Fix TreeTypeMap to correctly substitute type parameters

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

@@ -204,11 +204,23 @@ class TreeTypeMap(
       lazy val origCls = mapped.zip(syms).filter(_._1.isClass).toMap
       mapped.filter(_.isClass).foldLeft(substMap) { (tmap, cls) =>
         val origDcls = cls.info.decls.toList.filterNot(_.is(TypeParam))
-        val mappedDcls = mapSymbols(origDcls, tmap, mapAlways = true)
+        val tmap0 = tmap.withSubstitution(origCls(cls).typeParams, cls.typeParams)
+        val mappedDcls = mapSymbols(origDcls, tmap0, mapAlways = true)
         val tmap1 = tmap.withMappedSyms(
           origCls(cls).typeParams ::: origDcls,
           cls.typeParams ::: mappedDcls)
         origDcls.lazyZip(mappedDcls).foreach(cls.asClass.replace)
         tmap1
       }
+
+  override def toString =
+    def showSyms(syms: List[Symbol]) =
+      syms.map(sym => s"$sym#${sym.id}").mkString(", ")
+    s"""TreeTypeMap(
+       |typeMap   = $typeMap
+       |treeMap   = $treeMap
+       |oldOwners = ${showSyms(oldOwners)}
+       |newOwners = ${showSyms(newOwners)}
+       |substFrom = ${showSyms(substFrom)}
+       |substTo   = ${showSyms(substTo)}""".stripMargin
 }

compiler/src/dotty/tools/dotc/reporting/trace.scala

@@ -76,7 +76,7 @@ trait TraceSyntax:
     else
       // Avoid evaluating question multiple time, since each evaluation
       // may cause some extra logging output.
-      val q = question.replace('\n', ' ')
+      val q = question
       val leading = s"==> $q?"
       val trailing = (res: T) => s"<== $q = ${showOp(res)}"
       var finalized = false

tests/pos/i12508.scala

@@ -0,0 +1,8 @@
+class Test {
+  inline def test(fun: Any): Any = ???
+  test {
+    class Foo[X]:
+      def x: X = ???
+      def foo: Unit = this.x.toString
+  }
+}

tests/pos/i12508a.scala

@@ -0,0 +1,14 @@
+def fun(a: Any, b: Any = 2): Any = ???
+def test =
+  fun(
+    b = println(1),
+    a = {
+      class Foo[X]:
+        def x: X = ???
+        def foo: Unit = this.x.toString
+        locally {
+          def x: X = ???
+          println(x.toString)
+        }
+    }
+  )