Fix #4456: Pickle quote before compiling

compiler/src/dotty/tools/dotc/core/quoted/PickledQuotes.scala

@@ -22,7 +22,26 @@ import scala.reflect.ClassTag
 object PickledQuotes {
   import tpd._
 
-  /** Pickle the quote into strings */
+  /** Pickle the tree of the quoted.Expr */
+  def pickleExpr(tree: Tree)(implicit ctx: Context): scala.quoted.Expr[Any] = {
+    // Check that there are no free variables
+    new TreeTraverser {
+      private val definedHere = scala.collection.mutable.Set.empty[Symbol]
+      def traverse(tree: tpd.Tree)(implicit ctx: Context): Unit = tree match {
+        case tree: Ident if tree.symbol.exists && !definedHere(tree.symbol) =>
+          throw new scala.quoted.FreeVariableError(tree.name.toString)
+        case tree: DefTree =>
+          definedHere += tree.symbol
+          traverseChildren(tree)
+        case _ =>
+          traverseChildren(tree)
+      }
+    }.traverse(tree)
+    val pickled = pickleQuote(tree)
+    scala.runtime.quoted.Unpickler.unpickleExpr(pickled, Nil)
+  }
+
+  /** Pickle the tree of the quote into strings */
   def pickleQuote(tree: Tree)(implicit ctx: Context): scala.runtime.quoted.Unpickler.Pickled = {
     if (ctx.reporter.hasErrors) Nil
     else {

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -19,7 +19,7 @@ import scala.collection.{ mutable, immutable }
 import config.Printers.pickling
 import typer.Checking
 import config.Config
-import dotty.tools.dotc.core.quoted.PickledQuotes
+import core.quoted.PickledQuotes
 import scala.quoted
 import scala.quoted.Types.TreeType
 import scala.quoted.Exprs.TreeExpr
@@ -1142,7 +1142,7 @@ class TreeUnpickler(reader: TastyReader,
       val idx = readNat()
       val args = until(end)(readTerm())
       val splice = splices(idx)
-      val reifiedArgs = args.map(arg => if (arg.isTerm) new TreeExpr(arg) else new TreeType(arg))
+      val reifiedArgs = args.map(arg => if (arg.isTerm) new TreeExpr(arg, PickledQuotes.pickleExpr(arg)) else new TreeType(arg))
       if (isType) {
         val quotedType = splice.asInstanceOf[Seq[Any] => quoted.Type[_]](reifiedArgs)
         PickledQuotes.quotedTypeToTree(quotedType)

compiler/src/dotty/tools/dotc/quoted/Toolbox.scala

@@ -3,11 +3,13 @@ package dotty.tools.dotc.quoted
 import dotty.tools.dotc.ast.Trees._
 import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.core.Constants._
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.quoted.PickledQuotes
 import dotty.tools.dotc.printing.RefinedPrinter
 
 import scala.quoted.Expr
 import scala.runtime.BoxedUnit
-import scala.quoted.Exprs.LiftedExpr
+import scala.quoted.Exprs.{LiftedExpr, TreeExpr}
 import scala.runtime.quoted._
 
 /** Default runners for quoted expressions */
@@ -23,8 +25,12 @@ object Toolbox {
     ): Toolbox[T] = new Toolbox[T] {
 
     def run(expr: Expr[T]): T = expr match {
-      case expr: LiftedExpr[T] => expr.value
-      case _ => new QuoteDriver().run(expr, runSettings)
+      case expr: LiftedExpr[T] =>
+        expr.value
+      case expr: TreeExpr[Tree] @unchecked =>
+        new QuoteDriver().run(expr.pickled, runSettings)
+      case _ =>
+        new QuoteDriver().run(expr, runSettings)
     }
 
     def show(expr: Expr[T]): String = expr match {

compiler/src/dotty/tools/dotc/transform/ReifyQuotes.scala

@@ -560,7 +560,8 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
                 // see PostTyper `case Inlined(...) =>` for description of the simplification
                 val call2 = Ident(call.symbol.topLevelClass.typeRef).withPos(call.pos)
                 val spliced = Splicer.splice(body, call, bindings, tree.pos, macroClassLoader).withPos(tree.pos)
-                transform(cpy.Inlined(tree)(call2, bindings, spliced))
+                if (ctx.reporter.hasErrors) EmptyTree
+                else transform(cpy.Inlined(tree)(call2, bindings, spliced))
               }
               else super.transform(tree)
 

compiler/src/dotty/tools/dotc/transform/Splicer.scala

@@ -60,7 +60,8 @@ object Splicer {
           case (arg, tp) =>
             assert(!tp.hasAnnotation(defn.InlineParamAnnot))
             // Replace argument by its binding
-            new scala.quoted.Exprs.TreeExpr(bindMap.getOrElse(arg, arg))
+            val arg1 = bindMap.getOrElse(arg, arg)
+            new scala.quoted.Exprs.TreeExpr(arg1, PickledQuotes.pickleExpr(arg1))
         }
         args1 ::: liftArgs(tp.resType, args.tail)
       case tp: PolyType =>

