Merge pull request #6347 from dotty-staging/do-not-rename-quoted-bindings

 Do not rename names starting with `$` in quoted patterns

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -274,27 +274,21 @@ object desugar {
 
   /** Transforms a definition with a name starting with a `$` in a quoted pattern into a `quoted.binding.Binding` splice.
    *
-   *  The desugaring consists in renaming the the definition and adding the `@patternBindHole` annotation. This
-   *  annotation is used during typing to perform the full transformation.
+   *  The desugaring consists in adding the `@patternBindHole` annotation. This annotation is used during typing to perform the full transformation.
    *
    *  A definition
    *  ```scala
-   *    case '{ def $a(...) = ... a() ...; ... a() ... }
+   *    case '{ def $a(...) = ...; ... `$a`() ... } => a
    *  ```
    *  into
    *  ```scala
-   *    case '{ @patternBindHole def a(...) = ... a() ...; ... a() ... }
+   *    case '{ @patternBindHole def `$a`(...) = ...; ... `$a`() ... } => a
    *  ```
    */
   def transformQuotedPatternName(tree: ValOrDefDef)(implicit ctx: Context): ValOrDefDef = {
     if (ctx.mode.is(Mode.QuotedPattern) && !tree.isBackquoted && tree.name != nme.ANON_FUN && tree.name.startsWith("$")) {
-      val name = tree.name.toString.substring(1).toTermName
-      val newTree: ValOrDefDef = tree match {
-        case tree: ValDef => cpy.ValDef(tree)(name)
-        case tree: DefDef => cpy.DefDef(tree)(name)
-      }
       val mods = tree.mods.withAddedAnnotation(New(ref(defn.InternalQuoted_patternBindHoleAnnot.typeRef)).withSpan(tree.span))
-      newTree.withMods(mods)
+      tree.withMods(mods)
     } else tree
   }
 

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

@@ -1986,7 +1986,9 @@ class Typer extends Namer
               case t => t
             }
             val bindingExprTpe = AppliedType(defn.QuotedMatchingBindingType, bindingType :: Nil)
-            val sym = ctx0.newPatternBoundSymbol(ddef.name, bindingExprTpe, ddef.span)
+            assert(ddef.name.startsWith("$"))
+            val bindName = ddef.name.toString.stripPrefix("$").toTermName
+            val sym = ctx0.newPatternBoundSymbol(bindName, bindingExprTpe, ddef.span)
             patBuf += Bind(sym, untpd.Ident(nme.WILDCARD).withType(bindingExprTpe)).withSpan(ddef.span)
           }
           super.transform(tree)

tests/pos/quotedPatterns.scala

@@ -12,17 +12,13 @@ object Test {
     case '{ ((a: Int) => 3)($y) } => y
     case '{ 1 + ($y: Int)} => y
     case '{ val a = 1 + ($y: Int); 3 } => y
-      // currently gives an unreachable case warning
-      // but only when used in conjunction with the others.
-      // I believe this is because implicit arguments are not taken
-      // into account when checking whether we have already seen an `unapply` before.
-    case '{ val $y: Int = $z; 1 } =>
+    case '{ val $y: Int = $z; println(`$y`); 1 } =>
       val a: quoted.matching.Bind[Int] = y
       z
-    case '{ (($y: Int) => 1 + y + ($z: Int))(2) } =>
+    case '{ (($y: Int) => 1 + `$y` + ($z: Int))(2) } =>
       val a: quoted.matching.Bind[Int] = y
       z
-    case '{ def $ff: Int = $z; ff } =>
+    case '{ def $ff: Int = $z; `$ff` } =>
       val a: quoted.matching.Bind[Int] = ff
       z
     case '{ def $ff(i: Int): Int = $z; 2 } =>