logo
   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
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
//! Span and `Event` key-value data.
//!
//! Spans and events may be annotated with key-value data, referred to as known
//! as _fields_. These fields consist of a mapping from a key (corresponding to
//! a `&str` but represented internally as an array index) to a [`Value`].
//!
//! # `Value`s and `Subscriber`s
//!
//! `Subscriber`s consume `Value`s as fields attached to [span]s or [`Event`]s.
//! The set of field keys on a given span or is defined on its [`Metadata`].
//! When a span is created, it provides [`Attributes`] to the `Subscriber`'s
//! [`new_span`] method, containing any fields whose values were provided when
//! the span was created; and may call the `Subscriber`'s [`record`] method
//! with additional [`Record`]s if values are added for more of its fields.
//! Similarly, the [`Event`] type passed to the subscriber's [`event`] method
//! will contain any fields attached to each event.
//!
//! `tracing` represents values as either one of a set of Rust primitives
//! (`i64`, `u64`, `f64`, `bool`, and `&str`) or using a `fmt::Display` or
//! `fmt::Debug` implementation. `Subscriber`s are provided these primitive
//! value types as `dyn Value` trait objects.
//!
//! These trait objects can be formatted using `fmt::Debug`, but may also be
//! recorded as typed data by calling the [`Value::record`] method on these
//! trait objects with a _visitor_ implementing the [`Visit`] trait. This trait
//! represents the behavior used to record values of various types. For example,
//! we might record integers by incrementing counters for their field names,
//! rather than printing them.
//!
//! [`Value`]: trait.Value.html
//! [span]: ../span/
//! [`Event`]: ../event/struct.Event.html
//! [`Metadata`]: ../metadata/struct.Metadata.html
//! [`Attributes`]:  ../span/struct.Attributes.html
//! [`Record`]: ../span/struct.Record.html
//! [`new_span`]: ../subscriber/trait.Subscriber.html#method.new_span
//! [`record`]: ../subscriber/trait.Subscriber.html#method.record
//! [`event`]:  ../subscriber/trait.Subscriber.html#method.event
//! [`Value::record`]: trait.Value.html#method.record
//! [`Visit`]: trait.Visit.html
use crate::callsite;
use crate::stdlib::{
    borrow::Borrow,
    fmt,
    hash::{Hash, Hasher},
    num,
    ops::Range,
};

use self::private::ValidLen;

/// An opaque key allowing _O_(1) access to a field in a `Span`'s key-value
/// data.
///
/// As keys are defined by the _metadata_ of a span, rather than by an
/// individual instance of a span, a key may be used to access the same field
/// across all instances of a given span with the same metadata. Thus, when a
/// subscriber observes a new span, it need only access a field by name _once_,
/// and use the key for that name for all other accesses.
#[derive(Debug)]
pub struct Field {
    i: usize,
    fields: FieldSet,
}

/// An empty field.
///
/// This can be used to indicate that the value of a field is not currently
/// present but will be recorded later.
///
/// When a field's value is `Empty`. it will not be recorded.
#[derive(Debug, Eq, PartialEq)]
pub struct Empty;

/// Describes the fields present on a span.
pub struct FieldSet {
    /// The names of each field on the described span.
    names: &'static [&'static str],
    /// The callsite where the described span originates.
    callsite: callsite::Identifier,
}

/// A set of fields and values for a span.
pub struct ValueSet<'a> {
    values: &'a [(&'a Field, Option<&'a (dyn Value + 'a)>)],
    fields: &'a FieldSet,
}

/// An iterator over a set of fields.
#[derive(Debug)]
pub struct Iter {
    idxs: Range<usize>,
    fields: FieldSet,
}

