)
	at sbt.compiler.IC$$anonfun$compileInternal$1.apply(IncrementalCompiler.scala:160)
	at sbt.compiler.IC$$anonfun$compileInternal$1.apply(IncrementalCompiler.scala:160)
	at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply(Compile.scala:66)
	at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply(Compile.scala:64)
	at sbt.inc.IncrementalCommon.cycle(IncrementalCommon.scala:32)
	at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:72)
	at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:71)
	at sbt.inc.Incremental$.manageClassfiles(Incremental.scala:99)
	at sbt.inc.Incremental$.compile(Incremental.scala:71)
	at sbt.inc.IncrementalCompile$.apply(Compile.scala:54)
	at sbt.compiler.IC$.compileInternal(IncrementalCompiler.scala:160)
	at sbt.compiler.IC$.incrementalCompile(IncrementalCompiler.scala:138)
	at sbt.Compiler$.compile(Compiler.scala:155)
	at sbt.Compiler$.compile(Compiler.scala:141)
	at sbt.Defaults$.sbt$Defaults$$compileIncrementalTaskImpl(Defaults.scala:913)
	at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:904)
	at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:902)
	at scala.Function1$$anonfun$compose$1.apply(Function1.scala:47)
	at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:40)
	at sbt.std.Transform$$anon$4.work(System.scala:63)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:228)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:228)
	at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
	at sbt.Execute.work(Execute.scala:237)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:228)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:228)
	at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:159)
	at sbt.CompletionService$$anon$2.call(CompletionService.scala:28)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
[error] Error while emitting MetaBases.scala
[error] assertion failed:
[error]   MetaBases$MirrorBase$$anonfun$lambdaImpl$2
[error]      while compiling: squid/core/src/main/scala/squid/quasi/MetaBases.scala
[error]         during phase: jvm
[error]      library version: version 2.12.5
[error]     compiler version: version 2.12.5
[error]   reconstructed args: -deprecation -Xplugin:user/.ivy2/cache/org.scalamacros/paradise_2.12.5/jars/paradise_2.12.5-2.1.0.jar -feature -language:postfixOps -language:implicitConversions -language:higherKinds -classpath squid/core/target/scala-2.12/classes:squid/core_macros/target/scala-2.12/classes:user/.ivy2/cache/org.scala-lang/scala-compiler/jars/scala-compiler-2.12.5.jar:user/.ivy2/cache/org.scala-lang/scala-reflect/jars/scala-reflect-2.12.5.jar:user/.ivy2/cache/org.scala-lang.modules/scala-xml_2.12/bundles/scala-xml_2.12-1.0.6.jar:user/.ivy2/cache/org.scalactic/scalactic_2.12/bundles/scalactic_2.12-3.0.5.jar -unchecked -bootclasspath /Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/sunrsasign.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/classes:user/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.12.5.jar
[error]
[error]   last tree to typer: TypeTree(class Universe)
[error]        tree position: line 406 of squid/core/src/main/scala/squid/quasi/MetaBases.scala
[error]             tree tpe: scala.reflect.api.Universe
[error]               symbol: abstract class Universe in package api
[error]    symbol definition: abstract class Universe extends Symbols with Types with FlagSets with Scopes with Names with Trees with Constants with Annotations with Positions with Exprs with TypeTags with ImplicitTags with StandardDefinitions with StandardNames with StandardLiftables with Mirrors with Printers with Liftables with Quasiquotes with Internals (a ClassSymbol)
[error]       symbol package: scala.reflect.api
[error]        symbol owners: class Universe
[error]            call site: constructor MetaBases$Runtime$ScalaReflectionBase in object MetaBases$Runtime$ScalaReflectionBase in package quasi
[error]
[error] == Source file context for tree position ==
[error]
[error]    403
[error]    404 object MetaBases {
[error]    405
[error]    406   object Runtime extends MetaBases {
[error]    407     val u: sru.type = sru
[error]    408
[error]    409     private var varCount = 0
java.lang.AssertionError: assertion failed: MetaBases$MirrorBase$$anonfun$lambdaImpl$2
	at scala.reflect.internal.SymbolTable.throwAssertionError(SymbolTable.scala:163)
	at scala.tools.nsc.backend.jvm.BCodeHelpers.isAnonymousOrLocalClass(BCodeHelpers.scala:77)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.buildNonEmptyNestedInfo(BTypesFromSymbols.scala:471)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.$anonfun$computeClassInfo$22(BTypesFromSymbols.scala:432)
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.$anonfun$computeClassInfo$21(BTypesFromSymbols.scala:432)
	at scala.tools.nsc.backend.jvm.BTypes$Lazy$LazyWithLock.$anonfun$init$1(BTypes.scala:1009)
	at scala.tools.nsc.backend.jvm.BTypes$Lazy$LazyWithLock.init(BTypes.scala:1008)
	at scala.tools.nsc.backend.jvm.BTypes$Lazy$AbstractLazy.force(BTypes.scala:990)
	at scala.tools.nsc.backend.jvm.BTypes$ClassBType.$anonfun$isNestedClass$1(BTypes.scala:681)
	at scala.tools.nsc.backend.jvm.BTypes$ClassBType.isNestedClass(BTypes.scala:681)
	at scala.tools.nsc.backend.jvm.BTypes$ClassBType.$anonfun$checkInfoConsistency$10(BTypes.scala:657)
	at scala.tools.nsc.backend.jvm.BTypes$ClassBType.$anonfun$checkInfoConsistency$9(BTypes.scala:657)
	at scala.tools.nsc.backend.jvm.BTypes$ClassBType.$anonfun$checkInfoConsistency$7(BTypes.scala:657)
	at scala.tools.nsc.backend.jvm.BTypes$ClassBType.$anonfun$checkInfoConsistency$7$adapted(BTypes.scala:656)
	at scala.tools.nsc.backend.jvm.BTypes$Lazy$AbstractLazy.force(BTypes.scala:993)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$Collector.declaredNestedClasses(BackendUtils.scala:328)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$NestedClassesCollector.visit(BackendUtils.scala:604)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils.collectNestedClasses(BackendUtils.scala:344)
	at scala.tools.nsc.backend.jvm.PostProcessor.setInnerClasses(PostProcessor.scala:125)
