1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
use crate::{
    field::RecordFields,
    fmt::{format, FormatEvent, FormatFields, MakeWriter},
    layer::{self, Context},
    registry::{LookupSpan, SpanRef},
};
use format::{FmtSpan, TimingDisplay};
use std::{any::TypeId, cell::RefCell, fmt, io, marker::PhantomData, ops::Deref, time::Instant};
use tracing_core::{
    field,
    span::{Attributes, Id, Record},
    Event, Subscriber,
};

/// A [`Layer`] that logs formatted representations of `tracing` events.
///
/// ## Examples
///
/// Constructing a layer with the default configuration:
///
/// ```rust
/// use tracing_subscriber::{fmt, Registry};
/// use tracing_subscriber::prelude::*;
///
/// let subscriber = Registry::default()
///     .with(fmt::Layer::default());
///
/// tracing::subscriber::set_global_default(subscriber).unwrap();
/// ```
///
/// Overriding the layer's behavior:
///
/// ```rust
/// use tracing_subscriber::{fmt, Registry};
/// use tracing_subscriber::prelude::*;
///
/// let fmt_layer = fmt::layer()
///    .with_target(false) // don't include event targets when logging
///    .with_level(false); // don't include event levels when logging
///
/// let subscriber = Registry::default().with(fmt_layer);
/// # tracing::subscriber::set_global_default(subscriber).unwrap();
/// ```
///
/// Setting a custom event formatter:
///
/// ```rust
/// use tracing_subscriber::fmt::{self, format, time};
/// use tracing_subscriber::prelude::*;
///
/// let fmt = format().with_timer(time::Uptime::default());
/// let fmt_layer = fmt::layer()
///     .event_format(fmt)
///     .with_target(false);
/// # let subscriber = fmt_layer.with_subscriber(tracing_subscriber::registry::Registry::default());
/// # tracing::subscriber::set_global_default(subscriber).unwrap();
/// ```
///
/// [`Layer`]: ../layer/trait.Layer.html
#[derive(Debug)]
pub struct Layer<
    S,
    N = format::DefaultFields,
    E = format::Format<format::Full>,
    W = fn() -> io::Stdout,
> {
    make_writer: W,
    fmt_fields: N,
    fmt_event: E,
    fmt_span: format::FmtSpanConfig,
    _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()
    }
}

// This needs to be a seperate impl block because they place different bounds on the type paramaters.
impl<S, N, E, W> Layer<S, N, E, W>
where
    S: Subscriber + for<'a> LookupSpan<'a>,
    N: for<'writer> FormatFields<'writer> + 'static,
    W: MakeWriter + 'static,
{
    /// Sets the [event formatter][`FormatEvent`] that the layer will use to
    /// format events.
    ///
    /// The event formatter may be any type implementing the [`FormatEvent`]
    /// trait, which is implemented for all functions taking a [`FmtContext`], a
    /// `&mut dyn Write`, and an [`Event`].
    ///
    /// # Examples
    ///
    /// Setting a type implementing [`FormatEvent`] as the formatter:
    /// ```rust
    /// use tracing_subscriber::fmt::{self, format};
    ///
    /// let layer = fmt::layer()
    ///     .event_format(format().compact());
    /// # // this is necessary for type inference.
    /// # use tracing_subscriber::Layer as _;
    /// # let _ = layer.with_subscriber(tracing_subscriber::registry::Registry::default());
    /// ```
    /// [event formatter]: ../format/trait.FormatEvent.html
    /// [`FmtContext`]: ../struct.FmtContext.html
    /// [`Event`]: https://docs.rs/tracing/latest/tracing/struct.Event.html
    pub fn event_format<E2>(self, e: E2) -> Layer<S, N, E2, W>
    where
        E2: FormatEvent<S, N> + 'static,
    {
        Layer {
            fmt_fields: self.fmt_fields,
            fmt_event: e,
            fmt_span: self.fmt_span,
            make_writer: self.make_writer,
            _inner: self._inner,
        }
    }
}

