compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

   1 use crate::coercion::CoerceMany;
   2 use crate::fn_ctxt::arg_matrix::{ArgMatrix, Compatibility, Error, ExpectedIdx, ProvidedIdx};
   3 use crate::gather_locals::Declaration;
   4 use crate::method::MethodCallee;
   5 use crate::Expectation::*;
   6 use crate::TupleArgumentsFlag::*;
   7 use crate::{
   8     struct_span_err, BreakableCtxt, Diverges, Expectation, FnCtxt, LocalTy, Needs, RawTy,
   9     TupleArgumentsFlag,
  10 };
  11 use rustc_ast as ast;
  12 use rustc_data_structures::fx::FxIndexSet;
  13 use rustc_errors::{pluralize, Applicability, Diagnostic, DiagnosticId, MultiSpan};
  14 use rustc_hir as hir;
  15 use rustc_hir::def::{CtorOf, DefKind, Res};
  16 use rustc_hir::def_id::DefId;
  17 use rustc_hir::{ExprKind, Node, QPath};
  18 use rustc_hir_analysis::astconv::AstConv;
  19 use rustc_hir_analysis::check::intrinsicck::InlineAsmCtxt;
  20 use rustc_hir_analysis::check::potentially_plural_count;
  21 use rustc_hir_analysis::structured_errors::StructuredDiagnostic;
  22 use rustc_index::vec::IndexVec;
  23 use rustc_infer::infer::error_reporting::{FailureCode, ObligationCauseExt};
  24 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  25 use rustc_infer::infer::InferOk;
  26 use rustc_infer::infer::TypeTrace;
  27 use rustc_middle::ty::adjustment::AllowTwoPhase;
  28 use rustc_middle::ty::visit::TypeVisitable;
  29 use rustc_middle::ty::{self, DefIdTree, IsSuggestable, Ty, TypeSuperVisitable, TypeVisitor};
  30 use rustc_session::Session;
  31 use rustc_span::symbol::{kw, Ident};
  32 use rustc_span::{self, sym, Span};
  33 use rustc_trait_selection::traits::{self, ObligationCauseCode, SelectionContext};
  34
  35 use std::iter;
  36 use std::mem;
  37 use std::ops::ControlFlow;
  38 use std::slice;
  39
  40 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  41     pub(in super::super) fn check_casts(&mut self) {
  42         // don't hold the borrow to deferred_cast_checks while checking to avoid borrow checker errors
  43         // when writing to `self.param_env`.
  44         let mut deferred_cast_checks = mem::take(&mut *self.deferred_cast_checks.borrow_mut());
  45
  46         debug!("FnCtxt::check_casts: {} deferred checks", deferred_cast_checks.len());
  47         for cast in deferred_cast_checks.drain(..) {
  48             let prev_env = self.param_env;
  49             self.param_env = self.param_env.with_constness(cast.constness);
  50
  51             cast.check(self);
  52
  53             self.param_env = prev_env;
  54         }
  55
  56         *self.deferred_cast_checks.borrow_mut() = deferred_cast_checks;
  57     }
  58
  59     pub(in super::super) fn check_transmutes(&self) {
  60         let mut deferred_transmute_checks = self.deferred_transmute_checks.borrow_mut();
  61         debug!("FnCtxt::check_transmutes: {} deferred checks", deferred_transmute_checks.len());
  62         for (from, to, hir_id) in deferred_transmute_checks.drain(..) {
  63             self.check_transmute(from, to, hir_id);
  64         }
  65     }
  66
  67     pub(in super::super) fn check_asms(&self) {
  68         let mut deferred_asm_checks = self.deferred_asm_checks.borrow_mut();
  69         debug!("FnCtxt::check_asm: {} deferred checks", deferred_asm_checks.len());
  70         for (asm, hir_id) in deferred_asm_checks.drain(..) {
  71             let enclosing_id = self.tcx.hir().enclosing_body_owner(hir_id);
  72             let get_operand_ty = |expr| {
  73                 let ty = self.typeck_results.borrow().expr_ty_adjusted(expr);
  74                 let ty = self.resolve_vars_if_possible(ty);
  75                 if ty.has_non_region_infer() {
  76                     self.tcx.ty_error()
  77                 } else {
  78                     self.tcx.erase_regions(ty)
  79                 }
  80             };
  81             InlineAsmCtxt::new_in_fn(self.tcx, self.param_env, get_operand_ty)
  82                 .check_asm(asm, self.tcx.hir().local_def_id_to_hir_id(enclosing_id));
  83         }
  84     }
  85
  86     pub(in super::super) fn check_method_argument_types(
  87         &self,
  88         sp: Span,
  89         expr: &'tcx hir::Expr<'tcx>,
  90         method: Result<MethodCallee<'tcx>, ()>,
  91         args_no_rcvr: &'tcx [hir::Expr<'tcx>],
  92         tuple_arguments: TupleArgumentsFlag,
  93         expected: Expectation<'tcx>,
  94     ) -> Ty<'tcx> {
  95         let has_error = match method {
  96             Ok(method) => method.substs.references_error() || method.sig.references_error(),
  97             Err(_) => true,
  98         };
  99         if has_error {
 100             let err_inputs = self.err_args(args_no_rcvr.len());
 101
 102             let err_inputs = match tuple_arguments {
 103                 DontTupleArguments => err_inputs,
 104                 TupleArguments => vec![self.tcx.intern_tup(&err_inputs)],
 105             };
 106
 107             self.check_argument_types(
 108                 sp,
 109                 expr,
 110                 &err_inputs,
 111                 None,
 112                 args_no_rcvr,
 113                 false,
 114                 tuple_arguments,
 115                 method.ok().map(|method| method.def_id),
 116             );
 117             return self.tcx.ty_error();
 118         }
 119
 120         let method = method.unwrap();
 121         // HACK(eddyb) ignore self in the definition (see above).
