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
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
//! Trait Resolution. See the [rustc guide] for more information on how this works.
//!
//! [rustc guide]: https://rust-lang.github.io/rustc-guide/traits/resolution.html

#[allow(dead_code)]
pub mod auto_trait;
mod chalk_fulfill;
pub mod codegen;
mod coherence;
mod engine;
pub mod error_reporting;
mod fulfill;
pub mod misc;
mod object_safety;
mod on_unimplemented;
mod project;
pub mod query;
mod select;
mod specialize;
mod structural_impls;
mod structural_match;
mod util;
pub mod wf;

use crate::infer::outlives::env::OutlivesEnvironment;
use crate::infer::{InferCtxt, SuppressRegionErrors};
use crate::middle::region;
use crate::mir::interpret::ErrorHandled;
use crate::ty::error::{ExpectedFound, TypeError};
use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
use crate::ty::subst::{InternalSubsts, SubstsRef};
use crate::ty::{self, AdtKind, GenericParamDefKind, List, ToPredicate, Ty, TyCtxt, WithConstness};
use crate::util::common::ErrorReported;
use chalk_engine;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_macros::HashStable;
use rustc_span::{Span, DUMMY_SP};
use syntax::ast;

use std::fmt::Debug;
use std::rc::Rc;

pub use self::FulfillmentErrorCode::*;
pub use self::ObligationCauseCode::*;
pub use self::SelectionError::*;
pub use self::Vtable::*;

pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls};
pub use self::coherence::{OrphanCheckErr, OverlapResult};
pub use self::engine::{TraitEngine, TraitEngineExt};
pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
pub use self::object_safety::astconv_object_safety_violations;
pub use self::object_safety::is_vtable_safe_method;
pub use self::object_safety::object_safety_violations;
pub use self::object_safety::MethodViolationCode;
pub use self::object_safety::ObjectSafetyViolation;
pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
pub use self::project::MismatchedProjectionTypes;
pub use self::project::{normalize, normalize_projection_type, poly_project_and_unify_type};
pub use self::project::{Normalized, ProjectionCache, ProjectionCacheSnapshot, Reveal};
pub use self::select::{EvaluationCache, SelectionCache, SelectionContext};
pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
pub use self::specialize::find_associated_item;
pub use self::specialize::specialization_graph::FutureCompatOverlapError;
pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
pub use self::specialize::{specialization_graph, translate_substs, OverlapError};
pub use self::structural_match::search_for_structural_match_violation;
pub use self::structural_match::type_marked_structural;
pub use self::structural_match::NonStructuralMatchTy;
pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs};
pub use self::util::{expand_trait_aliases, TraitAliasExpander};
pub use self::util::{
    get_vtable_index_of_object_method, impl_is_default, impl_item_is_final,
    predicate_for_trait_def, upcast_choices,
};
pub use self::util::{
    supertrait_def_ids, supertraits, transitive_bounds, SupertraitDefIds, Supertraits,
};

pub use self::chalk_fulfill::{
    CanonicalGoal as ChalkCanonicalGoal, FulfillmentContext as ChalkFulfillmentContext,
};

pub use self::FulfillmentErrorCode::*;
pub use self::ObligationCauseCode::*;
pub use self::SelectionError::*;
pub use self::Vtable::*;

/// Whether to enable bug compatibility with issue #43355.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum IntercrateMode {
    Issue43355,
    Fixed,
}

/// The mode that trait queries run in.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum TraitQueryMode {
    // Standard/un-canonicalized queries get accurate
    // spans etc. passed in and hence can do reasonable
    // error reporting on their own.
    Standard,
    // Canonicalized queries get dummy spans and hence
    // must generally propagate errors to
    // pre-canonicalization callsites.
    Canonical,
}

/// An `Obligation` represents some trait reference (e.g., `int: Eq`) for
/// which the vtable must be found. The process of finding a vtable is
/// called "resolving" the `Obligation`. This process consists of
/// either identifying an `impl` (e.g., `impl Eq for int`) that
/// provides the required vtable, or else finding a bound that is in
/// scope. The eventual result is usually a `Selection` (defined below).
#[derive(Clone, PartialEq, Eq, Hash)]
pub struct Obligation<'tcx, T> {
    /// The reason we have to prove this thing.
    pub cause: ObligationCause<'tcx>,

    /// The environment in which we should prove this thing.
    pub param_env: ty::ParamEnv<'tcx>,

    /// The thing we are trying to prove.
    pub predicate: T,

    /// If we started proving this as a result of trying to prove
    /// something else, track the total depth to ensure termination.
    /// If this goes over a certain threshold, we abort compilation --
    /// in such cases, we can not say whether or not the predicate
    /// holds for certain. Stupid halting problem; such a drag.
    pub recursion_depth: usize,
}

pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;

// `PredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger.
#[cfg(target_arch = "x86_64")]
static_assert_size!(PredicateObligation<'_>, 112);

/// The reason why we incurred this obligation; used for error reporting.
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct ObligationCause<'tcx> {
    pub span: Span,

