Fix #4730: Detect nested calls to run on the same toolbox

Author: nicolasstucki

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

@@ -15,8 +15,17 @@ object ToolboxImpl {
 
     private[this] val driver: QuoteDriver = new QuoteDriver(appClassloader)
 
+    private[this] var running = false
+
     def run[T](exprBuilder: QuoteContext => Expr[T]): T = synchronized {
-      driver.run(exprBuilder, settings)
+      try {
+        if (running) // detected nested run
+          throw new scala.quoted.Toolbox.ToolboxAlreadyRunning()
+        running = true
+        driver.run(exprBuilder, settings)
+      } finally {
+        running = false
+      }
     }
 
   }

library/src/scala/quoted/Toolbox.scala

@@ -56,4 +56,7 @@ object Toolbox {
   }
 
   class ToolboxNotFoundException(msg: String, cause: ClassNotFoundException) extends Exception(msg, cause)
+
+  class ToolboxAlreadyRunning extends Exception("Cannot call `scala.quoted.run(...)` within another `run(...)`")
+
 }

library/src/scala/quoted/package.scala

@@ -15,8 +15,6 @@ package object quoted {
    *
    *  This method should not be called in a context where there is already has a `QuoteContext`
    *  such as within a `run` or a `withQuoteContext`.
-   *
-   *  May throw a FreeVariableError on expressions that came from a macro.
    */
   def run[T](expr: given QuoteContext => Expr[T]) given (toolbox: Toolbox): T = toolbox.run(expr given _)
 

tests/run-with-compiler/i4730.scala

@@ -0,0 +1,20 @@
+import scala.quoted._
+
+object Test {
+  implicit val toolbox: scala.quoted.Toolbox = scala.quoted.Toolbox.make(getClass.getClassLoader)
+  def ret given QuoteContext: Expr[Int => Int] = '{ (x: Int) =>
+    ${
+      val z = run('{x + 1}) // throws a ToolboxAlreadyRunning
+      z.toExpr
+    }
+  }
+  def main(args: Array[String]): Unit = {
+    try {
+      run(ret).apply(10)
+      throw new Exception
+    } catch {
+      case ex: scala.quoted.Toolbox.ToolboxAlreadyRunning =>
+        // ok
+    }
+  }
+}

tests/run-with-compiler/i6754.check

@@ -1,2 +1 @@
 foo
-bar

tests/run-with-compiler/i6754.scala

@@ -10,6 +10,12 @@ object Test {
       println("foo")
       run(x)
     }
-    run(y)
+    try {
+      run(y)
+      throw new Exception
+    } catch {
+      case ex: java.lang.reflect.InvocationTargetException =>
+        assert(ex.getTargetException.isInstanceOf[scala.quoted.Toolbox.ToolboxAlreadyRunning])
+    }
   }
 }