 122         let expected_input_tys = self.expected_inputs_for_expected_output(
 123             sp,
 124             expected,
 125             method.sig.output(),
 126             &method.sig.inputs()[1..],
 127         );
 128         self.check_argument_types(
 129             sp,
 130             expr,
 131             &method.sig.inputs()[1..],
 132             expected_input_tys,
 133             args_no_rcvr,
 134             method.sig.c_variadic,
 135             tuple_arguments,
 136             Some(method.def_id),
 137         );
 138
 139         method.sig.output()
 140     }
 141
 142     /// Generic function that factors out common logic from function calls,
 143     /// method calls and overloaded operators.
 144     pub(in super::super) fn check_argument_types(
 145         &self,
 146         // Span enclosing the call site
 147         call_span: Span,
 148         // Expression of the call site
 149         call_expr: &'tcx hir::Expr<'tcx>,
 150         // Types (as defined in the *signature* of the target function)
 151         formal_input_tys: &[Ty<'tcx>],
 152         // More specific expected types, after unifying with caller output types
 153         expected_input_tys: Option<Vec<Ty<'tcx>>>,
 154         // The expressions for each provided argument
 155         provided_args: &'tcx [hir::Expr<'tcx>],
 156         // Whether the function is variadic, for example when imported from C
 157         c_variadic: bool,
 158         // Whether the arguments have been bundled in a tuple (ex: closures)
 159         tuple_arguments: TupleArgumentsFlag,
 160         // The DefId for the function being called, for better error messages
 161         fn_def_id: Option<DefId>,
 162     ) {
 163         let tcx = self.tcx;
 164
 165         // Conceptually, we've got some number of expected inputs, and some number of provided arguments
 166         // and we can form a grid of whether each argument could satisfy a given input:
 167         //      in1 | in2 | in3 | ...
 168         // arg1  ?  |     |     |
 169         // arg2     |  ?  |     |
 170         // arg3     |     |  ?  |
 171         // ...
 172         // Initially, we just check the diagonal, because in the case of correct code
 173         // these are the only checks that matter
 174         // However, in the unhappy path, we'll fill in this whole grid to attempt to provide
 175         // better error messages about invalid method calls.
 176
 177         // All the input types from the fn signature must outlive the call
 178         // so as to validate implied bounds.
