Made Tag::from_u16, from_u16_exhaustive and to_u16 const

(cherry picked from commit 5c3c25e)

Author: dbartussek

src/tags.rs

@@ -20,15 +20,15 @@ macro_rules! tags {
 
         impl $name {
             #[inline(always)]
-            fn __from_inner_type(n: $ty) -> Result<Self, $ty> {
+            const fn __from_inner_type(n: $ty) -> Result<Self, $ty> {
                 match n {
                     $( $val => Ok($name::$tag), )*
                     n => Err(n),
                 }
             }
 
             #[inline(always)]
-            fn __to_inner_type(&self) -> $ty {
+            const fn __to_inner_type(&self) -> $ty {
                 match *self {
                     $( $name::$tag => $val, )*
                     $( $name::Unknown($unknown_doc) => { $unknown_doc }, )*
@@ -42,19 +42,25 @@ macro_rules! tags {
     ($name:tt, u16, $($unknown_doc:ident)*) => {
         impl $name {
             #[inline(always)]
-            pub fn from_u16(val: u16) -> Option<Self> {
-                Self::__from_inner_type(val).ok()
+            pub const fn from_u16(val: u16) -> Option<Self> {
+                match Self::__from_inner_type(val) {
+                    Ok(v) => Some(v),
+                    Err(_) => None,
+                }
             }
 
             $(
             #[inline(always)]
-            pub fn from_u16_exhaustive($unknown_doc: u16) -> Self {
-                Self::__from_inner_type($unknown_doc).unwrap_or_else(|_| $name::Unknown($unknown_doc))
+            pub const fn from_u16_exhaustive($unknown_doc: u16) -> Self {
+                match Self::__from_inner_type($unknown_doc) {
+                    Ok(v) => v,
+                    Err(_) => $name::Unknown($unknown_doc),
+                }
             }
             )*
 
             #[inline(always)]
-            pub fn to_u16(&self) -> u16 {
+            pub const fn to_u16(&self) -> u16 {
                 Self::__to_inner_type(self)
             }
         }