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
/*!

# typeck: check phase

Within the check phase of type check, we check each item one at a time
(bodies of function expressions are checked as part of the containing
function). Inference is used to supply types wherever they are unknown.

By far the most complex case is checking the body of a function. This
can be broken down into several distinct phases:

- gather: creates type variables to represent the type of each local
  variable and pattern binding.

- main: the main pass does the lion's share of the work: it
  determines the types of all expressions, resolves
  methods, checks for most invalid conditions, and so forth. In
  some cases, where a type is unknown, it may create a type or region
  variable and use that as the type of an expression.

  In the process of checking, various constraints will be placed on
  these type variables through the subtyping relationships requested
  through the `demand` module. The `infer` module is in charge
  of resolving those constraints.

- regionck: after main is complete, the regionck pass goes over all
  types looking for regions and making sure that they did not escape
  into places where they are not in scope. This may also influence the
  final assignments of the various region variables if there is some
  flexibility.

- writeback: writes the final types within a function body, replacing
  type variables with their final inferred types. These final types
  are written into the `tcx.node_types` table, which should *never* contain
  any reference to a type variable.

## Intermediate types

While type checking a function, the intermediate types for the
expressions, blocks, and so forth contained within the function are
stored in `fcx.node_types` and `fcx.node_args`. These types
may contain unresolved type variables. After type checking is
complete, the functions in the writeback module are used to take the
types from this table, resolve them, and then write them into their
permanent home in the type context `tcx`.

This means that during inferencing you should use `fcx.write_ty()`
and `fcx.expr_ty()` / `fcx.node_ty()` to write/obtain the types of
nodes within the function.

The types of top-level items, which never contain unbound type
variables, are stored directly into the `tcx` typeck_results.

N.B., a type variable is not the same thing as a type parameter. A
type variable is an instance of a type parameter. That is,
given a generic function `fn foo<T>(t: T)`, while checking the
function `foo`, the type `ty_param(0)` refers to the type `T`, which
is treated in abstract. However, when `foo()` is called, `T` will be
instantiated with a fresh type variable `N`. This variable will
eventually be resolved to some concrete type (which might itself be
a type parameter).

*/

mod check;
mod compare_impl_item;
pub mod dropck;
mod entry;
mod errs;
pub mod intrinsic;
pub mod intrinsicck;
mod region;
pub mod wfcheck;

pub use check::check_abi;

use std::num::NonZero;

use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
use rustc_errors::ErrorGuaranteed;
use rustc_errors::{pluralize, struct_span_code_err, Diag};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::intravisit::Visitor;
use rustc_index::bit_set::BitSet;
use rustc_infer::error_reporting::infer::ObligationCauseExt as _;
use rustc_infer::infer::outlives::env::OutlivesEnvironment;
use rustc_infer::infer::{self, TyCtxtInferExt as _};
use rustc_infer::traits::ObligationCause;
use rustc_middle::query::Providers;
use rustc_middle::ty::error::{ExpectedFound, TypeError};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::ty::{GenericArgs, GenericArgsRef};
use rustc_middle::{bug, span_bug};
use rustc_session::parse::feature_err;
use rustc_span::symbol::{kw, sym, Ident};
use rustc_span::{def_id::CRATE_DEF_ID, BytePos, Span, Symbol, DUMMY_SP};
use rustc_target::abi::VariantIdx;
use rustc_target::spec::abi::Abi;
use rustc_trait_selection::error_reporting::traits::suggestions::{
    ReturnsVisitor, TypeErrCtxtExt as _,
};
use rustc_trait_selection::error_reporting::traits::TypeErrCtxtExt as _;
use rustc_trait_selection::traits::ObligationCtxt;

use crate::errors;
use crate::require_c_abi_if_c_variadic;

use self::compare_impl_item::collect_return_position_impl_trait_in_trait_tys;
use self::region::region_scope_tree;

