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
use crate::diagnostic::IntoDiagnosticArg;
use crate::{
    Diagnostic, DiagnosticId, DiagnosticMessage, DiagnosticStyledString, ErrorGuaranteed,
    SubdiagnosticMessage,
};
use crate::{Handler, Level, MultiSpan, StashKey};
use rustc_lint_defs::Applicability;

use rustc_span::Span;
use std::borrow::Cow;
use std::fmt::{self, Debug};
use std::marker::PhantomData;
use std::ops::{Deref, DerefMut};
use std::thread::panicking;

/// Used for emitting structured error messages and other diagnostic information.
///
/// If there is some state in a downstream crate you would like to
/// access in the methods of `DiagnosticBuilder` here, consider
/// extending `HandlerFlags`, accessed via `self.handler.flags`.
#[must_use]
#[derive(Clone)]
pub struct DiagnosticBuilder<'a, G: EmissionGuarantee> {
    inner: DiagnosticBuilderInner<'a>,
    _marker: PhantomData<G>,
}

/// This type exists only for `DiagnosticBuilder::forget_guarantee`, because it:
/// 1. lacks the `G` parameter and therefore `DiagnosticBuilder<G1>` can be
///    converted into `DiagnosticBuilder<G2>` while reusing the `inner` field
/// 2. can implement the `Drop` "bomb" instead of `DiagnosticBuilder`, as it
///    contains all of the data (`state` + `diagnostic`) of `DiagnosticBuilder`
///
/// The `diagnostic` field is not `Copy` and can't be moved out of whichever
/// type implements the `Drop` "bomb", but because of the above two facts, that
/// never needs to happen - instead, the whole `inner: DiagnosticBuilderInner`
/// can be moved out of a `DiagnosticBuilder` and into another.
#[must_use]
#[derive(Clone)]
struct DiagnosticBuilderInner<'a> {
    state: DiagnosticBuilderState<'a>,

    /// `Diagnostic` is a large type, and `DiagnosticBuilder` is often used as a
    /// return value, especially within the frequently-used `PResult` type.
    /// In theory, return value optimization (RVO) should avoid unnecessary
    /// copying. In practice, it does not (at the time of writing).
    diagnostic: Box<Diagnostic>,
}

#[derive(Clone)]
enum DiagnosticBuilderState<'a> {
    /// Initial state of a `DiagnosticBuilder`, before `.emit()` or `.cancel()`.
    ///
    /// The `Diagnostic` will be emitted through this `Handler`.
    Emittable(&'a Handler),

    /// State of a `DiagnosticBuilder`, after `.emit()` or *during* `.cancel()`.
    ///
    /// The `Diagnostic` will be ignored when calling `.emit()`, and it can be
    /// assumed that `.emit()` was previously called, to end up in this state.
    ///
    /// While this is also used by `.cancel()`, this state is only observed by
    /// the `Drop` `impl` of `DiagnosticBuilderInner`, as `.cancel()` takes
    /// `self` by-value specifically to prevent any attempts to `.emit()`.
    ///
    // FIXME(eddyb) currently this doesn't prevent extending the `Diagnostic`,
    // despite that being potentially lossy, if important information is added
    // *after* the original `.emit()` call.
    AlreadyEmittedOrDuringCancellation,
}

// `DiagnosticBuilderState` should be pointer-sized.
rustc_data_structures::static_assert_size!(
    DiagnosticBuilderState<'_>,
    std::mem::size_of::<&Handler>()
);

/// Trait for types that `DiagnosticBuilder::emit` can return as a "guarantee"
/// (or "proof") token that the emission happened.
pub trait EmissionGuarantee: Sized {
    /// Implementation of `DiagnosticBuilder::emit`, fully controlled by each
    /// `impl` of `EmissionGuarantee`, to make it impossible to create a value
    /// of `Self` without actually performing the emission.
    #[track_caller]
    fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self;

    /// Creates a new `DiagnosticBuilder` that will return this type of guarantee.
    #[track_caller]
    fn make_diagnostic_builder(
        handler: &Handler,
        msg: impl Into<DiagnosticMessage>,
    ) -> DiagnosticBuilder<'_, Self>;
}

