C#: Only include top level tuples pattern match flow in the localExprStep relation.

Author: michaelnebel

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

@@ -560,10 +560,16 @@ module LocalFlow {
     or
     exists(AssignExpr ae | ae.getLeftOperand().(TupleExpr) = e2 and ae.getRightOperand() = e1)
     or
-    exists(ControlFlowElement cfe | cfe = e2.(TuplePatternExpr).getPatternMatch() |
-      cfe.(IsExpr).getExpr() = e1
-      or
-      exists(Switch sw | sw.getACase() = cfe and sw.getExpr() = e1)
+    exists(IsExpr e |
+      e1 = e.getExpr() and
+      e2 = e.getPattern() and
+      e2 instanceof TuplePatternExpr
+    )
+    or
+    exists(Switch sw |
+      e1 = sw.getExpr() and
+      e2 = sw.getACase().getPattern() and
+      e2 instanceof TuplePatternExpr
     )
   }
 

csharp/ql/test/library-tests/dataflow/tuples/DataFlowStep.expected

@@ -108,7 +108,6 @@
 | Tuples.cs:59:17:59:32 | (..., ...) | Tuples.cs:59:13:59:13 | access to local variable x |
 | Tuples.cs:60:17:60:17 | access to local variable x | Tuples.cs:62:18:62:57 | (String,(Int32,String),Int32) t |
 | Tuples.cs:60:17:60:17 | access to local variable x | Tuples.cs:67:18:67:35 | (..., ...) |
-| Tuples.cs:60:17:60:17 | access to local variable x | Tuples.cs:67:18:67:35 | (..., ...) |
 | Tuples.cs:60:17:60:17 | access to local variable x | Tuples.cs:87:13:87:13 | access to local variable x |
 | Tuples.cs:62:18:62:57 | (String,(Int32,String),Int32) t | Tuples.cs:62:18:62:57 | SSA def(t) |
 | Tuples.cs:62:18:62:57 | SSA def(t) | Tuples.cs:62:64:62:64 | access to local variable t |
@@ -144,7 +143,6 @@
 | Tuples.cs:75:13:75:30 | SSA qualifier def(y.Item2.Item2) | Tuples.cs:80:22:80:34 | access to field Item2 |
 | Tuples.cs:75:17:75:30 | (..., ...) | Tuples.cs:75:13:75:13 | access to local variable y |
 | Tuples.cs:75:18:75:18 | access to parameter s | Tuples.cs:75:25:75:25 | access to parameter s |
-| Tuples.cs:76:17:76:17 | access to local variable y | Tuples.cs:78:26:78:35 | (..., ...) |
 | Tuples.cs:76:17:76:17 | access to local variable y | Tuples.cs:79:22:79:22 | access to local variable y |
 | Tuples.cs:78:19:78:23 | SSA def(a) | Tuples.cs:78:46:78:46 | access to local variable a |
 | Tuples.cs:78:19:78:23 | String a | Tuples.cs:78:19:78:23 | SSA def(a) |
@@ -161,7 +159,6 @@
 | Tuples.cs:82:22:82:34 | access to field Item1 | Tuples.cs:82:22:82:34 | (...) ... |
 | Tuples.cs:83:22:83:22 | access to local variable b | Tuples.cs:83:22:83:22 | (...) ... |
 | Tuples.cs:87:13:87:13 | access to local variable x | Tuples.cs:87:18:87:35 | (..., ...) |
-| Tuples.cs:87:13:87:13 | access to local variable x | Tuples.cs:87:18:87:35 | (..., ...) |
 | Tuples.cs:87:23:87:23 | SSA def(p) | Tuples.cs:89:18:89:18 | access to local variable p |
 | Tuples.cs:87:23:87:23 | String p | Tuples.cs:87:23:87:23 | SSA def(p) |
 | Tuples.cs:87:27:87:27 | Int32 q | Tuples.cs:87:27:87:27 | SSA def(q) |

csharp/ql/test/library-tests/dataflow/tuples/Tuples.cs

@@ -142,4 +142,4 @@ public static void Sink(object o) { }
 namespace System.Runtime.CompilerServices
 {
     public class IsExternalInit { }
-}
+}