 179         for (&fn_input_ty, arg_expr) in iter::zip(formal_input_tys, provided_args) {
 180             self.register_wf_obligation(fn_input_ty.into(), arg_expr.span, traits::MiscObligation);
 181         }
 182
 183         let mut err_code = "E0061";
 184
 185         // If the arguments should be wrapped in a tuple (ex: closures), unwrap them here
 186         let (formal_input_tys, expected_input_tys) = if tuple_arguments == TupleArguments {
 187             let tuple_type = self.structurally_resolved_type(call_span, formal_input_tys[0]);
 188             match tuple_type.kind() {
 189                 // We expected a tuple and got a tuple
 190                 ty::Tuple(arg_types) => {
 191                     // Argument length differs
 192                     if arg_types.len() != provided_args.len() {
 193                         err_code = "E0057";
 194                     }
 195                     let expected_input_tys = match expected_input_tys {
 196                         Some(expected_input_tys) => match expected_input_tys.get(0) {
 197                             Some(ty) => match ty.kind() {
 198                                 ty::Tuple(tys) => Some(tys.iter().collect()),
 199                                 _ => None,
 200                             },
 201                             None => None,
 202                         },
 203                         None => None,
 204                     };
 205                     (arg_types.iter().collect(), expected_input_tys)
 206                 }
 207                 _ => {
 208                     // Otherwise, there's a mismatch, so clear out what we're expecting, and set
 209                     // our input types to err_args so we don't blow up the error messages
 210                     struct_span_err!(
 211                         tcx.sess,
 212                         call_span,
 213                         E0059,
 214                         "cannot use call notation; the first type parameter \
 215                          for the function trait is neither a tuple nor unit"
 216                     )
 217                     .emit();
 218                     (self.err_args(provided_args.len()), None)
 219                 }
 220             }
 221         } else {
 222             (formal_input_tys.to_vec(), expected_input_tys)
 223         };
 224
 225         // If there are no external expectations at the call site, just use the types from the function defn
 226         let expected_input_tys = if let Some(expected_input_tys) = expected_input_tys {
 227             assert_eq!(expected_input_tys.len(), formal_input_tys.len());
 228             expected_input_tys
 229         } else {
 230             formal_input_tys.clone()
 231         };
 232
 233         let minimum_input_count = expected_input_tys.len();
 234         let provided_arg_count = provided_args.len();
 235
 236         let is_const_eval_select = matches!(fn_def_id, Some(def_id) if
 237             self.tcx.def_kind(def_id) == hir::def::DefKind::Fn
 238             && self.tcx.is_intrinsic(def_id)
 239             && self.tcx.item_name(def_id) == sym::const_eval_select);
 240
 241         // We introduce a helper function to demand that a given argument satisfy a given input
 242         // This is more complicated than just checking type equality, as arguments could be coerced
 243         // This version writes those types back so further type checking uses the narrowed types
 244         let demand_compatible = |idx| {
 245             let formal_input_ty: Ty<'tcx> = formal_input_tys[idx];
 246             let expected_input_ty: Ty<'tcx> = expected_input_tys[idx];
 247             let provided_arg = &provided_args[idx];
 248
 249             debug!("checking argument {}: {:?} = {:?}", idx, provided_arg, formal_input_ty);
 250
 251             // We're on the happy path here, so we'll do a more involved check and write back types
 252             // To check compatibility, we'll do 3 things:
 253             // 1. Unify the provided argument with the expected type
 254             let expectation = Expectation::rvalue_hint(self, expected_input_ty);
 255
 256             let checked_ty = self.check_expr_with_expectation(provided_arg, expectation);
 257
 258             // 2. Coerce to the most detailed type that could be coerced
 259             //    to, which is `expected_ty` if `rvalue_hint` returns an
 260             //    `ExpectHasType(expected_ty)`, or the `formal_ty` otherwise.
 261             let coerced_ty = expectation.only_has_type(self).unwrap_or(formal_input_ty);
 262
 263             // Cause selection errors caused by resolving a single argument to point at the
 264             // argument and not the call. This lets us customize the span pointed to in the
 265             // fulfillment error to be more accurate.
 266             let coerced_ty = self.resolve_vars_with_obligations(coerced_ty);
 267
 268             let coerce_error = self
 269                 .try_coerce(provided_arg, checked_ty, coerced_ty, AllowTwoPhase::Yes, None)
 270                 .err();
 271
 272             if coerce_error.is_some() {
 273                 return Compatibility::Incompatible(coerce_error);
 274             }
 275
 276             // Check that second and third argument of `const_eval_select` must be `FnDef`, and additionally that
 277             // the second argument must be `const fn`. The first argument must be a tuple, but this is already expressed
 278             // in the function signature (`F: FnOnce<ARG>`), so I did not bother to add another check here.
 279             //
 280             // This check is here because there is currently no way to express a trait bound for `FnDef` types only.
