Exclude enums that implement the BitmaskType trait

Author: rvermeulen

cpp/autosar/src/rules/A4-5-1/EnumUsedInArithmeticContexts.ql

@@ -19,6 +19,7 @@
 import cpp
 import codingstandards.cpp.autosar
 import codingstandards.cpp.Operator
+import codingstandards.cpp.Type
 
 class AllowedOperatorUse extends OperatorUse {
   AllowedOperatorUse() {
@@ -36,5 +37,7 @@ where
     access.(EnumConstantAccess).getTarget().getDeclaringEnum() = enum or
     access.(VariableAccess).getType() = enum 
   ) and
-  not operatorUse instanceof AllowedOperatorUse
+  not operatorUse instanceof AllowedOperatorUse and
+  // Enums that implement the BitmaskType trait are an exception.
+  not enum instanceof BitmaskType
 select access, "Enum $@ is used as an operand of arithmetic operation.", enum, enum.getName()

cpp/autosar/test/rules/A4-5-1/EnumUsedInArithmeticContexts.expected

@@ -102,5 +102,3 @@
 | enum_class.cpp:102:3:102:3 | a | Enum $@ is used as an operand of arithmetic operation. | enum_class.cpp:1:12:1:25 | FunctionalLang | FunctionalLang |
 | enum_class.cpp:103:3:103:3 | a | Enum $@ is used as an operand of arithmetic operation. | enum_class.cpp:1:12:1:25 | FunctionalLang | FunctionalLang |
 | enum_class.cpp:103:6:103:6 | b | Enum $@ is used as an operand of arithmetic operation. | enum_class.cpp:1:12:1:25 | FunctionalLang | FunctionalLang |
-| enum_class.cpp:120:3:120:5 | one | Enum $@ is used as an operand of arithmetic operation. | enum_class.cpp:106:12:106:15 | byte | byte |
-| enum_class.cpp:120:8:120:10 | two | Enum $@ is used as an operand of arithmetic operation. | enum_class.cpp:106:12:106:15 | byte | byte |

cpp/autosar/test/rules/A4-5-1/enum_class.cpp

@@ -112,9 +112,8 @@ byte operator~(byte lhs) { return lhs; }
 byte operator&=(byte lhs, byte rhs) { return lhs; }
 byte operator|=(byte lhs, byte rhs) { return lhs; }
 
-void test_bitmasktype_enum_class() { // COMPLIANT[FALSE_POSITIVE] - Type
-                                     // implementing the BitmaskType trait
-                                     // should be excluded.
+void test_bitmasktype_enum_class() { // COMPLIANT - byte implements the
+                                     // BitmaskType trait.
   byte one, two;
 
   one &two;

cpp/common/src/codingstandards/cpp/Type.qll

@@ -22,3 +22,31 @@ class FundamentalType extends BuiltInType {
 class IncompleteType extends Class {
   IncompleteType() { not hasDefinition() }
 }
+
+/** A type that implements the BitmaskType trait.
+ * https://en.cppreference.com/w/cpp/named_req/BitmaskType
+ *
+*/
+abstract class BitmaskType extends Type { }
+
+/** Holds if `enum` implements required overload `overload` to implement
+ * the BitmaskType trait.
+*/
+private predicate isRequiredEnumOverload(Enum enum, Function overload) {
+      overload.getName().regexpMatch("operator([&|^~]|&=|\\|=)")
+    and
+      forex(Parameter p | p = overload.getAParameter() |
+        (
+          p.getType() = enum 
+          or
+          p.getType().(ReferenceType).getBaseType() = enum
+        )
+      )
+}
+
+private class EnumBitmaskType extends BitmaskType, Enum {
+  EnumBitmaskType() {
+    // Implements all the required overload
+    count(Function overload | isRequiredEnumOverload(this, overload)) = 6
+  }
+}