-
Notifications
You must be signed in to change notification settings - Fork 12.1k
/
generics.rs
633 lines (584 loc) · 28.3 KB
/
generics.rs
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
use crate::astconv::{
AstConv, ExplicitLateBound, GenericArgCountMismatch, GenericArgCountResult, GenericArgPosition,
};
use crate::errors::AssocTypeBindingNotAllowed;
use rustc_ast::ast::ParamKindOrd;
use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorReported};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::{GenericArg, GenericArgs};
use rustc_middle::ty::{
self, subst, subst::SubstsRef, GenericParamDef, GenericParamDefKind, Ty, TyCtxt,
};
use rustc_session::{lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS, Session};
use rustc_span::{symbol::kw, MultiSpan, Span};
use smallvec::SmallVec;
impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
/// Report an error that a generic argument did not match the generic parameter that was
/// expected.
fn generic_arg_mismatch_err(
sess: &Session,
arg: &GenericArg<'_>,
kind: &'static str,
help: Option<&str>,
) {
let mut err = struct_span_err!(
sess,
arg.span(),
E0747,
"{} provided when a {} was expected",
arg.descr(),
kind,
);
let unordered = sess.features_untracked().const_generics;
let kind_ord = match kind {
"lifetime" => ParamKindOrd::Lifetime,
"type" => ParamKindOrd::Type,
"constant" => ParamKindOrd::Const { unordered },
// It's more concise to match on the string representation, though it means
// the match is non-exhaustive.
_ => bug!("invalid generic parameter kind {}", kind),
};
let arg_ord = match arg {
GenericArg::Lifetime(_) => ParamKindOrd::Lifetime,
GenericArg::Type(_) => ParamKindOrd::Type,
GenericArg::Const(_) => ParamKindOrd::Const { unordered },
};
// This note is only true when generic parameters are strictly ordered by their kind.
if kind_ord.cmp(&arg_ord) != core::cmp::Ordering::Equal {
let (first, last) =
if kind_ord < arg_ord { (kind, arg.descr()) } else { (arg.descr(), kind) };
err.note(&format!("{} arguments must be provided before {} arguments", first, last));
if let Some(help) = help {
err.help(help);
}
}
err.emit();
}
/// Creates the relevant generic argument substitutions
/// corresponding to a set of generic parameters. This is a
/// rather complex function. Let us try to explain the role
/// of each of its parameters:
///
/// To start, we are given the `def_id` of the thing we are
/// creating the substitutions for, and a partial set of
/// substitutions `parent_substs`. In general, the substitutions
/// for an item begin with substitutions for all the "parents" of
/// that item -- e.g., for a method it might include the
/// parameters from the impl.
///
/// Therefore, the method begins by walking down these parents,
/// starting with the outermost parent and proceed inwards until
/// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
/// first to see if the parent's substitutions are listed in there. If so,
/// we can append those and move on. Otherwise, it invokes the
/// three callback functions:
///
/// - `args_for_def_id`: given the `DefId` `P`, supplies back the
/// generic arguments that were given to that parent from within
/// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
/// might refer to the trait `Foo`, and the arguments might be
/// `[T]`. The boolean value indicates whether to infer values
/// for arguments whose values were not explicitly provided.
/// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
/// instantiate a `GenericArg`.
/// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
/// creates a suitable inference variable.
pub fn create_substs_for_generic_args<'b>(
tcx: TyCtxt<'tcx>,
def_id: DefId,
parent_substs: &[subst::GenericArg<'tcx>],
has_self: bool,
self_ty: Option<Ty<'tcx>>,
arg_count: GenericArgCountResult,
args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
mut provided_kind: impl FnMut(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
mut inferred_kind: impl FnMut(
Option<&[subst::GenericArg<'tcx>]>,
&GenericParamDef,
bool,
) -> subst::GenericArg<'tcx>,
) -> SubstsRef<'tcx> {
// Collect the segments of the path; we need to substitute arguments
// for parameters throughout the entire path (wherever there are
// generic parameters).
let mut parent_defs = tcx.generics_of(def_id);
let count = parent_defs.count();
let mut stack = vec![(def_id, parent_defs)];
while let Some(def_id) = parent_defs.parent {
parent_defs = tcx.generics_of(def_id);
stack.push((def_id, parent_defs));
}
// We manually build up the substitution, rather than using convenience
// methods in `subst.rs`, so that we can iterate over the arguments and
// parameters in lock-step linearly, instead of trying to match each pair.
let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
// Iterate over each segment of the path.
while let Some((def_id, defs)) = stack.pop() {
let mut params = defs.params.iter().peekable();
// If we have already computed substitutions for parents, we can use those directly.