 281             if is_const_eval_select && (1..=2).contains(&idx) {
 282                 if let ty::FnDef(def_id, _) = checked_ty.kind() {
 283                     if idx == 1 && !self.tcx.is_const_fn_raw(*def_id) {
 284                         self.tcx
 285                             .sess
 286                             .struct_span_err(provided_arg.span, "this argument must be a `const fn`")
 287                             .help("consult the documentation on `const_eval_select` for more information")
 288                             .emit();
 289                     }
 290                 } else {
 291                     self.tcx
 292                         .sess
 293                         .struct_span_err(provided_arg.span, "this argument must be a function item")
 294                         .note(format!("expected a function item, found {checked_ty}"))
 295                         .help(
 296                             "consult the documentation on `const_eval_select` for more information",
 297                         )
 298                         .emit();
 299                 }
 300             }
 301
 302             // 3. Check if the formal type is a supertype of the checked one
 303             //    and register any such obligations for future type checks
 304             let supertype_error = self
 305                 .at(&self.misc(provided_arg.span), self.param_env)
 306                 .sup(formal_input_ty, coerced_ty);
 307             let subtyping_error = match supertype_error {
 308                 Ok(InferOk { obligations, value: () }) => {
 309                     self.register_predicates(obligations);
 310                     None
 311                 }
 312                 Err(err) => Some(err),
 313             };
 314
 315             // If neither check failed, the types are compatible
 316             match subtyping_error {
 317                 None => Compatibility::Compatible,
 318                 Some(_) => Compatibility::Incompatible(subtyping_error),
 319             }
 320         };
 321
 322         // To start, we only care "along the diagonal", where we expect every
 323         // provided arg to be in the right spot
 324         let mut compatibility_diagonal =
 325             vec![Compatibility::Incompatible(None); provided_args.len()];
 326
 327         // Keep track of whether we *could possibly* be satisfied, i.e. whether we're on the happy path
 328         // if the wrong number of arguments were supplied, we CAN'T be satisfied,
 329         // and if we're c_variadic, the supplied arguments must be >= the minimum count from the function
 330         // otherwise, they need to be identical, because rust doesn't currently support variadic functions
 331         let mut call_appears_satisfied = if c_variadic {
 332             provided_arg_count >= minimum_input_count
 333         } else {
 334             provided_arg_count == minimum_input_count
 335         };
 336
 337         // Check the arguments.
 338         // We do this in a pretty awful way: first we type-check any arguments
 339         // that are not closures, then we type-check the closures. This is so
 340         // that we have more information about the types of arguments when we
 341         // type-check the functions. This isn't really the right way to do this.
 342         for check_closures in [false, true] {
 343             // More awful hacks: before we check argument types, try to do
 344             // an "opportunistic" trait resolution of any trait bounds on
 345             // the call. This helps coercions.
 346             if check_closures {
 347                 self.select_obligations_where_possible(|_| {})
 348             }
 349
 350             // Check each argument, to satisfy the input it was provided for
 351             // Visually, we're traveling down the diagonal of the compatibility matrix
 352             for (idx, arg) in provided_args.iter().enumerate() {
 353                 // Warn only for the first loop (the "no closures" one).
 354                 // Closure arguments themselves can't be diverging, but
 355                 // a previous argument can, e.g., `foo(panic!(), || {})`.
 356                 if !check_closures {
 357                     self.warn_if_unreachable(arg.hir_id, arg.span, "expression");
 358                 }
 359
 360                 // For C-variadic functions, we don't have a declared type for all of
 361                 // the arguments hence we only do our usual type checking with
 362                 // the arguments who's types we do know. However, we *can* check
 363                 // for unreachable expressions (see above).
 364                 // FIXME: unreachable warning current isn't emitted
 365                 if idx >= minimum_input_count {
 366                     continue;
 367                 }
 368
 369                 let is_closure = matches!(arg.kind, ExprKind::Closure { .. });
 370                 if is_closure != check_closures {
 371                     continue;
 372                 }
 373
 374                 let compatible = demand_compatible(idx);
 375                 let is_compatible = matches!(compatible, Compatibility::Compatible);
 376                 compatibility_diagonal[idx] = compatible;
 377
 378                 if !is_compatible {
 379                     call_appears_satisfied = false;
 380                 }
 381             }
 382         }
 383
 384         if c_variadic && provided_arg_count < minimum_input_count {
 385             err_code = "E0060";
 386         }
 387
 388         for arg in provided_args.iter().skip(minimum_input_count) {
 389             // Make sure we've checked this expr at least once.
 390             let arg_ty = self.check_expr(&arg);
 391
 392             // If the function is c-style variadic, we skipped a bunch of arguments
 393             // so we need to check those, and write out the types
 394             // Ideally this would be folded into the above, for uniform style
 395             // but c-variadic is already a corner case
 396             if c_variadic {
 397                 fn variadic_error<'tcx>(
 398                     sess: &'tcx Session,
 399                     span: Span,
 400                     ty: Ty<'tcx>,
 401                     cast_ty: &str,
 402                 ) {
 403                     use rustc_hir_analysis::structured_errors::MissingCastForVariadicArg;
 404
 405                     MissingCastForVariadicArg { sess, span, ty, cast_ty }.diagnostic().emit();
 406                 }
 407
 408                 // There are a few types which get autopromoted when passed via varargs
 409                 // in C but we just error out instead and require explicit casts.