pub fn provide(providers: &mut Providers) {
    wfcheck::provide(providers);
    *providers = Providers {
        adt_destructor,
        adt_async_destructor,
        region_scope_tree,
        collect_return_position_impl_trait_in_trait_tys,
        compare_impl_const: compare_impl_item::compare_impl_const_raw,
        check_coroutine_obligations: check::check_coroutine_obligations,
        ..*providers
    };
}

fn adt_destructor(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::Destructor> {
    tcx.calculate_dtor(def_id.to_def_id(), dropck::check_drop_impl)
}

fn adt_async_destructor(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::AsyncDestructor> {
    tcx.calculate_async_dtor(def_id.to_def_id(), dropck::check_drop_impl)
}

/// Given a `DefId` for an opaque type in return position, find its parent item's return
/// expressions.
fn get_owner_return_paths(
    tcx: TyCtxt<'_>,
    def_id: LocalDefId,
) -> Option<(LocalDefId, ReturnsVisitor<'_>)> {
    let hir_id = tcx.local_def_id_to_hir_id(def_id);
    let parent_id = tcx.hir().get_parent_item(hir_id).def_id;
    tcx.hir_node_by_def_id(parent_id).body_id().map(|body_id| {
        let body = tcx.hir().body(body_id);
        let mut visitor = ReturnsVisitor::default();
        visitor.visit_body(body);
        (parent_id, visitor)
    })
}

/// Forbid defining intrinsics in Rust code,
/// as they must always be defined by the compiler.
// FIXME: Move this to a more appropriate place.
pub fn forbid_intrinsic_abi(tcx: TyCtxt<'_>, sp: Span, abi: Abi) {
    if let Abi::RustIntrinsic = abi {
        tcx.dcx().span_err(sp, "intrinsic must be in `extern \"rust-intrinsic\" { ... }` block");
    }
}

fn maybe_check_static_with_link_section(tcx: TyCtxt<'_>, id: LocalDefId) {
    // Only restricted on wasm target for now
    if !tcx.sess.target.is_like_wasm {
        return;
    }

    // If `#[link_section]` is missing, then nothing to verify
    let attrs = tcx.codegen_fn_attrs(id);
    if attrs.link_section.is_none() {
        return;
    }

    // For the wasm32 target statics with `#[link_section]` are placed into custom
    // sections of the final output file, but this isn't link custom sections of
    // other executable formats. Namely we can only embed a list of bytes,
    // nothing with provenance (pointers to anything else). If any provenance
    // show up, reject it here.
    // `#[link_section]` may contain arbitrary, or even undefined bytes, but it is
    // the consumer's responsibility to ensure all bytes that have been read
    // have defined values.
    if let Ok(alloc) = tcx.eval_static_initializer(id.to_def_id())
        && alloc.inner().provenance().ptrs().len() != 0
    {
        let msg = "statics with a custom `#[link_section]` must be a \
                        simple list of bytes on the wasm target with no \
                        extra levels of indirection such as references";
        tcx.dcx().span_err(tcx.def_span(id), msg);
    }
}

fn report_forbidden_specialization(tcx: TyCtxt<'_>, impl_item: DefId, parent_impl: DefId) {
    let span = tcx.def_span(impl_item);
    let ident = tcx.item_name(impl_item);

    let err = match tcx.span_of_impl(parent_impl) {
        Ok(sp) => errors::ImplNotMarkedDefault::Ok { span, ident, ok_label: sp },
        Err(cname) => errors::ImplNotMarkedDefault::Err { span, ident, cname },
    };

    tcx.dcx().emit_err(err);
}

fn missing_items_err(
    tcx: TyCtxt<'_>,
    impl_def_id: LocalDefId,
    missing_items: &[ty::AssocItem],
    full_impl_span: Span,
) {
    let missing_items =
        missing_items.iter().filter(|trait_item| !trait_item.is_impl_trait_in_trait());

