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compiler crash in new JVM backend with shapeless #9392

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scabug opened this issue Jul 11, 2015 · 10 comments
Closed

compiler crash in new JVM backend with shapeless #9392

scabug opened this issue Jul 11, 2015 · 10 comments
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@retronym
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backend
Milestone
2.12.0-M2

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@scabug
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scabug commented Jul 11, 2015

Compiling the following,

import shapeless._
case class Quux()
Lazy[Generic[Quux]]

with Scala 2.12.0-M2 against the shapeless-2.2.4 source tree results in the following crash,

java.lang.AssertionError: assertion failed: Cannot create ClassBType from non-class symbol value <local L                                                                                                                                      azyTests>                                                                                                                                                                                                                                      
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol(BTypesFromSymbols.scala:105                                                                                                                                      )                                                                                                                                                                                                                                              
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.buildNestedInfo(BTypesFromSymbols.scala:379)                                                                                                                                          
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.setClassInfo(BTypesFromSymbols.scala:340)                                                                                                                                             
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.scala$tools$nsc$backend$jvm$BTypesFromSymbols$$$                                                                                                                                      anonfun$4(BTypesFromSymbols.scala:120)                                                                                                                                                                                                         
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols$$Lambda$1335/31327414.apply(Unknown Source)                                                                                                                                           
        at scala.collection.MapLike$class.getOrElse(MapLike.scala:128)                                                                                                                                                                         
        at scala.collection.concurrent.TrieMap.getOrElse(TrieMap.scala:633)                                                                                                                                                                    
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol(BTypesFromSymbols.scala:112                                                                                                                                      )                                                                                                                                                                                                                                              
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.scala$tools$nsc$backend$jvm$BTypesFromSymbols$$$                                                                                                                                      anonfun$8(BTypesFromSymbols.scala:153)                                                                                                                                                                                                         
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols$$Lambda$1372/756156527.apply(Unknown Source)                                                                                                                                          
        at scala.collection.MapLike$class.getOrElse(MapLike.scala:128)                                                                                                                                                                         
        at scala.collection.AbstractMap.getOrElse(Map.scala:59)                                                                                                                                                                                
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.primitiveOrClassToBType$1(BTypesFromSymbols.scal                                                                                                                                      a:153)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.typeToBType(BTypesFromSymbols.scala:168)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.methodBTypeFromSymbol(BTypesFromSymbols.scala:133)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.scala$tools$nsc$backend$jvm$BTypesFromSymbols$$$anonfun$37(BTypesFromSymbols.scala:412)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols$$Lambda$1391/428986689.apply(Unknown Source)
        at scala.tools.nsc.backend.jvm.BCodeAsmCommon.scala$tools$nsc$backend$jvm$BCodeAsmCommon$$$anonfun$21(BCodeAsmCommon.scala:394)
        at scala.tools.nsc.backend.jvm.BCodeAsmCommon$$Lambda$1393/936737348.apply(Unknown Source)
        at scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:435)
        at scala.collection.Iterator$class.foreach(Iterator.scala:781)
        at scala.collection.AbstractIterator.foreach(Iterator.scala:1267)
        at scala.collection.TraversableOnce$class.toMap(TraversableOnce.scala:314)
        at scala.collection.AbstractIterator.toMap(Iterator.scala:1267)
        at scala.tools.nsc.backend.jvm.BCodeAsmCommon.buildInlineInfoFromClassSymbol(BCodeAsmCommon.scala:436)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.buildFromSymbol$1(BTypesFromSymbols.scala:412)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.buildInlineInfo(BTypesFromSymbols.scala:417)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.setClassInfo(BTypesFromSymbols.scala:342)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.scala$tools$nsc$backend$jvm$BTypesFromSymbols$$$anonfun$4(BTypesFromSymbols.scala:120)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols$$Lambda$1335/31327414.apply(Unknown Source)
        at scala.collection.MapLike$class.getOrElse(MapLike.scala:128)
        at scala.collection.concurrent.TrieMap.getOrElse(TrieMap.scala:633)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol(BTypesFromSymbols.scala:112)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.scala$tools$nsc$backend$jvm$BTypesFromSymbols$$$anonfun$31(BTypesFromSymbols.scala:338)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols$$Lambda$1347/1555324219.apply(Unknown Source)
        at scala.collection.immutable.List.map(List.scala:277)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.setClassInfo(BTypesFromSymbols.scala:338)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.scala$tools$nsc$backend$jvm$BTypesFromSymbols$$$anonfun$4(BTypesFromSymbols.scala:120)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols$$Lambda$1335/31327414.apply(Unknown Source)
        at scala.collection.MapLike$class.getOrElse(MapLike.scala:128)
        at scala.collection.concurrent.TrieMap.getOrElse(TrieMap.scala:633)
        at scala.tools.nsc.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol(BTypesFromSymbols.scala:112)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.getClassBTypeAndRegisterInnerClass(BCodeHelpers.scala:345)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.internalName(BCodeHelpers.scala:334)
        at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.internalName(BCodeSkelBuilder.scala:50)
        at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:103)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.visit(GenBCode.scala:183)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.scala$tools$nsc$backend$jvm$GenBCode$BCodePhase$Worker1$$$anonfun$1(GenBCode.scala:137)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1$$Lambda$1319/1693557037.apply$mcV$sp(Unknown Source)
        at scala.tools.nsc.Global$GlobalPhase.withCurrentUnit(Global.scala:431)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.run(GenBCode.scala:137)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.buildAndSendToDisk(GenBCode.scala:355)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:324)
        at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1505)
        at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1490)
        at scala.tools.nsc.Global$Run.compileSources(Global.scala:1485)
        at scala.tools.nsc.Global$Run.compile(Global.scala:1586)
        at xsbt.CachedCompiler0.run(CompilerInterface.scala:116)
        at xsbt.CachedCompiler0.run(CompilerInterface.scala:95)
        at xsbt.CompilerInterface.run(CompilerInterface.scala:26)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:101)
        at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:47)
        at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:41)
        at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply$mcV$sp(MixedAnalyzingCompiler.scala:51)
        at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:51)
        at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:51)
        at sbt.compiler.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:75)
        at sbt.compiler.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:50)
        at sbt.compiler.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:65)
        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:31)
        at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:62)
        at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:61)
        at sbt.inc.Incremental$.manageClassfiles(Incremental.scala:89)
        at sbt.inc.Incremental$.compile(Incremental.scala:61)
        at sbt.inc.IncrementalCompile$.apply(Compile.scala:54)
        at sbt.compiler.IC$.compileInternal(IncrementalCompiler.scala:160)
        at sbt.compiler.IC$.incrementalCompile(IncrementalCompiler.scala:138)
        at sbt.Compiler$.compile(Compiler.scala:128)
        at sbt.Compiler$.compile(Compiler.scala:114)
        at sbt.Defaults$.sbt$Defaults$$compileIncrementalTaskImpl(Defaults.scala:814)
        at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:805)
        at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:803)
        at scala.Function1$$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$$anonfun$apply$1.apply(Execute.scala:226)
        at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:226)
        at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
        at sbt.Execute.work(Execute.scala:235)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:226)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:226)
        at sbt.ConcurrentRestrictions$$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)

