DeadCode: Add MISRA C 2012 Rule 2.3

Adds a query to check for unused type declarations, based on the shared
library.

Note: the expected results for the C++ test case have been updated to
include a compiler generated class. This is because shared queries do
not properly apply the exclusion mechanism. See:
github/coding-standards-team#1126

Author: lcartey

c/common/test/rules/unusedtypedeclarations/UnusedTypeDeclarations.expected

@@ -0,0 +1,5 @@
+| file://:0:0:0:0 | __va_list_tag | Type declaration __va_list_tag is not used. |
+| test.c:4:8:4:8 | A | Type declaration A is not used. |
+| test.c:7:18:7:18 | D | Type declaration D is not used. |
+| test.c:30:11:30:11 | R | Type declaration R is not used. |
+| test.c:43:12:43:12 | struct <unnamed> | Type declaration struct <unnamed> is not used. |

c/common/test/rules/unusedtypedeclarations/UnusedTypeDeclarations.ql

@@ -0,0 +1,2 @@
+// GENERATED FILE - DO NOT MODIFY
+import codingstandards.cpp.rules.unusedtypedeclarations.UnusedTypeDeclarations

c/common/test/rules/unusedtypedeclarations/test.c

@@ -0,0 +1,54 @@
+// NOTICE: THE TEST CASES BELOW ARE ALSO INCLUDED IN THE C++ TEST CASE AND CHANGES
+//         SHOULD BE REFLECTED THERE AS WELL.
+
+struct A {}; // NON_COMPLIANT - unused
+
+struct C {};  // COMPLIANT - used in the type def
+typedef struct C D; // NON_COMPLIANT - typedef itself not used
+
+struct F {}; // COMPLIANT - used as a global function return type
+
+struct F test_return_value() {
+  struct F f;
+  return f;
+}
+
+struct G {}; // COMPLIANT - used as a global function parameter type
+
+void test_global_function(struct G g) {}
+
+enum M { C1, C2, C3 };       // COMPLIANT - used in an enum type access below
+
+void test_enum_access() {
+  int i = C1;
+}
+
+struct O {}; // COMPLIANT - used in typedef below
+
+typedef struct O P; // COMPLIANT - used in typedef below
+typedef P Q; // COMPLIANT - used in function below
+typedef Q R; // NON_COMPLIANT - never used
+
+Q test_type_def() {}
+
+struct {     // COMPLIANT - used in type definition
+  union {    // COMPLIANT - f1 and f3 is accessed
+    struct { // COMPLIANT - f1 is accessed
+      int f1;
+    };
+    struct { // COMPLIANT - f3 is accessed
+      float f2;
+      float f3;
+    };
+    struct { // NON_COMPLIANT - f4 is never accessed
+      long f4;
+    };
+  };
+  int f5;
+} s;
+
+void test_nested_struct() {
+  s.f1;
+  s.f3;
+  s.f5;
+}

c/misra/src/rules/RULE-2-3/UnusedTypeDeclarations.ql

@@ -0,0 +1,21 @@
+/**
+ * @id c/misra/unused-type-declarations
+ * @name RULE-2-3: A project should not contain unused type declarations
+ * @description Unused type 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-2-3
+ *       readability
+ *       maintainability
+ *       external/misra/obligation/advisory
+ */
+
+import cpp
+import codingstandards.c.misra
+import codingstandards.cpp.rules.unusedtypedeclarations.UnusedTypeDeclarations
+
+class UnusedTypeDeclarationsQuery extends UnusedTypeDeclarationsSharedQuery {
+  UnusedTypeDeclarationsQuery() { this = DeadCodePackage::unusedTypeDeclarationsQuery() }
+}

c/misra/test/rules/RULE-2-3/UnusedTypeDeclarations.testref

@@ -0,0 +1 @@
+c/common/test/rules/unusedtypedeclarations/UnusedTypeDeclarations.ql

cpp/common/test/rules/unusedtypedeclarations/UnusedTypeDeclarations.expected

@@ -1,6 +1,7 @@
-| test.cpp:1:7:1:7 | A | Type declaration A is not used. |
-| test.cpp:3:7:3:7 | B | Type declaration B is not used. |
-| test.cpp:10:11:10:11 | D | Type declaration D is not used. |
-| test.cpp:74:11:74:11 | R | Type declaration R is not used. |
-| test.cpp:87:12:87:12 | struct <unnamed> | Type declaration struct <unnamed> is not used. |
-| test.cpp:108:29:108:30 | AA | Type declaration AA is not used. |
+| file://:0:0:0:0 | __va_list_tag | Type declaration __va_list_tag is not used. |
+| test.cpp:4:7:4:7 | A | Type declaration A is not used. |
+| test.cpp:6:7:6:7 | B | Type declaration B is not used. |
+| test.cpp:13:11:13:11 | D | Type declaration D is not used. |
+| test.cpp:77:11:77:11 | R | Type declaration R is not used. |
+| test.cpp:90:12:90:12 | struct <unnamed> | Type declaration struct <unnamed> is not used. |
+| test.cpp:111:29:111:30 | AA | Type declaration AA is not used. |

cpp/common/test/rules/unusedtypedeclarations/test.cpp

@@ -1,3 +1,6 @@
+// NOTICE: SOME OF THE TEST CASES BELOW ARE ALSO INCLUDED IN THE C TEST CASE AND CHANGES
+//         SHOULD BE REFLECTED THERE AS WELL.
+
 class A {}; // NON_COMPLIANT - unused
 
 class B { // NON_COMPLIANT - only used within itself