    /// The ID of the fn body that triggered this obligation. This is
    /// used for region obligations to determine the precise
    /// environment in which the region obligation should be evaluated
    /// (in particular, closures can add new assumptions). See the
    /// field `region_obligations` of the `FulfillmentContext` for more
    /// information.
    pub body_id: hir::HirId,

    pub code: ObligationCauseCode<'tcx>,
}

impl ObligationCause<'_> {
    pub fn span(&self, tcx: TyCtxt<'_>) -> Span {
        match self.code {
            ObligationCauseCode::CompareImplMethodObligation { .. }
            | ObligationCauseCode::MainFunctionType
            | ObligationCauseCode::StartFunctionType => tcx.sess.source_map().def_span(self.span),
            ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
                arm_span,
                ..
            }) => arm_span,
            _ => self.span,
        }
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub enum ObligationCauseCode<'tcx> {
    /// Not well classified or should be obvious from the span.
    MiscObligation,

    /// A slice or array is WF only if `T: Sized`.
    SliceOrArrayElem,

    /// A tuple is WF only if its middle elements are `Sized`.
    TupleElem,

    /// This is the trait reference from the given projection.
    ProjectionWf(ty::ProjectionTy<'tcx>),

    /// In an impl of trait `X` for type `Y`, type `Y` must
    /// also implement all supertraits of `X`.
    ItemObligation(DefId),

    /// Like `ItemObligation`, but with extra detail on the source of the obligation.
    BindingObligation(DefId, Span),

    /// A type like `&'a T` is WF only if `T: 'a`.
    ReferenceOutlivesReferent(Ty<'tcx>),

    /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
    ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),

    /// Obligation incurred due to an object cast.
    ObjectCastObligation(/* Object type */ Ty<'tcx>),

    /// Obligation incurred due to a coercion.
    Coercion {
        source: Ty<'tcx>,
        target: Ty<'tcx>,
    },

    /// Various cases where expressions must be `Sized` / `Copy` / etc.
    /// `L = X` implies that `L` is `Sized`.
    AssignmentLhsSized,
    /// `(x1, .., xn)` must be `Sized`.
    TupleInitializerSized,
    /// `S { ... }` must be `Sized`.
    StructInitializerSized,
    /// Type of each variable must be `Sized`.
    VariableType(hir::HirId),
    /// Argument type must be `Sized`.
    SizedArgumentType,
    /// Return type must be `Sized`.
    SizedReturnType,
    /// Yield type must be `Sized`.
    SizedYieldType,
    /// `[T, ..n]` implies that `T` must be `Copy`.
    /// If `true`, suggest `const_in_array_repeat_expressions` feature flag.
    RepeatVec(bool),

    /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
    FieldSized {
        adt_kind: AdtKind,
        last: bool,
    },

    /// Constant expressions must be sized.
    ConstSized,

    /// `static` items must have `Sync` type.
    SharedStatic,

    BuiltinDerivedObligation(DerivedObligationCause<'tcx>),

    ImplDerivedObligation(DerivedObligationCause<'tcx>),

    /// Error derived when matching traits/impls; see ObligationCause for more details
    CompareImplMethodObligation {
        item_name: ast::Name,
        impl_item_def_id: DefId,
        trait_item_def_id: DefId,
    },

    /// Error derived when matching traits/impls; see ObligationCause for more details
    CompareImplTypeObligation {
        item_name: ast::Name,
        impl_item_def_id: DefId,
        trait_item_def_id: DefId,
    },

    /// Checking that this expression can be assigned where it needs to be
    // FIXME(eddyb) #11161 is the original Expr required?
    ExprAssignable,

    /// Computing common supertype in the arms of a match expression
    MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),

    /// Type error arising from type checking a pattern against an expected type.
    Pattern {
        /// The span of the scrutinee or type expression which caused the `root_ty` type.
        span: Option<Span>,
        /// The root expected type induced by a scrutinee or type expression.
        root_ty: Ty<'tcx>,
        /// Whether the `Span` came from an expression or a type expression.
        origin_expr: bool,
    },

    /// Constants in patterns must have `Structural` type.
    ConstPatternStructural,

    /// Computing common supertype in an if expression
    IfExpression(Box<IfExpressionCause>),

    /// Computing common supertype of an if expression with no else counter-part
    IfExpressionWithNoElse,

    /// `main` has wrong type
    MainFunctionType,

    /// `start` has wrong type
    StartFunctionType,

    /// Intrinsic has wrong type
    IntrinsicType,

    /// Method receiver
    MethodReceiver,

    /// `return` with no expression
    ReturnNoExpression,

    /// `return` with an expression
    ReturnValue(hir::HirId),

    /// Return type of this function
    ReturnType,

    /// Block implicit return
    BlockTailExpression(hir::HirId),

    /// #[feature(trivial_bounds)] is not enabled
    TrivialBound,

    AssocTypeBound(Box<AssocTypeBoundData>),
}

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct AssocTypeBoundData {
    pub impl_span: Option<Span>,
    pub original: Span,
    pub bounds: Vec<Span>,
}

// `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
#[cfg(target_arch = "x86_64")]
static_assert_size!(ObligationCauseCode<'_>, 32);

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct MatchExpressionArmCause<'tcx> {
    pub arm_span: Span,
    pub source: hir::MatchSource,
    pub prior_arms: Vec<Span>,
    pub last_ty: Ty<'tcx>,
    pub scrut_hir_id: hir::HirId,
}

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct IfExpressionCause {
    pub then: Span,
    pub outer: Option<Span>,
    pub semicolon: Option<Span>,
}

