Test side effects in unused-variable queries

Cover side-effecting initializers for local and static variables, recording the current alerts as spurious. Also cover constructor and destructor side effects for static global objects.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jketema

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

@@ -6,6 +6,7 @@
 | code2.cpp:64:7:64:8 | v3 | Variable v3 is not used. |
 | code2.cpp:108:11:108:12 | v2 | Variable v2 is not used. |
 | code2.cpp:128:9:128:9 | b | Variable b is not used. |
+| code2.cpp:194:6:194:16 | initialized | Variable initialized is not used. |
 | code.c:10:18:10:18 | y | Variable y is not used. |
 | code.c:11:18:11:18 | z | Variable z is not used. |
 | code.c:18:7:18:7 | x | Variable x is not used. |

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedLocals/code2.cpp

@@ -181,3 +181,15 @@ void test_maybe_unused()
 {
 	[[maybe_unused]] int unused; // GOOD: explicitly marked as maybe_unused
 }
+
+int globalVar;
+
+int initialize()
+{
+	return ++globalVar;
+}
+
+void test_initializer_side_effect()
+{
+	int initialized = initialize(); // $ SPURIOUS: Alert // GOOD (initializer has a side effect)
+}

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

@@ -2,3 +2,4 @@
 | test.cpp:8:12:8:21 | staticVar6 | Static variable staticVar6 is never read. |
 | test.cpp:10:11:10:19 | constVar8 | Static variable constVar8 is never read. |
 | test.cpp:12:12:12:22 | staticVar10 | Static variable staticVar10 is never read. |
+| test.cpp:38:12:38:22 | initialized | Static variable initialized is never read. |

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

@@ -29,3 +29,23 @@ class MyTemplateClass // never instantiated
 		// ...
 	}
 };
+
+int initialize()
+{
+	return ++globalVar;
+}
+
+static int initialized = initialize(); // $ SPURIOUS: Alert // GOOD (initializer has a side effect)
+
+struct WithConstructor
+{
+	WithConstructor() { ++globalVar; }
+};
+
+struct WithDestructor
+{
+	~WithDestructor() { ++globalVar; }
+};
+
+static WithConstructor constructed; // GOOD (constructor has a side effect)
+static WithDestructor destructed; // GOOD (destructor has a side effect)