Merge pull request #414 from github/lcartey/a0-1-1-ignore-incomplete-or-compiler-generated-vars

`A0-1-1`: Ignore incomplete or compiler generated variables

Author: rvermeulen

change_notes/2023-10-25-a0-1-1.md

@@ -0,0 +1,4 @@
+ * `A0-1-1` - address a number of false positive issues:
+   * Exclude compiler-generated variables, such as those generated for range-based for loops.
+   * Exclude variables in uninstantiated templates, for which we have no precise data on uses.
+   * Deviations should now be applied to the useless assignment instead of the variable itself.

cpp/autosar/src/rules/A0-1-1/UselessAssignment.ql

@@ -20,6 +20,6 @@ import codingstandards.cpp.deadcode.UselessAssignments
 
 from SsaDefinition ultimateDef, InterestingStackVariable v
 where
-  not isExcluded(v, DeadCodePackage::uselessAssignmentQuery()) and
+  not isExcluded(ultimateDef, DeadCodePackage::uselessAssignmentQuery()) and
   isUselessSsaDefinition(ultimateDef, v)
 select ultimateDef, "Definition of $@ is unused.", v, v.getName()

cpp/autosar/test/rules/A0-1-1/test.cpp

@@ -112,4 +112,15 @@ int test_useless_assignment(int &x, int p) {
   return y;
 }
 
-int main() { return 0; }
+int main() { return 0; }
+
+#include <vector>
+template <typename T> void test_range_based_for_loop_template() {
+  std::vector<A> values_;
+  for (auto &elem : values_) { // COMPLIANT - should not report either elem or
+                               //             the compiler generated (__range)
+                               //             variable in the uninstantiated
+                               //             template
+    elem;
+  }
+}

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

@@ -43,7 +43,11 @@ class InterestingStackVariable extends StackVariable {
     // A reference parameter can have an affect outside the enclosing function
     not mayEscape(this) and
     // Not a loop control variable, explicitly excluded
-    not this instanceof LoopControlVariable
+    not this instanceof LoopControlVariable and
+    // Ignore variables in uninstantiated templates
+    not this.isFromUninstantiatedTemplate(_) and
+    // Ignore compiler generated variables, such as those generated for range based for loops
+    not this.isCompilerGenerated()
   }
 }