Merge #218

218: Add const Uuid::from_uuid_bytes r=kinggoesgaming a=mokeyish

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**I'm submitting a  const Uuid::from_uuid_bytes for creating const uuid value.**  [ref uuid_macro](uuid-rs/uuid_macro#1)
  - [ ] bug fix
  - [x] feature enhancement
  - [ ] deprecation or removal
  - [ ] refactor

# Description
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# Motivation
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# Tests
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# Related Issue(s)
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Co-authored-by: MOKEYISH <[email protected]>
Co-authored-by: YISH <[email protected]>

.cargo/.gitignore

@@ -0,0 +1 @@
+/config

Cargo.toml

@@ -33,6 +33,7 @@ serde_test = "1.0.19"
 
 [features]
 default = ["std"]
+nightly = []
 std = []
 use_std = ["std"] # Compatibility shim for 0.5 and earlier
 v1 = []

src/lib.rs

@@ -111,6 +111,8 @@
 )]
 #![deny(warnings)]
 #![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(feature = "nightly", feature(const_fn))]
+
 
 #[macro_use]
 extern crate cfg_if;
@@ -714,10 +716,16 @@ impl Uuid {
     ///
     /// let uuid = Uuid::from_uuid_bytes(bytes);
     /// ```
+    #[cfg(not(feature = "nightly"))]
     pub fn from_uuid_bytes(b: UuidBytes) -> Uuid {
         Uuid { bytes: b }
     }
 
+    #[cfg(feature = "nightly")]
+    pub const fn from_uuid_bytes(b: UuidBytes) -> Uuid {
+        Uuid { bytes: b }
+    }
+
     /// Creates a v4 Uuid from random bytes (e.g. bytes supplied from `Rand` crate)
     ///
     /// # Examples