C#: Remove YieldReturnKind

Author: tamasvajk

csharp/ql/src/semmle/code/csharp/dataflow/internal/DataFlowDispatch.qll

@@ -82,7 +82,6 @@ private module Cached {
   cached
   newtype TReturnKind =
     TNormalReturnKind() { Stages::DataFlowStage::forceCachingInSameStage() } or
-    TYieldReturnKind() or
     TOutReturnKind(int i) {
       exists(Parameter p | callableReturnsOutOrRef(_, p, _) and p.isOut() | i = p.getPosition())
     } or
@@ -200,11 +199,6 @@ class NormalReturnKind extends ReturnKind, TNormalReturnKind {
   override string toString() { result = "return" }
 }
 
-/** A value returned from a callable using a `yield return` statement. */
-class YieldReturnKind extends ReturnKind, TYieldReturnKind {
-  override string toString() { result = "yield return" }
-}
-
 /** A value returned from a callable using an `out` or a `ref` parameter. */
 abstract class OutRefReturnKind extends ReturnKind {
   /** Gets the position of the `out`/`ref` parameter. */

csharp/ql/src/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll

@@ -1393,7 +1393,7 @@ private module ReturnNodes {
 
     YieldReturnStmt getYieldReturnStmt() { result = yrs }
 
-    override YieldReturnKind getKind() { any() }
+    override NormalReturnKind getKind() { any() }
 
     override Callable getEnclosingCallableImpl() { result = yrs.getEnclosingCallable() }
 
@@ -1516,21 +1516,6 @@ private module OutNodes {
     result = TExplicitDelegateLikeCall(cfn, e)
   }
 
-  /** A valid return type for a method that uses `yield return`. */
-  private class YieldReturnType extends Type {
-    YieldReturnType() {
-      exists(Type t | t = this.getUnboundDeclaration() |
-        t instanceof SystemCollectionsIEnumerableInterface
-        or
-        t instanceof SystemCollectionsIEnumeratorInterface
-        or
-        t instanceof SystemCollectionsGenericIEnumerableTInterface
-        or
-        t instanceof SystemCollectionsGenericIEnumeratorInterface
-      )
-    }
-  }
-
   /**
    * A data-flow node that reads a value returned directly by a callable,
    * either via a C# call or a CIL call.
@@ -1551,9 +1536,6 @@ private module OutNodes {
       (
         kind instanceof NormalReturnKind and
         not call.getExpr().getType() instanceof VoidType
-        or
-        kind instanceof YieldReturnKind and
-        call.getExpr().getType() instanceof YieldReturnType
       )
     }
   }