/// Visits typed values.
///
/// An instance of `Visit` ("a visitor") represents the logic necessary to
/// record field values of various types. When an implementor of [`Value`] is
/// [recorded], it calls the appropriate method on the provided visitor to
/// indicate the type that value should be recorded as.
///
/// When a [`Subscriber`] implementation [records an `Event`] or a
/// [set of `Value`s added to a `Span`], it can pass an `&mut Visit` to the
/// `record` method on the provided [`ValueSet`] or [`Event`]. This visitor
/// will then be used to record all the field-value pairs present on that
/// `Event` or `ValueSet`.
///
/// # Examples
///
/// A simple visitor that writes to a string might be implemented like so:
/// ```
/// # extern crate tracing_core as tracing;
/// use std::fmt::{self, Write};
/// use tracing::field::{Value, Visit, Field};
/// pub struct StringVisitor<'a> {
///     string: &'a mut String,
/// }
///
/// impl<'a> Visit for StringVisitor<'a> {
///     fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
///         write!(self.string, "{} = {:?}; ", field.name(), value).unwrap();
///     }
/// }
/// ```
/// This visitor will format each recorded value using `fmt::Debug`, and
/// append the field name and formatted value to the provided string,
/// regardless of the type of the recorded value. When all the values have
/// been recorded, the `StringVisitor` may be dropped, allowing the string
/// to be printed or stored in some other data structure.
///
/// The `Visit` trait provides default implementations for `record_i64`,
/// `record_u64`, `record_bool`, `record_str`, and `record_error`, which simply
/// forward the recorded value to `record_debug`. Thus, `record_debug` is the
/// only method which a `Visit` implementation *must* implement. However,
/// visitors may override the default implementations of these functions in
/// order to implement type-specific behavior.
///
/// Additionally, when a visitor receives a value of a type it does not care
/// about, it is free to ignore those values completely. For example, a
/// visitor which only records numeric data might look like this:
///
/// ```
/// # extern crate tracing_core as tracing;
/// # use std::fmt::{self, Write};
/// # use tracing::field::{Value, Visit, Field};
/// pub struct SumVisitor {
///     sum: i64,
/// }
///
/// impl Visit for SumVisitor {
///     fn record_i64(&mut self, _field: &Field, value: i64) {
///        self.sum += value;
///     }
///
///     fn record_u64(&mut self, _field: &Field, value: u64) {
///         self.sum += value as i64;
///     }
///
///     fn record_debug(&mut self, _field: &Field, _value: &fmt::Debug) {
///         // Do nothing
///     }
/// }
/// ```
///
/// This visitor (which is probably not particularly useful) keeps a running
/// sum of all the numeric values it records, and ignores all other values. A
/// more practical example of recording typed values is presented in
/// `examples/counters.rs`, which demonstrates a very simple metrics system
/// implemented using `tracing`.
///
/// <div class="example-wrap" style="display:inline-block">
/// <pre class="ignore" style="white-space:normal;font:inherit;">
/// <strong>Note</strong>: The <code>record_error</code> trait method is only
/// available when the Rust standard library is present, as it requires the
/// <code>std::error::Error</code> trait.
/// </pre></div>
///
/// [`Value`]: trait.Value.html
/// [recorded]: trait.Value.html#method.record
/// [`Subscriber`]: ../subscriber/trait.Subscriber.html
/// [records an `Event`]: ../subscriber/trait.Subscriber.html#method.event
/// [set of `Value`s added to a `Span`]: ../subscriber/trait.Subscriber.html#method.record
/// [`Event`]: ../event/struct.Event.html
/// [`ValueSet`]: struct.ValueSet.html
pub trait Visit {
    /// Visit a double-precision floating point value.
    fn record_f64(&mut self, field: &Field, value: f64) {
        self.record_debug(field, &value)
    }

    /// Visit a signed 64-bit integer value.
    fn record_i64(&mut self, field: &Field, value: i64) {
        self.record_debug(field, &value)
    }

    /// Visit an unsigned 64-bit integer value.
    fn record_u64(&mut self, field: &Field, value: u64) {
        self.record_debug(field, &value)
    }

    /// Visit a boolean value.
    fn record_bool(&mut self, field: &Field, value: bool) {
        self.record_debug(field, &value)
    }

    /// Visit a string value.
    fn record_str(&mut self, field: &Field, value: &str) {
        self.record_debug(field, &value)
    }

    /// Records a type implementing `Error`.
    ///
    /// <div class="example-wrap" style="display:inline-block">
    /// <pre class="ignore" style="white-space:normal;font:inherit;">
    /// <strong>Note</strong>: This is only enabled when the Rust standard library is
    /// present.
    /// </pre>
    #[cfg(feature = "std")]
    #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
    fn record_error(&mut self, field: &Field, value: &(dyn std::error::Error + 'static)) {
        self.record_debug(field, &format_args!("{}", value))
    }

    /// Visit a value implementing `fmt::Debug`.
    fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug);
}

