misc: clippy fixes (#126)

tracing-core/src/field.rs

@@ -508,6 +508,12 @@ impl FieldSet {
     pub fn len(&self) -> usize {
         self.names.len()
     }
+
+    /// Returns whether or not this `FieldSet` has fields.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.names.is_empty()
+    }
 }
 
 impl<'a> IntoIterator for &'a FieldSet {
@@ -531,7 +537,7 @@ impl fmt::Debug for FieldSet {
 impl fmt::Display for FieldSet {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_set()
-            .entries(self.names.iter().map(|n| display(n)))
+            .entries(self.names.iter().map(display))
             .finish()
     }
 }

tracing-core/src/subscriber.rs

@@ -1,10 +1,7 @@
 //! Subscribers collect and record trace data.
 use crate::{span, Event, Metadata};
 
-use std::{
-    any::{Any, TypeId},
-    ptr,
-};
+use std::any::{Any, TypeId};
 
 /// Trait representing the functions required to collect trace data.
 ///
@@ -109,9 +106,10 @@ pub trait Subscriber: 'static {
     /// [`enabled`]: #method.enabled
     /// [`rebuild_interest_cache`]: ../callsite/fn.rebuild_interest_cache.html
     fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest {
-        match self.enabled(metadata) {
-            true => Interest::always(),
-            false => Interest::never(),
+        if self.enabled(metadata) {
+            Interest::always()
+        } else {
+            Interest::never()
         }
     }
 
@@ -363,7 +361,7 @@ impl dyn Subscriber {
     pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
         unsafe {
             let raw = self.downcast_raw(TypeId::of::<T>())?;
-            if raw == ptr::null() {
+            if raw.is_null() {
                 None
             } else {
                 Some(&*(raw as *const _))

tracing-fmt/src/filter/env.rs

@@ -57,9 +57,7 @@ impl EnvFilter {
     /// Returns a new `EnvFilter` from the value of the given environment
     /// variable, ignoring any invalid filter directives.
     pub fn from_env<A: AsRef<str>>(env: A) -> Self {
-        env::var(env.as_ref())
-            .map(|ref var| Self::new(var))
-            .unwrap_or_default()
+        env::var(env.as_ref()).map(Self::new).unwrap_or_default()
     }
 
     /// Returns a new `EnvFilter` from the directives in the given string,