DeadCode: Add MISRA C 2012 Rule 2.5

Adds a query to find unused macro declarations. The query is mostly
straightforward, however #undefs are not connected in our database
schema with the #defines they undefine. This means that we cannot
accurately identify unused macros when there is a sequence of defs
and undefs.

Author: lcartey

c/misra/src/rules/RULE-2-5/UnusedMacroDeclaration.ql

@@ -0,0 +1,28 @@
+/**
+ * @id c/misra/unused-macro-declaration
+ * @name RULE-2-5: A project should not contain unused macro declarations
+ * @description Unused macro declarations are either redundant or indicate a possible mistake on the
+ *              part of the programmer.
+ * @kind problem
+ * @precision very-high
+ * @problem.severity warning
+ * @tags external/misra/id/rule-2-5
+ *       readability
+ *       maintainability
+ *       external/misra/obligation/advisory
+ */
+
+import cpp
+import codingstandards.c.misra
+
+from Macro m
+where
+  not isExcluded(m, DeadCodePackage::unusedMacroDeclarationQuery()) and
+  not exists(MacroAccess ma | ma.getMacro() = m) and
+  // We consider a macro "used" if the name is undef-ed at some point in the same file, or a file
+  // that includes the file defining the macro. This will over approximate use in the case of a
+  // macro which is defined, then undefined, then re-defined but not used.
+  not exists(PreprocessorUndef u |
+    u.getName() = m.getName() and u.getFile().getAnIncludedFile*() = m.getFile()
+  )
+select m, "Macro " + m.getName() + " is unused."

c/misra/test/rules/RULE-2-5/UnusedMacroDeclaration.expected

@@ -0,0 +1,2 @@
+| test.c:4:1:4:16 | #define MACRO3 3 | Macro MACRO3 is unused. |
+| test.h:3:1:3:21 | #define HEADER_MACRO3 | Macro HEADER_MACRO3 is unused. |

c/misra/test/rules/RULE-2-5/UnusedMacroDeclaration.qlref

@@ -0,0 +1 @@
+rules/RULE-2-5/UnusedMacroDeclaration.ql

c/misra/test/rules/RULE-2-5/test.c

@@ -0,0 +1,16 @@
+#include "test.h"
+#define MACRO1 1 // COMPLIANT
+#define MACRO2 2 // COMPLIANT
+#define MACRO3 3 // NON_COMPLIANT
+
+#undef MACRO1
+
+// This case is not captured by the query
+#define MACRO1 1 // NON_COMPLIANT[FALSE_NEGATIVE]
+
+#undef HEADER_MACRO1
+
+void test() {
+  MACRO2;
+  HEADER_MACRO2;
+}

c/misra/test/rules/RULE-2-5/test.h

@@ -0,0 +1,3 @@
+#define HEADER_MACRO1 // COMPLIANT
+#define HEADER_MACRO2 // COMPLIANT
+#define HEADER_MACRO3 // NON_COMPLIANT