while let Some(¶m) = params.peek() {
if let Some(&kind) = parent_substs.get(param.index as usize) {
substs.push(kind);
params.next();
} else {
break;
}
}
// `Self` is handled first, unless it's been handled in `parent_substs`.
if has_self {
if let Some(¶m) = params.peek() {
if param.index == 0 {
if let GenericParamDefKind::Type { .. } = param.kind {
substs.push(
self_ty
.map(|ty| ty.into())
.unwrap_or_else(|| inferred_kind(None, param, true)),
);
params.next();
}
}
}
}
// Check whether this segment takes generic arguments and the user has provided any.
let (generic_args, infer_args) = args_for_def_id(def_id);
let mut args =
generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
// If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
// If we later encounter a lifetime, we know that the arguments were provided in the
// wrong order. `force_infer_lt` records the type or const that forced lifetimes to be
// inferred, so we can use it for diagnostics later.
let mut force_infer_lt = None;
loop {
// We're going to iterate through the generic arguments that the user
// provided, matching them with the generic parameters we expect.
// Mismatches can occur as a result of elided lifetimes, or for malformed
// input. We try to handle both sensibly.
match (args.peek(), params.peek()) {
(Some(&arg), Some(¶m)) => {
match (arg, ¶m.kind, arg_count.explicit_late_bound) {
(GenericArg::Lifetime(_), GenericParamDefKind::Lifetime, _)
| (GenericArg::Type(_), GenericParamDefKind::Type { .. }, _)
| (GenericArg::Const(_), GenericParamDefKind::Const, _) => {
substs.push(provided_kind(param, arg));
args.next();
params.next();
}
(
GenericArg::Type(_) | GenericArg::Const(_),
GenericParamDefKind::Lifetime,
_,
) => {
// We expected a lifetime argument, but got a type or const
// argument. That means we're inferring the lifetimes.
substs.push(inferred_kind(None, param, infer_args));
force_infer_lt = Some(arg);
params.next();
}
(GenericArg::Lifetime(_), _, ExplicitLateBound::Yes) => {
// We've come across a lifetime when we expected something else in
// the presence of explicit late bounds. This is most likely
// due to the presence of the explicit bound so we're just going to
// ignore it.
args.next();
}
(_, kind, _) => {
// We expected one kind of parameter, but the user provided
// another. This is an error. However, if we already know that
// the arguments don't match up with the parameters, we won't issue
// an additional error, as the user already knows what's wrong.
if arg_count.correct.is_ok()
&& arg_count.explicit_late_bound == ExplicitLateBound::No
{
// We're going to iterate over the parameters to sort them out, and
// show that order to the user as a possible order for the parameters
let mut param_types_present = defs
.params
.clone()
.into_iter()
.map(|param| {
(
match param.kind {
GenericParamDefKind::Lifetime => {
ParamKindOrd::Lifetime
}
GenericParamDefKind::Type { .. } => {
ParamKindOrd::Type
}
GenericParamDefKind::Const => {
ParamKindOrd::Const {
unordered: tcx
.sess
.features_untracked()
.const_generics,
}
}
},
param,
)
})
.collect::<Vec<(ParamKindOrd, GenericParamDef)>>();
param_types_present.sort_by_key(|(ord, _)| *ord);
let (mut param_types_present, ordered_params): (
Vec<ParamKindOrd>,
Vec<GenericParamDef>,
) = param_types_present.into_iter().unzip();
param_types_present.dedup();
Self::generic_arg_mismatch_err(
tcx.sess,
arg,
kind.descr(),
Some(&format!(
"reorder the arguments: {}: `<{}>`",
param_types_present
.into_iter()
.map(|ord| format!("{}s", ord.to_string()))
.collect::<Vec<String>>()
.join(", then "),
ordered_params
.into_iter()
.filter_map(|param| {
if param.name == kw::SelfUpper {
None
} else {
Some(param.name.to_string())
}
})
.collect::<Vec<String>>()
.join(", ")
)),
);
}
// We've reported the error, but we want to make sure that this
// problem doesn't bubble down and create additional, irrelevant
// errors. In this case, we're simply going to ignore the argument
// and any following arguments. The rest of the parameters will be
// inferred.
while args.next().is_some() {}
}
}
}
(Some(&arg), None) => {
// We should never be able to reach this point with well-formed input.
// There are three situations in which we can encounter this issue.
//
// 1. The number of arguments is incorrect. In this case, an error
// will already have been emitted, and we can ignore it.
// 2. There are late-bound lifetime parameters present, yet the
// lifetime arguments have also been explicitly specified by the
// user.
// 3. We've inferred some lifetimes, which have been provided later (i.e.
