chore: fix nightly clippy warnings (#991) (#1025)

This backports PR #991 to v0.1.x. This is primarily necessary for the MSRV
bump, since some dependencies no longer compile on Rust 1.40.0.

This has already been approved on `master`, in PR #991, so it should be 
fine to ship.

## Motivation

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

## Solution

- 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 warning 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
```

As a side note, this found a bug in clippy 😆 rust-lang/rust-clippy#6089

Author: hawkw

.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

README.md

@@ -256,7 +256,7 @@ attachment that `Future::instrument` does.
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.40. The current Tracing version is not guaranteed to build on Rust
+version is 1.42. The current Tracing version is not guaranteed to build on Rust
 versions earlier than the minimum supported version.
 
 Tracing follows the same compiler support policies as the rest of the Tokio

tracing-appender/README.md

@@ -36,7 +36,7 @@ allows events and spans to be recorded in a non-blocking manner through a
 dedicated logging thread. It also provides a [`RollingFileAppender`][file_appender] 
 that can be used with _or_ without the non-blocking writer.
 
-*Compiler support: [requires `rustc` 1.40+][msrv]*
+*Compiler support: [requires `rustc` 1.42+][msrv]*
 
 [msrv]: #supported-rust-versions
 
@@ -146,7 +146,7 @@ fn main() {
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.40. The current Tracing version is not guaranteed to build on Rust
+version is 1.42. The current Tracing version is not guaranteed to build on Rust
 versions earlier than the minimum supported version.
 
 Tracing follows the same compiler support policies as the rest of the Tokio

tracing-appender/src/lib.rs

@@ -7,7 +7,7 @@
 //! a dedicated logging thread. It also provides a [`RollingFileAppender`][file_appender] that can
 //! be used with _or_ without the non-blocking writer.
 //!
-//! *Compiler support: [requires `rustc` 1.40+][msrv]*
+//! *Compiler support: [requires `rustc` 1.42+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //! [file_appender]: ./rolling/struct.RollingFileAppender.html
@@ -111,7 +111,7 @@
 //! ## Supported Rust Versions
 //!
 //! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.40. The current Tracing version is not guaranteed to build on
+//! version is 1.42. The current Tracing version is not guaranteed to build on
 //! Rust versions earlier than the minimum supported version.
 //!
 //! Tracing follows the same compiler support policies as the rest of the Tokio

tracing-attributes/README.md

@@ -37,7 +37,7 @@ structured, event-based diagnostic information. This crate provides the
 
 Note that this macro is also re-exported by the main `tracing` crate.
 
-*Compiler support: [requires `rustc` 1.40+][msrv]*
+*Compiler support: [requires `rustc` 1.42+][msrv]*
 
 [msrv]: #supported-rust-versions
 
@@ -69,7 +69,7 @@ pub fn my_function(my_arg: usize) {
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.40. The current Tracing version is not guaranteed to build on Rust
+version is 1.42. The current Tracing version is not guaranteed to build on Rust
 versions earlier than the minimum supported version.
 
 Tracing follows the same compiler support policies as the rest of the Tokio

tracing-attributes/src/lib.rs

@@ -6,7 +6,7 @@
 //!
 //! Note that this macro is also re-exported by the main `tracing` crate.
 //!
-//! *Compiler support: [requires `rustc` 1.40+][msrv]*
+//! *Compiler support: [requires `rustc` 1.42+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //!
@@ -41,7 +41,7 @@
 //! ## Supported Rust Versions
 //!
 //! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.40. The current Tracing version is not guaranteed to build on
+//! version is 1.42. The current Tracing version is not guaranteed to build on
 //! Rust versions earlier than the minimum supported version.
 //!
 //! Tracing follows the same compiler support policies as the rest of the Tokio

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/README.md

@@ -53,7 +53,7 @@ The crate provides:
 In addition, it defines the global callsite registry and per-thread current
 dispatcher which other components of the tracing system rely on.
 
-*Compiler support: [requires `rustc` 1.40+][msrv]*
+*Compiler support: [requires `rustc` 1.42+][msrv]*
 
 [msrv]: #supported-rust-versions
 
@@ -99,7 +99,7 @@ The following crate feature flags are available:
 ## Supported Rust Versions
 
 Tracing is built against the latest stable release. The minimum supported
-version is 1.40. The current Tracing version is not guaranteed to build on Rust
+version is 1.42. The current Tracing version is not guaranteed to build on Rust
 versions earlier than the minimum supported version.
 
 Tracing follows the same compiler support policies as the rest of the Tokio

tracing-core/src/event.rs

@@ -101,10 +101,7 @@ 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
@@ -115,10 +112,7 @@ 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/lib.rs

@@ -23,7 +23,7 @@
 //! In addition, it defines the global callsite registry and per-thread current
 //! dispatcher which other components of the tracing system rely on.
 //!
-//! *Compiler support: [requires `rustc` 1.40+][msrv]*
+//! *Compiler support: [requires `rustc` 1.42+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //!
@@ -61,7 +61,7 @@
 //! ## Supported Rust Versions
 //!
 //! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.40. The current Tracing version is not guaranteed to build on
+//! version is 1.42. The current Tracing version is not guaranteed to build on
 //! Rust versions earlier than the minimum supported version.
 //!
 //! Tracing follows the same compiler support policies as the rest of the Tokio