subscriber: use struct update syntax when constructing from self (tokio-rs#1289)

This backports tokio-rs#1289 from `master`.

This PR aims to remove a lot of initializer boilerplate code by adopting
the`struct update syntax.  If the [RFC 2528]  gets merged and
implemented, we can remove more. 😸

[RFC 2528]: rust-lang/rfcs#2528

Author: Folyd

tracing-subscriber/src/fmt/fmt_layer.rs

@@ -279,11 +279,8 @@ where
     /// [time]: #method.without_time
     pub fn with_span_events(self, kind: FmtSpan) -> Self {
         Layer {
-            fmt_event: self.fmt_event,
-            fmt_fields: self.fmt_fields,
             fmt_span: self.fmt_span.with_kind(kind),
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 
@@ -293,32 +290,23 @@ where
     pub fn with_ansi(self, ansi: bool) -> Layer<S, N, format::Format<L, T>, W> {
         Layer {
             fmt_event: self.fmt_event.with_ansi(ansi),
-            fmt_fields: self.fmt_fields,
-            fmt_span: self.fmt_span,
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 
     /// Sets whether or not an event's target is displayed.
     pub fn with_target(self, display_target: bool) -> Layer<S, N, format::Format<L, T>, W> {
         Layer {
             fmt_event: self.fmt_event.with_target(display_target),
-            fmt_fields: self.fmt_fields,
-            fmt_span: self.fmt_span,
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 
     /// Sets whether or not an event's level is displayed.
     pub fn with_level(self, display_level: bool) -> Layer<S, N, format::Format<L, T>, W> {
         Layer {
             fmt_event: self.fmt_event.with_level(display_level),
-            fmt_fields: self.fmt_fields,
-            fmt_span: self.fmt_span,
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 
@@ -329,10 +317,7 @@ where
     pub fn with_thread_ids(self, display_thread_ids: bool) -> Layer<S, N, format::Format<L, T>, W> {
         Layer {
             fmt_event: self.fmt_event.with_thread_ids(display_thread_ids),
-            fmt_fields: self.fmt_fields,
-            fmt_span: self.fmt_span,
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 
@@ -346,10 +331,7 @@ where
     ) -> Layer<S, N, format::Format<L, T>, W> {
         Layer {
             fmt_event: self.fmt_event.with_thread_names(display_thread_names),
-            fmt_fields: self.fmt_fields,
-            fmt_span: self.fmt_span,
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 
@@ -422,9 +404,7 @@ impl<S, T, W> Layer<S, format::JsonFields, format::Format<format::Json, T>, W> {
         Layer {
             fmt_event: self.fmt_event.flatten_event(flatten_event),
             fmt_fields: format::JsonFields::new(),
-            fmt_span: self.fmt_span,
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 
@@ -439,9 +419,7 @@ impl<S, T, W> Layer<S, format::JsonFields, format::Format<format::Json, T>, W> {
         Layer {
             fmt_event: self.fmt_event.with_current_span(display_current_span),
             fmt_fields: format::JsonFields::new(),
-            fmt_span: self.fmt_span,
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 
@@ -456,9 +434,7 @@ impl<S, T, W> Layer<S, format::JsonFields, format::Format<format::Json, T>, W> {
         Layer {
             fmt_event: self.fmt_event.with_span_list(display_span_list),
             fmt_fields: format::JsonFields::new(),
-            fmt_span: self.fmt_span,
-            make_writer: self.make_writer,
-            _inner: self._inner,
+            ..self
         }
     }
 }