// This needs to be a seperate impl block because they place different bounds on the type paramaters.
impl<S, N, E, W> Layer<S, N, E, W> {
    /// Sets the [`MakeWriter`] that the [`Layer`] being built will use to write events.
    ///
    /// # Examples
    ///
    /// Using `stderr` rather than `stdout`:
    ///
    /// ```rust
    /// use std::io;
    /// use tracing_subscriber::fmt;
    ///
    /// let layer = fmt::layer()
    ///     .with_writer(io::stderr);
    /// # // this is necessary for type inference.
    /// # use tracing_subscriber::Layer as _;
    /// # let _ = layer.with_subscriber(tracing_subscriber::registry::Registry::default());
    /// ```
    ///
    /// [`MakeWriter`]: ../fmt/trait.MakeWriter.html
    /// [`Layer`]: ../layer/trait.Layer.html
    pub fn with_writer<W2>(self, make_writer: W2) -> Layer<S, N, E, W2>
    where
        W2: MakeWriter + 'static,
    {
        Layer {
            fmt_fields: self.fmt_fields,
            fmt_event: self.fmt_event,
            fmt_span: self.fmt_span,
            make_writer,
            _inner: self._inner,
        }
    }
}

impl<S, N, L, T, W> Layer<S, N, format::Format<L, T>, W>
where
    N: for<'writer> FormatFields<'writer> + 'static,
{
    /// Use the given [`timer`] for span and event timestamps.
    ///
    /// See [`time`] for the provided timer implementations.
    ///
    /// Note that using the `chrono` feature flag enables the
    /// additional time formatters [`ChronoUtc`] and [`ChronoLocal`].
    ///
    /// [`time`]: ./time/index.html
    /// [`timer`]: ./time/trait.FormatTime.html
    /// [`ChronoUtc`]: ./time/struct.ChronoUtc.html
    /// [`ChronoLocal`]: ./time/struct.ChronoLocal.html
    pub fn with_timer<T2>(self, timer: T2) -> Layer<S, N, format::Format<L, T2>, W> {
        Layer {
            fmt_event: self.fmt_event.with_timer(timer),
            fmt_fields: self.fmt_fields,
            fmt_span: self.fmt_span,
            make_writer: self.make_writer,
            _inner: self._inner,
        }
    }

    /// Do not emit timestamps with spans and event.
    pub fn without_time(self) -> Layer<S, N, format::Format<L, ()>, W> {
        Layer {
            fmt_event: self.fmt_event.without_time(),
            fmt_fields: self.fmt_fields,
            fmt_span: self.fmt_span.without_time(),
            make_writer: self.make_writer,
            _inner: self._inner,
        }
    }

    /// Configures how synthesized events are emitted at points in the [span
    /// lifecycle][lifecycle].
    ///
    /// The following options are available:
    ///
    /// - `FmtSpan::NONE`: No events will be synthesized when spans are
    ///    created, entered, exited, or closed. Data from spans will still be
    ///    included as the context for formatted events. This is the default.
    /// - `FmtSpan::ACTIVE`: Events will be synthesized when spans are entered
    ///    or exited.
    /// - `FmtSpan::CLOSE`: An event will be synthesized when a span closes. If
    ///    [timestamps are enabled][time] for this formatter, the generated
    ///    event will contain fields with the span's _busy time_ (the total
    ///    time for which it was entered) and _idle time_ (the total time that
    ///    the span existed but was not entered).
    /// - `FmtSpan::FULL`: Events will be synthesized whenever a span is
    ///    created, entered, exited, or closed. If timestamps are enabled, the
    ///    close event will contain the span's busy and idle time, as
    ///    described above.
    ///
    /// Note that the generated events will only be part of the log output by
    /// this formatter; they will not be recorded by other `Subscriber`s or by
    /// `Layer`s added to this subscriber.
    ///
    /// [lifecycle]: https://docs.rs/tracing/latest/tracing/span/index.html#the-span-lifecycle
    /// [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,
        }
    }

    /// Enable ANSI encoding for formatted events.
    #[cfg(feature = "ansi")]
    #[cfg_attr(docsrs, doc(cfg(feature = "ansi")))]
    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,
        }
    }

    /// 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,
        }
    }

    /// 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,
        }
    }

    /// Sets whether or not the [thread ID] of the current thread is displayed
    /// when formatting events
    ///
    /// [thread ID]: https://doc.rust-lang.org/stable/std/thread/struct.ThreadId.html
    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,
        }
    }