Followed by a large number of follow on exceptions of the following form,

java.lang.AssertionError: assertion failed: ClassBType.info not yet assigned: Lshapeless/LazyTests;
        at scala.tools.nsc.backend.jvm.BTypes$ClassBType.info(BTypes.scala:820)
        at scala.tools.nsc.backend.jvm.BTypes$ClassBType.isNestedClass(BTypes.scala:883)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.toTypeKind(BCodeHelpers.scala:356)
        at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.toTypeKind(BCodeSkelBuilder.scala:50)
        at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.symInfoTK(BCodeSkelBuilder.scala:82)
        at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.scala$tools$nsc$backend$jvm$BCodeSkelBuilder$PlainSkelBuilder$$$anonfun$10(BCodeSkelBuilder.scala:270)
        at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.scala$tools$nsc$backend$jvm$BCodeSkelBuilder$PlainSkelBuilder$$$anonfun$10$adapted(BCodeSkelBuilder.scala:263)
        at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.addClassFields(BCodeSkelBuilder.scala:263)
        at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:122)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.visit(GenBCode.scala:183)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.scala$tools$nsc$backend$jvm$GenBCode$BCodePhase$Worker1$$$anonfun$1(GenBCode.scala:137)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1$$Lambda$1319/1693557037.apply$mcV$sp(Unknown Source)
        at scala.tools.nsc.Global$GlobalPhase.withCurrentUnit(Global.scala:431)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase$Worker1.run(GenBCode.scala:137)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.buildAndSendToDisk(GenBCode.scala:355)
        at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:324)
        at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1505)
        at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1490)
        at scala.tools.nsc.Global$Run.compileSources(Global.scala:1485)
        at scala.tools.nsc.Global$Run.compile(Global.scala:1586)
        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:101)
        at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:47)
        at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:41)
        at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply$mcV$sp(MixedAnalyzingCompiler.scala:51)
        at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:51)
        at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:51)
        at sbt.compiler.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:75)
        at sbt.compiler.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:50)
        at sbt.compiler.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:65)
        at sbt.compiler.IC$$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$$anonfun$doCompile$1.apply(Compile.scala:64)
        at sbt.inc.IncrementalCommon.cycle(IncrementalCommon.scala:31)
        at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:62)
        at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:61)
        at sbt.inc.Incremental$.manageClassfiles(Incremental.scala:89)
        at sbt.inc.Incremental$.compile(Incremental.scala:61)
        at sbt.inc.IncrementalCompile$.apply(Compile.scala:54)
        at sbt.compiler.IC$.compileInternal(IncrementalCompiler.scala:160)
        at sbt.compiler.IC$.incrementalCompile(IncrementalCompiler.scala:138)
        at sbt.Compiler$.compile(Compiler.scala:128)
        at sbt.Compiler$.compile(Compiler.scala:114)
        at sbt.Defaults$.sbt$Defaults$$compileIncrementalTaskImpl(Defaults.scala:814)
        at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:805)
        at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:803)
        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:226)
        at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:226)
        at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
        at sbt.Execute.work(Execute.scala:235)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:226)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:226)
        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)
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scabug commented Jul 11, 2015