/// Private module for sealing the `IsError` helper trait.
mod sealed_level_is_error {
    use crate::Level;

    /// Sealed helper trait for statically checking that a `Level` is an error.
    pub(crate) trait IsError<const L: Level> {}

    impl IsError<{ Level::Bug }> for () {}
    impl IsError<{ Level::DelayedBug }> for () {}
    impl IsError<{ Level::Fatal }> for () {}
    // NOTE(eddyb) `Level::Error { lint: true }` is also an error, but lints
    // don't need error guarantees, as their levels are always dynamic.
    impl IsError<{ Level::Error { lint: false } }> for () {}
}

impl<'a> DiagnosticBuilder<'a, ErrorGuaranteed> {
    /// Convenience function for internal use, clients should use one of the
    /// `struct_*` methods on [`Handler`].
    pub(crate) fn new_guaranteeing_error<M: Into<DiagnosticMessage>, const L: Level>(
        handler: &'a Handler,
        message: M,
    ) -> Self
    where
        (): sealed_level_is_error::IsError<L>,
    {
        Self {
            inner: DiagnosticBuilderInner {
                state: DiagnosticBuilderState::Emittable(handler),
                diagnostic: Box::new(Diagnostic::new_with_code(L, None, message)),
            },
            _marker: PhantomData,
        }
    }

    /// Discard the guarantee `.emit()` would return, in favor of having the
    /// type `DiagnosticBuilder<'a, ()>`. This may be necessary whenever there
    /// is a common codepath handling both errors and warnings.
    pub fn forget_guarantee(self) -> DiagnosticBuilder<'a, ()> {
        DiagnosticBuilder { inner: self.inner, _marker: PhantomData }
    }
}

// FIXME(eddyb) make `ErrorGuaranteed` impossible to create outside `.emit()`.
impl EmissionGuarantee for ErrorGuaranteed {
    fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self {
        match db.inner.state {
            // First `.emit()` call, the `&Handler` is still available.
            DiagnosticBuilderState::Emittable(handler) => {
                db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;

                let guar = handler.emit_diagnostic(&mut db.inner.diagnostic);

                // Only allow a guarantee if the `level` wasn't switched to a
                // non-error - the field isn't `pub`, but the whole `Diagnostic`
                // can be overwritten with a new one, thanks to `DerefMut`.
                assert!(
                    db.inner.diagnostic.is_error(),
                    "emitted non-error ({:?}) diagnostic \
                     from `DiagnosticBuilder<ErrorGuaranteed>`",
                    db.inner.diagnostic.level,
                );
                guar.unwrap()
            }
            // `.emit()` was previously called, disallowed from repeating it,
            // but can take advantage of the previous `.emit()`'s guarantee
            // still being applicable (i.e. as a form of idempotency).
            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {
                // Only allow a guarantee if the `level` wasn't switched to a
                // non-error - the field isn't `pub`, but the whole `Diagnostic`
                // can be overwritten with a new one, thanks to `DerefMut`.
                assert!(
                    db.inner.diagnostic.is_error(),
                    "`DiagnosticBuilder<ErrorGuaranteed>`'s diagnostic \
                     became non-error ({:?}), after original `.emit()`",
                    db.inner.diagnostic.level,
                );
                ErrorGuaranteed::unchecked_claim_error_was_emitted()
            }
        }
    }

    fn make_diagnostic_builder(
        handler: &Handler,
        msg: impl Into<DiagnosticMessage>,
    ) -> DiagnosticBuilder<'_, Self> {
        DiagnosticBuilder::new_guaranteeing_error::<_, { Level::Error { lint: false } }>(
            handler, msg,
        )
    }
}

impl<'a> DiagnosticBuilder<'a, ()> {
    /// Convenience function for internal use, clients should use one of the
    /// `struct_*` methods on [`Handler`].
    pub(crate) fn new<M: Into<DiagnosticMessage>>(
        handler: &'a Handler,
        level: Level,
        message: M,
    ) -> Self {
        let diagnostic = Diagnostic::new_with_code(level, None, message);
        Self::new_diagnostic(handler, diagnostic)
    }