    /// Sets whether or not the [name] of the current thread is displayed
    /// when formatting events
    ///
    /// [name]: https://doc.rust-lang.org/stable/std/thread/index.html#naming-threads
    pub fn with_thread_names(
        self,
        display_thread_names: bool,
    ) -> 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,
        }
    }

    /// Sets the layer being built to use a [less verbose formatter](../fmt/format/struct.Compact.html).
    pub fn compact(self) -> Layer<S, N, format::Format<format::Compact, T>, W>
    where
        N: for<'writer> FormatFields<'writer> + 'static,
    {
        Layer {
            fmt_event: self.fmt_event.compact(),
            fmt_fields: self.fmt_fields,
            fmt_span: self.fmt_span,
            make_writer: self.make_writer,
            _inner: self._inner,
        }
    }

    /// Sets the layer being built to use a [JSON formatter](../fmt/format/struct.Json.html).
    ///
    /// The full format includes fields from all entered spans.
    ///
    /// # Example Output
    ///
    /// ```ignore,json
    /// {"timestamp":"Feb 20 11:28:15.096","level":"INFO","target":"mycrate","fields":{"message":"some message", "key": "value"}}
    /// ```
    ///
    /// # Options
    ///
    /// - [`Layer::flatten_event`] can be used to enable flattening event fields into the root
    /// object.
    ///
    /// [`Layer::flatten_event`]: #method.flatten_event
    #[cfg(feature = "json")]
    #[cfg_attr(docsrs, doc(cfg(feature = "json")))]
    pub fn json(self) -> Layer<S, format::JsonFields, format::Format<format::Json, T>, W> {
        Layer {
            fmt_event: self.fmt_event.json(),
            fmt_fields: format::JsonFields::new(),
            fmt_span: self.fmt_span,
            make_writer: self.make_writer,
            _inner: self._inner,
        }
    }
}

#[cfg(feature = "json")]
#[cfg_attr(docsrs, doc(cfg(feature = "json")))]
impl<S, T, W> Layer<S, format::JsonFields, format::Format<format::Json, T>, W> {
    /// Sets the JSON layer being built to flatten event metadata.
    ///
    /// See [`format::Json`](../fmt/format/struct.Json.html)
    pub fn flatten_event(
        self,
        flatten_event: bool,
    ) -> 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,
        }
    }

    /// Sets whether or not the formatter will include the current span in
    /// formatted events.
    ///
    /// See [`format::Json`](../fmt/format/struct.Json.html)
    pub fn with_current_span(
        self,
        display_current_span: bool,
    ) -> 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,
        }
    }

    /// Sets whether or not the formatter will include a list (from root to leaf)
    /// of all currently entered spans in formatted events.
    ///
    /// See [`format::Json`](../fmt/format/struct.Json.html)
    pub fn with_span_list(
        self,
        display_span_list: bool,
    ) -> 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,
        }
    }
}

impl<S, N, E, W> Layer<S, N, E, W> {
    /// Sets the field formatter that the layer being built will use to record
    /// fields.
    pub fn fmt_fields<N2>(self, fmt_fields: N2) -> Layer<S, N2, E, W>
    where
        N2: for<'writer> FormatFields<'writer> + 'static,
    {
        Layer {
            fmt_event: self.fmt_event,
            fmt_fields,
            fmt_span: self.fmt_span,
            make_writer: self.make_writer,
            _inner: self._inner,
        }
    }
}

#[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: MakeWriter + '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 {
            fmt_fields: format::DefaultFields::default(),
            fmt_event: format::Format::default(),
            fmt_span: format::FmtSpanConfig::default(),
            make_writer: io::stdout,
            _inner: PhantomData,
        }
    }
}

impl<S, N, E, W> Layer<S, N, E, W>
where
    S: Subscriber + for<'a> LookupSpan<'a>,
    N: for<'writer> FormatFields<'writer> + 'static,
    E: FormatEvent<S, N> + 'static,
    W: MakeWriter + 'static,
{
    #[inline]
    fn make_ctx<'a>(&'a self, ctx: Context<'a, S>) -> FmtContext<'a, S, N> {
        FmtContext {
            ctx,
            fmt_fields: &self.fmt_fields,
        }
    }
}

