Consider possible use as template argument

Author: rvermeulen

cpp/autosar/src/rules/M0-1-3/UnusedGlobalOrNamespaceVariable.ql

@@ -22,5 +22,7 @@ from PotentiallyUnusedGlobalOrNamespaceVariable v
 where
   not isExcluded(v, DeadCodePackage::unusedGlobalOrNamespaceVariableQuery()) and
   // No variable access
-  not exists(v.getAnAccess())
+  not exists(v.getAnAccess()) and
+  // Exclude members whose value is compile time and is potentially used to inintialize a template
+  not maybeACompileTimeTemplateArgument(v)
 select v, "Variable " + v.getQualifiedName() + " is unused."

cpp/autosar/src/rules/M0-1-3/UnusedMemberVariable.ql

@@ -25,5 +25,7 @@ where
   // No variable access
   not exists(v.getAnAccess()) and
   // No explicit initialization in a constructor
-  not exists(UserProvidedConstructorFieldInit cfi | cfi.getTarget() = v)
+  not exists(UserProvidedConstructorFieldInit cfi | cfi.getTarget() = v) and
+  // Exclude members whose value is compile time and is potentially used to inintialize a template
+  not maybeACompileTimeTemplateArgument(v)
 select v, "Member variable " + v.getName() + " is unused."

cpp/autosar/test/rules/M0-1-3/test_global_or_namespace.cpp

@@ -41,4 +41,22 @@ void test_ns() { x2 = 1; }
 m1(); // ignore dead code in macros
 } // namespace N1
 
-int test_access_variable() { return N1::x5; }
+int test_access_variable() { return N1::x5; }
+
+template <int t> struct C1 {
+  int array[t]; // COMPLIANT
+};
+
+constexpr int g5 = 1; // COMPLIANT - used as template parameter
+
+namespace ns1 {
+constexpr int m1 = 1; // COMPLIANT - used a template parameter
+}
+
+void test_fp_reported_in_384() {
+  struct C1<g5> l1;
+  struct C1<ns1::m1> l2;
+
+  l1.array[0] = 1;
+  l2.array[0] = 1;
+}

cpp/autosar/test/rules/M0-1-3/test_member.cpp

@@ -47,4 +47,18 @@ void test_d() {
   d.getT();
 }
 
+template <int t> struct C1 {
+  int array[t]; // COMPLIANT
+};
+
+struct C2 {
+  static constexpr int m1 = 1; // COMPLIANT - used as template parameter
+};
+
+void test_fp_reported_in_384() {
+  struct C1<C2::m1> l1;
+
+  l1.array[0] = 1;
+}
+
 } // namespace test

cpp/common/src/codingstandards/cpp/deadcode/UnusedVariables.qll

@@ -1,5 +1,6 @@
 import cpp
 import codingstandards.cpp.FunctionEquivalence
+import codingstandards.cpp.Scope
 
 /**
  * A type that contains a template parameter type (doesn't count pointers or references).
@@ -121,3 +122,17 @@ class UserProvidedConstructorFieldInit extends ConstructorFieldInit {
     not getEnclosingFunction().isCompilerGenerated()
   }
 }
+
+predicate maybeACompileTimeTemplateArgument(Variable v) {
+  v.isConstexpr() and
+  exists(ClassTemplateInstantiation cti, TranslationUnit tu |
+    cti.getATemplateArgument().(Expr).getValue() = v.getInitializer().getExpr().getValue() and
+    (
+      cti.getFile() = tu and
+      (
+        v.getADeclarationEntry().getFile() = tu or
+        tu.getATransitivelyIncludedFile() = v.getADeclarationEntry().getFile()
+      )
+    )
+  )
+}