Compiler crash when quoting an inline argument of function type

[TomasMikula]

$ dotty-0.8.0-RC1/bin/dotr
Starting dotty REPL...
scala> inline def h(inline f: Int => String): String = ~ '(f(42)) 

Exception in thread "main" java.lang.AssertionError: assertion failed: unresolved symbols: value f$1 when pickling rs$line$1
	at dotty.DottyPredef$.assertFail(DottyPredef.scala:36)
	at dotty.tools.dotc.core.tasty.TreePickler.pickle(TreePickler.scala:634)
	at dotty.tools.dotc.core.quoted.PickledQuotes$.pickle(PickledQuotes.scala:98)
	at dotty.tools.dotc.core.quoted.PickledQuotes$.pickleQuote(PickledQuotes.scala:31)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.pickleAsTasty$1(ReifyQuotes.scala:394)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.pickledQuote(ReifyQuotes.scala:413)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.quotation(ReifyQuotes.scala:382)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:547)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transformWithCapturer$2(ReifyQuotes.scala:472)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.body$4(ReifyQuotes.scala:499)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.$anonfun$4(ReifyQuotes.scala:505)
	at dotty.tools.dotc.ast.tpd$.polyDefDef(tpd.scala:229)
	at dotty.tools.dotc.ast.tpd$.DefDef(tpd.scala:191)
	at dotty.tools.dotc.ast.tpd$.Closure(tpd.scala:103)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.makeLambda(ReifyQuotes.scala:505)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.split(ReifyQuotes.scala:523)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.splice(ReifyQuotes.scala:431)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:552)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transform(MacroTransformWithImplicits.scala:84)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.mapOverTree$1(ReifyQuotes.scala:539)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:606)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:585)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.traverse$1(MacroTransformWithImplicits.scala:53)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transformStats(MacroTransformWithImplicits.scala:60)
	at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:60)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transform(MacroTransformWithImplicits.scala:86)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.mapOverTree$1(ReifyQuotes.scala:539)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:606)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1211)
	at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:54)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transform(MacroTransformWithImplicits.scala:86)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.mapOverTree$1(ReifyQuotes.scala:539)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:606)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform$$anonfun$2(Trees.scala:1231)
	at scala.collection.immutable.List.mapConserve(List.scala:176)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1231)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transformStats(Trees.scala:1229)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1217)
	at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:54)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transform(MacroTransformWithImplicits.scala:86)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.mapOverTree$1(ReifyQuotes.scala:539)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:606)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.transform.MacroTransform.run(MacroTransform.scala:22)
	at dotty.tools.dotc.transform.ReifyQuotes.run(ReifyQuotes.scala:104)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:295)
	at scala.collection.immutable.List.map(List.scala:283)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:297)
	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:171)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:18)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:32)
	at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:29)
	at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:191)
	at dotty.tools.dotc.Run.runPhases$5(Run.scala:186)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:194)
	at scala.compat.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:88)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:201)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:141)
	at dotty.tools.repl.ReplCompiler.runCompilationUnit(ReplCompiler.scala:188)
	at dotty.tools.repl.ReplCompiler.compile(ReplCompiler.scala:197)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:229)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:202)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:150)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:154)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput$$anonfun$2$$anonfun$1(ReplDriver.scala:163)
	at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
	at scala.Console$.withErr(Console.scala:192)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput$$anonfun$1(ReplDriver.scala:163)
	at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
	at scala.Console$.withOut(Console.scala:163)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:163)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:154)
	at dotty.tools.repl.Main$.main(Main.scala:6)
	at dotty.tools.repl.Main.main(Main.scala)

[nicolasstucki]

The issue here is that we do not support inline functions as they have no value we can use. In this stage, they are just code. One solution would be to simply disallow the inline keyword on method types.

[nicolasstucki]

The same lack of support is cought correctly by the folowing assertion as stated in #4433