    let missing_items_msg = missing_items
        .clone()
        .map(|trait_item| trait_item.name.to_string())
        .collect::<Vec<_>>()
        .join("`, `");

    let sugg_sp = if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(full_impl_span)
        && snippet.ends_with("}")
    {
        // `Span` before impl block closing brace.
        let hi = full_impl_span.hi() - BytePos(1);
        // Point at the place right before the closing brace of the relevant `impl` to suggest
        // adding the associated item at the end of its body.
        full_impl_span.with_lo(hi).with_hi(hi)
    } else {
        full_impl_span.shrink_to_hi()
    };

    // Obtain the level of indentation ending in `sugg_sp`.
    let padding =
        tcx.sess.source_map().indentation_before(sugg_sp).unwrap_or_else(|| String::new());
    let (mut missing_trait_item, mut missing_trait_item_none, mut missing_trait_item_label) =
        (Vec::new(), Vec::new(), Vec::new());

    for &trait_item in missing_items {
        let snippet = suggestion_signature(
            tcx,
            trait_item,
            tcx.impl_trait_ref(impl_def_id).unwrap().instantiate_identity(),
        );
        let code = format!("{padding}{snippet}\n{padding}");
        if let Some(span) = tcx.hir().span_if_local(trait_item.def_id) {
            missing_trait_item_label
                .push(errors::MissingTraitItemLabel { span, item: trait_item.name });
            missing_trait_item.push(errors::MissingTraitItemSuggestion {
                span: sugg_sp,
                code,
                snippet,
            });
        } else {
            missing_trait_item_none.push(errors::MissingTraitItemSuggestionNone {
                span: sugg_sp,
                code,
                snippet,
            })
        }
    }

    tcx.dcx().emit_err(errors::MissingTraitItem {
        span: tcx.span_of_impl(impl_def_id.to_def_id()).unwrap(),
        missing_items_msg,
        missing_trait_item_label,
        missing_trait_item,
        missing_trait_item_none,
    });
}

fn missing_items_must_implement_one_of_err(
    tcx: TyCtxt<'_>,
    impl_span: Span,
    missing_items: &[Ident],
    annotation_span: Option<Span>,
) {
    let missing_items_msg =
        missing_items.iter().map(Ident::to_string).collect::<Vec<_>>().join("`, `");

    tcx.dcx().emit_err(errors::MissingOneOfTraitItem {
        span: impl_span,
        note: annotation_span,
        missing_items_msg,
    });
}

fn default_body_is_unstable(
    tcx: TyCtxt<'_>,
    impl_span: Span,
    item_did: DefId,
    feature: Symbol,
    reason: Option<Symbol>,
    issue: Option<NonZero<u32>>,
) {
    let missing_item_name = tcx.associated_item(item_did).name;
    let (mut some_note, mut none_note, mut reason_str) = (false, false, String::new());
    match reason {
        Some(r) => {
            some_note = true;
            reason_str = r.to_string();
        }
        None => none_note = true,
    };

    let mut err = tcx.dcx().create_err(errors::MissingTraitItemUnstable {
        span: impl_span,
        some_note,
        none_note,
        missing_item_name,
        feature,
        reason: reason_str,
    });

    let inject_span = item_did
        .as_local()
        .and_then(|id| tcx.crate_level_attribute_injection_span(tcx.local_def_id_to_hir_id(id)));
    rustc_session::parse::add_feature_diagnostics_for_issue(
        &mut err,
        &tcx.sess,
        feature,
        rustc_feature::GateIssue::Library(issue),
        false,
        inject_span,
    );

