Merge pull request #9696 from dotty-staging/dissalow-vars-in-higher-order-patterns

Fix #9692 and fix #9693: Emit error when var is used in HO pattern

Author: nicolasstucki

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

@@ -237,6 +237,10 @@ trait QuotesAndSplices {
           val newSplice = ref(defn.InternalQuoted_exprSplice).appliedToType(tpt1.tpe).appliedTo(Typed(pat, exprTpt))
           transform(newSplice)
         case Apply(TypeApply(fn, targs), Apply(sp, pat :: Nil) :: args :: Nil) if fn.symbol == defn.InternalQuotedMatcher_patternHigherOrderHole =>
+          args match // TODO support these patterns. Possibly using scala.quoted.util.Var
+            case SeqLiteral(args, _) =>
+              for arg <- args; if arg.symbol.is(Mutable) do
+                report.error("References to `var`s cannot be used in higher-order pattern", arg.srcPos)
           try ref(defn.InternalQuotedMatcher_higherOrderHole.termRef).appliedToTypeTrees(targs).appliedTo(args).withSpan(tree.span)
           finally {
             val patType = pat.tpe.widen

tests/neg-staging/i9692.scala

@@ -0,0 +1,20 @@
+import scala.quoted._
+import scala.quoted.staging._
+
+object Test extends App {
+
+  // make available the necessary toolbox for runtime code generation
+  given Toolbox = Toolbox.make(getClass.getClassLoader)
+
+  run {
+    val expr: Expr[Int] = '{ var x = 1; x = 2; 42 }
+
+    expr match {
+      case '{ var x: Int = $binding; $body(x): Int } => // error
+    val res = Expr.betaReduce('{ $body(4) })
+    println(res.show)
+    res
+      case _ => println(expr.show); '{0}
+    }
+  }
+}

tests/neg-staging/i9693.scala

@@ -0,0 +1,20 @@
+import scala.quoted._
+import scala.quoted.staging._
+
+object Test extends App {
+
+  // make available the necessary toolbox for runtime code generation
+  given Toolbox = Toolbox.make(getClass.getClassLoader)
+
+  run {
+    val expr: Expr[Int] = '{ var x = 1; x = 2; 42 }
+
+    expr match {
+      case '{ var x: Int = $binding; $body(x): Int } => // error
+    val res = '{ var y = $binding; ${ Expr.betaReduce('{ $body(y) })}}
+    println(res.show)
+    res
+      case _ => println(expr.show); '{0}
+    }
+  }
+}