Macro expansion failed with missing positions

[liufengyun]

The macro system should have set default positions to all trees, however when compile ScalaTest, we encountered the following exception:

[error] ## Exception when compiling 511 sources to /Users/fliu/Documents/scalatest-upstream/scalatest.dotty/target/scala-0.14/classes
[error] assertion failed: position not set for org.scalactic.anyvals.PosZInt.+$extension3(SizeParam.this.minSize)(
[error]   org.scalactic.anyvals.PosZInt.widenToInt(SizeParam.this.sizeRange)
[error] ) # 2326942 of class dotty.tools.dotc.ast.Trees$Apply in /Users/fliu/Documents/dotty/library/src-bootstrapped/scala/tasty/reflect/utils/TreeUtils.scala
[error] dotty.DottyPredef$.assertFail(DottyPredef.scala:16)
[error] dotty.tools.dotc.typer.Typer$.assertPositioned(Typer.scala:62)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2096)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2112)
[error] dotty.tools.dotc.typer.Typer.typedInlined(Typer.scala:1246)
[error] dotty.tools.dotc.transform.Erasure$Typer.typedInlined(Erasure.scala:559)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2032)

These kind of errors will cause a lot of troubles to macro authors -- as there is no way to explain why it happens and how to avoid that.