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct DerivedObligationCause<'tcx> {
    /// The trait reference of the parent obligation that led to the
    /// current obligation. Note that only trait obligations lead to
    /// derived obligations, so we just store the trait reference here
    /// directly.
    parent_trait_ref: ty::PolyTraitRef<'tcx>,

    /// The parent trait had this cause.
    parent_code: Rc<ObligationCauseCode<'tcx>>,
}

pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;

/// The following types:
/// * `WhereClause`,
/// * `WellFormed`,
/// * `FromEnv`,
/// * `DomainGoal`,
/// * `Goal`,
/// * `Clause`,
/// * `Environment`,
/// * `InEnvironment`,
/// are used for representing the trait system in the form of
/// logic programming clauses. They are part of the interface
/// for the chalk SLG solver.
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable, Lift)]
pub enum WhereClause<'tcx> {
    Implemented(ty::TraitPredicate<'tcx>),
    ProjectionEq(ty::ProjectionPredicate<'tcx>),
    RegionOutlives(ty::RegionOutlivesPredicate<'tcx>),
    TypeOutlives(ty::TypeOutlivesPredicate<'tcx>),
}

#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable, Lift)]
pub enum WellFormed<'tcx> {
    Trait(ty::TraitPredicate<'tcx>),
    Ty(Ty<'tcx>),
}

#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable, Lift)]
pub enum FromEnv<'tcx> {
    Trait(ty::TraitPredicate<'tcx>),
    Ty(Ty<'tcx>),
}

#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable, Lift)]
pub enum DomainGoal<'tcx> {
    Holds(WhereClause<'tcx>),
    WellFormed(WellFormed<'tcx>),
    FromEnv(FromEnv<'tcx>),
    Normalize(ty::ProjectionPredicate<'tcx>),
}

pub type PolyDomainGoal<'tcx> = ty::Binder<DomainGoal<'tcx>>;

#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum QuantifierKind {
    Universal,
    Existential,
}

#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable, Lift)]
pub enum GoalKind<'tcx> {
    Implies(Clauses<'tcx>, Goal<'tcx>),
    And(Goal<'tcx>, Goal<'tcx>),
    Not(Goal<'tcx>),
    DomainGoal(DomainGoal<'tcx>),
    Quantified(QuantifierKind, ty::Binder<Goal<'tcx>>),
    Subtype(Ty<'tcx>, Ty<'tcx>),
    CannotProve,
}

pub type Goal<'tcx> = &'tcx GoalKind<'tcx>;

pub type Goals<'tcx> = &'tcx List<Goal<'tcx>>;

impl<'tcx> DomainGoal<'tcx> {
    pub fn into_goal(self) -> GoalKind<'tcx> {
        GoalKind::DomainGoal(self)
    }

    pub fn into_program_clause(self) -> ProgramClause<'tcx> {
        ProgramClause {
            goal: self,
            hypotheses: ty::List::empty(),
            category: ProgramClauseCategory::Other,
        }
    }
}

impl<'tcx> GoalKind<'tcx> {
    pub fn from_poly_domain_goal(
        domain_goal: PolyDomainGoal<'tcx>,
        tcx: TyCtxt<'tcx>,
    ) -> GoalKind<'tcx> {
        match domain_goal.no_bound_vars() {
            Some(p) => p.into_goal(),
            None => GoalKind::Quantified(
                QuantifierKind::Universal,
                domain_goal.map_bound(|p| tcx.mk_goal(p.into_goal())),
            ),
        }
    }
}

/// This matches the definition from Page 7 of "A Proof Procedure for the Logic of Hereditary
/// Harrop Formulas".
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable)]
pub enum Clause<'tcx> {
    Implies(ProgramClause<'tcx>),
    ForAll(ty::Binder<ProgramClause<'tcx>>),
}

impl Clause<'tcx> {
    pub fn category(self) -> ProgramClauseCategory {
        match self {
            Clause::Implies(clause) => clause.category,
            Clause::ForAll(clause) => clause.skip_binder().category,
        }
    }
}

/// Multiple clauses.
pub type Clauses<'tcx> = &'tcx List<Clause<'tcx>>;

/// A "program clause" has the form `D :- G1, ..., Gn`. It is saying
/// that the domain goal `D` is true if `G1...Gn` are provable. This
/// is equivalent to the implication `G1..Gn => D`; we usually write
/// it with the reverse implication operator `:-` to emphasize the way
/// that programs are actually solved (via backchaining, which starts
/// with the goal to solve and proceeds from there).
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable)]
pub struct ProgramClause<'tcx> {
    /// This goal will be considered true ...
    pub goal: DomainGoal<'tcx>,

    /// ... if we can prove these hypotheses (there may be no hypotheses at all):
    pub hypotheses: Goals<'tcx>,

    /// Useful for filtering clauses.
    pub category: ProgramClauseCategory,
}

#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum ProgramClauseCategory {
    ImpliedBound,
    WellFormed,
    Other,
}

/// A set of clauses that we assume to be true.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable)]
pub struct Environment<'tcx> {
    pub clauses: Clauses<'tcx>,
}

impl Environment<'tcx> {
    pub fn with<G>(self, goal: G) -> InEnvironment<'tcx, G> {
        InEnvironment { environment: self, goal }
    }
}