/// A field value of an erased type.
///
/// Implementors of `Value` may call the appropriate typed recording methods on
/// the [visitor] passed to their `record` method in order to indicate how
/// their data should be recorded.
///
/// [visitor]: trait.Visit.html
pub trait Value: crate::sealed::Sealed {
    /// Visits this value with the given `Visitor`.
    fn record(&self, key: &Field, visitor: &mut dyn Visit);
}

/// A `Value` which serializes using `fmt::Display`.
///
/// Uses `record_debug` in the `Value` implementation to
/// avoid an unnecessary evaluation.
#[derive(Clone)]
pub struct DisplayValue<T: fmt::Display>(T);

/// A `Value` which serializes as a string using `fmt::Debug`.
#[derive(Clone)]
pub struct DebugValue<T: fmt::Debug>(T);

/// Wraps a type implementing `fmt::Display` as a `Value` that can be
/// recorded using its `Display` implementation.
pub fn display<T>(t: T) -> DisplayValue<T>
where
    T: fmt::Display,
{
    DisplayValue(t)
}

/// Wraps a type implementing `fmt::Debug` as a `Value` that can be
/// recorded using its `Debug` implementation.
pub fn debug<T>(t: T) -> DebugValue<T>
where
    T: fmt::Debug,
{
    DebugValue(t)
}

// ===== impl Visit =====

impl<'a, 'b> Visit for fmt::DebugStruct<'a, 'b> {
    fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
        self.field(field.name(), value);
    }
}

impl<'a, 'b> Visit for fmt::DebugMap<'a, 'b> {
    fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
        self.entry(&format_args!("{}", field), value);
    }
}

impl<F> Visit for F
where
    F: FnMut(&Field, &dyn fmt::Debug),
{
    fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
        (self)(field, value)
    }
}

// ===== impl Value =====

macro_rules! impl_values {
    ( $( $record:ident( $( $whatever:tt)+ ) ),+ ) => {
        $(
            impl_value!{ $record( $( $whatever )+ ) }
        )+
    }
}

macro_rules! ty_to_nonzero {
    (u8) => {
        NonZeroU8
    };
    (u16) => {
        NonZeroU16
    };
    (u32) => {
        NonZeroU32
    };
    (u64) => {
        NonZeroU64
    };
    (u128) => {
        NonZeroU128
    };
    (usize) => {
        NonZeroUsize
    };
    (i8) => {
        NonZeroI8
    };
    (i16) => {
        NonZeroI16
    };
    (i32) => {
        NonZeroI32
    };
    (i64) => {
        NonZeroI64
    };
    (i128) => {
        NonZeroI128
    };
    (isize) => {
        NonZeroIsize
    };
}

macro_rules! impl_one_value {
    (f32, $op:expr, $record:ident) => {
        impl_one_value!(normal, f32, $op, $record);
    };
    (f64, $op:expr, $record:ident) => {
        impl_one_value!(normal, f64, $op, $record);
    };
    (bool, $op:expr, $record:ident) => {
        impl_one_value!(normal, bool, $op, $record);
    };
    ($value_ty:tt, $op:expr, $record:ident) => {
        impl_one_value!(normal, $value_ty, $op, $record);
        impl_one_value!(nonzero, $value_ty, $op, $record);
    };
    (normal, $value_ty:tt, $op:expr, $record:ident) => {
        impl $crate::sealed::Sealed for $value_ty {}
        impl $crate::field::Value for $value_ty {
            fn record(&self, key: &$crate::field::Field, visitor: &mut dyn $crate::field::Visit) {
                visitor.$record(key, $op(*self))
            }
        }
    };
    (nonzero, $value_ty:tt, $op:expr, $record:ident) => {
        // This `use num::*;` is reported as unused because it gets emitted
        // for every single invocation of this macro, so there are multiple `use`s.
        // All but the first are useless indeed.
        // We need this import because we can't write a path where one part is
        // the `ty_to_nonzero!($value_ty)` invocation.
        #[allow(clippy::useless_attribute, unused)]
        use num::*;
        impl $crate::sealed::Sealed for ty_to_nonzero!($value_ty) {}
        impl $crate::field::Value for ty_to_nonzero!($value_ty) {
            fn record(&self, key: &$crate::field::Field, visitor: &mut dyn $crate::field::Visit) {
                visitor.$record(key, $op(self.get()))
            }
        }
    };
}

macro_rules! impl_value {
    ( $record:ident( $( $value_ty:tt ),+ ) ) => {
        $(
            impl_one_value!($value_ty, |this: $value_ty| this, $record);
        )+
    };
    ( $record:ident( $( $value_ty:tt ),+ as $as_ty:ty) ) => {
        $(
            impl_one_value!($value_ty, |this: $value_ty| this as $as_ty, $record);
        )+
    };
}

