Merge pull request #1176 from castler/fix_7_0_1_bool_reference_fp

Fix RULE-7-0-1 false positives for bool-to-reference bindings

Author: MichaelRFairhurst

change_notes/2026-08-20-fix-fp-rule-7-0-1-bool-reference.md

@@ -0,0 +1,9 @@
+ - `RULE-7-0-1` - `NoConversionFromBool.ql`:
+   - Fixed false positives where a `bool` value is bound to a reference whose
+     referenced type is also `bool` (e.g. `bool&`, `const bool&`), including
+     when this happens via a generic/forwarding-reference parameter (e.g.
+     `template<class T> void f(T&& t)`, or class template forwarding
+     constructors such as `std::pair`'s `pair(U1&&, U2&&)`) that happens to be
+     instantiated with `bool`. Binding a value to a reference of its own type
+     does not change the type or representation of the value, so this is not
+     a conversion from `bool` in the sense intended by the rule.

cpp/misra/src/rules/RULE-7-0-1/NoConversionFromBool.ql

@@ -23,6 +23,18 @@ where
   conv = e.getConversion() and
   conv.getExpr().getType().stripTopLevelSpecifiers() instanceof BoolType and
   not conv.getType().stripTopLevelSpecifiers() instanceof BoolType and
+  // Exclude conversions that only bind a `bool` value to a reference to `bool`
+  // (e.g. `bool&`, `const bool&`). Binding a value to a reference of its own
+  // type does not change the type or representation of the value, so this is
+  // not a "conversion from bool" in the sense intended by the rule. This
+  // commonly occurs when a `bool` argument is forwarded through a generic
+  // `bool&`/`const bool&` parameter (e.g. logging helpers, `std::pair`-style
+  // structured bindings/aggregates).
+  not conv.getType()
+      .stripTopLevelSpecifiers()
+      .(ReferenceType)
+      .getBaseType()
+      .stripTopLevelSpecifiers() instanceof BoolType and
   // Exclude cases that are explicitly allowed
   not (
     // Exception: equality operators with both bool operands

cpp/misra/test/rules/RULE-7-0-1/test.cpp

@@ -122,4 +122,39 @@ void test_bool_conversion_compliant() {
 
   // Bit-field assignment exception - compliant
   bf.bit = b1; // COMPLIANT
+}
+
+void f3(bool &b) {}
+void f4(const bool &b) {}
+
+template <typename T> void f5(T &&t) {}
+
+template <typename T1, typename T2> struct Pair {
+  template <typename U1, typename U2> Pair(U1 &&x, U2 &&y) : a(x), b(y) {}
+  T1 a;
+  T2 b;
+};
+
+void test_bool_reference_conversion_compliant() {
+  bool b1 = true;
+
+  // Binding a bool lvalue to a bool reference parameter - compliant, no
+  // actual type conversion takes place.
+  f3(b1); // COMPLIANT
+
+  // Binding a bool value to a const bool reference parameter - compliant.
+  f4(b1);   // COMPLIANT
+  f4(true); // COMPLIANT
+
+  // Binding a bool value to a forwarding reference parameter deduced as
+  // bool - compliant.
+  f5(b1);   // COMPLIANT
+  f5(true); // COMPLIANT
+
+  // Binding a bool value through a generic forwarding-reference constructor,
+  // where the second template parameter is deduced as bool - compliant. This
+  // mirrors idiomatic `return {value, overflow_flag};` and structured-binding
+  // patterns (e.g. std::pair and std::map::insert()'s return value).
+  Pair<int, bool> p1{1, true};  // COMPLIANT
+  Pair<int, bool> p2 = {1, b1}; // COMPLIANT
 }