Add STATIC_ASSERT_INCOMPLETE_CLASS to enforce include minimality.

Add enforcments against `Dictionary` for `ustring.h` and two for `Dictionary` and `String` from `array.h`.

Author: Ivorforce

core/string/ustring.cpp

@@ -30,6 +30,8 @@
 
 #include "ustring.h"
 
+STATIC_ASSERT_INCOMPLETE_CLASS(Dictionary);
+
 #include "core/crypto/crypto_core.h"
 #include "core/math/color.h"
 #include "core/math/math_funcs.h"

core/typedefs.h

@@ -440,3 +440,23 @@ inline constexpr bool is_zero_constructible_v = is_zero_constructible<T>::value;
 #define GODOT_MSVC_WARNING_POP
 #define GODOT_MSVC_WARNING_PUSH_AND_IGNORE(m_warning)
 #endif
+
+template <typename T, typename = void>
+struct is_incomplete_type : std::true_type {};
+
+template <typename T>
+struct is_incomplete_type<T, std::void_t<decltype(sizeof(T))>> : std::false_type {};
+
+template <typename T>
+constexpr bool is_incomplete_type_v = is_incomplete_type<T>::value;
+
+#ifndef SCU_BUILD
+/// Enforces the requirement that a class is not fully defined.
+/// This can be used to reduce include coupling and keep compile times low.
+/// The check must be made at the top of the corresponding .cpp file of a header.
+#define STATIC_ASSERT_INCOMPLETE_CLASS(m_type) \
+	class m_type;                              \
+	static_assert(is_incomplete_type_v<m_type>, #m_type " was fully defined when it should not be. Please check include hierarchy of " __FILE__);
+#else
+#define STATIC_ASSERT_INCOMPLETE_CLASS(m_type)
+#endif

core/variant/array.cpp

@@ -30,6 +30,9 @@
 
 #include "array.h"
 
+STATIC_ASSERT_INCOMPLETE_CLASS(Dictionary);
+STATIC_ASSERT_INCOMPLETE_CLASS(String);
+
 #include "container_type_validate.h"
 #include "core/math/math_funcs.h"
 #include "core/object/script_language.h"

methods.py

@@ -69,6 +69,7 @@ def add_source_files_scu(self, sources, files, allow_gen=False):
 
         # Add all the gen.cpp files in the SCU directory
         add_source_files_orig(self, sources, subdir + ".scu/scu_*.gen.cpp", True)
+        self.Append(CPPDEFINES=["SCU_BUILD"])
         return True
     return False