Fix #7142: Detect escaped variables across macro expansion

Author: nicolasstucki

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

@@ -41,13 +41,13 @@ object Splicer {
     case Quoted(quotedTree) => quotedTree
     case _ =>
       val interpreter = new Interpreter(pos, classLoader)
-      val macroOwner = ctx.newSymbol(ctx.owner, NameKinds.UniqueName.fresh(nme.MACROkw), Synthetic, defn.AnyType, coord = tree.span)
+      val macroOwner = ctx.newSymbol(ctx.owner, nme.MACROkw, Macro | Synthetic, defn.AnyType, coord = tree.span)
       try {
         given Context = ctx.withOwner(macroOwner)
         // Some parts of the macro are evaluated during the unpickling performed in quotedExprToTree
         val interpretedExpr = interpreter.interpret[scala.quoted.QuoteContext => scala.quoted.Expr[Any]](tree)
         val interpretedTree = interpretedExpr.fold(tree)(macroClosure => PickledQuotes.quotedExprToTree(macroClosure(QuoteContext())))
-        checkEscapedVariables(interpretedTree, macroOwner).changeOwner(macroOwner, ctx.owner)
+        checkEscapedVariables(interpretedTree).changeOwner(macroOwner, ctx.owner)
       }
       catch {
         case ex: CompilationUnit.SuspendException =>
@@ -70,7 +70,7 @@ object Splicer {
   }
 
   /** Checks that no symbol that whas generated within the macro expansion has an out of scope reference */
-  def checkEscapedVariables(tree: Tree, expansionOwner: Symbol)(given ctx: Context): tree.type =
+  def checkEscapedVariables(tree: Tree)(given ctx: Context): tree.type =
     new TreeTraverser {
       private[this] var locals = Set.empty[Symbol]
       private def markSymbol(sym: Symbol)(implicit ctx: Context): Unit =
@@ -100,7 +100,7 @@ object Splicer {
             traverseChildren(tree)
       private def isEscapedVariable(sym: Symbol)(given ctx: Context): Boolean =
         sym.exists && !sym.is(Package)
-        && sym.owner.ownersIterator.contains(expansionOwner) // symbol was generated within the macro expansion
+        && sym.owner.ownersIterator.exists(x => x.is(Macro, butNot = Method) && x.name == nme.MACROkw) // symbol was generated within a macro expansion
         && !locals.contains(sym) // symbol is not in current scope
     }.traverse(tree)
     tree

staging/src/scala/quoted/staging/QuoteCompiler.scala

@@ -72,7 +72,7 @@ private class QuoteCompiler extends Compiler {
             given Context = unitCtx.withOwner(meth)
             val qctx = dotty.tools.dotc.quoted.QuoteContext()
             val quoted = PickledQuotes.quotedExprToTree(exprUnit.exprBuilder.apply(qctx))
-            checkEscapedVariables(quoted, meth)
+            checkEscapedVariables(quoted)
           }
 
           getLiteral(quoted) match {

tests/neg-macros/i7142h/Macro_1.scala

@@ -0,0 +1,11 @@
+package macros
+import scala.quoted._
+
+var saved = Option.empty[Expr[Int]]
+
+def oops(given QuoteContext) = {
+  if (saved.isEmpty) '{ (x: Int) => ${ saved = Some('{x}); 'x } }
+  else saved.get
+}
+
+inline def test = ${oops}

tests/neg-macros/i7142h/Test_2.scala

@@ -0,0 +1,4 @@
+object Test {
+  macros.test
+  macros.test // error
+}