// ===== impl Value =====

impl_values! {
    record_u64(u64),
    record_u64(usize, u32, u16, u8 as u64),
    record_i64(i64),
    record_i64(isize, i32, i16, i8 as i64),
    record_bool(bool),
    record_f64(f64, f32 as f64)
}

impl<T: crate::sealed::Sealed> crate::sealed::Sealed for Wrapping<T> {}
impl<T: crate::field::Value> crate::field::Value for Wrapping<T> {
    fn record(&self, key: &crate::field::Field, visitor: &mut dyn crate::field::Visit) {
        self.0.record(key, visitor)
    }
}

impl crate::sealed::Sealed for str {}

impl Value for str {
    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
        visitor.record_str(key, self)
    }
}

#[cfg(feature = "std")]
impl crate::sealed::Sealed for dyn std::error::Error + 'static {}

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl Value for dyn std::error::Error + 'static {
    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
        visitor.record_error(key, self)
    }
}

impl<'a, T: ?Sized> crate::sealed::Sealed for &'a T where T: Value + crate::sealed::Sealed + 'a {}

impl<'a, T: ?Sized> Value for &'a T
where
    T: Value + 'a,
{
    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
        (*self).record(key, visitor)
    }
}

impl<'a, T: ?Sized> crate::sealed::Sealed for &'a mut T where T: Value + crate::sealed::Sealed + 'a {}

impl<'a, T: ?Sized> Value for &'a mut T
where
    T: Value + 'a,
{
    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
        // Don't use `(*self).record(key, visitor)`, otherwise would
        // cause stack overflow due to `unconditional_recursion`.
        T::record(self, key, visitor)
    }
}

impl<'a> crate::sealed::Sealed for fmt::Arguments<'a> {}

impl<'a> Value for fmt::Arguments<'a> {
    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
        visitor.record_debug(key, self)
    }
}

impl fmt::Debug for dyn Value {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // We are only going to be recording the field value, so we don't
        // actually care about the field name here.
        struct NullCallsite;
        static NULL_CALLSITE: NullCallsite = NullCallsite;
        impl crate::callsite::Callsite for NullCallsite {
            fn set_interest(&self, _: crate::subscriber::Interest) {
                unreachable!("you somehow managed to register the null callsite?")
            }

            fn metadata(&self) -> &crate::Metadata<'_> {
                unreachable!("you somehow managed to access the null callsite?")
            }
        }

        static FIELD: Field = Field {
            i: 0,
            fields: FieldSet::new(&[], crate::identify_callsite!(&NULL_CALLSITE)),
        };

        let mut res = Ok(());
        self.record(&FIELD, &mut |_: &Field, val: &dyn fmt::Debug| {
            res = write!(f, "{:?}", val);
        });
        res
    }
}

impl fmt::Display for dyn Value {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Debug::fmt(self, f)
    }
}

// ===== impl DisplayValue =====

impl<T: fmt::Display> crate::sealed::Sealed for DisplayValue<T> {}

impl<T> Value for DisplayValue<T>
where
    T: fmt::Display,
{
    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
        visitor.record_debug(key, &format_args!("{}", self.0))
    }
}

impl<T: fmt::Display> fmt::Debug for DisplayValue<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.0)
    }
}

impl<T: fmt::Display> fmt::Display for DisplayValue<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(&self.0, f)
    }
}

// ===== impl DebugValue =====

impl<T: fmt::Debug> crate::sealed::Sealed for DebugValue<T> {}

impl<T> Value for DebugValue<T>
where
    T: fmt::Debug,
{
    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
        visitor.record_debug(key, &self.0)
    }
}

impl<T: fmt::Debug> fmt::Debug for DebugValue<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{:?}", self.0)
    }
}

impl crate::sealed::Sealed for Empty {}
impl Value for Empty {
    #[inline]
    fn record(&self, _: &Field, _: &mut dyn Visit) {}
}

impl<T: Value> crate::sealed::Sealed for Option<T> {}

impl<T: Value> Value for Option<T> {
    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
        if let Some(v) = &self {
            v.record(key, visitor)
        }
    }
}