	at scala.tools.nsc.backend.jvm.PostProcessor.sendToDisk(PostProcessor.scala:59)
	at scala.tools.nsc.backend.jvm.GeneratedClassHandler$WritingClassHandler.$anonfun$postProcessUnit$3(GeneratedClassHandler.scala:112)
	at scala.tools.nsc.backend.jvm.GeneratedClassHandler$WritingClassHandler.$anonfun$postProcessUnit$2(GeneratedClassHandler.scala:112)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at scala.tools.nsc.backend.jvm.PostProcessorFrontendAccess$PostProcessorFrontendAccessImpl.withThreadLocalReporter(PostProcessorFrontendAccess.scala:213)
	at scala.tools.nsc.backend.jvm.GeneratedClassHandler$WritingClassHandler.$anonfun$postProcessUnit$1(GeneratedClassHandler.scala:111)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at scala.concurrent.Future$.$anonfun$apply$1(Future.scala:654)
	at scala.util.Success.$anonfun$map$1(Try.scala:251)
	at scala.util.Success.map(Try.scala:209)
	at scala.concurrent.Future.$anonfun$map$1(Future.scala:288)
	at scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:29)
	at scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:29)
	at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
	at scala.tools.nsc.backend.jvm.GeneratedClassHandler$SyncWritingClassHandler$$anonfun$$lessinit$greater$1.execute(GeneratedClassHandler.scala:165)
	at scala.concurrent.impl.ExecutionContextImpl.execute(ExecutionContextImpl.scala:20)
	at scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:68)
	at scala.concurrent.impl.Promise$KeptPromise$Kept.onComplete(Promise.scala:368)
	at scala.concurrent.impl.Promise$KeptPromise$Kept.onComplete$(Promise.scala:367)
	at scala.concurrent.impl.Promise$KeptPromise$Successful.onComplete(Promise.scala:375)
	at scala.concurrent.impl.Promise.transform(Promise.scala:29)
	at scala.concurrent.impl.Promise.transform$(Promise.scala:27)
	at scala.concurrent.impl.Promise$KeptPromise$Successful.transform(Promise.scala:375)
	at scala.concurrent.Future.map(Future.scala:288)
	at scala.concurrent.Future.map$(Future.scala:288)
	at scala.concurrent.impl.Promise$KeptPromise$Successful.map(Promise.scala:375)
	at scala.tools.nsc.backend.jvm.GeneratedClassHandler$WritingClassHandler.postProcessUnit(GeneratedClassHandler.scala:107)
	at scala.tools.nsc.backend.jvm.GeneratedClassHandler$WritingClassHandler.process(GeneratedClassHandler.scala:100)
	at scala.tools.nsc.backend.jvm.CodeGen.genUnit(CodeGen.scala:61)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.apply(GenBCode.scala:67)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$applyPhase$1(Global.scala:426)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:419)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1(Global.scala:390)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1$adapted(Global.scala:390)
	at scala.collection.Iterator.foreach(Iterator.scala:944)
	at scala.collection.Iterator.foreach$(Iterator.scala:944)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1432)
	at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:390)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.super$run(GenBCode.scala:73)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.$anonfun$run$1(GenBCode.scala:73)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:71)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1446)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1430)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1423)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1539)
	at xsbt.CachedCompiler0.run(CompilerInterface.scala:116)
	at xsbt.CachedCompiler0.run(CompilerInterface.scala:95)
	at xsbt.CompilerInterface.run(CompilerInterface.scala:26)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:107)
	at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:53)
	at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:47)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply$mcV$sp(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:74)
	at sbt.compiler.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:49)
	at sbt.compiler.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:64)
	at sbt.compiler.IC$$anonfun$compileInternal$1.apply(IncrementalCompiler.scala:160)
	at sbt.compiler.IC$$anonfun$compileInternal$1.apply(IncrementalCompiler.scala:160)
	at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply(Compile.scala:66)
	at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply(Compile.scala:64)
	at sbt.inc.IncrementalCommon.cycle(IncrementalCommon.scala:32)
	at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:72)
	at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:71)
	at sbt.inc.Incremental$.manageClassfiles(Incremental.scala:99)
	at sbt.inc.Incremental$.compile(Incremental.scala:71)
	at sbt.inc.IncrementalCompile$.apply(Compile.scala:54)
	at sbt.compiler.IC$.compileInternal(IncrementalCompiler.scala:160)
	at sbt.compiler.IC$.incrementalCompile(IncrementalCompiler.scala:138)
	at sbt.Compiler$.compile(Compiler.scala:155)
	at sbt.Compiler$.compile(Compiler.scala:141)
	at sbt.Defaults$.sbt$Defaults$$compileIncrementalTaskImpl(Defaults.scala:913)
	at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:904)
	at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:902)
	at scala.Function1$$anonfun$compose$1.apply(Function1.scala:47)
	at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:40)
	at sbt.std.Transform$$anon$4.work(System.scala:63)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:228)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:228)
	at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
	at sbt.Execute.work(Execute.scala:237)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:228)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:228)
	at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:159)
	at sbt.CompletionService$$anon$2.call(CompletionService.scala:28)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
[error] Error while emitting squid/quasi/MetaBases$MirrorBase
[error] assertion failed: MetaBases$MirrorBase$$anonfun$lambdaImpl$2
[error] two errors found
[error] (core/compile:compileIncremental) Compilation failed