/// Something (usually a goal), along with an environment.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable)]
pub struct InEnvironment<'tcx, G> {
    pub environment: Environment<'tcx>,
    pub goal: G,
}

pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;

#[derive(Clone, Debug, TypeFoldable)]
pub enum SelectionError<'tcx> {
    Unimplemented,
    OutputTypeParameterMismatch(
        ty::PolyTraitRef<'tcx>,
        ty::PolyTraitRef<'tcx>,
        ty::error::TypeError<'tcx>,
    ),
    TraitNotObjectSafe(DefId),
    ConstEvalFailure(ErrorHandled),
    Overflow,
}

pub struct FulfillmentError<'tcx> {
    pub obligation: PredicateObligation<'tcx>,
    pub code: FulfillmentErrorCode<'tcx>,
    /// Diagnostics only: we opportunistically change the `code.span` when we encounter an
    /// obligation error caused by a call argument. When this is the case, we also signal that in
    /// this field to ensure accuracy of suggestions.
    pub points_at_arg_span: bool,
}

#[derive(Clone)]
pub enum FulfillmentErrorCode<'tcx> {
    CodeSelectionError(SelectionError<'tcx>),
    CodeProjectionError(MismatchedProjectionTypes<'tcx>),
    CodeSubtypeError(ExpectedFound<Ty<'tcx>>, TypeError<'tcx>), // always comes from a SubtypePredicate
    CodeAmbiguity,
}

/// When performing resolution, it is typically the case that there
/// can be one of three outcomes:
///
/// - `Ok(Some(r))`: success occurred with result `r`
/// - `Ok(None)`: could not definitely determine anything, usually due
///   to inconclusive type inference.
/// - `Err(e)`: error `e` occurred
pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;

/// Given the successful resolution of an obligation, the `Vtable`
/// indicates where the vtable comes from. Note that while we call this
/// a "vtable", it does not necessarily indicate dynamic dispatch at
/// runtime. `Vtable` instances just tell the compiler where to find
/// methods, but in generic code those methods are typically statically
/// dispatched -- only when an object is constructed is a `Vtable`
/// instance reified into an actual vtable.
///
/// For example, the vtable may be tied to a specific impl (case A),
/// or it may be relative to some bound that is in scope (case B).
///
/// ```
/// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
/// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
/// impl Clone for int { ... }             // Impl_3
///
/// fn foo<T:Clone>(concrete: Option<Box<int>>,
///                 param: T,
///                 mixed: Option<T>) {
///
///    // Case A: Vtable points at a specific impl. Only possible when
///    // type is concretely known. If the impl itself has bounded
///    // type parameters, Vtable will carry resolutions for those as well:
///    concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
///
///    // Case B: Vtable must be provided by caller. This applies when
///    // type is a type parameter.
///    param.clone();    // VtableParam
///
///    // Case C: A mix of cases A and B.
///    mixed.clone();    // Vtable(Impl_1, [VtableParam])
/// }
/// ```
///
/// ### The type parameter `N`
///
/// See explanation on `VtableImplData`.
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub enum Vtable<'tcx, N> {
    /// Vtable identifying a particular impl.
    VtableImpl(VtableImplData<'tcx, N>),

    /// Vtable for auto trait implementations.
    /// This carries the information and nested obligations with regards
    /// to an auto implementation for a trait `Trait`. The nested obligations
    /// ensure the trait implementation holds for all the constituent types.
    VtableAutoImpl(VtableAutoImplData<N>),

    /// Successful resolution to an obligation provided by the caller
    /// for some type parameter. The `Vec<N>` represents the
    /// obligations incurred from normalizing the where-clause (if
    /// any).
    VtableParam(Vec<N>),

    /// Virtual calls through an object.
    VtableObject(VtableObjectData<'tcx, N>),

    /// Successful resolution for a builtin trait.
    VtableBuiltin(VtableBuiltinData<N>),

    /// Vtable automatically generated for a closure. The `DefId` is the ID
    /// of the closure expression. This is a `VtableImpl` in spirit, but the
    /// impl is generated by the compiler and does not appear in the source.
    VtableClosure(VtableClosureData<'tcx, N>),

    /// Same as above, but for a function pointer type with the given signature.
    VtableFnPointer(VtableFnPointerData<'tcx, N>),

    /// Vtable automatically generated for a generator.
    VtableGenerator(VtableGeneratorData<'tcx, N>),

    /// Vtable for a trait alias.
    VtableTraitAlias(VtableTraitAliasData<'tcx, N>),
}

/// Identifies a particular impl in the source, along with a set of
/// substitutions from the impl's type/lifetime parameters. The
/// `nested` vector corresponds to the nested obligations attached to
/// the impl's type parameters.
///
/// The type parameter `N` indicates the type used for "nested
/// obligations" that are required by the impl. During type-check, this
/// is `Obligation`, as one might expect. During codegen, however, this
/// is `()`, because codegen only requires a shallow resolution of an
/// impl, and nested obligations are satisfied later.
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub struct VtableImplData<'tcx, N> {
    pub impl_def_id: DefId,
    pub substs: SubstsRef<'tcx>,
    pub nested: Vec<N>,
}

#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub struct VtableGeneratorData<'tcx, N> {
    pub generator_def_id: DefId,
    pub substs: SubstsRef<'tcx>,
    /// Nested obligations. This can be non-empty if the generator
    /// signature contains associated types.
    pub nested: Vec<N>,
}