// ===== impl Field =====

impl Field {
    /// Returns an [`Identifier`] that uniquely identifies the [`Callsite`]
    /// which defines this field.
    ///
    /// [`Identifier`]: ../callsite/struct.Identifier.html
    /// [`Callsite`]: ../callsite/trait.Callsite.html
    #[inline]
    pub fn callsite(&self) -> callsite::Identifier {
        self.fields.callsite()
    }

    /// Returns a string representing the name of the field.
    pub fn name(&self) -> &'static str {
        self.fields.names[self.i]
    }
}

impl fmt::Display for Field {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.pad(self.name())
    }
}

impl AsRef<str> for Field {
    fn as_ref(&self) -> &str {
        self.name()
    }
}

impl PartialEq for Field {
    fn eq(&self, other: &Self) -> bool {
        self.callsite() == other.callsite() && self.i == other.i
    }
}

impl Eq for Field {}

impl Hash for Field {
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher,
    {
        self.callsite().hash(state);
        self.i.hash(state);
    }
}

impl Clone for Field {
    fn clone(&self) -> Self {
        Field {
            i: self.i,
            fields: FieldSet {
                names: self.fields.names,
                callsite: self.fields.callsite(),
            },
        }
    }
}

// ===== impl FieldSet =====

impl FieldSet {
    /// Constructs a new `FieldSet` with the given array of field names and callsite.
    pub const fn new(names: &'static [&'static str], callsite: callsite::Identifier) -> Self {
        Self { names, callsite }
    }

    /// Returns an [`Identifier`] that uniquely identifies the [`Callsite`]
    /// which defines this set of fields..
    ///
    /// [`Identifier`]: ../callsite/struct.Identifier.html
    /// [`Callsite`]: ../callsite/trait.Callsite.html
    pub(crate) fn callsite(&self) -> callsite::Identifier {
        callsite::Identifier(self.callsite.0)
    }

    /// Returns the [`Field`] named `name`, or `None` if no such field exists.
    ///
    /// [`Field`]: ../struct.Field.html
    pub fn field<Q: ?Sized>(&self, name: &Q) -> Option<Field>
    where
        Q: Borrow<str>,
    {
        let name = &name.borrow();
        self.names.iter().position(|f| f == name).map(|i| Field {
            i,
            fields: FieldSet {
                names: self.names,
                callsite: self.callsite(),
            },
        })
    }

    /// Returns `true` if `self` contains the given `field`.
    ///
    /// <div class="example-wrap" style="display:inline-block">
    /// <pre class="ignore" style="white-space:normal;font:inherit;">
    /// <strong>Note</strong>: If <code>field</code> shares a name with a field
    /// in this <code>FieldSet</code>, but was created by a <code>FieldSet</code>
    /// with a different callsite, this <code>FieldSet</code> does <em>not</em>
    /// contain it. This is so that if two separate span callsites define a field
    /// named "foo", the <code>Field</code> corresponding to "foo" for each
    /// of those callsites are not equivalent.
    /// </pre></div>
    pub fn contains(&self, field: &Field) -> bool {
        field.callsite() == self.callsite() && field.i <= self.len()
    }

    /// Returns an iterator over the `Field`s in this `FieldSet`.
    pub fn iter(&self) -> Iter {
        let idxs = 0..self.len();
        Iter {
            idxs,
            fields: FieldSet {
                names: self.names,
                callsite: self.callsite(),
            },
        }
    }

    /// Returns a new `ValueSet` with entries for this `FieldSet`'s values.
    ///
    /// Note that a `ValueSet` may not be constructed with arrays of over 32
    /// elements.
    #[doc(hidden)]
    pub fn value_set<'v, V>(&'v self, values: &'v V) -> ValueSet<'v>
    where
        V: ValidLen<'v>,
    {
        ValueSet {
            fields: self,
            values: values.borrow(),
        }
    }

    /// Returns the number of fields in this `FieldSet`.
    #[inline]
    pub fn len(&self) -> usize {
        self.names.len()
    }

