JS: fix FP in js/superfluous-trailing-arguments related to Function.arguments

change-notes/1.24/analysis-javascript.md

@@ -80,6 +80,7 @@
 | Use of password hash with insufficient computational effort (`js/insufficient-password-hash`) | Fewer false positive results | This query now recognizes additional cases that do not require secure hashing. |
 | Useless regular-expression character escape (`js/useless-regexp-character-escape`) | Fewer false positive results | This query now distinguishes escapes in strings and regular expression literals. |
 | Identical operands (`js/redundant-operation`) | Fewer results | This query now recognizes cases where the operands change a value using ++/-- expressions. |
+| Superfluous trailing arguments (`js/superfluous-trailing-arguments`) | Fewer results | This query now recognizes cases where a function uses the `Function.arguments` value to process a variable number of parameters. |
 
 ## Changes to libraries
 

javascript/ql/src/semmle/javascript/Functions.qll

@@ -117,7 +117,14 @@ class Function extends @function, Parameterized, TypeParameterized, StmtContaine
   ArgumentsVariable getArgumentsVariable() { result.getFunction() = this }
 
   /** Holds if the body of this function refers to the function's `arguments` variable. */
-  predicate usesArgumentsObject() { exists(getArgumentsVariable().getAnAccess()) }
+  predicate usesArgumentsObject() {
+    exists(getArgumentsVariable().getAnAccess())
+    or
+    exists(PropAccess read |
+      read.getBase() = getVariable().getAnAccess() and
+      read.getPropertyName() = "arguments"
+    )
+  }
 
   /**
    * Holds if this function declares a parameter or local variable named `arguments`.

javascript/ql/test/query-tests/LanguageFeatures/SpuriousArguments/tst.js

@@ -120,3 +120,13 @@ parseFloat("123", 10);
 	throwerWithParam(42, 87); // NOT OK
 	throwerIndirect(42); // OK, but still flagged due to complexity
 });
+
+function sum2() {
+	var result = 0;
+	for (var i=0,n=sum2.arguments.length; i<n; ++i)
+		result += sum2.arguments[i];
+	return result;
+}
+
+// OK
+sum2(1, 2, 3);