fix nightly clippy warnings

This will avoid breaking CI on new releases of clippy. It also makes the
code a little easier to read.

- Convert `match val { pat => true, _ => false }` to `matches!(val, pat)`
- Remove unnecessary closures
- Convert `self: &mut Self` to `&mut self`

This bumps the MSRV to 1.42.0 for `matches!`.
The latest version of rust is 1.46.0, so as per
https://github.com/tokio-rs/tracing#supported-rust-versions this is not
considered a breaking change.

I didn't fix the following error because the fix was not trivial/needed
a decision:

```
warning: you are deriving `Ord` but have implemented `PartialOrd` explicitly
   --> tracing-subscriber/src/filter/env/field.rs:16:32
    |
16  | #[derive(Debug, Eq, PartialEq, Ord)]
    |                                ^^^
    |
    = note: `#[warn(clippy::derive_ord_xor_partial_ord)]` on by default
note: `PartialOrd` implemented here
   --> tracing-subscriber/src/filter/env/field.rs:98:1
    |
98  | / impl PartialOrd for Match {
99  | |     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
100 | |         // Ordering for `Match` directives is based first on _whether_ a value
101 | |         // is matched or not. This is semantically meaningful --- we would
...   |
121 | |     }
122 | | }
    | |_^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_ord_xor_partial_ord
```

.github/workflows/CI.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        rust: [stable, 1.40.0]
+        rust: [stable, 1.42.0]
     steps:
     - uses: actions/checkout@main
     - uses: actions-rs/toolchain@v1
@@ -145,7 +145,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        rust: [stable, beta, nightly, 1.40.0]
+        rust: [stable, beta, nightly, 1.42.0]
     steps:
     - uses: actions/checkout@main
     - uses: actions-rs/toolchain@v1

tracing-attributes/tests/async_fn.rs

@@ -223,7 +223,7 @@ fn async_fn_with_async_trait_and_fields_expressions_with_generic_parameter() {
         async fn call_with_self(&self) {}
 
         #[instrument(fields(Self=std::any::type_name::<Self>()))]
-        async fn call_with_mut_self(self: &mut Self) {}
+        async fn call_with_mut_self(&mut self) {}
     }
 
     //let span = span::mock().named("call");

tracing-core/src/event.rs

@@ -103,10 +103,7 @@ impl<'a> Event<'a> {
 
     /// Returns true if the new event should be a root.
     pub fn is_root(&self) -> bool {
-        match self.parent {
-            Parent::Root => true,
-            _ => false,
-        }
+        matches!(self.parent, Parent::Root)
     }
 
     /// Returns true if the new event's parent should be determined based on the
@@ -117,10 +114,7 @@ impl<'a> Event<'a> {
     /// thread is _not_ inside a span, then the new event will be the root of its
     /// own trace tree.
     pub fn is_contextual(&self) -> bool {
-        match self.parent {
-            Parent::Current => true,
-            _ => false,
-        }
+        matches!(self.parent, Parent::Current)
     }
 
     /// Returns the new event's explicitly-specified parent, if there is one.

tracing-core/src/metadata.rs

@@ -251,18 +251,12 @@ impl Kind {
 
     /// Return true if the callsite kind is `Span`
     pub fn is_span(&self) -> bool {
-        match self {
-            Kind(KindInner::Span) => true,
-            _ => false,
-        }
+        matches!(self, Kind(KindInner::Span))
     }
 
     /// Return true if the callsite kind is `Event`
     pub fn is_event(&self) -> bool {
-        match self {
-            Kind(KindInner::Event) => true,
-            _ => false,
-        }
+        matches!(self, Kind(KindInner::Event))
     }
 }
 
@@ -553,8 +547,7 @@ impl FromStr for LevelFilter {
                 s if s.eq_ignore_ascii_case("trace") => Some(LevelFilter::TRACE),
                 s if s.eq_ignore_ascii_case("off") => Some(LevelFilter::OFF),
                 _ => None,
-            })
-            .ok_or_else(|| ParseLevelFilterError(()))
+            }).ok_or(ParseLevelFilterError(()))
     }
 }
 

tracing-core/src/span.rs

@@ -153,10 +153,7 @@ impl<'a> Attributes<'a> {
 
     /// Returns true if the new span should be a root.
     pub fn is_root(&self) -> bool {
-        match self.parent {
-            Parent::Root => true,
-            _ => false,
-        }
+        matches!(self.parent, Parent::Root)
     }
 