#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub struct VtableClosureData<'tcx, N> {
    pub closure_def_id: DefId,
    pub substs: SubstsRef<'tcx>,
    /// Nested obligations. This can be non-empty if the closure
    /// signature contains associated types.
    pub nested: Vec<N>,
}

#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub struct VtableAutoImplData<N> {
    pub trait_def_id: DefId,
    pub nested: Vec<N>,
}

#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub struct VtableBuiltinData<N> {
    pub nested: Vec<N>,
}

/// A vtable for some object-safe trait `Foo` automatically derived
/// for the object type `Foo`.
#[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub struct VtableObjectData<'tcx, N> {
    /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
    pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,

    /// The vtable is formed by concatenating together the method lists of
    /// the base object trait and all supertraits; this is the start of
    /// `upcast_trait_ref`'s methods in that vtable.
    pub vtable_base: usize,

    pub nested: Vec<N>,
}

#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub struct VtableFnPointerData<'tcx, N> {
    pub fn_ty: Ty<'tcx>,
    pub nested: Vec<N>,
}

#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
pub struct VtableTraitAliasData<'tcx, N> {
    pub alias_def_id: DefId,
    pub substs: SubstsRef<'tcx>,
    pub nested: Vec<N>,
}

/// Creates predicate obligations from the generic bounds.
pub fn predicates_for_generics<'tcx>(
    cause: ObligationCause<'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    generic_bounds: &ty::InstantiatedPredicates<'tcx>,
) -> PredicateObligations<'tcx> {
    util::predicates_for_generics(cause, 0, param_env, generic_bounds)
}

/// Determines whether the type `ty` is known to meet `bound` and
/// returns true if so. Returns false if `ty` either does not meet
/// `bound` or is not known to meet bound (note that this is
/// conservative towards *no impl*, which is the opposite of the
/// `evaluate` methods).
pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
    infcx: &InferCtxt<'a, 'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    ty: Ty<'tcx>,
    def_id: DefId,
    span: Span,
) -> bool {
    debug!(
        "type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
        ty,
        infcx.tcx.def_path_str(def_id)
    );

    let trait_ref = ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) };
    let obligation = Obligation {
        param_env,
        cause: ObligationCause::misc(span, hir::DUMMY_HIR_ID),
        recursion_depth: 0,
        predicate: trait_ref.without_const().to_predicate(),
    };

    let result = infcx.predicate_must_hold_modulo_regions(&obligation);
    debug!(
        "type_known_to_meet_ty={:?} bound={} => {:?}",
        ty,
        infcx.tcx.def_path_str(def_id),
        result
    );

    if result && (ty.has_infer_types() || ty.has_closure_types()) {
        // Because of inference "guessing", selection can sometimes claim
        // to succeed while the success requires a guess. To ensure
        // this function's result remains infallible, we must confirm
        // that guess. While imperfect, I believe this is sound.

        // The handling of regions in this area of the code is terrible,
        // see issue #29149. We should be able to improve on this with
        // NLL.
        let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();

        // We can use a dummy node-id here because we won't pay any mind
        // to region obligations that arise (there shouldn't really be any
        // anyhow).
        let cause = ObligationCause::misc(span, hir::DUMMY_HIR_ID);

        fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);

        // Note: we only assume something is `Copy` if we can
        // *definitively* show that it implements `Copy`. Otherwise,
        // assume it is move; linear is always ok.
        match fulfill_cx.select_all_or_error(infcx) {
            Ok(()) => {
                debug!(
                    "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
                    ty,
                    infcx.tcx.def_path_str(def_id)
                );
                true
            }
            Err(e) => {
                debug!(
                    "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} errors={:?}",
                    ty,
                    infcx.tcx.def_path_str(def_id),
                    e
                );
                false
            }
        }
    } else {
        result
    }
}

fn do_normalize_predicates<'tcx>(
    tcx: TyCtxt<'tcx>,
    region_context: DefId,
    cause: ObligationCause<'tcx>,
    elaborated_env: ty::ParamEnv<'tcx>,
    predicates: Vec<ty::Predicate<'tcx>>,
) -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported> {
    debug!(
        "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
        predicates, region_context, cause,
    );
    let span = cause.span;
    tcx.infer_ctxt().enter(|infcx| {
        // FIXME. We should really... do something with these region
        // obligations. But this call just continues the older
        // behavior (i.e., doesn't cause any new bugs), and it would
        // take some further refactoring to actually solve them. In
        // particular, we would have to handle implied bounds
        // properly, and that code is currently largely confined to
        // regionck (though I made some efforts to extract it
        // out). -nmatsakis
        //
        // @arielby: In any case, these obligations are checked
        // by wfcheck anyway, so I'm not sure we have to check
        // them here too, and we will remove this function when
        // we move over to lazy normalization *anyway*.
        let fulfill_cx = FulfillmentContext::new_ignoring_regions();
        let predicates =
            match fully_normalize(&infcx, fulfill_cx, cause, elaborated_env, &predicates) {
                Ok(predicates) => predicates,
                Err(errors) => {
                    infcx.report_fulfillment_errors(&errors, None, false);
                    return Err(ErrorReported);
                }
            };

        debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);

        let region_scope_tree = region::ScopeTree::default();