 410                 let arg_ty = self.structurally_resolved_type(arg.span, arg_ty);
 411                 match arg_ty.kind() {
 412                     ty::Float(ty::FloatTy::F32) => {
 413                         variadic_error(tcx.sess, arg.span, arg_ty, "c_double");
 414                     }
 415                     ty::Int(ty::IntTy::I8 | ty::IntTy::I16) | ty::Bool => {
 416                         variadic_error(tcx.sess, arg.span, arg_ty, "c_int");
 417                     }
 418                     ty::Uint(ty::UintTy::U8 | ty::UintTy::U16) => {
 419                         variadic_error(tcx.sess, arg.span, arg_ty, "c_uint");
 420                     }
 421                     ty::FnDef(..) => {
 422                         let ptr_ty = self.tcx.mk_fn_ptr(arg_ty.fn_sig(self.tcx));
 423                         let ptr_ty = self.resolve_vars_if_possible(ptr_ty);
 424                         variadic_error(tcx.sess, arg.span, arg_ty, &ptr_ty.to_string());
 425                     }
 426                     _ => {}
 427                 }
 428             }
 429         }
 430
 431         if !call_appears_satisfied {
 432             let compatibility_diagonal = IndexVec::from_raw(compatibility_diagonal);
 433             let provided_args = IndexVec::from_iter(provided_args.iter().take(if c_variadic {
 434                 minimum_input_count
 435             } else {
 436                 provided_arg_count
 437             }));
 438             debug_assert_eq!(
 439                 formal_input_tys.len(),
 440                 expected_input_tys.len(),
 441                 "expected formal_input_tys to be the same size as expected_input_tys"
 442             );
 443             let formal_and_expected_inputs = IndexVec::from_iter(
 444                 formal_input_tys
 445                     .iter()
 446                     .copied()
 447                     .zip(expected_input_tys.iter().copied())
 448                     .map(|vars| self.resolve_vars_if_possible(vars)),
 449             );
 450
 451             self.report_arg_errors(
 452                 compatibility_diagonal,
 453                 formal_and_expected_inputs,
 454                 provided_args,
 455                 c_variadic,
 456                 err_code,
 457                 fn_def_id,
 458                 call_span,
 459                 call_expr,
 460             );
 461         }
 462     }
 463
 464     fn report_arg_errors(
 465         &self,
 466         compatibility_diagonal: IndexVec<ProvidedIdx, Compatibility<'tcx>>,
 467         formal_and_expected_inputs: IndexVec<ExpectedIdx, (Ty<'tcx>, Ty<'tcx>)>,
 468         provided_args: IndexVec<ProvidedIdx, &'tcx hir::Expr<'tcx>>,
 469         c_variadic: bool,
 470         err_code: &str,
 471         fn_def_id: Option<DefId>,
 472         call_span: Span,
 473         call_expr: &hir::Expr<'tcx>,
 474     ) {
 475         // Next, let's construct the error
 476         let (error_span, full_call_span, call_name, is_method) = match &call_expr.kind {
 477             hir::ExprKind::Call(
 478                 hir::Expr { hir_id, span, kind: hir::ExprKind::Path(qpath), .. },
 479                 _,
 480             ) => {
 481                 if let Res::Def(DefKind::Ctor(of, _), _) =
 482                     self.typeck_results.borrow().qpath_res(qpath, *hir_id)
 483                 {
 484                     let name = match of {
 485                         CtorOf::Struct => "struct",
 486                         CtorOf::Variant => "enum variant",
 487                     };
 488                     (call_span, *span, name, false)
 489                 } else {
 490                     (call_span, *span, "function", false)
 491                 }
 492             }
 493             hir::ExprKind::Call(hir::Expr { span, .. }, _) => (call_span, *span, "function", false),
 494             hir::ExprKind::MethodCall(path_segment, _, _, span) => {
 495                 let ident_span = path_segment.ident.span;
 496                 let ident_span = if let Some(args) = path_segment.args {
 497                     ident_span.with_hi(args.span_ext.hi())
 498                 } else {
 499                     ident_span
 500                 };
 501                 (*span, ident_span, "method", true)
 502             }
 503             k => span_bug!(call_span, "checking argument types on a non-call: `{:?}`", k),
 504         };
 505         let args_span = error_span.trim_start(full_call_span).unwrap_or(error_span);
 506
 507         // Don't print if it has error types or is just plain `_`
 508         fn has_error_or_infer<'tcx>(tys: impl IntoIterator<Item = Ty<'tcx>>) -> bool {
 509             tys.into_iter().any(|ty| ty.references_error() || ty.is_ty_var())
 510         }
 511
 512         let tcx = self.tcx;
 513         // FIXME: taint after emitting errors and pass through an `ErrorGuaranteed`
 514         self.set_tainted_by_errors(
 515             tcx.sess.delay_span_bug(call_span, "no errors reported for args"),
 516         );
 517
 518         // Get the argument span in the context of the call span so that
 519         // suggestions and labels are (more) correct when an arg is a
 520         // macro invocation.
