C++: Test for unreachable return statement

This test shows that the previous fix did not solve the problem where a
bad return statement exists but is unreachable.

cpp/ql/test/query-tests/jsf/4.10 Classes/AV Rule 82/AV Rule 82.cpp

@@ -133,6 +133,43 @@ public:
   }
 };
 
+class Reachability {
+  Reachability &operator=(Reachability &that) { // GOOD [FALSE POSITIVE]
+    int one = 1;
+    if (one)
+      return *this;
+    else
+      return that; // unreachable
+  }
+
+  // helper function that always returns a reference to `*this`.
+  Reachability &returnThisReference() {
+    int one = 1;
+    if (one)
+      return *this;
+    else
+      return staticInstance; // unreachable
+  }
+
+  // helper function that always returns `this`.
+  Reachability *const returnThisPointer() {
+    int one = 1;
+    if (one)
+      return this;
+    else
+      return &staticInstance; // unreachable
+  }
+
+  Reachability &operator=(int _val) { // GOOD [FALSE POSITIVE]
+    return returnThisReference();
+  }
+
+  Reachability &operator=(short _val) { // GOOD [FALSE POSITIVE]
+    return *returnThisPointer();
+  }
+
+  static Reachability staticInstance;
+};
 
 int main() {
   Container c;

cpp/ql/test/query-tests/jsf/4.10 Classes/AV Rule 82/AV Rule 82.expected

@@ -2,3 +2,6 @@
 | AV Rule 82.cpp:24:8:24:16 | operator= | Assignment operator in class Bad2 should have return type Bad2&. Otherwise a copy is created at each call. |
 | AV Rule 82.cpp:63:29:63:37 | operator= | Assignment operator in class TemplateReturnAssignment<T> does not return a reference to *this. |
 | AV Rule 82.cpp:63:29:63:37 | operator= | Assignment operator in class TemplateReturnAssignment<int> does not return a reference to *this. |
+| AV Rule 82.cpp:137:17:137:25 | operator= | Assignment operator in class Reachability does not return a reference to *this. |
+| AV Rule 82.cpp:163:17:163:25 | operator= | Assignment operator in class Reachability does not return a reference to *this. |
+| AV Rule 82.cpp:167:17:167:25 | operator= | Assignment operator in class Reachability does not return a reference to *this. |