Imported From: https://issues.scala-lang.org/browse/SI-9392?orig=1
Reporter: @milessabin
Affected Versions: 2.12.0-M2

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scabug commented Jul 12, 2015

@retronym said:
Crashes since 2.11.3 with -Ybackend:GenBCode. The assertion error mentions a class symbol generated by a macro expansion.

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scabug commented Jul 12, 2015

@retronym said (edited on Jul 12, 2015 4:19:38 AM UTC):
Regressed in scala/scala@f73f026, /cc @lrytz

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scabug commented Jul 12, 2015

@retronym said:
Looks like the Lazy macro of shapeless is generating incoherent trees, see the two different symbol IDs for the highlighted class:

https://www.dropbox.com/s/wq6kf239ra983hy/Screenshot%202015-07-12%2015.24.19.png?dl=0

This is because of the way that the macro untypechecks the nested tree (https://github.com/milessabin/shapeless/blob/shapeless-2.2.4/core/src/main/scala/shapeless/lazy.scala#L220) but nevertheless uses a type (actualType) (https://github.com/milessabin/shapeless/blob/shapeless-2.2.4/core/src/main/scala/shapeless/lazy.scala#L192) that refers to a symbol from the original tree. This in turn is because it doesn't take measures to "pack" the type, which would prevent leaking a reference from a block-local class to the type of that block. This is pretty hard to do in the retypechecking model of macros. I'll take a deeper look at this next week and see if I recommend a better approach for that macro.

But I think we can demote this error to a dev-warning in the compiler.

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scabug commented Jul 12, 2015

@milessabin said:
Is there anything I could/should do in Lazy to prevent this happening? You mention taking measures to "pack" the type ... can you say what would be involved in doing that?

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scabug commented Jul 12, 2015

@retronym said (edited on Jul 12, 2015 8:47:33 AM UTC):
Here's a standalone test case:

% tail sandbox/{macro,client}.scala
==> sandbox/macro.scala <==
  def impl(c: Context)(): c.Tree = {
    import c.universe._
    val tree = q"""class C; new C"""
    val tree1 = c.typecheck(tree)
    val tpe = tree1.tpe
    val tree2 = c.typecheck(c.untypecheck(tree1))
    q"""$tree2.asInstanceOf[$tpe]"""
  }
  def apply(): Any = macro impl
}

==> sandbox/client.scala <==
class Client {
  Macro()
}

% scalac-hash v2.11.3 sandbox/macro.scala && scalac-hash v2.11.3 -Ybackend:GenASM sandbox/client.scala

% scalac-hash v2.11.3 sandbox/macro.scala && scalac-hash v2.11.3 -Ybackend:GenBCode sandbox/client.scala
java.lang.AssertionError: assertion failed: Cannot create ClassBType from non-class symbol value <local Client>
	at scala.tools.nsc.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol(BTypesFromSymbols.scala:86)

And a potential workaround for shapeless: milessabin/shapeless#429

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scabug commented Jul 12, 2015

@retronym said:
@milessabin The compiler will pack types when computing an inferred type of a member, or when computing the type of a match.

scala> import scala.tools.reflect.ToolBox; val m = reflect.runtime.currentMirror; val u = m.universe; import u._; val tb = m.mkToolBox();

scala> tb.typecheck(q"{class C extends Serializable; new C}").tpe
res13: tb.u.Type = C

scala> tb.typecheck(q"null match { case _ => class C extends Serializable; new C}").tpe
res14: tb.u.Type = Serializable

scala> tb.typecheck(q"def f = {class C extends Serializable; 0; new C}; f").tpe
res15: tb.u.Type = Serializable

However, the best practice is for a macro to generate an tree that ends with a type ascription to the desired type, rather than referring to an expansion-local class and relying on these implementation details.

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scabug commented Jul 13, 2015

@retronym said (edited on Jul 13, 2015 6:41:04 AM UTC):
Compiler workaround: scala/scala#4623.

We're going to recut 2.12.0-M2 with this included.

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scabug commented Jul 13, 2015

@milessabin said:
Awesome thanks :-)

@scabug scabug closed this as completed Jul 13, 2015
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scabug commented Jul 15, 2015

@lrytz said:
follow-up in scala/scala#4630

@scabug scabug added this to the 2.12.0-M2 milestone Apr 7, 2017
@scabug scabug mentioned this issue Apr 7, 2017
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