        // We can use the `elaborated_env` here; the region code only
        // cares about declarations like `'a: 'b`.
        let outlives_env = OutlivesEnvironment::new(elaborated_env);

        infcx.resolve_regions_and_report_errors(
            region_context,
            &region_scope_tree,
            &outlives_env,
            SuppressRegionErrors::default(),
        );

        let predicates = match infcx.fully_resolve(&predicates) {
            Ok(predicates) => predicates,
            Err(fixup_err) => {
                // If we encounter a fixup error, it means that some type
                // variable wound up unconstrained. I actually don't know
                // if this can happen, and I certainly don't expect it to
                // happen often, but if it did happen it probably
                // represents a legitimate failure due to some kind of
                // unconstrained variable, and it seems better not to ICE,
                // all things considered.
                tcx.sess.span_err(span, &fixup_err.to_string());
                return Err(ErrorReported);
            }
        };
        if predicates.has_local_value() {
            // FIXME: shouldn't we, you know, actually report an error here? or an ICE?
            Err(ErrorReported)
        } else {
            Ok(predicates)
        }
    })
}

// FIXME: this is gonna need to be removed ...
/// Normalizes the parameter environment, reporting errors if they occur.
pub fn normalize_param_env_or_error<'tcx>(
    tcx: TyCtxt<'tcx>,
    region_context: DefId,
    unnormalized_env: ty::ParamEnv<'tcx>,
    cause: ObligationCause<'tcx>,
) -> ty::ParamEnv<'tcx> {
    // I'm not wild about reporting errors here; I'd prefer to
    // have the errors get reported at a defined place (e.g.,
    // during typeck). Instead I have all parameter
    // environments, in effect, going through this function
    // and hence potentially reporting errors. This ensures of
    // course that we never forget to normalize (the
    // alternative seemed like it would involve a lot of
    // manual invocations of this fn -- and then we'd have to
    // deal with the errors at each of those sites).
    //
    // In any case, in practice, typeck constructs all the
    // parameter environments once for every fn as it goes,
    // and errors will get reported then; so after typeck we
    // can be sure that no errors should occur.

    debug!(
        "normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
        region_context, unnormalized_env, cause
    );

    let mut predicates: Vec<_> =
        util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec()).collect();

    debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);

    let elaborated_env = ty::ParamEnv::new(
        tcx.intern_predicates(&predicates),
        unnormalized_env.reveal,
        unnormalized_env.def_id,
    );

    // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
    // normalization expects its param-env to be already normalized, which means we have
    // a circularity.
    //
    // The way we handle this is by normalizing the param-env inside an unnormalized version
    // of the param-env, which means that if the param-env contains unnormalized projections,
    // we'll have some normalization failures. This is unfortunate.
    //
    // Lazy normalization would basically handle this by treating just the
    // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
    //
    // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
    // types, so to make the situation less bad, we normalize all the predicates *but*
    // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
    // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
    //
    // This works fairly well because trait matching  does not actually care about param-env
    // TypeOutlives predicates - these are normally used by regionck.
    let outlives_predicates: Vec<_> = predicates
        .drain_filter(|predicate| match predicate {
            ty::Predicate::TypeOutlives(..) => true,
            _ => false,
        })
        .collect();

    debug!(
        "normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
        predicates, outlives_predicates
    );
    let non_outlives_predicates = match do_normalize_predicates(
        tcx,
        region_context,
        cause.clone(),
        elaborated_env,
        predicates,
    ) {
        Ok(predicates) => predicates,
        // An unnormalized env is better than nothing.
        Err(ErrorReported) => {
            debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
            return elaborated_env;
        }
    };

    debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);

    // Not sure whether it is better to include the unnormalized TypeOutlives predicates
    // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
    // predicates here anyway. Keeping them here anyway because it seems safer.
    let outlives_env: Vec<_> =
        non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
    let outlives_env =
        ty::ParamEnv::new(tcx.intern_predicates(&outlives_env), unnormalized_env.reveal, None);
    let outlives_predicates = match do_normalize_predicates(
        tcx,
        region_context,
        cause,
        outlives_env,
        outlives_predicates,
    ) {
        Ok(predicates) => predicates,
        // An unnormalized env is better than nothing.
        Err(ErrorReported) => {
            debug!("normalize_param_env_or_error: errored resolving outlives predicates");
            return elaborated_env;
        }
    };
    debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);

    let mut predicates = non_outlives_predicates;
    predicates.extend(outlives_predicates);
    debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
    ty::ParamEnv::new(
        tcx.intern_predicates(&predicates),
        unnormalized_env.reveal,
        unnormalized_env.def_id,
    )
}

pub fn fully_normalize<'a, 'tcx, T>(
    infcx: &InferCtxt<'a, 'tcx>,
    mut fulfill_cx: FulfillmentContext<'tcx>,
    cause: ObligationCause<'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    value: &T,
) -> Result<T, Vec<FulfillmentError<'tcx>>>
where
    T: TypeFoldable<'tcx>,
{
    debug!("fully_normalize_with_fulfillcx(value={:?})", value);
    let selcx = &mut SelectionContext::new(infcx);
    let Normalized { value: normalized_value, obligations } =
        project::normalize(selcx, param_env, cause, value);
    debug!(
        "fully_normalize: normalized_value={:?} obligations={:?}",
        normalized_value, obligations
    );
    for obligation in obligations {
        fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
    }

    debug!("fully_normalize: select_all_or_error start");
    fulfill_cx.select_all_or_error(infcx)?;
    debug!("fully_normalize: select_all_or_error complete");
    let resolved_value = infcx.resolve_vars_if_possible(&normalized_value);
    debug!("fully_normalize: resolved_value={:?}", resolved_value);
    Ok(resolved_value)
}

