Merge pull request #617 from geoffw0/unusedstatic

CPP: Fix false positives in UnusedStaticVariables.ql

Author: jbj

change-notes/1.20/analysis-cpp.md

@@ -0,0 +1,16 @@
+# Improvements to C/C++ analysis
+
+## General improvements
+
+## New queries
+
+| **Query**                   | **Tags**  | **Purpose**                                                        |
+|-----------------------------|-----------|--------------------------------------------------------------------|
+
+## Changes to existing queries
+
+| **Query**                  | **Expected impact**    | **Change**                                                       |
+|----------------------------|------------------------|------------------------------------------------------------------|
+| Unused static variable (`cpp/unused-static-variable`) | Fewer false positive results | Variables with the attribute `unused` are now excluded from the query. |
+
+## Changes to QL libraries

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

@@ -25,4 +25,5 @@ where v.isStatic()
   and not v instanceof MemberVariable
   and not declarationHasSideEffects(v)
   and not v.getAnAttribute().hasName("used")
+  and not v.getAnAttribute().hasName("unused")
 select v, "Static variable " + v.getName() + " is never read"

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

@@ -0,0 +1,2 @@
+| test.cpp:7:12:7:21 | staticVar5 | Static variable staticVar5 is never read |
+| test.cpp:8:12:8:21 | staticVar6 | Static variable staticVar6 is never read |

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

@@ -0,0 +1 @@
+Best Practices/Unused Entities/UnusedStaticVariables.ql

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

@@ -0,0 +1,18 @@
+
+int globalVar; // GOOD (not static)
+static int staticVar1; // GOOD (used)
+static int staticVar2; // GOOD (used)
+static int staticVar3 = 3; // GOOD (used)
+static int staticVar4 = staticVar3; // GOOD (used)
+static int staticVar5; // BAD (unused)
+static int staticVar6 = 6; // BAD (unused)
+static __attribute__((__unused__)) int staticVar7; // GOOD (unused but this is expected)
+
+void f()
+{
+	int *ptr = &staticVar4;
+
+	staticVar1 = staticVar2;
+	(*ptr) = 0;
+}
+