     /// Returns true if the new span's parent should be determined based on the
@@ -167,10 +164,7 @@ impl<'a> Attributes<'a> {
     /// thread is _not_ inside a span, then the new span will be the root of its
     /// own trace tree.
     pub fn is_contextual(&self) -> bool {
-        match self.parent {
-            Parent::Current => true,
-            _ => false,
-        }
+        matches!(self.parent, Parent::Current)
     }
 
     /// Returns the new span's explicitly-specified parent, if there is one.
@@ -270,10 +264,7 @@ impl Current {
     /// [`metadata`]: #method.metadata
     /// [`into_inner`]: #method.into_inner
     pub fn is_known(&self) -> bool {
-        match self.inner {
-            CurrentInner::Unknown => false,
-            _ => true,
-        }
+        !matches!(self.inner, CurrentInner::Unknown)
     }
 
     /// Consumes `self` and returns the span `Id` and `Metadata` of the current

tracing-core/src/subscriber.rs

@@ -528,30 +528,21 @@ impl Interest {
     /// about this callsite.
     #[inline]
     pub fn is_never(&self) -> bool {
-        match self.0 {
-            InterestKind::Never => true,
-            _ => false,
-        }
+        matches!(self.0, InterestKind::Never)
     }
 
     /// Returns `true` if the subscriber is sometimes interested in being notified
     /// about this callsite.
     #[inline]
     pub fn is_sometimes(&self) -> bool {
-        match self.0 {
-            InterestKind::Sometimes => true,
-            _ => false,
-        }
+        matches!(self.0, InterestKind::Sometimes)
     }
 
     /// Returns `true` if the subscriber is always interested in being notified
     /// about this callsite.
     #[inline]
     pub fn is_always(&self) -> bool {
-        match self.0 {
-            InterestKind::Always => true,
-            _ => false,
-        }
+        matches!(self.0, InterestKind::Always)
     }
 
     /// Returns the common interest between these two Interests.

tracing-subscriber/src/fmt/format/mod.rs

@@ -1052,22 +1052,13 @@ impl FmtSpanConfig {
         }
     }
     pub(super) fn trace_new(&self) -> bool {
-        match self.kind {
-            FmtSpan::FULL => true,
-            _ => false,
-        }
+        matches!(self.kind, FmtSpan::FULL)
     }
     pub(super) fn trace_active(&self) -> bool {
-        match self.kind {
-            FmtSpan::ACTIVE | FmtSpan::FULL => true,
-            _ => false,
-        }
+        matches!(self.kind, FmtSpan::ACTIVE | FmtSpan::FULL)
     }
     pub(super) fn trace_close(&self) -> bool {
-        match self.kind {
-            FmtSpan::CLOSE | FmtSpan::FULL => true,
-            _ => false,
-        }
+        matches!(self.kind, FmtSpan::CLOSE | FmtSpan::FULL)
     }
 }
 

tracing-subscriber/src/reload.rs

@@ -210,19 +210,13 @@ impl Error {
     /// Returns `true` if this error occurred because the layer was poisoned by
     /// a panic on another thread.
     pub fn is_poisoned(&self) -> bool {
-        match self.kind {
-            ErrorKind::Poisoned => true,
-            _ => false,
-        }
+        matches!(self.kind, ErrorKind::Poisoned)
     }
 
     /// Returns `true` if this error occurred because the `Subscriber`
     /// containing the reloadable layer was dropped.
     pub fn is_dropped(&self) -> bool {
-        match self.kind {
-            ErrorKind::SubscriberGone => true,
-            _ => false,
-        }
+        matches!(self.kind, ErrorKind::SubscriberGone)
     }
 }
 

tracing/tests/support/subscriber.rs

@@ -213,11 +213,7 @@ where
             "[{}] record: {}; id={:?}; values={:?};",
             self.name, span.name, id, values
         );
-        let was_expected = if let Some(Expect::Visit(_, _)) = expected.front() {
-            true
-        } else {
-            false
-        };
+        let was_expected = matches!(expected.front(), Some(Expect::Visit(_, _)));
         if was_expected {
             if let Expect::Visit(expected_span, mut expected_values) = expected.pop_front().unwrap()
             {
@@ -319,10 +315,7 @@ where
             id
         );
         let mut expected = self.expected.lock().unwrap();
-        let was_expected = match expected.front() {
-            Some(Expect::NewSpan(_)) => true,
-            _ => false,
-        };
+        let was_expected = matches!(expected.front(), Some(Expect::NewSpan(_)));
         let mut spans = self.spans.lock().unwrap();
         if was_expected {
             if let Expect::NewSpan(mut expected) = expected.pop_front().unwrap() {