    /// Creates a new `DiagnosticBuilder` with an already constructed
    /// diagnostic.
    pub(crate) fn new_diagnostic(handler: &'a Handler, diagnostic: Diagnostic) -> Self {
        debug!("Created new diagnostic");
        Self {
            inner: DiagnosticBuilderInner {
                state: DiagnosticBuilderState::Emittable(handler),
                diagnostic: Box::new(diagnostic),
            },
            _marker: PhantomData,
        }
    }
}

// FIXME(eddyb) should there be a `Option<ErrorGuaranteed>` impl as well?
impl EmissionGuarantee for () {
    fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self {
        match db.inner.state {
            // First `.emit()` call, the `&Handler` is still available.
            DiagnosticBuilderState::Emittable(handler) => {
                db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;

                handler.emit_diagnostic(&mut db.inner.diagnostic);
            }
            // `.emit()` was previously called, disallowed from repeating it.
            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
        }
    }

    fn make_diagnostic_builder(
        handler: &Handler,
        msg: impl Into<DiagnosticMessage>,
    ) -> DiagnosticBuilder<'_, Self> {
        DiagnosticBuilder::new(handler, Level::Warning(None), msg)
    }
}

impl<'a> DiagnosticBuilder<'a, !> {
    /// Convenience function for internal use, clients should use one of the
    /// `struct_*` methods on [`Handler`].
    pub(crate) fn new_fatal(handler: &'a Handler, message: impl Into<DiagnosticMessage>) -> Self {
        let diagnostic = Diagnostic::new_with_code(Level::Fatal, None, message);
        Self::new_diagnostic_fatal(handler, diagnostic)
    }

    /// Creates a new `DiagnosticBuilder` with an already constructed
    /// diagnostic.
    pub(crate) fn new_diagnostic_fatal(handler: &'a Handler, diagnostic: Diagnostic) -> Self {
        debug!("Created new diagnostic");
        Self {
            inner: DiagnosticBuilderInner {
                state: DiagnosticBuilderState::Emittable(handler),
                diagnostic: Box::new(diagnostic),
            },
            _marker: PhantomData,
        }
    }
}

impl EmissionGuarantee for ! {
    fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self {
        match db.inner.state {
            // First `.emit()` call, the `&Handler` is still available.
            DiagnosticBuilderState::Emittable(handler) => {
                db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;

                handler.emit_diagnostic(&mut db.inner.diagnostic);
            }
            // `.emit()` was previously called, disallowed from repeating it.
            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
        }
        // Then fatally error, returning `!`
        crate::FatalError.raise()
    }

    fn make_diagnostic_builder(
        handler: &Handler,
        msg: impl Into<DiagnosticMessage>,
    ) -> DiagnosticBuilder<'_, Self> {
        DiagnosticBuilder::new_fatal(handler, msg)
    }
}

/// In general, the `DiagnosticBuilder` uses deref to allow access to
/// the fields and methods of the embedded `diagnostic` in a
/// transparent way. *However,* many of the methods are intended to
/// be used in a chained way, and hence ought to return `self`. In
/// that case, we can't just naively forward to the method on the
/// `diagnostic`, because the return type would be a `&Diagnostic`
/// instead of a `&DiagnosticBuilder<'a>`. This `forward!` macro makes
/// it easy to declare such methods on the builder.
macro_rules! forward {
    // Forward pattern for &mut self -> &mut Self
    (
        $(#[$attrs:meta])*
        pub fn $n:ident(&mut self, $($name:ident: $ty:ty),* $(,)?) -> &mut Self
    ) => {
        $(#[$attrs])*
        #[doc = concat!("See [`Diagnostic::", stringify!($n), "()`].")]
        pub fn $n(&mut self, $($name: $ty),*) -> &mut Self {
            self.inner.diagnostic.$n($($name),*);
            self
        }
    };
}