// after a type or const). We want to throw an error in this case.
if arg_count.correct.is_ok()
&& arg_count.explicit_late_bound == ExplicitLateBound::No
{
let kind = arg.descr();
assert_eq!(kind, "lifetime");
let provided =
force_infer_lt.expect("lifetimes ought to have been inferred");
Self::generic_arg_mismatch_err(tcx.sess, provided, kind, None);
}
break;
}
(None, Some(¶m)) => {
// If there are fewer arguments than parameters, it means
// we're inferring the remaining arguments.
substs.push(inferred_kind(Some(&substs), param, infer_args));
params.next();
}
(None, None) => break,
}
}
}
tcx.intern_substs(&substs)
}
/// Checks that the correct number of generic arguments have been provided.
/// Used specifically for function calls.
pub fn check_generic_arg_count_for_call(
tcx: TyCtxt<'_>,
span: Span,
def: &ty::Generics,
seg: &hir::PathSegment<'_>,
is_method_call: bool,
) -> GenericArgCountResult {
let empty_args = hir::GenericArgs::none();
let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
Self::check_generic_arg_count(
tcx,
span,
def,
if let Some(ref args) = seg.args { args } else { &empty_args },
if is_method_call { GenericArgPosition::MethodCall } else { GenericArgPosition::Value },
def.parent.is_none() && def.has_self, // `has_self`
seg.infer_args || suppress_mismatch, // `infer_args`
)
}
/// Checks that the correct number of generic arguments have been provided.
/// This is used both for datatypes and function calls.
pub(crate) fn check_generic_arg_count(
tcx: TyCtxt<'_>,
span: Span,
def: &ty::Generics,
args: &hir::GenericArgs<'_>,
position: GenericArgPosition,
has_self: bool,
infer_args: bool,
) -> GenericArgCountResult {
// At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
// that lifetimes will proceed types. So it suffices to check the number of each generic
// arguments in order to validate them with respect to the generic parameters.
let param_counts = def.own_counts();
let arg_counts = args.own_counts();
let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
let mut defaults: ty::GenericParamCount = Default::default();
for param in &def.params {
match param.kind {
GenericParamDefKind::Lifetime => {}
GenericParamDefKind::Type { has_default, .. } => {
defaults.types += has_default as usize
}
GenericParamDefKind::Const => {
// FIXME(const_generics:defaults)
}
};
}
if position != GenericArgPosition::Type && !args.bindings.is_empty() {
AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
}
let explicit_late_bound =
Self::prohibit_explicit_late_bound_lifetimes(tcx, def, args, position);
let check_kind_count = |kind,
required,
permitted,
provided,
offset,
unexpected_spans: &mut Vec<Span>,
silent| {
debug!(
"check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
kind, required, permitted, provided, offset
);
// We enforce the following: `required` <= `provided` <= `permitted`.
// For kinds without defaults (e.g.., lifetimes), `required == permitted`.
// For other kinds (i.e., types), `permitted` may be greater than `required`.
if required <= provided && provided <= permitted {
return Ok(());
}
if silent {
return Err((0i32, None));
}
// Unfortunately lifetime and type parameter mismatches are typically styled
// differently in diagnostics, which means we have a few cases to consider here.
let (bound, quantifier) = if required != permitted {
if provided < required {
(required, "at least ")
} else {
// provided > permitted
(permitted, "at most ")
}
} else {
(required, "")
};
let (spans, label) = if required == permitted && provided > permitted {
// In the case when the user has provided too many arguments,
// we want to point to the unexpected arguments.
let spans: Vec<Span> = args.args[offset + permitted..offset + provided]
.iter()
.map(|arg| arg.span())
.collect();
unexpected_spans.extend(spans.clone());
(spans, format!("unexpected {} argument", kind))
} else {
(
vec![span],
format!(
"expected {}{} {} argument{}",
quantifier,
bound,
kind,
pluralize!(bound),
),
)
};
let mut err = tcx.sess.struct_span_err_with_code(
spans.clone(),
&format!(
"wrong number of {} arguments: expected {}{}, found {}",
kind, quantifier, bound, provided,
),
DiagnosticId::Error("E0107".into()),
);
for span in spans {
err.span_label(span, label.as_str());
}
assert_ne!(bound, provided);
Err((bound as i32 - provided as i32, Some(err)))
};
let mut unexpected_spans = vec![];
let mut lifetime_count_correct = Ok(());
if !infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes {
lifetime_count_correct = check_kind_count(
"lifetime",
param_counts.lifetimes,
param_counts.lifetimes,
arg_counts.lifetimes,
0,
&mut unexpected_spans,
explicit_late_bound == ExplicitLateBound::Yes,
);
}
// FIXME(const_generics:defaults)
let mut const_count_correct = Ok(());
if !infer_args || arg_counts.consts > param_counts.consts {
const_count_correct = check_kind_count(
"const",
param_counts.consts,
param_counts.consts,
arg_counts.consts,
arg_counts.lifetimes + arg_counts.types,
&mut unexpected_spans,
false,
);
}
// Note that type errors are currently be emitted *after* const errors.