/// A formatted representation of a span's fields stored in its [extensions].
///
/// Because `FormattedFields` is generic over the type of the formatter that
/// produced it, multiple versions of a span's formatted fields can be stored in
/// the [`Extensions`][extensions] type-map. This means that when multiple
/// formatters are in use, each can store its own formatted representation
/// without conflicting.
///
/// [extensions]: ../registry/extensions/index.html
#[derive(Default)]
pub struct FormattedFields<E> {
    _format_event: PhantomData<fn(E)>,
    /// The formatted fields of a span.
    pub fields: String,
}

impl<E> FormattedFields<E> {
    /// Returns a new `FormattedFields`.
    pub fn new(fields: String) -> Self {
        Self {
            fields,
            _format_event: PhantomData,
        }
    }
}

impl<E> fmt::Debug for FormattedFields<E> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("FormattedFields")
            .field("fields", &self.fields)
            .finish()
    }
}

impl<E> fmt::Display for FormattedFields<E> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.fields)
    }
}

impl<E> Deref for FormattedFields<E> {
    type Target = String;
    fn deref(&self) -> &Self::Target {
        &self.fields
    }
}

// === impl FmtLayer ===

macro_rules! with_event_from_span {
    ($id:ident, $span:ident, $($field:literal = $value:expr),*, |$event:ident| $code:block) => {
        let meta = $span.metadata();
        let cs = meta.callsite();
        let fs = field::FieldSet::new(&[$($field),*], cs);
        #[allow(unused)]
        let mut iter = fs.iter();
        let v = [$(
            (&iter.next().unwrap(), Some(&$value as &dyn field::Value)),
        )*];
        let vs = fs.value_set(&v);
        let $event = Event::new_child_of($id, meta, &vs);
        $code
    };
}

impl<S, N, E, W> layer::Layer<S> for Layer<S, N, E, W>
where
    S: Subscriber + for<'a> LookupSpan<'a>,
    N: for<'writer> FormatFields<'writer> + 'static,
    E: FormatEvent<S, N> + 'static,
    W: MakeWriter + 'static,
{
    fn new_span(&self, attrs: &Attributes<'_>, id: &Id, ctx: Context<'_, S>) {
        let span = ctx.span(id).expect("Span not found, this is a bug");
        let mut extensions = span.extensions_mut();

        if extensions.get_mut::<FormattedFields<N>>().is_none() {
            let mut buf = String::new();
            if self.fmt_fields.format_fields(&mut buf, attrs).is_ok() {
                let fmt_fields = FormattedFields {
                    fields: buf,
                    _format_event: PhantomData::<fn(N)>,
                };
                extensions.insert(fmt_fields);
            }
        }

        if self.fmt_span.fmt_timing
            && self.fmt_span.trace_close()
            && extensions.get_mut::<Timings>().is_none()
        {
            extensions.insert(Timings::new());
        }

        if self.fmt_span.trace_new() {
            with_event_from_span!(id, span, "message" = "new", |event| {
                drop(extensions);
                drop(span);
                self.on_event(&event, ctx);
            });
        }
    }

    fn on_record(&self, id: &Id, values: &Record<'_>, ctx: Context<'_, S>) {
        let span = ctx.span(id).expect("Span not found, this is a bug");
        let mut extensions = span.extensions_mut();
        if let Some(FormattedFields { ref mut fields, .. }) =
            extensions.get_mut::<FormattedFields<N>>()
        {
            let _ = self.fmt_fields.add_fields(fields, values);
        } else {
            let mut buf = String::new();
            if self.fmt_fields.format_fields(&mut buf, values).is_ok() {
                let fmt_fields = FormattedFields {
                    fields: buf,
                    _format_event: PhantomData::<fn(N)>,
                };
                extensions.insert(fmt_fields);
            }
        }
    }

    fn on_enter(&self, id: &Id, ctx: Context<'_, S>) {
        if self.fmt_span.trace_active() || self.fmt_span.trace_close() && self.fmt_span.fmt_timing {
            let span = ctx.span(id).expect("Span not found, this is a bug");
            let mut extensions = span.extensions_mut();
            if let Some(timings) = extensions.get_mut::<Timings>() {
                let now = Instant::now();
                timings.idle += (now - timings.last).as_nanos() as u64;
                timings.last = now;
            }

