Merge pull request #1178 from castler/fix_7_0_4_overloaded_operators_fp

Fix RULE-7-0-4 false positives for non-built-in operators

Author: MichaelRFairhurst

change_notes/2026-08-20-fix-fp-rule-7-0-4-non-numeric-operand-types.md

@@ -0,0 +1,11 @@
+- `RULE-7-0-4` - `InappropriateBitwiseOrShiftOperands.ql`:
+  - Fixes #1177 - the rule no longer reports operands whose type is not a MISRA numeric type. The
+    operand checks used `not isUnsignedType(operandType)`, which is vacuously true for every type
+    that has no MISRA numeric type at all, such as class types and the unresolved dependent types
+    of uninstantiated template bodies. As a result the rule reported operations that do not use
+    the built-in operators, most notably the stream insertion and extraction operators. The checks
+    now use `isSignedType(operandType)` instead.
+  - Operands of character type, of a non-standard integral type, and of an unscoped enumeration
+    type without a fixed underlying type are consequently no longer reported, because none of them
+    has a MISRA numeric type. Unscoped enumerations without a fixed underlying type are covered by
+    `RULE-10-2-3`.

cpp/misra/src/rules/RULE-7-0-4/InappropriateBitwiseOrShiftOperands.ql

@@ -63,15 +63,15 @@ where
     |
       x = op.getLeftOperand() and
       operandType = op.getLeftOperand().getExplicitlyConverted().getType() and
-      not MisraCpp23BuiltInTypes::isUnsignedType(operandType) and
+      MisraCpp23BuiltInTypes::isSignedType(operandType) and
       message =
         "Bitwise operator '" + op.getOperator() +
           "' requires unsigned numeric operands, but the left operand has type '" + operandType +
           "'."
       or
       x = op.getRightOperand() and
       operandType = op.getRightOperand().getExplicitlyConverted().getType() and
-      not MisraCpp23BuiltInTypes::isUnsignedType(operandType) and
+      MisraCpp23BuiltInTypes::isSignedType(operandType) and
       message =
         "Bitwise operator '" + op.getOperator() +
           "' requires unsigned numeric operands, but the right operand has type '" + operandType +
@@ -82,7 +82,7 @@ where
     exists(ComplementExpr comp, Type opType |
       x = comp.getOperand() and
       opType = comp.getOperand().getExplicitlyConverted().getType() and
-      not MisraCpp23BuiltInTypes::isUnsignedType(opType) and
+      MisraCpp23BuiltInTypes::isSignedType(opType) and
       message =
         "Bit complement operator '~' requires unsigned operand, but has type '" + opType + "'."
     )
@@ -91,7 +91,7 @@ where
     exists(BinaryShiftOpOrAssignOp shift, Type leftType |
       x = shift.getLeftOperand() and
       leftType = shift.getLeftOperand().getExplicitlyConverted().getType() and
-      not MisraCpp23BuiltInTypes::isUnsignedType(leftType) and
+      MisraCpp23BuiltInTypes::isSignedType(leftType) and
       not isSignedConstantLeftShiftException(shift) and
       message =
         "Shift operator '" + shift.getOperator() +
@@ -112,7 +112,7 @@ where
           "Shift operator '" + shift.getOperator() + "' shifts by " + right.getValue().toInt() +
             " which is not within the valid range 0.." + ((leftType.getSize() * 8) - 1) + "."
       else (
-        not MisraCpp23BuiltInTypes::isUnsignedType(rightType) and
+        MisraCpp23BuiltInTypes::isSignedType(rightType) and
         message =
           "Shift operator '" + shift.getOperator() +
             "' requires unsigned right operand, but has type '" + rightType + "'."

cpp/misra/test/rules/RULE-7-0-4/InappropriateBitwiseOrShiftOperands.expected

@@ -47,3 +47,6 @@
 | test.cpp:156:3:156:12 | 1073741824 | Shift operator '<<' requires unsigned left operand, but has type 'int'. |
 | test.cpp:162:3:162:5 | s32 | Shift operator '<<' requires unsigned left operand, but has type 'int32_t'. |
 | test.cpp:170:3:170:5 | s32 | Shift operator '>>' requires unsigned left operand, but has type 'int32_t'. |
+| test.cpp:201:3:201:7 | value | Shift operator '<<' requires unsigned left operand, but has type 'signed int'. |
+| test.cpp:226:3:226:4 | e3 | Bitwise operator '&' requires unsigned numeric operands, but the left operand has type 'UnscopedEnumSignedUnderlyingType'. |
+| test.cpp:226:7:226:8 | e3 | Bitwise operator '&' requires unsigned numeric operands, but the right operand has type 'UnscopedEnumSignedUnderlyingType'. |

cpp/misra/test/rules/RULE-7-0-4/test.cpp

@@ -168,4 +168,70 @@ void test_right_shift_signed_operands() {
 
   u32 >> 1U; // COMPLIANT
   s32 >> 1U; // NON_COMPLIANT
-}
+}
+
+class TestStream {
+public:
+  TestStream &operator<<(std::int32_t value);
+  TestStream &operator>>(std::int32_t &value);
+};
+
+void test_overloaded_shift_operators() {
+  TestStream stream;
+  std::int32_t s32 = 1;
+
+  // User provided operators, not the built-in shift operators
+  stream << 1;   // COMPLIANT
+  stream << s32; // COMPLIANT
+  stream >> s32; // COMPLIANT
+}
+
+template <typename T>
+void test_overloaded_shift_operators_in_template(TestStream &stream,
+                                                 const T &value) {
+  // The left operand of the second `<<` is the `TestStream &` returned by the
+  // first one, and the right operand is dependent, so the operation is
+  // unresolved in the uninstantiated template body
+  stream << 1 << value; // COMPLIANT
+}
+
+template <typename T> void test_dependent_shift_operands(T value) {
+  // Dependent operands are unresolved in the uninstantiated template body, but
+  // reported through the instantiation below
+  value << 2; // NON_COMPLIANT
+}
+
+void test_template_instantiations() {
+  TestStream stream;
+  test_overloaded_shift_operators_in_template(stream, 1);
+  test_dependent_shift_operands<std::int32_t>(1);
+}
+enum UnscopedEnumNoFixedUnderlyingType { EnumeratorA = 1, EnumeratorB = 2 };
+
+enum UnscopedEnumUnsignedUnderlyingType : unsigned int { EnumeratorC = 1 };
+
+enum UnscopedEnumSignedUnderlyingType : int { EnumeratorD = 1 };
+
+void test_enum_operands() {
+  UnscopedEnumNoFixedUnderlyingType e1 = EnumeratorA;
+  UnscopedEnumUnsignedUnderlyingType e2 = EnumeratorC;
+  UnscopedEnumSignedUnderlyingType e3 = EnumeratorD;
+
+  // Without a fixed underlying type the enum has no MISRA numeric type, so the
+  // operands are not analysed by this rule
+  e1 &e1; // COMPLIANT
+
+  e2 &e2; // COMPLIANT
+
+  e3 &e3; // NON_COMPLIANT
+}
+
+void test_character_type_operands() {
+  char32_t c32 = 1;
+
+  // `char32_t` is of character type, not of numeric type, and is always
+  // unsigned
+  c32 &c32;  // COMPLIANT
+  c32 << 1U; // COMPLIANT
+  ~c32;      // COMPLIANT
+}