Rule 2.5: Consider macros accessed before definition

lcartey · lcartey · commit dd07767d6a57 · 2024-10-22T22:58:36.000+01:00
diff --git a/c/misra/src/rules/RULE-2-5/UnusedMacroDeclaration.ql b/c/misra/src/rules/RULE-2-5/UnusedMacroDeclaration.ql
@@ -19,7 +19,18 @@ import codingstandards.c.misra
 from Macro m
 where
   not isExcluded(m, DeadCodePackage::unusedMacroDeclarationQuery()) and
+  // We consider a macro "used" if there is a macro access
   not exists(MacroAccess ma | ma.getMacro() = m) and
+  // Or if there exists a check whether the macro is defined which the extractor
+  // hasn't been able to tie to a macro (usually because this use came before
+  // the macro was defined e.g. a header guard)
+  not exists(PreprocessorBranchDirective bd |
+    // Covers the #ifdef and #ifndef cases
+    bd.getHead() = m.getName()
+    or
+    // Covers the use of defined() to check if a macro is defined
+    m.getName() = bd.getHead().regexpCapture(".*defined\\((.*)\\).*", 1)
+  ) 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.
diff --git a/c/misra/test/rules/RULE-2-5/test.c b/c/misra/test/rules/RULE-2-5/test.c
@@ -13,4 +13,35 @@
 void test() {
   MACRO2;
   HEADER_MACRO2;
-}
+}
+
+#define CHECKED_MACRO_1 // COMPLIANT - used in branch
+#define CHECKED_MACRO_2 // COMPLIANT - used in branch
+#define CHECKED_MACRO_3 // COMPLIANT - used in branch
+
+#ifdef CHECKED_MACRO_1
+#endif
+
+#ifndef CHECKED_MACRO_2
+#endif
+
+#if defined(CHECKED_MACRO_3)
+#endif
+
+// In the case above, the extractor will identify macro accesses with each use
+// of the macro. In the case above, the extractor does not tie them together,
+// but the standard considers this acceptable usage. Notably, this type of
+// pattern occurs for header guards.
+
+#ifdef CHECKED_MACRO_BEFORE_1
+#endif
+
+#ifndef CHECKED_MACRO_BEFORE_2
+#endif
+
+#if defined(CHECKED_MACRO_BEFORE_3)
+#endif
+
+#define CHECKED_MACRO_BEFORE_1 // COMPLIANT - used in branch
+#define CHECKED_MACRO_BEFORE_2 // COMPLIANT - used in branch
+#define CHECKED_MACRO_BEFORE_3 // COMPLIANT - used in branch
diff --git a/change_notes/2024-10-22-rule-2-5.md b/change_notes/2024-10-22-rule-2-5.md
@@ -0,0 +1,2 @@
+ - `RULE-2-5` - `UnusedMacroDeclaration.ql`:
+   - Exclude false positives where a macro was used before definition, for example a header guard.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+ - `RULE-2-5` - `UnusedMacroDeclaration.ql`:
	`2`	`+ - Exclude false positives where a macro was used before definition, for example a header guard.`