    /// Returns whether or not this `FieldSet` has fields.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.names.is_empty()
    }
}

impl<'a> IntoIterator for &'a FieldSet {
    type IntoIter = Iter;
    type Item = Field;
    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        self.iter()
    }
}

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

impl fmt::Display for FieldSet {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_set()
            .entries(self.names.iter().map(display))
            .finish()
    }
}

// ===== impl Iter =====

impl Iterator for Iter {
    type Item = Field;
    fn next(&mut self) -> Option<Field> {
        let i = self.idxs.next()?;
        Some(Field {
            i,
            fields: FieldSet {
                names: self.fields.names,
                callsite: self.fields.callsite(),
            },
        })
    }
}

// ===== impl ValueSet =====

impl<'a> ValueSet<'a> {
    /// Returns an [`Identifier`] that uniquely identifies the [`Callsite`]
    /// defining the fields this `ValueSet` refers to.
    ///
    /// [`Identifier`]: ../callsite/struct.Identifier.html
    /// [`Callsite`]: ../callsite/trait.Callsite.html
    #[inline]
    pub fn callsite(&self) -> callsite::Identifier {
        self.fields.callsite()
    }

    /// Visits all the fields in this `ValueSet` with the provided [visitor].
    ///
    /// [visitor]: ../trait.Visit.html
    pub(crate) fn record(&self, visitor: &mut dyn Visit) {
        let my_callsite = self.callsite();
        for (field, value) in self.values {
            if field.callsite() != my_callsite {
                continue;
            }
            if let Some(value) = value {
                value.record(field, visitor);
            }
        }
    }

    /// Returns `true` if this `ValueSet` contains a value for the given `Field`.
    pub(crate) fn contains(&self, field: &Field) -> bool {
        field.callsite() == self.callsite()
            && self
                .values
                .iter()
                .any(|(key, val)| *key == field && val.is_some())
    }

    /// Returns true if this `ValueSet` contains _no_ values.
    pub(crate) fn is_empty(&self) -> bool {
        let my_callsite = self.callsite();
        self.values
            .iter()
            .all(|(key, val)| val.is_none() || key.callsite() != my_callsite)
    }

    pub(crate) fn field_set(&self) -> &FieldSet {
        self.fields
    }
}

impl<'a> fmt::Debug for ValueSet<'a> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.values
            .iter()
            .fold(&mut f.debug_struct("ValueSet"), |dbg, (key, v)| {
                if let Some(val) = v {
                    val.record(key, dbg);
                }
                dbg
            })
            .field("callsite", &self.callsite())
            .finish()
    }
}

impl<'a> fmt::Display for ValueSet<'a> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.values
            .iter()
            .fold(&mut f.debug_map(), |dbg, (key, v)| {
                if let Some(val) = v {
                    val.record(key, dbg);
                }
                dbg
            })
            .finish()
    }
}

// ===== impl ValidLen =====

mod private {
    use super::*;

    /// Marker trait implemented by arrays which are of valid length to
    /// construct a `ValueSet`.
    ///
    /// `ValueSet`s may only be constructed from arrays containing 32 or fewer
    /// elements, to ensure the array is small enough to always be allocated on the
    /// stack. This trait is only implemented by arrays of an appropriate length,
    /// ensuring that the correct size arrays are used at compile-time.
    pub trait ValidLen<'a>: Borrow<[(&'a Field, Option<&'a (dyn Value + 'a)>)]> {}
}

macro_rules! impl_valid_len {
    ( $( $len:tt ),+ ) => {
        $(
            impl<'a> private::ValidLen<'a> for
                [(&'a Field, Option<&'a (dyn Value + 'a)>); $len] {}
        )+
    }
}

impl_valid_len! {
    0, 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
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::metadata::{Kind, Level, Metadata};
    use crate::stdlib::{borrow::ToOwned, string::String};

    struct TestCallsite1;
    static TEST_CALLSITE_1: TestCallsite1 = TestCallsite1;
    static TEST_META_1: Metadata<'static> = metadata! {
        name: "field_test1",
        target: module_path!(),
        level: Level::INFO,
        fields: &["foo", "bar", "baz"],
        callsite: &TEST_CALLSITE_1,
        kind: Kind::SPAN,
    };

    impl crate::callsite::Callsite for TestCallsite1 {
        fn set_interest(&self, _: crate::subscriber::Interest) {
            unimplemented!()
        }

