From 58e32e173b76450ead43f095aee1f8650aae2fad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20=C5=A0ach?= <martin.sachin@gmail.com>
Date: Wed, 13 Mar 2024 12:13:31 +0100
Subject: [PATCH] Disable nil_value() for enum and remove NilValue<Enum>.

Fixes: https://github.com/prusa3d/PrusaSlicer/issues/12455.
---
 src/libslic3r/Config.hpp | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/src/libslic3r/Config.hpp b/src/libslic3r/Config.hpp
index 24bbe7a5b1..c3e4ac2c8f 100644
--- a/src/libslic3r/Config.hpp
+++ b/src/libslic3r/Config.hpp
@@ -324,7 +324,6 @@ typedef const ConfigOption* ConfigOptionConstPtr;
 template<class T, class En = void> struct NilValueTempl
 {
     using NilType = T;
-    static_assert(always_false<T>::value, "Type has no well defined nil value");
 };
 
 template<class T> struct NilValueTempl<T, std::enable_if_t<std::is_integral_v<T>, void>> {
@@ -334,14 +333,6 @@ template<class T> struct NilValueTempl<T, std::enable_if_t<std::is_integral_v<T>
 
 template<> struct NilValueTempl<bool> : public NilValueTempl<int>{};
 
-// For enums the nil is the max value of the underlying type.
-template<class T>
-struct NilValueTempl<T, std::enable_if_t<std::is_enum_v<T>, void>>
-{
-    using NilType = T;
-    static constexpr auto value = static_cast<T>(std::numeric_limits<std::underlying_type_t<T>>::max());
-};
-
 template<class T> struct NilValueTempl<T, std::enable_if_t<std::is_floating_point_v<T>, void>> {
     using NilType = T;
     static constexpr auto value = std::numeric_limits<T>::quiet_NaN();
@@ -375,7 +366,7 @@ public:
     T value;
     explicit ConfigOptionSingle(T value) : value(std::move(value)) {}
     operator T() const { return this->value; }
-    
+
     void set(const ConfigOption *rhs) override
     {
         if (rhs->type() != this->type())
@@ -440,7 +431,8 @@ public:
 
     bool nullable() const override { return NULLABLE; }
 
-    static constexpr NilType<T> nil_value() { return NilValue<T>(); }
+    template<bool IsNullable = NULLABLE, typename std::enable_if_t<IsNullable, bool> = true>
+    static constexpr NilType<T> nil_value() { return NilType<T>(); }
 
     // A scalar is nil, or all values of a vector are nil.
     bool is_nil() const override
@@ -717,7 +709,7 @@ public:
         std::istringstream iss(str);
 
         if (str == "nil") {
-            if (NULLABLE)
+            if constexpr (NULLABLE)
                 this->value = this->nil_value();
             else
                 throw ConfigurationError("Deserializing nil into a non-nullable object");
@@ -890,7 +882,8 @@ public:
     std::string serialize() const override 
     {
         std::ostringstream ss;
-        if (this->value == this->nil_value()) {
+
+        if (this->value == std::numeric_limits<int>::max()) {
             if (NULLABLE)
                 ss << "nil";
             else
@@ -907,7 +900,7 @@ public:
         std::istringstream iss(str);
 
         if (str == "nil") {
-            if (NULLABLE)
+            if constexpr (NULLABLE)
                 this->value = this->nil_value();
             else
                 throw ConfigurationError("Deserializing nil into a non-nullable object");