Merge pull request #22961 from github/copilot/unused-static-empty-pack-22931

C++: Ignore compiler-generated variables in unused-static-variable query

Author: jketema

cpp/ql/src/Best Practices/Unused Entities/UnusedStaticVariables.ql

@@ -22,6 +22,7 @@ predicate declarationHasSideEffects(Variable v) {
 from Variable v
 where
   v.isStatic() and
+  not v.isCompilerGenerated() and
   v.hasDefinition() and
   not v.isConstexpr() and
   not exists(VariableAccess a | a.getTarget() = v) and

cpp/ql/src/change-notes/2026-10-30-unused-static-compiler-generated.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The `cpp/unused-static-variable` query no longer reports compiler-generated variables, such as placeholders for empty function parameter packs.

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticVariables/test.cpp

@@ -1,4 +1,4 @@
-// semmle-extractor-options: -std=c++17
+// semmle-extractor-options: -std=c++20
 int globalVar; // GOOD (not static)
 static int staticVar1; // GOOD (used)
 static int staticVar2; // GOOD (used)
@@ -49,3 +49,10 @@ struct WithDestructor
 
 static WithConstructor constructed; // GOOD (constructor has a side effect)
 static WithDestructor destructed; // GOOD (destructor has a side effect)
+
+static auto sum(auto... values)
+{
+	return (0 + ... + values);
+}
+
+int globalVar2 = sum() + sum(2);