let mut type_count_correct = Ok(());
if !infer_args || arg_counts.types > param_counts.types - defaults.types - has_self as usize
{
type_count_correct = check_kind_count(
"type",
param_counts.types - defaults.types - has_self as usize,
param_counts.types - has_self as usize,
arg_counts.types,
arg_counts.lifetimes,
&mut unexpected_spans,
false,
);
}
// Emit a help message if it's possible that a type could be surrounded in braces
if let Err((c_mismatch, Some(ref mut _const_err))) = const_count_correct {
if let Err((_, Some(ref mut type_err))) = type_count_correct {
let possible_matches = args.args[arg_counts.lifetimes..]
.iter()
.filter(|arg| {
matches!(
arg,
GenericArg::Type(hir::Ty { kind: hir::TyKind::Path { .. }, .. })
)
})
.take(c_mismatch.max(0) as usize);
for arg in possible_matches {
let suggestions = vec![
(arg.span().shrink_to_lo(), String::from("{ ")),
(arg.span().shrink_to_hi(), String::from(" }")),
];
type_err.multipart_suggestion(
"If this generic argument was intended as a const parameter, \
try surrounding it with braces:",
suggestions,
Applicability::MaybeIncorrect,
);
}
}
}
let emit_correct =
|correct: Result<(), (_, Option<rustc_errors::DiagnosticBuilder<'_>>)>| match correct {
Ok(()) => Ok(()),
Err((_, None)) => Err(()),
Err((_, Some(mut err))) => {
err.emit();
Err(())
}
};
let arg_count_correct = emit_correct(lifetime_count_correct)
.and(emit_correct(const_count_correct))
.and(emit_correct(type_count_correct));
GenericArgCountResult {
explicit_late_bound,
correct: arg_count_correct.map_err(|()| GenericArgCountMismatch {
reported: Some(ErrorReported),
invalid_args: unexpected_spans,
}),
}
}
/// Report error if there is an explicit type parameter when using `impl Trait`.
pub(crate) fn check_impl_trait(
tcx: TyCtxt<'_>,
seg: &hir::PathSegment<'_>,
generics: &ty::Generics,
) -> bool {
let explicit = !seg.infer_args;
let impl_trait = generics.params.iter().any(|param| match param.kind {
ty::GenericParamDefKind::Type {
synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
..
} => true,
_ => false,
});
if explicit && impl_trait {
let spans = seg
.generic_args()
.args
.iter()
.filter_map(|arg| match arg {
GenericArg::Type(_) | GenericArg::Const(_) => Some(arg.span()),
_ => None,
})
.collect::<Vec<_>>();
let mut err = struct_span_err! {
tcx.sess,
spans.clone(),
E0632,
"cannot provide explicit generic arguments when `impl Trait` is \
used in argument position"
};
for span in spans {
err.span_label(span, "explicit generic argument not allowed");
}
err.emit();
}
impl_trait
}
/// Emits an error regarding forbidden type binding associations
pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
tcx.sess.emit_err(AssocTypeBindingNotAllowed { span });
}
/// Prohibits explicit lifetime arguments if late-bound lifetime parameters
/// are present. This is used both for datatypes and function calls.
pub(crate) fn prohibit_explicit_late_bound_lifetimes(
tcx: TyCtxt<'_>,
def: &ty::Generics,
args: &hir::GenericArgs<'_>,
position: GenericArgPosition,
) -> ExplicitLateBound {
let param_counts = def.own_counts();
let arg_counts = args.own_counts();
let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
if infer_lifetimes {
ExplicitLateBound::No
} else if let Some(span_late) = def.has_late_bound_regions {
let msg = "cannot specify lifetime arguments explicitly \
if late bound lifetime parameters are present";
let note = "the late bound lifetime parameter is introduced here";
let span = args.args[0].span();
if position == GenericArgPosition::Value
&& arg_counts.lifetimes != param_counts.lifetimes
{
let mut err = tcx.sess.struct_span_err(span, msg);
err.span_note(span_late, note);
err.emit();
} else {
let mut multispan = MultiSpan::from_span(span);
multispan.push_span_label(span_late, note.to_string());
tcx.struct_span_lint_hir(
LATE_BOUND_LIFETIME_ARGUMENTS,
args.args[0].id(),
multispan,
|lint| lint.build(msg).emit(),
);
}
ExplicitLateBound::Yes
} else {
ExplicitLateBound::No
}
}
}