Handle failures to pickle macro parameters

Author: nicolasstucki

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

@@ -24,6 +24,19 @@ object PickledQuotes {
 
   /** Pickle the tree of the a 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)
   }

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)
 

library/src/scala/quoted/FreeVariableError.scala

@@ -0,0 +1,3 @@
+package scala.quoted
+
+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

@@ -1,2 +1,3 @@
 1
 4
+5

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

@@ -3,7 +3,7 @@ import scala.quoted._
 import dotty.tools.dotc.quoted.Toolbox._
 
 object Macros {
-  inline def foo(i: Int): Int = ~{
+  inline def foo(i: => Int): Int = ~{
     val y: Int = ('(i)).run
     y.toExpr
   }

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

@@ -3,5 +3,10 @@ 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))
+  }
+}