impl<G: EmissionGuarantee> Deref for DiagnosticBuilder<'_, G> {
    type Target = Diagnostic;

    fn deref(&self) -> &Diagnostic {
        &self.inner.diagnostic
    }
}

impl<G: EmissionGuarantee> DerefMut for DiagnosticBuilder<'_, G> {
    fn deref_mut(&mut self) -> &mut Diagnostic {
        &mut self.inner.diagnostic
    }
}

impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
    /// Emit the diagnostic.
    #[track_caller]
    pub fn emit(&mut self) -> G {
        G::diagnostic_builder_emit_producing_guarantee(self)
    }

    /// Emit the diagnostic unless `delay` is true,
    /// in which case the emission will be delayed as a bug.
    ///
    /// See `emit` and `delay_as_bug` for details.
    #[track_caller]
    pub fn emit_unless(&mut self, delay: bool) -> G {
        if delay {
            self.downgrade_to_delayed_bug();
        }
        self.emit()
    }

    /// Cancel the diagnostic (a structured diagnostic must either be emitted or
    /// cancelled or it will panic when dropped).
    ///
    /// This method takes `self` by-value to disallow calling `.emit()` on it,
    /// which may be expected to *guarantee* the emission of an error, either
    /// at the time of the call, or through a prior `.emit()` call.
    pub fn cancel(mut self) {
        self.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
        drop(self);
    }

    /// Stashes diagnostic for possible later improvement in a different,
    /// later stage of the compiler. The diagnostic can be accessed with
    /// the provided `span` and `key` through [`Handler::steal_diagnostic()`].
    ///
    /// As with `buffer`, this is unless the handler has disabled such buffering.
    pub fn stash(self, span: Span, key: StashKey) {
        if let Some((diag, handler)) = self.into_diagnostic() {
            handler.stash_diagnostic(span, key, diag);
        }
    }

    /// Converts the builder to a `Diagnostic` for later emission,
    /// unless handler has disabled such buffering, or `.emit()` was called.
    pub fn into_diagnostic(mut self) -> Option<(Diagnostic, &'a Handler)> {
        let handler = match self.inner.state {
            // No `.emit()` calls, the `&Handler` is still available.
            DiagnosticBuilderState::Emittable(handler) => handler,
            // `.emit()` was previously called, nothing we can do.
            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {
                return None;
            }
        };

        if handler.flags.dont_buffer_diagnostics || handler.flags.treat_err_as_bug.is_some() {
            self.emit();
            return None;
        }

        // Take the `Diagnostic` by replacing it with a dummy.
        let dummy = Diagnostic::new(Level::Allow, DiagnosticMessage::Str("".to_string()));
        let diagnostic = std::mem::replace(&mut *self.inner.diagnostic, dummy);

        // Disable the ICE on `Drop`.
        self.cancel();

        // Logging here is useful to help track down where in logs an error was
        // actually emitted.
        debug!("buffer: diagnostic={:?}", diagnostic);

        Some((diagnostic, handler))
    }

    /// Buffers the diagnostic for later emission,
    /// unless handler has disabled such buffering.
    pub fn buffer(self, buffered_diagnostics: &mut Vec<Diagnostic>) {
        buffered_diagnostics.extend(self.into_diagnostic().map(|(diag, _)| diag));
    }

    /// Delay emission of this diagnostic as a bug.
    ///
    /// This can be useful in contexts where an error indicates a bug but
    /// typically this only happens when other compilation errors have already
    /// happened. In those cases this can be used to defer emission of this
    /// diagnostic as a bug in the compiler only if no other errors have been
    /// emitted.
    ///
    /// In the meantime, though, callsites are required to deal with the "bug"
    /// locally in whichever way makes the most sense.
    #[track_caller]
    pub fn delay_as_bug(&mut self) {
        self.downgrade_to_delayed_bug();
        self.emit();
    }

    forward!(
        #[track_caller]
        pub fn downgrade_to_delayed_bug(&mut self,) -> &mut Self
    );