            if self.fmt_span.trace_active() {
                with_event_from_span!(id, span, "message" = "enter", |event| {
                    drop(extensions);
                    drop(span);
                    self.on_event(&event, ctx);
                });
            }
        }
    }

    fn on_exit(&self, id: &Id, ctx: Context<'_, S>) {
        if self.fmt_span.trace_active() || self.fmt_span.trace_close() && self.fmt_span.fmt_timing {
            let span = ctx.span(id).expect("Span not found, this is a bug");
            let mut extensions = span.extensions_mut();
            if let Some(timings) = extensions.get_mut::<Timings>() {
                let now = Instant::now();
                timings.busy += (now - timings.last).as_nanos() as u64;
                timings.last = now;
            }

            if self.fmt_span.trace_active() {
                with_event_from_span!(id, span, "message" = "exit", |event| {
                    drop(extensions);
                    drop(span);
                    self.on_event(&event, ctx);
                });
            }
        }
    }

    fn on_close(&self, id: Id, ctx: Context<'_, S>) {
        if self.fmt_span.trace_close() {
            let span = ctx.span(&id).expect("Span not found, this is a bug");
            let extensions = span.extensions();
            if let Some(timing) = extensions.get::<Timings>() {
                let Timings {
                    busy,
                    mut idle,
                    last,
                } = *timing;
                idle += (Instant::now() - last).as_nanos() as u64;

                let t_idle = field::display(TimingDisplay(idle));
                let t_busy = field::display(TimingDisplay(busy));

                with_event_from_span!(
                    id,
                    span,
                    "message" = "close",
                    "time.busy" = t_busy,
                    "time.idle" = t_idle,
                    |event| {
                        drop(extensions);
                        drop(span);
                        self.on_event(&event, ctx);
                    }
                );
            } else {
                with_event_from_span!(id, span, "message" = "close", |event| {
                    drop(extensions);
                    drop(span);
                    self.on_event(&event, ctx);
                });
            }
        }
    }

    fn on_event(&self, event: &Event<'_>, ctx: Context<'_, S>) {
        thread_local! {
            static BUF: RefCell<String> = RefCell::new(String::new());
        }

        BUF.with(|buf| {
            let borrow = buf.try_borrow_mut();
            let mut a;
            let mut b;
            let mut buf = match borrow {
                Ok(buf) => {
                    a = buf;
                    &mut *a
                }
                _ => {
                    b = String::new();
                    &mut b
                }
            };

            let ctx = self.make_ctx(ctx);
            if self.fmt_event.format_event(&ctx, &mut buf, event).is_ok() {
                let mut writer = self.make_writer.make_writer();
                let _ = io::Write::write_all(&mut writer, buf.as_bytes());
            }

            buf.clear();
        });
    }

    unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> {
        // This `downcast_raw` impl allows downcasting a `fmt` layer to any of
        // its components (event formatter, field formatter, and `MakeWriter`)
        // as well as to the layer's type itself. The potential use-cases for
        // this *may* be somewhat niche, though...
        match () {
            _ if id == TypeId::of::<Self>() => Some(self as *const Self as *const ()),
            _ if id == TypeId::of::<E>() => Some(&self.fmt_event as *const E as *const ()),
            _ if id == TypeId::of::<N>() => Some(&self.fmt_fields as *const N as *const ()),
            _ if id == TypeId::of::<W>() => Some(&self.make_writer as *const W as *const ()),
            _ => None,
        }
    }
}

