Add nodiscard to core math classes to catch c++ errors.

A common source of errors is to call functions (such as round()) expecting them to work in place, but them actually being designed only to return the processed value. Not using the return value in this case in indicative of a bug, and can be flagged as a warning by using the [[nodiscard]] attribute.

core/math/aabb.h

@@ -40,7 +40,7 @@
  * This is implemented by a point (position) and the box size
  */
 
-class AABB {
+class _NO_DISCARD_CLASS_ AABB {
 public:
 	Vector3 position;
 	Vector3 size;

core/math/basis.h

@@ -34,7 +34,7 @@
 #include "core/math/quat.h"
 #include "core/math/vector3.h"
 
-class Basis {
+class _NO_DISCARD_CLASS_ Basis {
 public:
 	Vector3 elements[3] = {
 		Vector3(1, 0, 0),

core/math/face3.h

@@ -36,7 +36,7 @@
 #include "core/math/transform.h"
 #include "core/math/vector3.h"
 
-class Face3 {
+class _NO_DISCARD_CLASS_ Face3 {
 public:
 	enum Side {
 		SIDE_OVER,

core/math/plane.h

@@ -33,7 +33,7 @@
 
 #include "core/math/vector3.h"
 
-class Plane {
+class _NO_DISCARD_CLASS_ Plane {
 public:
 	Vector3 normal;
 	real_t d;

core/math/quat.h

@@ -36,7 +36,7 @@
 #include "core/math/vector3.h"
 #include "core/ustring.h"
 
-class Quat {
+class _NO_DISCARD_CLASS_ Quat {
 public:
 	real_t x, y, z, w;
 
@@ -127,7 +127,7 @@ public:
 			w(p_q.w) {
 	}
 
-	Quat operator=(const Quat &p_q) {
+	Quat &operator=(const Quat &p_q) {
 		x = p_q.x;
 		y = p_q.y;
 		z = p_q.z;

core/math/rect2.h

@@ -35,7 +35,7 @@
 
 struct Transform2D;
 
-struct Rect2 {
+struct _NO_DISCARD_CLASS_ Rect2 {
 	Point2 position;
 	Size2 size;
 
@@ -259,7 +259,7 @@ struct Rect2 {
 	}
 };
 
-struct Rect2i {
+struct _NO_DISCARD_CLASS_ Rect2i {
 	Point2i position;
 	Size2i size;
 

core/math/transform.h

@@ -36,7 +36,7 @@
 #include "core/math/plane.h"
 #include "core/pool_vector.h"
 
-class Transform {
+class _NO_DISCARD_CLASS_ Transform {
 public:
 	Basis basis;
 	Vector3 origin;

core/math/transform_2d.h

@@ -34,7 +34,7 @@
 #include "core/math/rect2.h" // also includes vector2, math_funcs, and ustring
 #include "core/pool_vector.h"
 
-struct Transform2D {
+struct _NO_DISCARD_CLASS_ Transform2D {
 	// Warning #1: basis of Transform2D is stored differently from Basis. In terms of elements array, the basis matrix looks like "on paper":
 	// M = (elements[0][0] elements[1][0])
 	//     (elements[0][1] elements[1][1])

core/math/vector2.h

@@ -36,7 +36,7 @@
 
 struct Vector2i;
 
-struct Vector2 {
+struct _NO_DISCARD_CLASS_ Vector2 {
 	static const int AXIS_COUNT = 2;
 
 	enum Axis {
@@ -269,7 +269,7 @@ typedef Vector2 Point2;
 
 /* INTEGER STUFF */
 
-struct Vector2i {
+struct _NO_DISCARD_CLASS_ Vector2i {
 	enum Axis {
 		AXIS_X,
 		AXIS_Y,

core/math/vector3.h

@@ -36,7 +36,7 @@
 
 class Basis;
 
-struct Vector3 {
+struct _NO_DISCARD_CLASS_ Vector3 {
 	static const int AXIS_COUNT = 3;
 
 	enum Axis {