Merge pull request #10195 from dotty-staging/fix-#10178

Fix #10178: Put the wildcard demon back in the bottle

Author: bishabosha

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

@@ -1456,10 +1456,15 @@ object desugar {
 
       /** If `pat` is not an Identifier, a Typed(Ident, _), or a Bind, wrap
        *  it in a Bind with a fresh name. Return the transformed pattern, and the identifier
-       *  that refers to the bound variable for the pattern.
+       *  that refers to the bound variable for the pattern. Wildcard Binds are
+       *  also replaced by Binds with fresh names.
        */
       def makeIdPat(pat: Tree): (Tree, Ident) = pat match {
-        case Bind(name, _) => (pat, Ident(name))
+        case Bind(name, pat1) =>
+          if name == nme.WILDCARD then
+            val name = UniqueName.fresh()
+            (cpy.Bind(pat)(name, pat1), Ident(name))
+          else (pat, Ident(name))
         case id: Ident if isVarPattern(id) && id.name != nme.WILDCARD => (id, id)
         case Typed(id: Ident, _) if isVarPattern(id) && id.name != nme.WILDCARD => (pat, id)
         case _ =>

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

@@ -232,7 +232,7 @@ class Typer extends Namer
                 fail(em"reference to `$name` is ambiguous; it is imported twice")
               found
 
-            if adjustExtension(selector.rename) == termName then
+            if adjustExtension(selector.rename) == termName && selector.rename != nme.WILDCARD then
               val memberName =
                 if selector.name == termName then name
                 else if name.isTypeName then selector.name.toTypeName

tests/run/i10178.scala

@@ -0,0 +1,5 @@
+@main def Test: Unit =
+  for
+    x <- Option(23)
+    given Int = x
+  do assert(summon[Int] == 23)