    err.emit();
}

/// Re-sugar `ty::GenericPredicates` in a way suitable to be used in structured suggestions.
fn bounds_from_generic_predicates<'tcx>(
    tcx: TyCtxt<'tcx>,
    predicates: impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>,
) -> (String, String) {
    let mut types: FxIndexMap<Ty<'tcx>, Vec<DefId>> = FxIndexMap::default();
    let mut projections = vec![];
    for (predicate, _) in predicates {
        debug!("predicate {:?}", predicate);
        let bound_predicate = predicate.kind();
        match bound_predicate.skip_binder() {
            ty::ClauseKind::Trait(trait_predicate) => {
                let entry = types.entry(trait_predicate.self_ty()).or_default();
                let def_id = trait_predicate.def_id();
                if Some(def_id) != tcx.lang_items().sized_trait() {
                    // Type params are `Sized` by default, do not add that restriction to the list
                    // if it is a positive requirement.
                    entry.push(trait_predicate.def_id());
                }
            }
            ty::ClauseKind::Projection(projection_pred) => {
                projections.push(bound_predicate.rebind(projection_pred));
            }
            _ => {}
        }
    }

    let mut where_clauses = vec![];
    let mut types_str = vec![];
    for (ty, bounds) in types {
        if let ty::Param(_) = ty.kind() {
            let mut bounds_str = vec![];
            for bound in bounds {
                let mut projections_str = vec![];
                for projection in &projections {
                    let p = projection.skip_binder();
                    if bound == tcx.parent(p.projection_term.def_id)
                        && p.projection_term.self_ty() == ty
                    {
                        let name = tcx.item_name(p.projection_term.def_id);
                        projections_str.push(format!("{} = {}", name, p.term));
                    }
                }
                let bound_def_path = tcx.def_path_str(bound);
                if projections_str.is_empty() {
                    where_clauses.push(format!("{}: {}", ty, bound_def_path));
                } else {
                    bounds_str.push(format!("{}<{}>", bound_def_path, projections_str.join(", ")));
                }
            }
            if bounds_str.is_empty() {
                types_str.push(ty.to_string());
            } else {
                types_str.push(format!("{}: {}", ty, bounds_str.join(" + ")));
            }
        } else {
            // Avoid suggesting the following:
            // fn foo<T, <T as Trait>::Bar>(_: T) where T: Trait, <T as Trait>::Bar: Other {}
            where_clauses.extend(
                bounds.into_iter().map(|bound| format!("{}: {}", ty, tcx.def_path_str(bound))),
            );
        }
    }

    let generics =
        if types_str.is_empty() { "".to_string() } else { format!("<{}>", types_str.join(", ")) };

    let where_clauses = if where_clauses.is_empty() {
        "".to_string()
    } else {
        format!(" where {}", where_clauses.join(", "))
    };

    (generics, where_clauses)
}

/// Return placeholder code for the given function.
fn fn_sig_suggestion<'tcx>(
    tcx: TyCtxt<'tcx>,
    sig: ty::FnSig<'tcx>,
    ident: Ident,
    predicates: impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>,
    assoc: ty::AssocItem,
) -> String {
    let args = sig
        .inputs()
        .iter()
        .enumerate()
        .map(|(i, ty)| {
            Some(match ty.kind() {
                ty::Param(_) if assoc.fn_has_self_parameter && i == 0 => "self".to_string(),
                ty::Ref(reg, ref_ty, mutability) if i == 0 => {
                    let reg = format!("{reg} ");
                    let reg = match &reg[..] {
                        "'_ " | " " => "",
                        reg => reg,
                    };
                    if assoc.fn_has_self_parameter {
                        match ref_ty.kind() {
                            ty::Param(param) if param.name == kw::SelfUpper => {
                                format!("&{}{}self", reg, mutability.prefix_str())
                            }

