Add bitfield support

Author: ZXShady

include/libassert/assert-macros.hpp

@@ -5,9 +5,42 @@
 // https://github.com/jeremy-rifkin/libassert
 
 #include <libassert/platform.hpp>
-
+#include <libassert/expression-decomposition.hpp>
 #include <string_view>
 
+LIBASSERT_BEGIN_NAMESPACE
+namespace detail {
+
+std::false_type is_referencable_expression(...);
+
+template <typename Concept>
+auto is_referencable_expression(Concept c)
+    -> decltype(c(detail::expression_decomposer<>{}), std::true_type{});
+
+// A macro that checks whether an expression can be decomposed by the
+// decomposer. An expression that fails is a bitfield for example.
+#define LIBASSERT_IS_DECOMPOSABLE_EXPR(expr)                                   \
+  decltype(libassert::detail::is_referencable_expression(                      \
+      [](auto expr_decomposer) -> decltype(std::move(expr_decomposer)          \
+                                           << expr) {}))::value
+
+// The decomposer is passed as a template parameter to not evaluate the other
+// path and cause a hard error
+#define LIBASSERT_DECOMPOSER(expr)                                             \
+  [&](auto decomposer) {                                                       \
+    if constexpr (sizeof(decomposer) &&                                        \
+                  LIBASSERT_IS_DECOMPOSABLE_EXPR(expr)) {                      \
+      return libassert::detail::expression_decomposer(std::move(decomposer)    \
+                                                      << expr);                \
+    } else {                                                                   \
+      return std::move(decomposer) << (expr);                                  \
+    }                                                                          \
+  }(libassert::detail::expression_decomposer{})
+
+} // namespace detail
+LIBASSERT_END_NAMESPACE
+
+
 #if LIBASSERT_IS_CLANG || LIBASSERT_IS_GCC || !LIBASSERT_NON_CONFORMANT_MSVC_PREPROCESSOR
  // Macro mapping utility by William Swanson https://github.com/swansontec/map-macro/blob/master/map.h
  #define LIBASSERT_EVAL0(...) __VA_ARGS__
@@ -208,9 +241,7 @@ LIBASSERT_END_NAMESPACE
         if constexpr(false) { (void)(expr);} \
         LIBASSERT_WARNING_PRAGMA_PUSH \
         LIBASSERT_EXPRESSION_DECOMP_WARNING_PRAGMA \
-        auto libassert_decomposer = libassert::detail::expression_decomposer( \
-            libassert::detail::expression_decomposer{} << expr \
-        ); \
+        auto libassert_decomposer = LIBASSERT_DECOMPOSER(expr);\
         LIBASSERT_WARNING_PRAGMA_POP \
         LIBASSERT_ASSERT_MAIN_BODY( \
             expr, \

tests/unit/assertion_tests.cpp

@@ -275,6 +275,27 @@ TEST(LibassertBasic, NULLMacroComparison) {
     );
 }
 
+TEST(LibassertBasic, Bitfields) {
+    struct Bit {
+    int bit : 1;
+  };
+ Bit bit{1};
+  ASSERT_VAL(bit.bit == 1);
+  CHECK(
+      ASSERT(bit.bit == 1),
+       R"XX(
+        |Assertion failed at <LOCATION>:
+        |    ASSERT(bit.bit == 1);
+        )XX"
+  );
+
+  CHECK(ASSERT(1 == bit.bit),
+        R"XX(
+        |Assertion failed at <LOCATION>:
+        |    ASSERT(1 == bit.bit);
+        )XX");
+}
+
 
 TEST(LibassertBasic, LiteralFormatting) {
     const uint16_t flags = 0b000101010;
@@ -700,6 +721,7 @@ TEST(LibassertBasic, ExpressionDecomposition) {
         |        x -= x -= 1 => 0
         )XX"
     );
+
     CHECK(
         ASSERT(true ? false : true, "pffft"),
         R"XX(