Skipping inlined tree reduction of type member selection

Author: soronpo

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

@@ -569,6 +569,7 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
    *  This avoids the situation where we have a Select node that does not have a symbol.
    */
   def constToLiteral(tree: Tree)(using Context): Tree = {
+    assert(!tree.isType)
     val tree1 = ConstFold(tree)
     tree1.tpe.widenTermRefExpr.dealias.normalized match {
       case ConstantType(Constant(_: Type)) if tree.isInstanceOf[Block] =>

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

@@ -1504,13 +1504,18 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(using Context) {
       assert(tree.hasType, tree)
       val qual1 = typed(tree.qualifier, shallowSelectionProto(tree.name, pt, this))
       val resNoReduce = untpd.cpy.Select(tree)(qual1, tree.name).withType(tree.typeOpt)
-      val resMaybeReduced = constToLiteral(reducer.reduceProjection(resNoReduce))
-      if (resNoReduce ne resMaybeReduced)
-        typed(resMaybeReduced, pt) // redo typecheck if reduction changed something
+      val reducedProjection = reducer.reduceProjection(resNoReduce)
+      if (reducedProjection.isType)
+        //in case the projection leads to a typed tree, then there is nothing to reduce
+        resNoReduce
       else
-        val res = resMaybeReduced
-        ensureAccessible(res.tpe, tree.qualifier.isInstanceOf[untpd.Super], tree.srcPos)
-        inlineIfNeeded(res)
+        val resMaybeReduced = constToLiteral(reducedProjection)
+        if (resNoReduce ne resMaybeReduced)
+          typed(resMaybeReduced, pt) // redo typecheck if reduction changed something
+        else
+          val res = resMaybeReduced
+          ensureAccessible(res.tpe, tree.qualifier.isInstanceOf[untpd.Super], tree.srcPos)
+          inlineIfNeeded(res)
     }
 
     override def typedIf(tree: untpd.If, pt: Type)(using Context): Tree =

tests/pos/i13503.scala

@@ -0,0 +1,8 @@
+trait First {type Out}
+given First with {type Out = 123}
+
+trait Second {type Out}
+transparent inline given (using f: First): Second = new Second {type Out = f.Out}
+
+val s = summon[Second]
+val x = summon[s.Out =:= 123]