/// Provides the current span context to a formatter.
pub struct FmtContext<'a, S, N> {
    pub(crate) ctx: Context<'a, S>,
    pub(crate) fmt_fields: &'a N,
}

impl<'a, S, N> fmt::Debug for FmtContext<'a, S, N> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("FmtContext").finish()
    }
}

impl<'a, S, N> FormatFields<'a> for FmtContext<'a, S, N>
where
    S: Subscriber + for<'lookup> LookupSpan<'lookup>,
    N: for<'writer> FormatFields<'writer> + 'static,
{
    fn format_fields<R: RecordFields>(
        &self,
        writer: &'a mut dyn fmt::Write,
        fields: R,
    ) -> fmt::Result {
        self.fmt_fields.format_fields(writer, fields)
    }
}

impl<'a, S, N> FmtContext<'a, S, N>
where
    S: Subscriber + for<'lookup> LookupSpan<'lookup>,
    N: for<'writer> FormatFields<'writer> + 'static,
{
    /// Visits every span in the current context with a closure.
    ///
    /// The provided closure will be called first with the current span,
    /// and then with that span's parent, and then that span's parent,
    /// and so on until a root span is reached.
    pub fn visit_spans<E, F>(&self, mut f: F) -> Result<(), E>
    where
        F: FnMut(&SpanRef<'_, S>) -> Result<(), E>,
    {
        // visit all the current spans
        for span in self.ctx.scope() {
            f(&span)?;
        }
        Ok(())
    }
}

struct Timings {
    idle: u64,
    busy: u64,
    last: Instant,
}

impl Timings {
    fn new() -> Self {
        Self {
            idle: 0,
            busy: 0,
            last: Instant::now(),
        }
    }
}

#[cfg(test)]
mod test {
    use crate::fmt::{
        self,
        format::{self, test::MockTime, Format},
        layer::Layer as _,
        test::MockWriter,
        time,
    };
    use crate::Registry;
    use format::FmtSpan;
    use lazy_static::lazy_static;
    use regex::Regex;
    use std::sync::Mutex;
    use tracing::subscriber::with_default;
    use tracing_core::dispatcher::Dispatch;

    #[test]
    fn impls() {
        let f = Format::default().with_timer(time::Uptime::default());
        let fmt = fmt::Layer::default().event_format(f);
        let subscriber = fmt.with_subscriber(Registry::default());
        let _dispatch = Dispatch::new(subscriber);

        let f = format::Format::default();
        let fmt = fmt::Layer::default().event_format(f);
        let subscriber = fmt.with_subscriber(Registry::default());
        let _dispatch = Dispatch::new(subscriber);

        let f = format::Format::default().compact();
        let fmt = fmt::Layer::default().event_format(f);
        let subscriber = fmt.with_subscriber(Registry::default());
        let _dispatch = Dispatch::new(subscriber);
    }

    #[test]
    fn fmt_layer_downcasts() {
        let f = format::Format::default();
        let fmt = fmt::Layer::default().event_format(f);
        let subscriber = fmt.with_subscriber(Registry::default());

        let dispatch = Dispatch::new(subscriber);
        assert!(dispatch.downcast_ref::<fmt::Layer<Registry>>().is_some());
    }

    #[test]
    fn fmt_layer_downcasts_to_parts() {
        let f = format::Format::default();
        let fmt = fmt::Layer::default().event_format(f);
        let subscriber = fmt.with_subscriber(Registry::default());
        let dispatch = Dispatch::new(subscriber);
        assert!(dispatch.downcast_ref::<format::DefaultFields>().is_some());
        assert!(dispatch.downcast_ref::<format::Format>().is_some())
    }

    #[test]
    fn is_lookup_span() {
        fn assert_lookup_span<T: for<'a> crate::registry::LookupSpan<'a>>(_: T) {}
        let fmt = fmt::Layer::default();
        let subscriber = fmt.with_subscriber(Registry::default());
        assert_lookup_span(subscriber)
    }

    fn sanitize_timings(s: String) -> String {
        let re = Regex::new("time\\.(idle|busy)=([0-9.]+)[mµn]s").unwrap();
        re.replace_all(s.as_str(), "timing").to_string()
    }

    #[test]
    fn synthesize_span_none() {
        lazy_static! {
            static ref BUF: Mutex<Vec<u8>> = Mutex::new(vec![]);
        }

        let make_writer = || MockWriter::new(&BUF);
        let subscriber = crate::fmt::Subscriber::builder()
            .with_writer(make_writer)
            .with_level(false)
            .with_ansi(false)
            .with_timer(MockTime)
            // check that FmtSpan::NONE is the default
            .finish();

        with_default(subscriber, || {
            let span1 = tracing::info_span!("span1", x = 42);
            let _e = span1.enter();
        });
        let actual = sanitize_timings(String::from_utf8(BUF.try_lock().unwrap().to_vec()).unwrap());
        assert_eq!("", actual.as_str());
    }

