src/dinterpret.d

@@ -1470,7 +1470,7 @@ public:
                 result = e; // bubbled up from ReturnStatement
                 return;
             }
-            e = interpret(s.increment, istate); // TODO: ctfeNeedNothing is better?
+            e = interpret(s.increment, istate, ctfeNeedNothing);
             if (exceptionOrCant(e))
                 return;
         }
@@ -5446,9 +5446,9 @@ public:
         if (exceptionOrCant(e1))
             return;
         // If the expression has been cast to void, do nothing.
-        if (e.to.ty == Tvoid && goal == ctfeNeedNothing)
+        if (e.to.ty == Tvoid)
         {
-            result = e1;
+            result = CTFEExp.voidexp;
             return;
         }
         if (e.to.ty == Tpointer && e1.op != TOKnull)

test/compilable/interpret3.d

@@ -7652,3 +7652,17 @@ auto structInCaseScope()
 }
 
 static assert(!structInCaseScope());
+
+/**************************************************
+    15251 - void cast in ForStatement.increment
+**************************************************/
+
+int test15251()
+{
+    for (ubyte lwr = 19;
+        lwr != 20;
+        cast(void)++lwr)    // have to to be evaluated with ctfeNeedNothing
+    {}
+    return 1;
+}
+static assert(test15251());