a bunch more backports #1381

This PR simply fixes some cargo docs warnings.

Filtering log events using the `target[span{field=value}]=level` syntax doesn't work when the span name contains a special char. This PR closes #1367 by adding support for span names with any characters other than `{` and `]` to `EnvFilter`. Co-authored-by: Eliza Weisman <eliza@buoyant.io>

In some cases, users may wish to erase the type of a `Subscriber` implementation, such as when it is dynamically constructed from a complex parameterized type. When doing so, it's important to ensure that all trait methods with default implementations are properly forwarded to the inner erased type. For example, if the type does not implement `try_close`, but the inner erased subscriber does, then the the subscriber will not be notified when spans close — which could result in a memory leak. To avoid potential footguns resulting from users implementing type-erased subscribers incorrectly, this branch adds a new `impl Subscriber for Box<dyn Subscriber + Send + Sync + 'static>` in `tracing-core`. This is also somewhat more ergonomic than any solution in another crate, since the implementation is for `Box<dyn Subscriber + ...>` directly, rather than some `BoxedSubscriber` newtype.

It turns out that when using the global dispatcher, emitting tracing events in a panic hook will capture the span in which the program panicked. This is very handy for debugging panics! Thanks a lot to @nate_mara for pointing this out to me on twitter --- I hadn't even thought of it! Since it isn't necessarily immediately obvious that this works, I thought it would be nice to add an example.

## Motivation (#1374) Users may wish to erase the type of a `Subscriber` implementation, such as when it is dynamically constructed from a complex parameterized type. PR #1358 added a `Subscriber` implementation for `Box<dyn Subscriber + Send + Sync + 'static>`, allowing the use of type-erased trait objects. In some cases, it may also be useful to share a type-erased subscriber, _without_ using `Dispatch` --- such as when different sets of `tracing-subscriber` subscribers are layered on one shared subscriber. ## Solution This branch builds on #1358 by adding an `impl Subscriber for Arc<dyn Subscriber + Send + Sync + 'static>`. I also added quick tests for both `Arc`ed and `Box`ed subscribers. Signed-off-by: Eliza Weisman <eliza@buoyant.io>

## Motivation  The following code compiles failed: ```rust use tracing; fn main() { let span = tracing::info_span!("my_span").entered(); tracing::info!(parent: &span, "test span"); } ``` ```log Compiling playground v0.0.1 (/playground) error[E0277]: the trait bound `Option<Id>: From<&EnteredSpan>` is not satisfied --> src/main.rs:6:5 | 6 | tracing::info!(parent: &span, "test span"); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `From<&EnteredSpan>` is not implemented for `Option<Id>` ``` ## Solution - `impl<'a> From<&'a EnteredSpan> for Option<&'a Id>`. - `impl<'a> From<&'a EnteredSpan> for Option<Id>` - Add `id()` method into `EnteredSpan`. Co-authored-by: Eliza Weisman <eliza@buoyant.io>

## Motivation `span.in_scope()` had a link def in the main tracing docs which was unused, this function is quite handy to know about and I almost re-implemented something similar to it. I almost reimplemented this as a macro. ## Solution Document it at top-level! Co-authored-by: Eliza Weisman <eliza@buoyant.io>

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a bunch more backports #1381

a bunch more backports #1381

Commits on Apr 30, 2021