CPP: Fix false positive.

Author: geoffw0

cpp/ql/src/Likely Bugs/ContinueInFalseLoop.ql

@@ -21,15 +21,25 @@ DoStmt getAFalseLoop() {
 }
 
 /**
- * Gets a `do` ... `while` loop surrounding a statement.
+ * Gets a `do` ... `while` loop surrounding a statement.  This is blocked by a
+ * `switch` statement, since a `continue` inside a `switch` inside a loop may be
+ * jusitifed (`continue` breaks out of the loop whereas `break` only escapes the
+ * `switch`).
  */
 DoStmt enclosingLoop(Stmt s) {
   exists(Stmt parent |
     parent = s.getParent() and
-    if parent instanceof Loop then
-      result = parent
-    else
-      result = enclosingLoop(parent))
+    (
+      (
+        parent instanceof Loop and
+        result = parent
+      ) or (
+        not parent instanceof Loop and
+        not parent instanceof SwitchStmt and
+        result = enclosingLoop(parent)
+      )
+    )
+  )
 }
 
 from DoStmt loop, ContinueStmt continue

cpp/ql/test/query-tests/Likely Bugs/ContinueInFalseLoop/ContinueInFalseLoop.expected

@@ -1,3 +1,2 @@
 | test.cpp:13:4:13:12 | continue; | This 'continue' never re-runs the loop - the $@ is always false. | test.cpp:16:11:16:15 | 0 | loop condition |
 | test.cpp:59:5:59:13 | continue; | This 'continue' never re-runs the loop - the $@ is always false. | test.cpp:62:12:62:16 | 0 | loop condition |
-| test.cpp:88:4:88:12 | continue; | This 'continue' never re-runs the loop - the $@ is always false. | test.cpp:93:11:93:11 | 0 | loop condition |

cpp/ql/test/query-tests/Likely Bugs/ContinueInFalseLoop/test.cpp

@@ -85,7 +85,7 @@ void test1(int x)
 		default:
 			// do [2]
 
-			continue; // break out of the loop entirely, skipping [3] [FALSE POSITIVE]
+			continue; // GOOD; break out of the loop entirely, skipping [3]
 		};
 
 		// do [3]