[hrhino]

Seems like a manifestation of #2806.

[SethTisue]

agree, I suggest this be a comment on #2806 and we close it here.

[sjrd]

Here is a self-contained, probably close to minimal reproduction:

package test

class JSFunction

trait JSFunction0[+R] extends JSFunction {
  def apply(): R
}

object A {
  def lambdaAnything() = test(() => 1)
  def test(cmp: JSFunction0[Int]) = ()
}

$ cs launch scalac:2.13.8 -- Test.scala 
error: Error while emitting Test.scala
assertion failed:
  A$$anonfun$lambdaAnything$2
     while compiling: Test.scala
        during phase: jvm
     library version: version 2.13.8
    compiler version: version 2.13.8
  reconstructed args:

  last tree to typer: TypeTree(<$anon: test.JSFunction with test.JSFunction0>)
       tree position: line 10 of Test.scala
            tree tpe: test.anonfun$lambdaAnything$2
              symbol: final <$anon: test.JSFunction with test.JSFunction0> in package test
   symbol definition: final class anonfun$lambdaAnything$2 extends JSFunction with JSFunction0 (a ClassSymbol)
      symbol package: test
       symbol owners: <$anon: test.JSFunction with test.JSFunction0>
           call site: constructor A$$anonfun$lambdaAnything$2 in package test

== Source file context for tree position ==

     7 }
     8
     9 object A {
    10   def lambdaAnything() = test(() => 1)
    11   def test(cmp: JSFunction0[Int]) = ()
    12 }
    13
error: Error while emitting Test.scala
assertion failed: A$$anonfun$lambdaAnything$2
2 errors

Reproducible with 2.12.15 and 2.13.8.