    #[test]
    fn synthesize_span_active() {
        lazy_static! {
            static ref BUF: Mutex<Vec<u8>> = Mutex::new(vec![]);
        }

        let make_writer = || MockWriter::new(&BUF);
        let subscriber = crate::fmt::Subscriber::builder()
            .with_writer(make_writer)
            .with_level(false)
            .with_ansi(false)
            .with_timer(MockTime)
            .with_span_events(FmtSpan::ACTIVE)
            .finish();

        with_default(subscriber, || {
            let span1 = tracing::info_span!("span1", x = 42);
            let _e = span1.enter();
        });
        let actual = sanitize_timings(String::from_utf8(BUF.try_lock().unwrap().to_vec()).unwrap());
        assert_eq!(
            "fake time span1{x=42}: tracing_subscriber::fmt::fmt_layer::test: enter\n\
             fake time span1{x=42}: tracing_subscriber::fmt::fmt_layer::test: exit\n",
            actual.as_str()
        );
    }

    #[test]
    fn synthesize_span_close() {
        lazy_static! {
            static ref BUF: Mutex<Vec<u8>> = Mutex::new(vec![]);
        }

        let make_writer = || MockWriter::new(&BUF);
        let subscriber = crate::fmt::Subscriber::builder()
            .with_writer(make_writer)
            .with_level(false)
            .with_ansi(false)
            .with_timer(MockTime)
            .with_span_events(FmtSpan::CLOSE)
            .finish();

        with_default(subscriber, || {
            let span1 = tracing::info_span!("span1", x = 42);
            let _e = span1.enter();
        });
        let actual = sanitize_timings(String::from_utf8(BUF.try_lock().unwrap().to_vec()).unwrap());
        assert_eq!(
            "fake time span1{x=42}: tracing_subscriber::fmt::fmt_layer::test: close timing timing\n",
            actual.as_str()
        );
    }

    #[test]
    fn synthesize_span_close_no_timing() {
        lazy_static! {
            static ref BUF: Mutex<Vec<u8>> = Mutex::new(vec![]);
        }

        let make_writer = || MockWriter::new(&BUF);
        let subscriber = crate::fmt::Subscriber::builder()
            .with_writer(make_writer)
            .with_level(false)
            .with_ansi(false)
            .with_timer(MockTime)
            .without_time()
            .with_span_events(FmtSpan::CLOSE)
            .finish();

        with_default(subscriber, || {
            let span1 = tracing::info_span!("span1", x = 42);
            let _e = span1.enter();
        });
        let actual = sanitize_timings(String::from_utf8(BUF.try_lock().unwrap().to_vec()).unwrap());
        assert_eq!(
            " span1{x=42}: tracing_subscriber::fmt::fmt_layer::test: close\n",
            actual.as_str()
        );
    }

    #[test]
    fn synthesize_span_full() {
        lazy_static! {
            static ref BUF: Mutex<Vec<u8>> = Mutex::new(vec![]);
        }

        let make_writer = || MockWriter::new(&BUF);
        let subscriber = crate::fmt::Subscriber::builder()
            .with_writer(make_writer)
            .with_level(false)
            .with_ansi(false)
            .with_timer(MockTime)
            .with_span_events(FmtSpan::FULL)
            .finish();

        with_default(subscriber, || {
            let span1 = tracing::info_span!("span1", x = 42);
            let _e = span1.enter();
        });
        let actual = sanitize_timings(String::from_utf8(BUF.try_lock().unwrap().to_vec()).unwrap());
        assert_eq!(
            "fake time span1{x=42}: tracing_subscriber::fmt::fmt_layer::test: new\n\
             fake time span1{x=42}: tracing_subscriber::fmt::fmt_layer::test: enter\n\
             fake time span1{x=42}: tracing_subscriber::fmt::fmt_layer::test: exit\n\
             fake time span1{x=42}: tracing_subscriber::fmt::fmt_layer::test: close timing timing\n",
            actual.as_str()
        );
    }
}