M9-3-3: address fp issue 381

change_notes/2024-04-12-fix-fp-m9-3-3.md

@@ -0,0 +1,2 @@
+`M9-3-3`: `MemberFunctionConstIfPossible.ql`:
+    - Fix FP reported in 381. Omit member functions that return nonconst reference types.

cpp/autosar/src/rules/M9-3-3/MemberFunctionConstIfPossible.ql

@@ -37,6 +37,13 @@ class NonConstMemberFunction extends MemberFunction {
   NonConstMemberFunction() { not this.hasSpecifier("const") }
 }
 
+/**
+ * References that are not const
+ */
+class NonConstReferenceType extends ReferenceType {
+  NonConstReferenceType() { not this.isConst() }
+}
+
 /**
  * `MemberFunction`s that are not const
  * and not `Constructor`s ect as const constructors are
@@ -57,7 +64,9 @@ class ConstMemberFunctionCandidate extends NonConstMemberFunction {
     this.hasDefinition() and
     // For uninstantiated templates we have only partial information that prevents us from determining
     // if the candidate calls non-const functions. Therefore we exclude these.
-    not this.isFromUninstantiatedTemplate(_)
+    not this.isFromUninstantiatedTemplate(_) and
+    // Cannot recommend const if it returns a non-const reference.
+    not this.getType() instanceof NonConstReferenceType
   }
 
   /**

cpp/autosar/test/rules/M9-3-3/test.cpp

@@ -193,3 +193,25 @@ void test_template() {
 class Z3 {
   void f(int) = delete; // COMPLIANT
 };
+
+class Z4 {
+public:
+  int values[128];
+  template <typename T>
+  void fill(const T &val) { // COMPLIANT[FALSE_NEGATIVE|TRUE_NEGATIVE] -
+                            // exception not specified in the
+    // standard, we opt to not raise an issue because the template can be both
+    // compliant and non-compliant depending on instantiations.
+    for (auto &elem : values) {
+      elem = val;
+    }
+  }
+  constexpr int &front() noexcept { return values[0]; } // COMPLIANT
+};
+
+void fp_reported_in_381() {
+  // added to test template initialization effects/lack thereof
+  Z4 z;
+  int i = z.front();
+  z.fill(i);
+}