 521         let normalize_span = |span: Span| -> Span {
 522             let normalized_span = span.find_ancestor_inside(error_span).unwrap_or(span);
 523             // Sometimes macros mess up the spans, so do not normalize the
 524             // arg span to equal the error span, because that's less useful
 525             // than pointing out the arg expr in the wrong context.
 526             if normalized_span.source_equal(error_span) { span } else { normalized_span }
 527         };
 528
 529         // Precompute the provided types and spans, since that's all we typically need for below
 530         let provided_arg_tys: IndexVec<ProvidedIdx, (Ty<'tcx>, Span)> = provided_args
 531             .iter()
 532             .map(|expr| {
 533                 let ty = self
 534                     .typeck_results
 535                     .borrow()
 536                     .expr_ty_adjusted_opt(*expr)
 537                     .unwrap_or_else(|| tcx.ty_error());
 538                 (self.resolve_vars_if_possible(ty), normalize_span(expr.span))
 539             })
 540             .collect();
 541         let callee_expr = match &call_expr.peel_blocks().kind {
 542             hir::ExprKind::Call(callee, _) => Some(*callee),
 543             hir::ExprKind::MethodCall(_, receiver, ..) => {
 544                 if let Some((DefKind::AssocFn, def_id)) =
 545                     self.typeck_results.borrow().type_dependent_def(call_expr.hir_id)
 546                     && let Some(assoc) = tcx.opt_associated_item(def_id)
 547                     && assoc.fn_has_self_parameter
 548                 {
 549                     Some(*receiver)
 550                 } else {
 551                     None
 552                 }
 553             }
 554             _ => None,
 555         };
 556         let callee_ty = callee_expr
 557             .and_then(|callee_expr| self.typeck_results.borrow().expr_ty_adjusted_opt(callee_expr));
 558
 559         // A "softer" version of the `demand_compatible`, which checks types without persisting them,
 560         // and treats error types differently
 561         // This will allow us to "probe" for other argument orders that would likely have been correct
 562         let check_compatible = |provided_idx: ProvidedIdx, expected_idx: ExpectedIdx| {
 563             if provided_idx.as_usize() == expected_idx.as_usize() {
 564                 return compatibility_diagonal[provided_idx].clone();
 565             }
 566
 567             let (formal_input_ty, expected_input_ty) = formal_and_expected_inputs[expected_idx];
 568             // If either is an error type, we defy the usual convention and consider them to *not* be
 569             // coercible. This prevents our error message heuristic from trying to pass errors into
 570             // every argument.
 571             if (formal_input_ty, expected_input_ty).references_error() {
 572                 return Compatibility::Incompatible(None);
 573             }
 574
 575             let (arg_ty, arg_span) = provided_arg_tys[provided_idx];
 576
 577             let expectation = Expectation::rvalue_hint(self, expected_input_ty);
 578             let coerced_ty = expectation.only_has_type(self).unwrap_or(formal_input_ty);
 579             let can_coerce = self.can_coerce(arg_ty, coerced_ty);
 580             if !can_coerce {
 581                 return Compatibility::Incompatible(Some(ty::error::TypeError::Sorts(
 582                     ty::error::ExpectedFound::new(true, coerced_ty, arg_ty),
 583                 )));
 584             }
 585
 586             // Using probe here, since we don't want this subtyping to affect inference.
 587             let subtyping_error = self.probe(|_| {
 588                 self.at(&self.misc(arg_span), self.param_env).sup(formal_input_ty, coerced_ty).err()
 589             });
 590
 591             // Same as above: if either the coerce type or the checked type is an error type,
 592             // consider them *not* compatible.