$ dotty-0.8.0-RC1/bin/dotr
Starting dotty REPL...
scala> inline def g(inline p: Int => Boolean): Boolean = ~{
         if(p(5)) '(true)
         else '(false)
       } 
def g(p: (Int => Boolean) @InlineParam): Boolean
scala> 
scala> g(i => false) 
Exception in thread "main" java.lang.AssertionError: assertion failed
	at dotty.DottyPredef$.assertFail(DottyPredef.scala:35)
	at dotty.tools.dotc.transform.Splicer$.$anonfun$4(Splicer.scala:61)
	at scala.collection.immutable.List.map(List.scala:283)
	at dotty.tools.dotc.transform.Splicer$.liftArgs$1(Splicer.scala:64)
	at dotty.tools.dotc.transform.Splicer$.getLiftedArgs(Splicer.scala:72)
	at dotty.tools.dotc.transform.Splicer$.splice(Splicer.scala:36)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:568)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1204)
	at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:54)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transform(MacroTransformWithImplicits.scala:86)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.mapOverTree$1(ReifyQuotes.scala:539)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:606)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.traverse$1(MacroTransformWithImplicits.scala:53)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transformStats(MacroTransformWithImplicits.scala:60)
	at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:60)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transform(MacroTransformWithImplicits.scala:86)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.mapOverTree$1(ReifyQuotes.scala:539)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:606)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1211)
	at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:54)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transform(MacroTransformWithImplicits.scala:86)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.mapOverTree$1(ReifyQuotes.scala:539)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:606)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform$$anonfun$2(Trees.scala:1231)
	at scala.collection.immutable.List.mapConserve(List.scala:176)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1231)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transformStats(Trees.scala:1229)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1217)
	at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:54)
	at dotty.tools.dotc.transform.MacroTransformWithImplicits$ImplicitsTransformer.transform(MacroTransformWithImplicits.scala:86)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.mapOverTree$1(ReifyQuotes.scala:539)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.op1$1(ReifyQuotes.scala:606)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.transform(ReifyQuotes.scala:537)
	at dotty.tools.dotc.transform.MacroTransform.run(MacroTransform.scala:22)
	at dotty.tools.dotc.transform.ReifyQuotes.run(ReifyQuotes.scala:104)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:295)
	at scala.collection.immutable.List.map(List.scala:283)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:297)
	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:171)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:18)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:32)
	at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:29)
	at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:191)
	at dotty.tools.dotc.Run.runPhases$5(Run.scala:186)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:194)
	at scala.compat.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:88)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:201)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:141)
	at dotty.tools.repl.ReplCompiler.runCompilationUnit(ReplCompiler.scala:188)
	at dotty.tools.repl.ReplCompiler.compile(ReplCompiler.scala:197)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:229)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:202)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:150)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:154)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput$$anonfun$2$$anonfun$1(ReplDriver.scala:163)
	at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
	at scala.Console$.withErr(Console.scala:192)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput$$anonfun$1(ReplDriver.scala:163)
	at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
	at scala.Console$.withOut(Console.scala:163)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:163)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:154)
	at dotty.tools.repl.Main$.main(Main.scala:6)
	at dotty.tools.repl.Main.main(Main.scala)

[TomasMikula]

The issue here is that we do not support inline functions as they have no value we can use. In this stage, they are just code.

But my example doesn't need the value of the function at compile time, only its code. Also, the documentation states that

Quotes and splices are duals of each other. For arbitrary expressions e and types T we have:

~’(e) = e

so ~ '(f(42)) from my example should be equivalent to f(42).

---

One solution would be to simply disallow the inline keyword on method types.

Code using inline functions is part of the documentation:

inline def foreach(inline op: Int => Unit): Unit = {
  var i = from
  while (i < end) {
    op(i)
    i += 1
  }
}

---

I don't think this issue is the same as #4433, where the value of an inline function is actually needed at compile time.

[nicolasstucki]

True. The issue is that we may not be able to support inline functions in general an may need to disallow them. You could just write inline def h(f: Int => String): String = f(42) to achieve the same, which is much simpler. Or in more complex cases there is also you can quote the function and then use (~f).apply(~x) or just (~f)(~x) which will also inline the function (this apply is available in Expr).

[TomasMikula]

I suppose you meant ~{('(f))('(x))}, in order for it to be the apply you linked to.
Yeah, that does compile:

scala> inline def h(inline f: Int => String): String = ~{('(f))('(42))} 
def h(f: (Int => String) @InlineParam): String
scala>  

but I don't see why that should be different than ~{'(f(42))}.

The issue is that we may not be able to support inline functions in general an may need to disallow them.

I suppose this comment applies to #4433 only, where the function is actually run at compile time. Or do you mean that the foreach example from the docs which uses an inline function might be disallowed as well?

[nicolasstucki]

Both. At compile time in a inline def foo = ~{...}, all inline parameters become runtime parameters and functions do not have a runtime value at this stage (only after compilation). This is why should disallow the inline functions altogether in macros. There where some discussions about disallowing it for the foreach example, but this might not be needed.

[TomasMikula]

At compile time in a inline def foo = ~{...}, all inline parameters become runtime parameters

Unless they are quoted, no? Which is the case in this issue. After all, the example from my previous comment compiled.

[nicolasstucki]

Yes. And all non inlined parameters must be quoted. Quoting an inline parameter is possible but not really useful. Your previous example will break at use site.

[TomasMikula]

Heh, you're right that it breaks at runtime, which is even worse than a compiler crash.

Don't you agree that #4433 is a different issue, since there the inline parameter is not quoted? That's the use case I actually care about: moving some computation to compile time.

[nicolasstucki]

For me there are two distinct manifestations of the same root issue. Disallowing it would ensure that the programs generated do not crash.