Replaced static assert about TCHAR being not wider that ImWchar with a runtime check validating whether TCHAR values are in accepted range. Runtime check only happens on platforms where TCHAR is wider than ImWchar.

Source/ImGui/Private/ImGuiInputState.cpp

@@ -5,8 +5,45 @@
 #include "ImGuiInputState.h"
 
 #include <algorithm>
+#include <limits>
+#include <type_traits>
 
 
+// If TCHAR is wider than ImWchar, enable or disable validation of input character before conversions.
+#define VALIDATE_INPUT_CHARACTERS 1
+
+#if VALIDATE_INPUT_CHARACTERS
+DEFINE_LOG_CATEGORY_STATIC(LogImGuiInputState, Warning, All);
+#endif
+
+namespace
+{
+	template<typename T, std::enable_if_t<(sizeof(T) <= sizeof(ImWchar)), T>* = nullptr>
+	ImWchar CastInputChar(T Char)
+	{
+		return static_cast<ImWchar>(Char);
+	}
+
+	template<typename T, std::enable_if_t<!(sizeof(T) <= sizeof(ImWchar)), T>* = nullptr>
+	ImWchar CastInputChar(T Char)
+	{
+#if VALIDATE_INPUT_CHARACTERS
+		// We only need a runtime validation if TCHAR is wider than ImWchar.
+		// Signed and unsigned integral types with the same size as ImWchar should be safely converted. As long as the
+		// char value is in that range we can safely use it, otherwise we should log an error to notify about possible
+		// truncations.
+		static constexpr auto MinLimit = (std::numeric_limits<std::make_signed_t<ImWchar>>::min)();
+		static constexpr auto MaxLimit = (std::numeric_limits<std::make_unsigned_t<ImWchar>>::max)();
+		UE_CLOG(!(Char >= MinLimit && Char <= MaxLimit), LogImGuiInputState, Error,
+			TEXT("TCHAR value '%c' (%#x) is out of range %d (%#x) to %u (%#x) that can be safely converted to ImWchar. ")
+			TEXT("If you wish to disable this validation, please set VALIDATE_INPUT_CHARACTERS in ImGuiInputState.cpp to 0."),
+			Char, Char, MinLimit, MinLimit, MaxLimit, MaxLimit);
+#endif
+
+		return static_cast<ImWchar>(Char);
+	}
+}
+
 FImGuiInputState::FImGuiInputState()
 {
 	ResetState();
@@ -14,11 +51,9 @@ FImGuiInputState::FImGuiInputState()
 
 void FImGuiInputState::AddCharacter(TCHAR Char)
 {
-	static_assert(sizeof(TCHAR) <= sizeof(InputCharacters[0]), "Size of elements in Input Characters buffer is smaller than size of 'TCHAR'. Possible truncation.");
-
 	if (InputCharactersNum < Utilities::GetArraySize(InputCharacters))
 	{
-		InputCharacters[InputCharactersNum++] = static_cast<ImWchar>(Char);
+		InputCharacters[InputCharactersNum++] = CastInputChar(Char);
 		InputCharacters[InputCharactersNum] = 0;
 	}
 }