/// Normalizes the predicates and checks whether they hold in an empty
/// environment. If this returns false, then either normalize
/// encountered an error or one of the predicates did not hold. Used
/// when creating vtables to check for unsatisfiable methods.
pub fn normalize_and_test_predicates<'tcx>(
    tcx: TyCtxt<'tcx>,
    predicates: Vec<ty::Predicate<'tcx>>,
) -> bool {
    debug!("normalize_and_test_predicates(predicates={:?})", predicates);

    let result = tcx.infer_ctxt().enter(|infcx| {
        let param_env = ty::ParamEnv::reveal_all();
        let mut selcx = SelectionContext::new(&infcx);
        let mut fulfill_cx = FulfillmentContext::new();
        let cause = ObligationCause::dummy();
        let Normalized { value: predicates, obligations } =
            normalize(&mut selcx, param_env, cause.clone(), &predicates);
        for obligation in obligations {
            fulfill_cx.register_predicate_obligation(&infcx, obligation);
        }
        for predicate in predicates {
            let obligation = Obligation::new(cause.clone(), param_env, predicate);
            fulfill_cx.register_predicate_obligation(&infcx, obligation);
        }

        fulfill_cx.select_all_or_error(&infcx).is_ok()
    });
    debug!("normalize_and_test_predicates(predicates={:?}) = {:?}", predicates, result);
    result
}

fn substitute_normalize_and_test_predicates<'tcx>(
    tcx: TyCtxt<'tcx>,
    key: (DefId, SubstsRef<'tcx>),
) -> bool {
    debug!("substitute_normalize_and_test_predicates(key={:?})", key);

    let predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
    let result = normalize_and_test_predicates(tcx, predicates);

    debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}", key, result);
    result
}

/// Given a trait `trait_ref`, iterates the vtable entries
/// that come from `trait_ref`, including its supertraits.
#[inline] // FIXME(#35870): avoid closures being unexported due to `impl Trait`.
fn vtable_methods<'tcx>(
    tcx: TyCtxt<'tcx>,
    trait_ref: ty::PolyTraitRef<'tcx>,
) -> &'tcx [Option<(DefId, SubstsRef<'tcx>)>] {
    debug!("vtable_methods({:?})", trait_ref);

    tcx.arena.alloc_from_iter(supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
        let trait_methods = tcx
            .associated_items(trait_ref.def_id())
            .filter(|item| item.kind == ty::AssocKind::Method);

        // Now list each method's DefId and InternalSubsts (for within its trait).
        // If the method can never be called from this object, produce None.
        trait_methods.map(move |trait_method| {
            debug!("vtable_methods: trait_method={:?}", trait_method);
            let def_id = trait_method.def_id;

            // Some methods cannot be called on an object; skip those.
            if !is_vtable_safe_method(tcx, trait_ref.def_id(), &trait_method) {
                debug!("vtable_methods: not vtable safe");
                return None;
            }

            // The method may have some early-bound lifetimes; add regions for those.
            let substs = trait_ref.map_bound(|trait_ref| {
                InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
                    GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
                    GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
                        trait_ref.substs[param.index as usize]
                    }
                })
            });

            // The trait type may have higher-ranked lifetimes in it;
            // erase them if they appear, so that we get the type
            // at some particular call site.
            let substs =
                tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &substs);

            // It's possible that the method relies on where-clauses that
            // do not hold for this particular set of type parameters.
            // Note that this method could then never be called, so we
            // do not want to try and codegen it, in that case (see #23435).
            let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
            if !normalize_and_test_predicates(tcx, predicates.predicates) {
                debug!("vtable_methods: predicates do not hold");
                return None;
            }

            Some((def_id, substs))
        })
    }))
}

impl<'tcx, O> Obligation<'tcx, O> {
    pub fn new(
        cause: ObligationCause<'tcx>,
        param_env: ty::ParamEnv<'tcx>,
        predicate: O,
    ) -> Obligation<'tcx, O> {
        Obligation { cause, param_env, recursion_depth: 0, predicate }
    }

    fn with_depth(
        cause: ObligationCause<'tcx>,
        recursion_depth: usize,
        param_env: ty::ParamEnv<'tcx>,
        predicate: O,
    ) -> Obligation<'tcx, O> {
        Obligation { cause, param_env, recursion_depth, predicate }
    }

    pub fn misc(
        span: Span,
        body_id: hir::HirId,
        param_env: ty::ParamEnv<'tcx>,
        trait_ref: O,
    ) -> Obligation<'tcx, O> {
        Obligation::new(ObligationCause::misc(span, body_id), param_env, trait_ref)
    }

    pub fn with<P>(&self, value: P) -> Obligation<'tcx, P> {
        Obligation {
            cause: self.cause.clone(),
            param_env: self.param_env,
            recursion_depth: self.recursion_depth,
            predicate: value,
        }
    }
}