library/src/scala/quoted/Expr.scala

@@ -5,7 +5,14 @@ import scala.runtime.quoted.Unpickler.Pickled
 
 sealed abstract class Expr[T] {
   final def unary_~ : T = throw new Error("~ should have been compiled away")
+
+  /** Evaluate the contents of this expression and return the result.
+   *
+   *  May throw a FreeVariableError on expressions that came from an inline macro.
+   */
   final def run(implicit toolbox: Toolbox[T]): T = toolbox.run(this)
+
+  /** Show a source code like representation of this expression */
   final def show(implicit toolbox: Toolbox[T]): String = toolbox.show(this)
 }
 
@@ -36,8 +43,15 @@ object Exprs {
     override def toString: String = s"Expr($value)"
   }
 
-  /** An Expr backed by a tree. Only the current compiler trees are allowed. */
-  final class TreeExpr[Tree](val tree: Tree) extends quoted.Expr[Any] {
+  /** An Expr backed by a tree. Only the current compiler trees are allowed.
+   *
+   *  These expressions are used for arguments of inline macros. They contain and actual tree
+   *  from the program that is being expanded by the macro.
+   *
+   *  May contain references to code defined outside this Expr instance.
+   */
+  final class TreeExpr[Tree](val tree: Tree, pickle: => Expr[_]) extends quoted.Expr[Any] {
+    def pickled[T]: Expr[T] = pickle.asInstanceOf[Expr[T]]
     override def toString: String = s"Expr(<raw>)"
   }
 

library/src/scala/quoted/FreeVariableError.scala

@@ -0,0 +1,8 @@
+package scala.quoted
+
+/** Exception is thrown when trying to evaluate the contents of an expression
+ *  that has free variables (i.e. has some local references to code that is
+ *  outside of the expression). This can happen on Expr that passed as arguments to
+ *  an inline macro.
+ */
+class FreeVariableError(val name: String) extends QuoteError("Free variable " + name + " could not be handled")

tests/neg/quote-run-in-macro-1/quoted_1.scala

@@ -0,0 +1,10 @@
+import scala.quoted._
+
+import dotty.tools.dotc.quoted.Toolbox._
+
+object Macros {
+  inline def foo(i: => Int): Int = ~{
+    val y: Int = ('(i)).run
+    y.toExpr
+  }
+}

tests/neg/quote-run-in-macro-1/quoted_2.scala

@@ -0,0 +1,7 @@
+import Macros._
+object Test {
+  def main(args: Array[String]): Unit = {
+    val x = 3
+    println(foo(x)) // error
+  }
+}

tests/run/quote-run-in-macro-1.check

@@ -0,0 +1,3 @@
+1
+4
+5

tests/run/quote-run-in-macro-1/quoted_1.scala

@@ -0,0 +1,10 @@
+import scala.quoted._
+
+import dotty.tools.dotc.quoted.Toolbox._
+
+object Macros {
+  inline def foo(i: => Int): Int = ~{
+    val y: Int = ('(i)).run
+    y.toExpr
+  }
+}

tests/run/quote-run-in-macro-1/quoted_2.scala

@@ -0,0 +1,12 @@
+import Macros._
+object Test {
+  def main(args: Array[String]): Unit = {
+    println(foo(1))
+    println(foo(1  + 3))
+    val x = 3
+    println(foo {
+      val x = 5
+      x
+    })
+  }
+}

tests/run/quote-run-in-macro-2.check

@@ -0,0 +1,3 @@
+"> 3"
+"> 12"
+(x: scala.Int) => "> ".+(y).apply(3)

tests/run/quote-run-in-macro-2/quoted_1.scala

@@ -0,0 +1,18 @@
+import scala.quoted._
+
+import dotty.tools.dotc.quoted.Toolbox._
+
+object Macros {
+  inline def foo(f: => Int => String): String = ~bar('(f))
+  def bar(f: Expr[Int => String]): Expr[String] = {
+    try {
+      val y: Int => String = f.run
+      val res = y(3).toExpr // evaluate at compile time
+      res.show.toExpr
+    } catch {
+      case ex: scala.quoted.FreeVariableError =>
+        val res = ('((~f)(3))) // evaluate at run time
+        res.show.toExpr
+    }
+  }
+}

tests/run/quote-run-in-macro-2/quoted_2.scala

@@ -0,0 +1,9 @@
+import Macros._
+object Test {
+  def main(args: Array[String]): Unit = {
+    println(foo(x => "> " + x))
+    println(foo(x => "> " + 4 * x))
+    val y = 9
+    println(foo(x => "> " + y))
+  }
+}