diff options
-rw-r--r-- | src/reflect/scala/reflect/internal/Trees.scala | 7 | ||||
-rw-r--r-- | test/files/pos/t8947/Client_2.scala | 1 | ||||
-rw-r--r-- | test/files/pos/t8947/Macro_1.scala | 41 | ||||
-rw-r--r-- | test/junit/scala/tools/nsc/symtab/CannotHaveAttrsTest.scala | 12 |
4 files changed, 61 insertions, 0 deletions
diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala index 9dc4baee32..26e9c7f89d 100644 --- a/src/reflect/scala/reflect/internal/Trees.scala +++ b/src/reflect/scala/reflect/internal/Trees.scala @@ -10,6 +10,7 @@ package internal import Flags._ import pickling.PickleFormat._ import scala.collection.{ mutable, immutable } +import scala.reflect.macros.Attachments import util.Statistics trait Trees extends api.Trees { @@ -1075,6 +1076,12 @@ trait Trees extends api.Trees { override def setType(t: Type) = { requireLegal(t, NoType, "tpe"); this } override def tpe_=(t: Type) = setType(t) + // We silently ignore attempts to add attachments to `EmptyTree`. See SI-8947 for an + // example of a bug in macro expansion that this solves. + override def setAttachments(attachments: Attachments {type Pos = Position}): this.type = this + override def updateAttachment[T: ClassTag](attachment: T): this.type = this + override def removeAttachment[T: ClassTag]: this.type = this + private def requireLegal(value: Any, allowed: Any, what: String) = ( if (value != allowed) { log(s"can't set $what for $self to value other than $allowed") diff --git a/test/files/pos/t8947/Client_2.scala b/test/files/pos/t8947/Client_2.scala new file mode 100644 index 0000000000..1a5082a2f9 --- /dev/null +++ b/test/files/pos/t8947/Client_2.scala @@ -0,0 +1 @@ +object Test { X.extractor }
\ No newline at end of file diff --git a/test/files/pos/t8947/Macro_1.scala b/test/files/pos/t8947/Macro_1.scala new file mode 100644 index 0000000000..4a5de3decb --- /dev/null +++ b/test/files/pos/t8947/Macro_1.scala @@ -0,0 +1,41 @@ +import language.experimental.macros +import scala.reflect.macros._ +import blackbox.Context + +object X { + + def classTagOrNull[T](implicit t: reflect.ClassTag[T] = null) = t + // the failed search for ClassTag[T] does not issue a visible + // error as we fall back to the default argument. But, the + // macro engine things we have expanded the macro `materializeClassTag[D]()` + // to `EmptyTree`, and then attaches a backreference from the expansion + // to the expandee. This is the `MacroExpansionAttachment` tree attachment. + def foo[D] = classTagOrNull[D] + + def extractor: Any = macro X.extractorMacro + def extractorMacro(c: Context): c.Expr[Any] = { + // Later, in reify, an unrelated use of `EmptyTree` in the AST representing + // the argument is now treated as a macro expansion which should be rolled + // back in the tree we reify! This ends up generating a call to `implicitly` + // which leads to an ambiguous error. + // + // Any macro call that expands to EmptyTree could have triggered this problem. + c.universe.reify(new { def something(data: Any) = ??? }) + } + + // Workarounds: + // + // 1. Use quasiquotes rather than `reify`. (But, beware to fully qualify all references, e.g. `_root_.scala.Predef.???`) + // 2. Avoid failed ClassTag lookups (e.g. in the original bug report, annotate the type argument to `map`) + // 3. In the macro implementation, just before calling the `reify` macro, you could call another macro + // + // def prepareReify = macro prepareReifyImpl + // def prepareReifyImpl(c: Context) = { + // val symtab = c.universe.asInstanceOf[reflect.internal.SymbolTable] + // symtab.EmptyTree.setAttachments(symtab.NoPosition) + // } + // + // To make this visible to the macro implementaiton, it will need to be compiled in an earlier stage, + // e.g a separate SBT sub-project. + +} diff --git a/test/junit/scala/tools/nsc/symtab/CannotHaveAttrsTest.scala b/test/junit/scala/tools/nsc/symtab/CannotHaveAttrsTest.scala index d424f12710..69931c9e24 100644 --- a/test/junit/scala/tools/nsc/symtab/CannotHaveAttrsTest.scala +++ b/test/junit/scala/tools/nsc/symtab/CannotHaveAttrsTest.scala @@ -64,4 +64,16 @@ class CannotHaveAttrsTest { assertThrows[IllegalArgumentException] { t.setType(tpe) } } } + + class Attach + @Test + def attachmentsAreIgnored = { + attrlessTrees.foreach { t => + t.setAttachments(NoPosition.update(new Attach)) + assert(t.attachments == NoPosition) + t.updateAttachment(new Attach) + assert(t.attachments == NoPosition) + t.removeAttachment[Attach] // no exception + } + } } |