Suppress unused variable warning for template test cases

The variable initialization has test registration as a side-effect,
but as far as GCC is concerned, the variable itself is unused.
Because the macro substitution always happens at global scope, we
cannot use cast to `void` as is usually done.

src/catch2/catch_compiler_capabilities.h

@@ -53,6 +53,9 @@
 // for older versions of GCC.
 #    define CATCH_INTERNAL_SUPPRESS_PARENTHESES_WARNINGS \
          _Pragma( "GCC diagnostic ignored \"-Wparentheses\"" )
+
+#    define CATCH_INTERNAL_SUPPRESS_UNUSED_WARNINGS \
+         _Pragma( "GCC diagnostic ignored \"-Wunused-variable\"" )
 #endif
 
 #if defined(__clang__)

src/catch2/catch_test_registry.h

@@ -17,6 +17,15 @@
 
 #include <memory>
 
+// GCC 5 and older do not properly handle disabling unused-variable warning
+// with a _Pragma. This means that we have to leak the suppression to the
+// user code as well :-(
+#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ <= 5
+#pragma GCC diagnostic ignored "-Wunused-variable"
+#endif
+
+
+
 namespace Catch {
 
 template<typename C>
@@ -153,6 +162,7 @@ struct AutoReg : NonCopyable {
         CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_ZERO_VARIADIC_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_UNUSED_TEMPLATE_WARNINGS \
+        CATCH_INTERNAL_SUPPRESS_UNUSED_WARNINGS \
         INTERNAL_CATCH_DECLARE_SIG_TEST(TestFunc, INTERNAL_CATCH_REMOVE_PARENS(Signature));\
         namespace {\
         namespace INTERNAL_CATCH_MAKE_NAMESPACE(TestName){\
@@ -197,7 +207,8 @@ struct AutoReg : NonCopyable {
         CATCH_INTERNAL_START_WARNINGS_SUPPRESSION                      \
         CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS                      \
         CATCH_INTERNAL_SUPPRESS_ZERO_VARIADIC_WARNINGS                \
-        CATCH_INTERNAL_SUPPRESS_UNUSED_TEMPLATE_WARNINGS              \
+        CATCH_INTERNAL_SUPPRESS_UNUSED_TEMPLATE_WARNINGS       \
+        CATCH_INTERNAL_SUPPRESS_UNUSED_WARNINGS \
         template<typename TestType> static void TestFuncName();       \
         namespace {\
         namespace INTERNAL_CATCH_MAKE_NAMESPACE(TestName) {                                     \
@@ -246,6 +257,7 @@ struct AutoReg : NonCopyable {
         CATCH_INTERNAL_START_WARNINGS_SUPPRESSION \
         CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_UNUSED_TEMPLATE_WARNINGS \
+        CATCH_INTERNAL_SUPPRESS_UNUSED_WARNINGS \
         template<typename TestType> static void TestFunc();       \
         namespace {\
         namespace INTERNAL_CATCH_MAKE_NAMESPACE(TestName){\
@@ -278,6 +290,7 @@ struct AutoReg : NonCopyable {
         CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_ZERO_VARIADIC_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_UNUSED_TEMPLATE_WARNINGS \
+        CATCH_INTERNAL_SUPPRESS_UNUSED_WARNINGS \
         namespace {\
         namespace INTERNAL_CATCH_MAKE_NAMESPACE(TestName){ \
             INTERNAL_CATCH_TYPE_GEN\
@@ -323,6 +336,7 @@ struct AutoReg : NonCopyable {
         CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_ZERO_VARIADIC_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_UNUSED_TEMPLATE_WARNINGS \
+        CATCH_INTERNAL_SUPPRESS_UNUSED_WARNINGS \
         template<typename TestType> \
             struct TestName : INTERNAL_CATCH_REMOVE_PARENS(ClassName <TestType>) { \
                 void test();\
@@ -374,6 +388,7 @@ struct AutoReg : NonCopyable {
         CATCH_INTERNAL_START_WARNINGS_SUPPRESSION \
         CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_UNUSED_TEMPLATE_WARNINGS \
+        CATCH_INTERNAL_SUPPRESS_UNUSED_WARNINGS \
         template<typename TestType> \
         struct TestName : INTERNAL_CATCH_REMOVE_PARENS(ClassName <TestType>) { \
             void test();\