 593             let references_error = (coerced_ty, arg_ty).references_error();
 594             match (references_error, subtyping_error) {
 595                 (false, None) => Compatibility::Compatible,
 596                 (_, subtyping_error) => Compatibility::Incompatible(subtyping_error),
 597             }
 598         };
 599
 600         let mk_trace = |span, (formal_ty, expected_ty), provided_ty| {
 601             let mismatched_ty = if expected_ty == provided_ty {
 602                 // If expected == provided, then we must have failed to sup
 603                 // the formal type. Avoid printing out "expected Ty, found Ty"
 604                 // in that case.
 605                 formal_ty
 606             } else {
 607                 expected_ty
 608             };
 609             TypeTrace::types(&self.misc(span), true, mismatched_ty, provided_ty)
 610         };
 611
 612         // The algorithm here is inspired by levenshtein distance and longest common subsequence.
 613         // We'll try to detect 4 different types of mistakes:
 614         // - An extra parameter has been provided that doesn't satisfy *any* of the other inputs
 615         // - An input is missing, which isn't satisfied by *any* of the other arguments
 616         // - Some number of arguments have been provided in the wrong order
 617         // - A type is straight up invalid
 618
 619         // First, let's find the errors
 620         let (mut errors, matched_inputs) =
 621             ArgMatrix::new(provided_args.len(), formal_and_expected_inputs.len(), check_compatible)
 622                 .find_errors();
 623
 624         // First, check if we just need to wrap some arguments in a tuple.
 625         if let Some((mismatch_idx, terr)) =
 626             compatibility_diagonal.iter().enumerate().find_map(|(i, c)| {
 627                 if let Compatibility::Incompatible(Some(terr)) = c {
 628                     Some((i, *terr))
 629                 } else {
 630                     None
 631                 }
 632             })
 633         {
 634             // Is the first bad expected argument a tuple?
 635             // Do we have as many extra provided arguments as the tuple's length?
 636             // If so, we might have just forgotten to wrap some args in a tuple.
 637             if let Some(ty::Tuple(tys)) =
 638                 formal_and_expected_inputs.get(mismatch_idx.into()).map(|tys| tys.1.kind())
 639                 // If the tuple is unit, we're not actually wrapping any arguments.
 640                 && !tys.is_empty()
 641                 && provided_arg_tys.len() == formal_and_expected_inputs.len() - 1 + tys.len()
 642             {
 643                 // Wrap up the N provided arguments starting at this position in a tuple.
 644                 let provided_as_tuple = tcx.mk_tup(
 645                     provided_arg_tys.iter().map(|(ty, _)| *ty).skip(mismatch_idx).take(tys.len()),
 646                 );
 647
 648                 let mut satisfied = true;
 649                 // Check if the newly wrapped tuple + rest of the arguments are compatible.
 650                 for ((_, expected_ty), provided_ty) in std::iter::zip(
 651                     formal_and_expected_inputs.iter().skip(mismatch_idx),
 652                     [provided_as_tuple].into_iter().chain(
 653                         provided_arg_tys.iter().map(|(ty, _)| *ty).skip(mismatch_idx + tys.len()),
 654                     ),
 655                 ) {
 656                     if !self.can_coerce(provided_ty, *expected_ty) {
 657                         satisfied = false;
 658                         break;
 659                     }
 660                 }
 661
 662                 // If they're compatible, suggest wrapping in an arg, and we're done!
 663                 // Take some care with spans, so we don't suggest wrapping a macro's
 664                 // innards in parenthesis, for example.
 665                 if satisfied
 666                     && let Some((_, lo)) =
 667                         provided_arg_tys.get(ProvidedIdx::from_usize(mismatch_idx))
 668                     && let Some((_, hi)) =
 669                         provided_arg_tys.get(ProvidedIdx::from_usize(mismatch_idx + tys.len() - 1))
 670                 {
 671                     let mut err;
 672                     if tys.len() == 1 {
 673                         // A tuple wrap suggestion actually occurs within,
 674                         // so don't do anything special here.