                            _ => format!("self: {ty}"),
                        }
                    } else {
                        format!("_: {ty}")
                    }
                }
                _ => {
                    if assoc.fn_has_self_parameter && i == 0 {
                        format!("self: {ty}")
                    } else {
                        format!("_: {ty}")
                    }
                }
            })
        })
        .chain(std::iter::once(if sig.c_variadic { Some("...".to_string()) } else { None }))
        .flatten()
        .collect::<Vec<String>>()
        .join(", ");
    let mut output = sig.output();

    let asyncness = if tcx.asyncness(assoc.def_id).is_async() {
        output = if let ty::Alias(_, alias_ty) = *output.kind() {
            tcx.explicit_item_super_predicates(alias_ty.def_id)
                .iter_instantiated_copied(tcx, alias_ty.args)
                .find_map(|(bound, _)| {
                    bound.as_projection_clause()?.no_bound_vars()?.term.as_type()
                })
                .unwrap_or_else(|| {
                    span_bug!(
                        ident.span,
                        "expected async fn to have `impl Future` output, but it returns {output}"
                    )
                })
        } else {
            span_bug!(
                ident.span,
                "expected async fn to have `impl Future` output, but it returns {output}"
            )
        };
        "async "
    } else {
        ""
    };

    let output = if !output.is_unit() { format!(" -> {output}") } else { String::new() };

    let safety = sig.safety.prefix_str();
    let (generics, where_clauses) = bounds_from_generic_predicates(tcx, predicates);

    // FIXME: this is not entirely correct, as the lifetimes from borrowed params will
    // not be present in the `fn` definition, not will we account for renamed
    // lifetimes between the `impl` and the `trait`, but this should be good enough to
    // fill in a significant portion of the missing code, and other subsequent
    // suggestions can help the user fix the code.
    format!("{safety}{asyncness}fn {ident}{generics}({args}){output}{where_clauses} {{ todo!() }}")
}

/// Return placeholder code for the given associated item.
/// Similar to `ty::AssocItem::suggestion`, but appropriate for use as the code snippet of a
/// structured suggestion.
fn suggestion_signature<'tcx>(
    tcx: TyCtxt<'tcx>,
    assoc: ty::AssocItem,
    impl_trait_ref: ty::TraitRef<'tcx>,
) -> String {
    let args = ty::GenericArgs::identity_for_item(tcx, assoc.def_id).rebase_onto(
        tcx,
        assoc.container_id(tcx),
        impl_trait_ref.with_self_ty(tcx, tcx.types.self_param).args,
    );

    match assoc.kind {
        ty::AssocKind::Fn => fn_sig_suggestion(
            tcx,
            tcx.liberate_late_bound_regions(
                assoc.def_id,
                tcx.fn_sig(assoc.def_id).instantiate(tcx, args),
            ),
            assoc.ident(tcx),
            tcx.predicates_of(assoc.def_id).instantiate_own(tcx, args),
            assoc,
        ),
        ty::AssocKind::Type => {
            let (generics, where_clauses) = bounds_from_generic_predicates(
                tcx,
                tcx.predicates_of(assoc.def_id).instantiate_own(tcx, args),
            );
            format!("type {}{generics} = /* Type */{where_clauses};", assoc.name)
        }
        ty::AssocKind::Const => {
            let ty = tcx.type_of(assoc.def_id).instantiate_identity();
            let val = tcx
                .infer_ctxt()
                .build()
                .err_ctxt()
                .ty_kind_suggestion(tcx.param_env(assoc.def_id), ty)
                .unwrap_or_else(|| "value".to_string());
            format!("const {}: {} = {};", assoc.name, ty, val)
        }
    }
}

/// Emit an error when encountering two or more variants in a transparent enum.
fn bad_variant_count<'tcx>(tcx: TyCtxt<'tcx>, adt: ty::AdtDef<'tcx>, sp: Span, did: DefId) {
    let variant_spans: Vec<_> = adt
        .variants()
        .iter()
        .map(|variant| tcx.hir().span_if_local(variant.def_id).unwrap())
        .collect();
    let (mut spans, mut many) = (Vec::new(), None);
    if let [start @ .., end] = &*variant_spans {
        spans = start.to_vec();
        many = Some(*end);
    }
    tcx.dcx().emit_err(errors::TransparentEnumVariant {
        span: sp,
        spans,
        many,
        number: adt.variants().len(),
        path: tcx.def_path_str(did),
    });
}

