C#: Split pattern reads into two steps.

Author: michaelnebel

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

@@ -610,6 +610,20 @@ module LocalFlow {
           or
           exists(Switch sw | sw.getACase() = cfe and sw.getExpr() = e1 and scope = sw)
         )
+        or
+        isSuccessor = true and
+        scope =
+          any(IsExpr ie |
+            e1 = ie.getExpr() and
+            e2 = ie.getPattern()
+          )
+        or
+        isSuccessor = true and
+        scope =
+          any(Switch e |
+            e1 = e.getExpr() and
+            e2 = e.getACase().getPattern()
+          )
       )
     }
 
@@ -919,13 +933,13 @@ private predicate patternPropertyRead0(RecursivePatternExpr rpe, ContentSet c, V
 
 private predicate patternPropertyRead(Expr e1, ContentSet c, VariablePatternExpr e2) {
   exists(IsExpr ie, RecursivePatternExpr rpe |
-    e1 = ie.getExpr() and
+    e1 = rpe and
     rpe = ie.getPattern() and
     patternPropertyRead0(rpe, c, e2)
   )
   or
   exists(Switch sw, RecursivePatternExpr rpe |
-    e1 = sw.getExpr() and
+    e1 = rpe and
     rpe = sw.getACase().getPattern() and
     patternPropertyRead0(rpe, c, e2)
   )
@@ -2454,7 +2468,7 @@ private class ReadStepConfiguration extends ControlFlowReachabilityConfiguration
     isSuccessor = false
     or
     exactScope = false and
-    isSuccessor = true and
+    isSuccessor = false and
     patternPropertyRead(e1, _, e2) and
     scope = e1
   }