subscriber: remove deprecated APIs (#1673)

## Motivation

`tracing-subscriber` currently contains some APIs that were deprecated
in the v0.2.x series:
- `fmt::LayerBuilder`, which is now a type alias for `fmt::Layer` (as
  the `Layer` type can expose all the same methods as the builder)
- `registry::SpanRef::parent_id`, which doesn't play nice with per-layer
  filtering,
- `fmt::Layer::inherit_fields`, which no longer does anything as it's
  now the default behavior
- `fmt::Layer::on_event`, which was renamed to `fmt_event`
- the `SpanRef::parents` and `layer::Context::scope` iterators, which
  were replaced by the APIs added in #1431 and #1434

Prior to releasing v0.3, the deprecated APIs should be removed.

## Solution

This branch deletes the deprecated APIs, with the exception of
`SpanRef::parents` and `Context::scope` (which were already removed in
240d11a).

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

tracing-subscriber/src/fmt/fmt_layer.rs

@@ -72,34 +72,7 @@ pub struct Layer<
     _inner: PhantomData<S>,
 }
 
-/// A builder for [`Layer`](struct.Layer.html) that logs formatted representations of `tracing`
-/// events and spans.
-///
-/// **Note**: As of `tracing-subscriber` 0.2.4, the separate builder type is now
-/// deprecated, as the `Layer` type itself supports all the builder's
-/// configuration methods. This is now an alias for `Layer`.
-#[deprecated(
-    since = "0.2.4",
-    note = "a separate layer builder type is not necessary, `Layer`s now support configuration"
-)]
-pub type LayerBuilder<
-    S,
-    N = format::DefaultFields,
-    E = format::Format<format::Full>,
-    W = fn() -> io::Stdout,
-> = Layer<S, N, E, W>;
-
 impl<S> Layer<S> {
-    /// Returns a new [`LayerBuilder`](type.LayerBuilder.html) for configuring a `Layer`.
-    #[deprecated(
-        since = "0.2.4",
-        note = "a separate layer builder is not necessary, use `Layer::new`/`Layer::default` instead"
-    )]
-    #[allow(deprecated)]
-    pub fn builder() -> LayerBuilder<S> {
-        Layer::default()
-    }
-
     /// Returns a new [`Layer`](struct.Layer.html) with the default configuration.
     pub fn new() -> Self {
         Self::default()
@@ -475,26 +448,6 @@ impl<S, N, E, W> Layer<S, N, E, W> {
     }
 }
 
-#[allow(deprecated)]
-impl<S, N, E, W> LayerBuilder<S, N, E, W>
-where
-    S: Subscriber + for<'a> LookupSpan<'a>,
-    N: for<'writer> FormatFields<'writer> + 'static,
-    E: FormatEvent<S, N> + 'static,
-    W: for<'writer> MakeWriter<'writer> + 'static,
-{
-    /// Builds a [`Layer`] with the provided configuration.
-    ///
-    /// [`Layer`]: struct.Layer.html
-    #[deprecated(
-        since = "0.2.4",
-        note = "`LayerBuilder` is no longer a separate type; this method is not necessary"
-    )]
-    pub fn finish(self) -> Layer<S, N, E, W> {
-        self
-    }
-}
-
 impl<S> Default for Layer<S> {
     fn default() -> Self {
         Layer {

tracing-subscriber/src/fmt/mod.rs

@@ -267,8 +267,7 @@ pub mod format;
 pub mod time;
 #[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
 pub mod writer;
-#[allow(deprecated)]
-pub use fmt_layer::LayerBuilder;
+
 pub use fmt_layer::{FmtContext, FormattedFields, Layer};
 
 use crate::layer::Layer as _;
@@ -1002,26 +1001,6 @@ impl<N, E, F, W> SubscriberBuilder<N, E, F, W> {
         }
     }
 
-    /// Sets whether or not spans inherit their parents' field values (disabled
-    /// by default).
-    #[deprecated(since = "0.2.0", note = "this no longer does anything")]
-    pub fn inherit_fields(self, inherit_fields: bool) -> Self {
-        let _ = inherit_fields;
-        self
-    }
-
-    /// Sets the function that the subscriber being built should use to format
-    /// events that occur.
-    #[deprecated(since = "0.2.0", note = "renamed to `event_format`.")]
-    pub fn on_event<E2>(self, fmt_event: E2) -> SubscriberBuilder<N, E2, F, W>
-    where
-        E2: FormatEvent<Registry, N> + 'static,
-        N: for<'writer> FormatFields<'writer> + 'static,
-        W: for<'writer> MakeWriter<'writer> + 'static,
-    {
-        self.event_format(fmt_event)
-    }
-
     /// Sets the [`MakeWriter`] that the subscriber being built will use to write events.
     ///
     /// # Examples

tracing-subscriber/src/registry/mod.rs

@@ -365,45 +365,8 @@ where
         self.data.metadata().fields()
     }
 
-    /// Returns the ID of this span's parent, or `None` if this span is the root
-    /// of its trace tree.
-    #[deprecated(
-        note = "this method cannot properly support per-layer filtering, and may \
-            return the `Id` of a disabled span if per-layer filtering is in \
-            use. use `.parent().map(SpanRef::id)` instead.",
-        since = "0.2.21"
-    )]
-    pub fn parent_id(&self) -> Option<&Id> {
-        // XXX(eliza): this doesn't work with PLF because the ID is potentially
-        // borrowed from a parent we got from the registry, rather than from
-        // `self`, so we can't return a borrowed parent. so, right now, we just
-        // return the actual parent ID, and ignore PLF. which is not great.
-        //
-        // i think if we want this to play nice with PLF, we should just change
-        // it to return the `Id` by value instead of `&Id` (which we ought to do
-        // anyway since an `Id` is just a word) but that's a breaking change.
-        // alternatively, we could deprecate this method since it can't support
-        // PLF in its current form (which is what we would want to do if we want
-        // to release PLF in a minor version)...
-
-        // let mut id = self.data.parent()?;
-        // loop {
-        //     // Is this parent enabled by our filter?
-        //     if self
-        //         .filter
-        //         .map(|filter| self.registry.is_enabled_for(id, filter))
-        //         .unwrap_or(true)
-        //     {
-        //         return Some(id);
-        //     }
-        //     id = self.registry.span_data(id)?.parent()?;
-        // }
-        self.data.parent()
-    }
-
     /// Returns a `SpanRef` describing this span's parent, or `None` if this
     /// span is the root of its trace tree.
-
     pub fn parent(&self) -> Option<Self> {
         let id = self.data.parent()?;
         let data = self.registry.span_data(id)?;