Fix #3083: Check that all named parts of locally inferred types are d…

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

@@ -719,6 +719,22 @@ trait Checking {
       checkNoForwardDependencies(vparams1)
     case Nil =>
   }
+
+  /** Check that all named type that form part of this type have a denotation.
+   *  Called on inferred (result) types of ValDefs and DefDefs.
+   *  This could fail for types where the member was originally available as part
+   *  of the self type, yet is no longer visible once the `this` has been replaced
+   *  by some other prefix. See neg/i3083.scala
+   */
+  def checkMembersOK(tp: Type, pos: Position)(implicit ctx: Context): Type = {
+    val check: Type => Unit = {
+      case ref: NamedType if !ref.denot.exists =>
+        ctx.error(em"$ref is not defined in inferred type $tp", pos)
+      case _ =>
+    }
+    tp.foreachPart(check, stopAtStatic = true)
+    tp
+  }
 }
 
 trait NoChecking extends Checking {
@@ -738,4 +754,5 @@ trait NoChecking extends Checking {
   override def checkTraitInheritance(parentSym: Symbol, cls: ClassSymbol, pos: Position)(implicit ctx: Context) = ()
   override def checkCaseInheritance(parentSym: Symbol, caseCls: ClassSymbol, pos: Position)(implicit ctx: Context) = ()
   override def checkNoForwardDependencies(vparams: List[ValDef])(implicit ctx: Context): Unit = ()
+  override def checkMembersOK(tp: Type, pos: Position)(implicit ctx: Context): Type = tp
 }

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

@@ -1103,7 +1103,7 @@ class Namer { typer: Typer =>
       case _: untpd.DerivedTypeTree =>
         WildcardType
       case TypeTree() =>
-        inferredType
+        checkMembersOK(inferredType, mdef.pos)
       case DependentTypeTree(tpFun) =>
         tpFun(paramss.head)
       case TypedSplice(tpt: TypeTree) if !isFullyDefined(tpt.tpe, ForceDegree.none) =>

tests/neg/i3083.scala

@@ -0,0 +1,32 @@
+    object Main {
+
+      trait Literal {
+        type F[T]
+        def num(i: Int): F[Int]
+      }
+
+      trait Addition { self: Literal =>
+        def add(l: F[Int], r: F[Int]): F[Int]
+      }
+
+      def expression(adder: Addition) = {
+        import adder._
+        add(num(1), num(2)) // error // error (not found: num)
+        }
+      }
+
+      object Minimized {
+        trait Literal {
+          type F[T]
+        }
+
+        trait Addition { self: Literal =>
+          def foo: F[Int]
+        }
+
+        object Main {
+          def expression(adder: Addition) = { // error: adder.F is not defined in inferred type
+            adder.foo
+          }
+        }
+      }

tests/pos/i3083.scala

@@ -0,0 +1,15 @@
+object Minimized {
+  trait Literal {
+    type F[T]
+  }
+
+  trait Addition { self: Literal =>
+    def foo: F[Int]
+  }
+
+  object Main {
+    def expression(adder: Addition & Literal) = { // error: adder.F is not defined in inferred type
+      adder.foo
+    }
+  }
+}