Merge pull request #620 from github/lcartey/m0-1-3-comp-uninst

M0-1-3: Exclude uninstantiated variable templates

Author: knewbury01

change_notes/2024-06-07-m0-1-3-uninstantiated-templates.md

@@ -0,0 +1,2 @@
+ - `M0-1-3` - `UnusedGlobalOrNamespaceVariable.ql`
+   - Reduces false positives by excluding compiler generated variables, and variables in uninstantiated templates.

cpp/autosar/test/rules/M0-1-3/UnusedLocalVariable.expected

@@ -4,3 +4,4 @@
 | test.cpp:23:5:23:5 | t | Local variable 't' in 'f1' is not used. |
 | test.cpp:23:5:23:5 | t | Local variable 't' in 'f1' is not used. |
 | test.cpp:44:6:44:6 | a | Local variable 'a' in 'test_side_effect_init' is not used. |
+| test.cpp:91:5:91:5 | t | Local variable 't' in 'template_function' is not used. |

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

@@ -78,3 +78,24 @@ int baz() {
   test_constexpr_in_static_assert<int>();
   return 0;
 }
+
+template <bool... Args> extern constexpr bool all_of_v = true; // COMPLIANT
+
+template <bool B1, bool... Args>
+extern constexpr bool all_of_v<B1, Args...> =
+    B1 &&all_of_v<Args...>; // COMPLIANT
+
+void test_template_variable() { all_of_v<true, true, true>; }
+
+template <typename T> void template_function() {
+  T t;       // NON_COMPLIANT - t is never used
+  T t2;      // COMPLIANT - t is used
+  t2.test(); // Call may not be resolved in uninstantiated template
+}
+
+class ClassT {
+public:
+  void test() {}
+};
+
+void test_template_function() { template_function<ClassT>(); }

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

@@ -48,7 +48,11 @@ class PotentiallyUnusedLocalVariable extends LocalVariable {
       not exists(AsmStmt s | f = s.getEnclosingFunction()) and
       // Ignore functions with error expressions as they indicate expressions that the extractor couldn't process
       not any(ErrorExpr e).getEnclosingFunction() = f
-    )
+    ) and
+    // exclude uninstantiated template members
+    not this.isFromUninstantiatedTemplate(_) and
+    // Do not report compiler generated variables
+    not this.isCompilerGenerated()
   }
 }
 
@@ -95,7 +99,9 @@ class PotentiallyUnusedMemberVariable extends MemberVariable {
     // Lambda captures are not "real" member variables - it's an implementation detail that they are represented that way
     not this = any(LambdaCapture lc).getField() and
     // exclude uninstantiated template members
-    not this.isFromUninstantiatedTemplate(_)
+    not this.isFromUninstantiatedTemplate(_) and
+    // Do not report compiler generated variables
+    not this.isCompilerGenerated()
   }
 }
 
@@ -107,7 +113,11 @@ class PotentiallyUnusedGlobalOrNamespaceVariable extends GlobalOrNamespaceVariab
     // Not declared in a macro expansion
     not isInMacroExpansion() and
     // No side-effects from declaration
-    not declarationHasSideEffects(this)
+    not declarationHasSideEffects(this) and
+    // exclude uninstantiated template members
+    not this.isFromUninstantiatedTemplate(_) and
+    // Do not report compiler generated variables
+    not this.isCompilerGenerated()
   }
 }