impl<'tcx> ObligationCause<'tcx> {
    #[inline]
    pub fn new(
        span: Span,
        body_id: hir::HirId,
        code: ObligationCauseCode<'tcx>,
    ) -> ObligationCause<'tcx> {
        ObligationCause { span, body_id, code }
    }

    pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
        ObligationCause { span, body_id, code: MiscObligation }
    }

    pub fn dummy() -> ObligationCause<'tcx> {
        ObligationCause { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation }
    }
}

impl ObligationCauseCode<'_> {
    // Return the base obligation, ignoring derived obligations.
    pub fn peel_derives(&self) -> &Self {
        let mut base_cause = self;
        while let BuiltinDerivedObligation(cause) | ImplDerivedObligation(cause) = base_cause {
            base_cause = &cause.parent_code;
        }
        base_cause
    }
}

impl<'tcx, N> Vtable<'tcx, N> {
    pub fn nested_obligations(self) -> Vec<N> {
        match self {
            VtableImpl(i) => i.nested,
            VtableParam(n) => n,
            VtableBuiltin(i) => i.nested,
            VtableAutoImpl(d) => d.nested,
            VtableClosure(c) => c.nested,
            VtableGenerator(c) => c.nested,
            VtableObject(d) => d.nested,
            VtableFnPointer(d) => d.nested,
            VtableTraitAlias(d) => d.nested,
        }
    }

    pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M>
    where
        F: FnMut(N) -> M,
    {
        match self {
            VtableImpl(i) => VtableImpl(VtableImplData {
                impl_def_id: i.impl_def_id,
                substs: i.substs,
                nested: i.nested.into_iter().map(f).collect(),
            }),
            VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
            VtableBuiltin(i) => {
                VtableBuiltin(VtableBuiltinData { nested: i.nested.into_iter().map(f).collect() })
            }
            VtableObject(o) => VtableObject(VtableObjectData {
                upcast_trait_ref: o.upcast_trait_ref,
                vtable_base: o.vtable_base,
                nested: o.nested.into_iter().map(f).collect(),
            }),
            VtableAutoImpl(d) => VtableAutoImpl(VtableAutoImplData {
                trait_def_id: d.trait_def_id,
                nested: d.nested.into_iter().map(f).collect(),
            }),
            VtableClosure(c) => VtableClosure(VtableClosureData {
                closure_def_id: c.closure_def_id,
                substs: c.substs,
                nested: c.nested.into_iter().map(f).collect(),
            }),
            VtableGenerator(c) => VtableGenerator(VtableGeneratorData {
                generator_def_id: c.generator_def_id,
                substs: c.substs,
                nested: c.nested.into_iter().map(f).collect(),
            }),
            VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
                fn_ty: p.fn_ty,
                nested: p.nested.into_iter().map(f).collect(),
            }),
            VtableTraitAlias(d) => VtableTraitAlias(VtableTraitAliasData {
                alias_def_id: d.alias_def_id,
                substs: d.substs,
                nested: d.nested.into_iter().map(f).collect(),
            }),
        }
    }
}

impl<'tcx> FulfillmentError<'tcx> {
    fn new(
        obligation: PredicateObligation<'tcx>,
        code: FulfillmentErrorCode<'tcx>,
    ) -> FulfillmentError<'tcx> {
        FulfillmentError { obligation: obligation, code: code, points_at_arg_span: false }
    }
}

impl<'tcx> TraitObligation<'tcx> {
    fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
        self.predicate.map_bound(|p| p.self_ty())
    }
}

pub fn provide(providers: &mut ty::query::Providers<'_>) {
    misc::provide(providers);
    *providers = ty::query::Providers {
        is_object_safe: object_safety::is_object_safe_provider,
        specialization_graph_of: specialize::specialization_graph_provider,
        specializes: specialize::specializes,
        codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
        vtable_methods,
        substitute_normalize_and_test_predicates,
        ..*providers
    };
}

pub trait ExClauseFold<'tcx>
where
    Self: chalk_engine::context::Context + Clone,
{
    fn fold_ex_clause_with<F: TypeFolder<'tcx>>(
        ex_clause: &chalk_engine::ExClause<Self>,
        folder: &mut F,
    ) -> chalk_engine::ExClause<Self>;

    fn visit_ex_clause_with<V: TypeVisitor<'tcx>>(
        ex_clause: &chalk_engine::ExClause<Self>,
        visitor: &mut V,
    ) -> bool;
}

pub trait ChalkContextLift<'tcx>
where
    Self: chalk_engine::context::Context + Clone,
{
    type LiftedExClause: Debug + 'tcx;
    type LiftedDelayedLiteral: Debug + 'tcx;
    type LiftedLiteral: Debug + 'tcx;

    fn lift_ex_clause_to_tcx(
        ex_clause: &chalk_engine::ExClause<Self>,
        tcx: TyCtxt<'tcx>,
    ) -> Option<Self::LiftedExClause>;

    fn lift_delayed_literal_to_tcx(
        ex_clause: &chalk_engine::DelayedLiteral<Self>,
        tcx: TyCtxt<'tcx>,
    ) -> Option<Self::LiftedDelayedLiteral>;

    fn lift_literal_to_tcx(
        ex_clause: &chalk_engine::Literal<Self>,
        tcx: TyCtxt<'tcx>,
    ) -> Option<Self::LiftedLiteral>;
}