/// Emit an error when encountering two or more non-zero-sized fields in a transparent
/// enum.
fn bad_non_zero_sized_fields<'tcx>(
    tcx: TyCtxt<'tcx>,
    adt: ty::AdtDef<'tcx>,
    field_count: usize,
    field_spans: impl Iterator<Item = Span>,
    sp: Span,
) {
    if adt.is_enum() {
        tcx.dcx().emit_err(errors::TransparentNonZeroSizedEnum {
            span: sp,
            spans: field_spans.collect(),
            field_count,
            desc: adt.descr(),
        });
    } else {
        tcx.dcx().emit_err(errors::TransparentNonZeroSized {
            span: sp,
            spans: field_spans.collect(),
            field_count,
            desc: adt.descr(),
        });
    }
}

// FIXME: Consider moving this method to a more fitting place.
pub fn potentially_plural_count(count: usize, word: &str) -> String {
    format!("{} {}{}", count, word, pluralize!(count))
}

pub fn check_function_signature<'tcx>(
    tcx: TyCtxt<'tcx>,
    mut cause: ObligationCause<'tcx>,
    fn_id: DefId,
    expected_sig: ty::PolyFnSig<'tcx>,
) -> Result<(), ErrorGuaranteed> {
    fn extract_span_for_error_reporting<'tcx>(
        tcx: TyCtxt<'tcx>,
        err: TypeError<'_>,
        cause: &ObligationCause<'tcx>,
        fn_id: LocalDefId,
    ) -> rustc_span::Span {
        let mut args = {
            let node = tcx.expect_hir_owner_node(fn_id);
            let decl = node.fn_decl().unwrap_or_else(|| bug!("expected fn decl, found {:?}", node));
            decl.inputs.iter().map(|t| t.span).chain(std::iter::once(decl.output.span()))
        };

        match err {
            TypeError::ArgumentMutability(i)
            | TypeError::ArgumentSorts(ExpectedFound { .. }, i) => args.nth(i).unwrap(),
            _ => cause.span(),
        }
    }

    let local_id = fn_id.as_local().unwrap_or(CRATE_DEF_ID);

    let param_env = ty::ParamEnv::empty();

    let infcx = &tcx.infer_ctxt().build();
    let ocx = ObligationCtxt::new_with_diagnostics(infcx);

    let actual_sig = tcx.fn_sig(fn_id).instantiate_identity();

    let norm_cause = ObligationCause::misc(cause.span, local_id);
    let actual_sig = ocx.normalize(&norm_cause, param_env, actual_sig);

    match ocx.eq(&cause, param_env, expected_sig, actual_sig) {
        Ok(()) => {
            let errors = ocx.select_all_or_error();
            if !errors.is_empty() {
                return Err(infcx.err_ctxt().report_fulfillment_errors(errors));
            }
        }
        Err(err) => {
            let err_ctxt = infcx.err_ctxt();
            if fn_id.is_local() {
                cause.span = extract_span_for_error_reporting(tcx, err, &cause, local_id);
            }
            let failure_code = cause.as_failure_code_diag(err, cause.span, vec![]);
            let mut diag = tcx.dcx().create_err(failure_code);
            err_ctxt.note_type_err(
                &mut diag,
                &cause,
                None,
                Some(infer::ValuePairs::PolySigs(ExpectedFound {
                    expected: expected_sig,
                    found: actual_sig,
                })),
                err,
                false,
                false,
            );
            return Err(diag.emit());
        }
    }

    let outlives_env = OutlivesEnvironment::new(param_env);
    if let Err(e) = ocx.resolve_regions_and_report_errors(local_id, &outlives_env) {
        return Err(e);
    }

    Ok(())
}