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

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_subscriber.rs

@@ -249,11 +249,8 @@ where
     /// [time]: Subscriber::without_time()
     pub fn with_span_events(self, kind: FmtSpan) -> Self {
         Subscriber {
-            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
         }
     }
 
@@ -263,32 +260,23 @@ where
     pub fn with_ansi(self, ansi: bool) -> Subscriber<S, N, format::Format<L, T>, W> {
         Subscriber {
             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) -> Subscriber<S, N, format::Format<L, T>, W> {
         Subscriber {
             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) -> Subscriber<S, N, format::Format<L, T>, W> {
         Subscriber {
             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
         }
     }
 
@@ -302,10 +290,7 @@ where
     ) -> Subscriber<S, N, format::Format<L, T>, W> {
         Subscriber {
             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
         }
     }
 
@@ -319,10 +304,7 @@ where
     ) -> Subscriber<S, N, format::Format<L, T>, W> {
         Subscriber {
             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
         }
     }
 
@@ -394,9 +376,7 @@ impl<S, T, W> Subscriber<S, format::JsonFields, format::Format<format::Json, T>,
         Subscriber {
             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
         }
     }
 
@@ -411,9 +391,7 @@ impl<S, T, W> Subscriber<S, format::JsonFields, format::Format<format::Json, T>,
         Subscriber {
             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
         }
     }
 
@@ -428,9 +406,7 @@ impl<S, T, W> Subscriber<S, format::JsonFields, format::Format<format::Json, T>,
         Subscriber {
             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
         }
     }
 }

tracing-subscriber/src/fmt/mod.rs

@@ -662,8 +662,8 @@ where
     /// [time]: CollectorBuilder::without_time()
     pub fn with_span_events(self, kind: format::FmtSpan) -> Self {
         CollectorBuilder {
-            filter: self.filter,
             inner: self.inner.with_span_events(kind),
+            ..self
         }
     }
 
@@ -672,8 +672,8 @@ where
     #[cfg_attr(docsrs, doc(cfg(feature = "ansi")))]
     pub fn with_ansi(self, ansi: bool) -> CollectorBuilder<N, format::Format<L, T>, F, W> {
         CollectorBuilder {
-            filter: self.filter,
             inner: self.inner.with_ansi(ansi),
+            ..self
         }
     }
 
@@ -683,8 +683,8 @@ where
         display_target: bool,
     ) -> CollectorBuilder<N, format::Format<L, T>, F, W> {
         CollectorBuilder {
-            filter: self.filter,
             inner: self.inner.with_target(display_target),
+            ..self
         }
     }
 
@@ -694,8 +694,8 @@ where
         display_level: bool,
     ) -> CollectorBuilder<N, format::Format<L, T>, F, W> {
         CollectorBuilder {
-            filter: self.filter,
             inner: self.inner.with_level(display_level),
+            ..self
         }
     }
 
@@ -708,8 +708,8 @@ where
         display_thread_names: bool,
     ) -> CollectorBuilder<N, format::Format<L, T>, F, W> {
         CollectorBuilder {
-            filter: self.filter,
             inner: self.inner.with_thread_names(display_thread_names),
+            ..self
         }
     }
 
@@ -722,8 +722,8 @@ where
         display_thread_ids: bool,
     ) -> CollectorBuilder<N, format::Format<L, T>, F, W> {
         CollectorBuilder {
-            filter: self.filter,
             inner: self.inner.with_thread_ids(display_thread_ids),
+            ..self
         }
     }