    forward!(
    /// Appends a labeled span to the diagnostic.
    ///
    /// Labels are used to convey additional context for the diagnostic's primary span. They will
    /// be shown together with the original diagnostic's span, *not* with spans added by
    /// `span_note`, `span_help`, etc. Therefore, if the primary span is not displayable (because
    /// the span is `DUMMY_SP` or the source code isn't found), labels will not be displayed
    /// either.
    ///
    /// Implementation-wise, the label span is pushed onto the [`MultiSpan`] that was created when
    /// the diagnostic was constructed. However, the label span is *not* considered a
    /// ["primary span"][`MultiSpan`]; only the `Span` supplied when creating the diagnostic is
    /// primary.
    pub fn span_label(&mut self, span: Span, label: impl Into<SubdiagnosticMessage>) -> &mut Self);

    forward!(
    /// Labels all the given spans with the provided label.
    /// See [`Diagnostic::span_label()`] for more information.
    pub fn span_labels(
        &mut self,
        spans: impl IntoIterator<Item = Span>,
        label: impl AsRef<str>,
    ) -> &mut Self);

    forward!(pub fn note_expected_found(
        &mut self,
        expected_label: &dyn fmt::Display,
        expected: DiagnosticStyledString,
        found_label: &dyn fmt::Display,
        found: DiagnosticStyledString,
    ) -> &mut Self);

    forward!(pub fn note_expected_found_extra(
        &mut self,
        expected_label: &dyn fmt::Display,
        expected: DiagnosticStyledString,
        found_label: &dyn fmt::Display,
        found: DiagnosticStyledString,
        expected_extra: &dyn fmt::Display,
        found_extra: &dyn fmt::Display,
    ) -> &mut Self);

    forward!(pub fn note_unsuccessful_coercion(
        &mut self,
        expected: DiagnosticStyledString,
        found: DiagnosticStyledString,
    ) -> &mut Self);

    forward!(pub fn note(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self);
    forward!(pub fn note_once(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self);
    forward!(pub fn span_note(
        &mut self,
        sp: impl Into<MultiSpan>,
        msg: impl Into<SubdiagnosticMessage>,
    ) -> &mut Self);
    forward!(pub fn span_note_once(
        &mut self,
        sp: impl Into<MultiSpan>,
        msg: impl Into<SubdiagnosticMessage>,
    ) -> &mut Self);
    forward!(pub fn warn(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self);
    forward!(pub fn span_warn(
        &mut self,
        sp: impl Into<MultiSpan>,
        msg: impl Into<SubdiagnosticMessage>,
    ) -> &mut Self);
    forward!(pub fn help(&mut self, msg: impl Into<SubdiagnosticMessage>) -> &mut Self);
    forward!(pub fn span_help(
        &mut self,
        sp: impl Into<MultiSpan>,
        msg: impl Into<SubdiagnosticMessage>,
    ) -> &mut Self);
    forward!(pub fn help_use_latest_edition(&mut self,) -> &mut Self);
    forward!(pub fn set_is_lint(&mut self,) -> &mut Self);

    forward!(pub fn disable_suggestions(&mut self,) -> &mut Self);
    forward!(pub fn clear_suggestions(&mut self,) -> &mut Self);

