Fix bug so += File.separator is recognized

Author: owen-mc

java/ql/lib/semmle/code/java/security/PartialPathTraversal.qll

@@ -40,8 +40,11 @@ private class CharacterLiteralFileSeparatorExpr extends FileSeparatorExpr, Chara
   CharacterLiteralFileSeparatorExpr() { this.getValue() = "/" or this.getValue() = "\\" }
 }
 
-private class FileSeparatorAppend extends AddExpr {
-  FileSeparatorAppend() { this.getRightOperand() instanceof FileSeparatorExpr }
+private class FileSeparatorAppend extends BinaryExpr {
+  FileSeparatorAppend() {
+    this.(AddExpr).getRightOperand() instanceof FileSeparatorExpr or
+    this.(AssignAddExpr).getRightOperand() instanceof FileSeparatorExpr
+  }
 }
 
 private predicate isSafe(Expr expr) {

java/ql/test/query-tests/security/CWE-023/semmle/tests/PartialPathTraversal.expected

@@ -14,4 +14,3 @@
 | PartialPathTraversalTest.java:176:14:176:65 | startsWith(...) | Partial Path Traversal Vulnerability due to insufficient guard against path traversal. |
 | PartialPathTraversalTest.java:194:18:194:87 | startsWith(...) | Partial Path Traversal Vulnerability due to insufficient guard against path traversal. |
 | PartialPathTraversalTest.java:212:14:212:64 | startsWith(...) | Partial Path Traversal Vulnerability due to insufficient guard against path traversal. |
-| PartialPathTraversalTest.java:234:14:234:54 | startsWith(...) | Partial Path Traversal Vulnerability due to insufficient guard against path traversal. |

java/ql/test/query-tests/security/CWE-023/semmle/tests/PartialPathTraversalTest.java

@@ -231,7 +231,7 @@ void foo24(File parent) throws IOException {
     void foo25(File parent) throws IOException {
         String path = parent.getCanonicalPath();
         path += File.separator;
-        if (!dir().getCanonicalPath().startsWith(path)) { // $ SPURIOUS: Alert[java/partial-path-traversal-from-remote] Alert[java/partial-path-traversal]
+        if (!dir().getCanonicalPath().startsWith(path)) {
             throw new IOException("Invalid directory: " + dir().getCanonicalPath());
         }
     }