        fn metadata(&self) -> &Metadata<'_> {
            &TEST_META_1
        }
    }

    struct TestCallsite2;
    static TEST_CALLSITE_2: TestCallsite2 = TestCallsite2;
    static TEST_META_2: Metadata<'static> = metadata! {
        name: "field_test2",
        target: module_path!(),
        level: Level::INFO,
        fields: &["foo", "bar", "baz"],
        callsite: &TEST_CALLSITE_2,
        kind: Kind::SPAN,
    };

    impl crate::callsite::Callsite for TestCallsite2 {
        fn set_interest(&self, _: crate::subscriber::Interest) {
            unimplemented!()
        }

        fn metadata(&self) -> &Metadata<'_> {
            &TEST_META_2
        }
    }

    #[test]
    fn value_set_with_no_values_is_empty() {
        let fields = TEST_META_1.fields();
        let values = &[
            (&fields.field("foo").unwrap(), None),
            (&fields.field("bar").unwrap(), None),
            (&fields.field("baz").unwrap(), None),
        ];
        let valueset = fields.value_set(values);
        assert!(valueset.is_empty());
    }

    #[test]
    fn empty_value_set_is_empty() {
        let fields = TEST_META_1.fields();
        let valueset = fields.value_set(&[]);
        assert!(valueset.is_empty());
    }

    #[test]
    fn value_sets_with_fields_from_other_callsites_are_empty() {
        let fields = TEST_META_1.fields();
        let values = &[
            (&fields.field("foo").unwrap(), Some(&1 as &dyn Value)),
            (&fields.field("bar").unwrap(), Some(&2 as &dyn Value)),
            (&fields.field("baz").unwrap(), Some(&3 as &dyn Value)),
        ];
        let valueset = TEST_META_2.fields().value_set(values);
        assert!(valueset.is_empty())
    }

    #[test]
    fn sparse_value_sets_are_not_empty() {
        let fields = TEST_META_1.fields();
        let values = &[
            (&fields.field("foo").unwrap(), None),
            (&fields.field("bar").unwrap(), Some(&57 as &dyn Value)),
            (&fields.field("baz").unwrap(), None),
        ];
        let valueset = fields.value_set(values);
        assert!(!valueset.is_empty());
    }

    #[test]
    fn fields_from_other_callsets_are_skipped() {
        let fields = TEST_META_1.fields();
        let values = &[
            (&fields.field("foo").unwrap(), None),
            (
                &TEST_META_2.fields().field("bar").unwrap(),
                Some(&57 as &dyn Value),
            ),
            (&fields.field("baz").unwrap(), None),
        ];

        struct MyVisitor;
        impl Visit for MyVisitor {
            fn record_debug(&mut self, field: &Field, _: &dyn (crate::stdlib::fmt::Debug)) {
                assert_eq!(field.callsite(), TEST_META_1.callsite())
            }
        }
        let valueset = fields.value_set(values);
        valueset.record(&mut MyVisitor);
    }

    #[test]
    fn empty_fields_are_skipped() {
        let fields = TEST_META_1.fields();
        let values = &[
            (&fields.field("foo").unwrap(), Some(&Empty as &dyn Value)),
            (&fields.field("bar").unwrap(), Some(&57 as &dyn Value)),
            (&fields.field("baz").unwrap(), Some(&Empty as &dyn Value)),
        ];

        struct MyVisitor;
        impl Visit for MyVisitor {
            fn record_debug(&mut self, field: &Field, _: &dyn (crate::stdlib::fmt::Debug)) {
                assert_eq!(field.name(), "bar")
            }
        }
        let valueset = fields.value_set(values);
        valueset.record(&mut MyVisitor);
    }

    #[test]
    fn record_debug_fn() {
        let fields = TEST_META_1.fields();
        let values = &[
            (&fields.field("foo").unwrap(), Some(&1 as &dyn Value)),
            (&fields.field("bar").unwrap(), Some(&2 as &dyn Value)),
            (&fields.field("baz").unwrap(), Some(&3 as &dyn Value)),
        ];
        let valueset = fields.value_set(values);
        let mut result = String::new();
        valueset.record(&mut |_: &Field, value: &dyn fmt::Debug| {
            use crate::stdlib::fmt::Write;
            write!(&mut result, "{:?}", value).unwrap();
        });
        assert_eq!(result, "123".to_owned());
    }
}