    forward!(pub fn multipart_suggestion(
        &mut self,
        msg: impl Into<SubdiagnosticMessage>,
        suggestion: Vec<(Span, String)>,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn multipart_suggestion_verbose(
        &mut self,
        msg: impl Into<SubdiagnosticMessage>,
        suggestion: Vec<(Span, String)>,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn tool_only_multipart_suggestion(
        &mut self,
        msg: impl Into<SubdiagnosticMessage>,
        suggestion: Vec<(Span, String)>,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn span_suggestion(
        &mut self,
        sp: Span,
        msg: impl Into<SubdiagnosticMessage>,
        suggestion: impl ToString,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn span_suggestions(
        &mut self,
        sp: Span,
        msg: impl Into<SubdiagnosticMessage>,
        suggestions: impl Iterator<Item = String>,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn multipart_suggestions(
        &mut self,
        msg: impl Into<SubdiagnosticMessage>,
        suggestions: impl Iterator<Item = Vec<(Span, String)>>,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn span_suggestion_short(
        &mut self,
        sp: Span,
        msg: impl Into<SubdiagnosticMessage>,
        suggestion: impl ToString,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn span_suggestion_verbose(
        &mut self,
        sp: Span,
        msg: impl Into<SubdiagnosticMessage>,
        suggestion: impl ToString,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn span_suggestion_hidden(
        &mut self,
        sp: Span,
        msg: impl Into<SubdiagnosticMessage>,
        suggestion: impl ToString,
        applicability: Applicability,
    ) -> &mut Self);
    forward!(pub fn tool_only_span_suggestion(
        &mut self,
        sp: Span,
        msg: impl Into<SubdiagnosticMessage>,
        suggestion: impl ToString,
        applicability: Applicability,
    ) -> &mut Self);

    forward!(pub fn set_primary_message(&mut self, msg: impl Into<DiagnosticMessage>) -> &mut Self);
    forward!(pub fn set_span(&mut self, sp: impl Into<MultiSpan>) -> &mut Self);
    forward!(pub fn code(&mut self, s: DiagnosticId) -> &mut Self);
    forward!(pub fn set_arg(
        &mut self,
        name: impl Into<Cow<'static, str>>,
        arg: impl IntoDiagnosticArg,
    ) -> &mut Self);

    forward!(pub fn subdiagnostic(
        &mut self,
        subdiagnostic: impl crate::AddSubdiagnostic
    ) -> &mut Self);
}

impl<G: EmissionGuarantee> Debug for DiagnosticBuilder<'_, G> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.inner.diagnostic.fmt(f)
    }
}

/// Destructor bomb - a `DiagnosticBuilder` must be either emitted or cancelled
/// or we emit a bug.
impl Drop for DiagnosticBuilderInner<'_> {
    fn drop(&mut self) {
        match self.state {
            // No `.emit()` or `.cancel()` calls.
            DiagnosticBuilderState::Emittable(handler) => {
                if !panicking() {
                    handler.emit_diagnostic(&mut Diagnostic::new(
                        Level::Bug,
                        DiagnosticMessage::Str(
                            "the following error was constructed but not emitted".to_string(),
                        ),
                    ));
                    handler.emit_diagnostic(&mut self.diagnostic);
                    panic!("error was constructed but not emitted");
                }
            }
            // `.emit()` was previously called, or maybe we're during `.cancel()`.
            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
        }
    }
}

#[macro_export]
macro_rules! struct_span_err {
    ($session:expr, $span:expr, $code:ident, $($message:tt)*) => ({
        $session.struct_span_err_with_code(
            $span,
            &format!($($message)*),
            $crate::error_code!($code),
        )
    })
}

#[macro_export]
macro_rules! error_code {
    ($code:ident) => {{ $crate::DiagnosticId::Error(stringify!($code).to_owned()) }};
}

/// Wrapper around a `DiagnosticBuilder` for creating lints.
pub struct LintDiagnosticBuilder<'a, G: EmissionGuarantee>(DiagnosticBuilder<'a, G>);

impl<'a, G: EmissionGuarantee> LintDiagnosticBuilder<'a, G> {
    #[rustc_lint_diagnostics]
    /// Return the inner `DiagnosticBuilder`, first setting the primary message to `msg`.
    pub fn build(mut self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'a, G> {
        self.0.set_primary_message(msg);
        self.0.set_is_lint();
        self.0
    }

    /// Create a `LintDiagnosticBuilder` from some existing `DiagnosticBuilder`.
    pub fn new(err: DiagnosticBuilder<'a, G>) -> LintDiagnosticBuilder<'a, G> {
        LintDiagnosticBuilder(err)
    }
}

impl<'a> LintDiagnosticBuilder<'a, ErrorGuaranteed> {
    pub fn forget_guarantee(self) -> LintDiagnosticBuilder<'a, ()> {
        LintDiagnosticBuilder(self.0.forget_guarantee())
    }
}