feat(is_variant): add #[must_use] annotation

CHANGELOG.md

@@ -75,6 +75,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 
 - The `Constructor` and `IsVariant` derives now generate `const fn` functions.
+- Static methods derived by `IsVariant` are now marked `#[must_use]`.
 - The `Unwrap` and `IsVariant` derives now generate doc comments.
 - `#[automatically_derived]` is now emitted from all macro expansions. This
   should prevent code style linters from attempting to modify the generated

impl/doc/is_variant.md

@@ -33,11 +33,15 @@ The derive in the above example code generates the following code:
 #     Nothing
 # }
 impl <T> Maybe<T>{
+    #[inline]
+    #[must_use]
     pub const fn is_just(&self) -> bool {
-        match self {Self::Just(..) => true, _ => false}
+        matches!(self, Self::Just(..))
     }
+    #[inline]
+    #[must_use]
     pub const fn is_nothing(&self) -> bool {
-        match self {Self::Nothing => true, _ => false}
+        matches!(self, Self::Nothing)
     }
 }
 ```

impl/src/is_variant.rs

@@ -45,11 +45,9 @@ pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStre
             #[doc = #variant_name]
             #[doc = "`. Returns `false` otherwise"]
             #[inline]
+            #[must_use]
             pub const fn #fn_name(&self) -> bool {
-                match self {
-                    #enum_name ::#variant_ident #data_pattern => true,
-                    _ => false
-                }
+                matches!(self, #enum_name ::#variant_ident #data_pattern)
             }
         };
         funcs.push(func);