C++: Add predicates to support multidimensional subscript operators

Author: jketema

cpp/ql/lib/semmle/code/cpp/PrintAST.qll

@@ -1050,10 +1050,10 @@ private predicate namedExprChildPredicates(Expr expr, Element ele, string pred)
     expr.(Call).getQualifier() = ele and
     pred = "getQualifier()"
     or
-    // OverloadedArrayExpr::getArrayBase/0 and OverloadedArrayExpr::getArrayOffset/0 also consider arguments, and are already handled below.
+    // OverloadedArrayExpr::getArrayBase/0 and OverloadedArrayExpr::getArrayOffset/1 also consider arguments, and are already handled below.
     exists(int n, Expr arg | expr.(Call).getArgument(n) = arg |
       not expr.(OverloadedArrayExpr).getArrayBase() = arg and
-      not expr.(OverloadedArrayExpr).getArrayOffset() = arg and
+      not expr.(OverloadedArrayExpr).getAnArrayOffset() = arg and
       arg = ele and
       pred = "getArgument(" + n.toString() + ")"
     )
@@ -1062,7 +1062,10 @@ private predicate namedExprChildPredicates(Expr expr, Element ele, string pred)
     or
     expr.(OverloadedArrayExpr).getArrayBase() = ele and pred = "getArrayBase()"
     or
-    expr.(OverloadedArrayExpr).getArrayOffset() = ele and pred = "getArrayOffset()"
+    exists(int n |
+      expr.(OverloadedArrayExpr).getArrayOffset(n) = ele and
+      pred = "getArrayOffset(" + n.toString() + ")"
+    )
     or
     // OverloadedPointerDereferenceExpr::getExpr/0 also considers qualifiers, and is already handled above for all Call classes.
     not expr.(OverloadedPointerDereferenceExpr).getQualifier() =

cpp/ql/lib/semmle/code/cpp/exprs/Call.qll

@@ -388,9 +388,20 @@ class OverloadedArrayExpr extends FunctionCall {
   /**
    * Gets the expression giving the index.
    */
-  Expr getArrayOffset() {
-    if exists(this.getQualifier()) then result = this.getChild(0) else result = this.getChild(1)
+  Expr getArrayOffset() { result = this.getArrayOffset(0) }
+
+  /**
+   * Gets the expression giving the nth index.
+   */
+  Expr getArrayOffset(int n) {
+    n >= 0 and
+    if exists(this.getQualifier()) then result = this.getChild(n) else result = this.getChild(n + 1)
   }
+
+  /**
+   * Gets an expression giving an index.
+   */
+  Expr getAnArrayOffset() { result = this.getArrayOffset(_) }
 }
 
 /**