C#: Add some testcases to cover mixed assignment and declarations in tuples.

csharp/ql/test/library-tests/csharp10/Tuples.cs

@@ -0,0 +1,27 @@
+using System;
+
+public class Deconstruction
+{
+    public void M1()
+    {
+        // Declaration and Assignment
+        (int x1, int y1) = (10, 11);
+
+        // Assignment
+        int x2 = 0;
+        int y2 = 0;
+        (x2, y2) = (20, 21);
+
+        // Mixed
+        int y3 = 0;
+        (int x3, y3) = (30, 31);
+
+        int x4 = 0;
+        (x4, int y4) = (40, 41);
+
+        // Nested, Mixed
+        int x5 = 0;
+        int y51 = 0;
+        (x5, (int y50, y51)) = (50, (51, 52));
+    }
+}

csharp/ql/test/library-tests/csharp10/tuples.expected

@@ -0,0 +1,18 @@
+declarations
+| Tuples.cs:8:14:8:15 | Int32 x1 |
+| Tuples.cs:8:22:8:23 | Int32 y1 |
+| Tuples.cs:17:14:17:15 | Int32 x3 |
+| Tuples.cs:20:18:20:19 | Int32 y4 |
+| Tuples.cs:25:19:25:21 | Int32 y50 |
+assignments
+| Tuples.cs:8:9:8:35 | ... = ... | Tuples.cs:8:14:8:15 | x1 | 0 |
+| Tuples.cs:8:9:8:35 | ... = ... | Tuples.cs:8:22:8:23 | y1 | 1 |
+| Tuples.cs:13:9:13:27 | ... = ... | Tuples.cs:11:13:11:14 | x2 | 0 |
+| Tuples.cs:13:9:13:27 | ... = ... | Tuples.cs:12:13:12:14 | y2 | 1 |
+| Tuples.cs:17:9:17:31 | ... = ... | Tuples.cs:16:13:16:14 | y3 | 1 |
+| Tuples.cs:17:9:17:31 | ... = ... | Tuples.cs:17:14:17:15 | x3 | 0 |
+| Tuples.cs:20:9:20:31 | ... = ... | Tuples.cs:19:13:19:14 | x4 | 0 |
+| Tuples.cs:20:9:20:31 | ... = ... | Tuples.cs:20:18:20:19 | y4 | 1 |
+| Tuples.cs:25:9:25:45 | ... = ... | Tuples.cs:23:13:23:14 | x5 | 0 |
+| Tuples.cs:25:9:25:45 | ... = ... | Tuples.cs:24:13:24:15 | y51 | 2 |
+| Tuples.cs:25:9:25:45 | ... = ... | Tuples.cs:25:19:25:21 | y50 | 1 |

csharp/ql/test/library-tests/csharp10/tuples.ql

@@ -0,0 +1,14 @@
+import csharp
+
+private predicate relevant(Element e) { e.getFile().getBaseName() = "Tuples.cs" }
+
+query predicate declarations(LocalVariableDeclExpr d) {
+  relevant(d) and
+  d.getParent*() instanceof TupleExpr
+}
+
+query predicate assignments(AssignableDefinitions::TupleAssignmentDefinition t, Assignable a, int o) {
+  relevant(t.getAssignment()) and
+  a = t.getTarget() and
+  o = t.getEvaluationOrder()
+}