 675                         err = self.err_ctxt().report_and_explain_type_error(
 676                             mk_trace(
 677                                 *lo,
 678                                 formal_and_expected_inputs[mismatch_idx.into()],
 679                                 provided_arg_tys[mismatch_idx.into()].0,
 680                             ),
 681                             terr,
 682                         );
 683                         err.span_label(
 684                             full_call_span,
 685                             format!("arguments to this {} are incorrect", call_name),
 686                         );
 687                     } else {
 688                         err = tcx.sess.struct_span_err_with_code(
 689                             full_call_span,
 690                             &format!(
 691                                 "{call_name} takes {}{} but {} {} supplied",
 692                                 if c_variadic { "at least " } else { "" },
 693                                 potentially_plural_count(
 694                                     formal_and_expected_inputs.len(),
 695                                     "argument"
 696                                 ),
 697                                 potentially_plural_count(provided_args.len(), "argument"),
 698                                 pluralize!("was", provided_args.len())
 699                             ),
 700                             DiagnosticId::Error(err_code.to_owned()),
 701                         );
 702                         err.multipart_suggestion_verbose(
 703                             "wrap these arguments in parentheses to construct a tuple",
 704                             vec![
 705                                 (lo.shrink_to_lo(), "(".to_string()),
 706                                 (hi.shrink_to_hi(), ")".to_string()),
 707                             ],
 708                             Applicability::MachineApplicable,
 709                         );
 710                     };
 711                     self.label_fn_like(
 712                         &mut err,
 713                         fn_def_id,
 714                         callee_ty,
 715                         Some(mismatch_idx),
 716                         is_method,
 717                     );
 718                     err.emit();
 719                     return;
 720                 }
 721             }
 722         }
 723
 724         // Okay, so here's where it gets complicated in regards to what errors
 725         // we emit and how.
 726         // There are 3 different "types" of errors we might encounter.
 727         //   1) Missing/extra/swapped arguments
 728         //   2) Valid but incorrect arguments
 729         //   3) Invalid arguments
 730         //      - Currently I think this only comes up with `CyclicTy`
 731         //
 732         // We first need to go through, remove those from (3) and emit those
 733         // as their own error, particularly since they're error code and
 734         // message is special. From what I can tell, we *must* emit these
 735         // here (vs somewhere prior to this function) since the arguments
 736         // become invalid *because* of how they get used in the function.
 737         // It is what it is.
 738
 739         if errors.is_empty() {
 740             if cfg!(debug_assertions) {
 741                 span_bug!(error_span, "expected errors from argument matrix");
 742             } else {
 743                 tcx.sess
 744                     .struct_span_err(
 745                         error_span,
 746                         "argument type mismatch was detected, \
 747                         but rustc had trouble determining where",
 748                     )
 749                     .note(
 750                         "we would appreciate a bug report: \
 751                         https://github.com/rust-lang/rust/issues/new",
 752                     )
 753                     .emit();
 754             }
 755             return;
 756         }
 757
 758         errors.drain_filter(|error| {
 759                 let Error::Invalid(provided_idx, expected_idx, Compatibility::Incompatible(Some(e))) = error else { return false };
 760                 let (provided_ty, provided_span) = provided_arg_tys[*provided_idx];
 761                 let trace = mk_trace(provided_span, formal_and_expected_inputs[*expected_idx], provided_ty);
 762                 if !matches!(trace.cause.as_failure_code(*e), FailureCode::Error0308(_)) {
 763                     self.err_ctxt().report_and_explain_type_error(trace, *e).emit();
 764                     return true;
 765                 }
 766                 false
 767             });
 768
 769         // We're done if we found errors, but we already emitted them.
 770         if errors.is_empty() {
 771             return;
 772         }
 773
 774         // Okay, now that we've emitted the special errors separately, we
 775         // are only left missing/extra/swapped and mismatched arguments, both
 776         // can be collated pretty easily if needed.
 777
 778         // Next special case: if there is only one "Incompatible" error, just emit that
 779         if let [
 780             Error::Invalid(provided_idx, expected_idx, Compatibility::Incompatible(Some(err))),
 781         ] = &errors[..]
 782         {
 783             let (formal_ty, expected_ty) = formal_and_expected_inputs[*expected_idx];
 784             let (provided_ty, provided_arg_span) = provided_arg_tys[*provided_idx];
 785             let trace = mk_trace(provided_arg_span, (formal_ty, expected_ty), provided_ty);
 786             let mut err = self.err_ctxt().report_and_explain_type_error(trace, *err);
 787             self.emit_coerce_suggestions(
 788                 &mut err,
 789                 &provided_args[*provided_idx],
 790                 provided_ty,
 791                 Expectation::rvalue_hint(self, expected_ty)
 792                     .only_has_type(self)
 793                     .unwrap_or(formal_ty),
 794                 None,
 795                 None,
 796             );
 797             err.span_label(
 798                 full_call_span,
 799                 format!("arguments to this {} are incorrect", call_name),
 800             );
 801             if let (Some(callee_ty), hir::ExprKind::MethodCall(_, rcvr, _, _)) =
 802                 (callee_ty, &call_expr.kind)
 803             {
 804                 // Type that would have accepted this argument if it hadn't been inferred earlier.
 805                 // FIXME: We leave an inference variable for now, but it'd be nice to get a more
 806                 // specific type to increase the accuracy of the diagnostic.
 807                 let expected = self.infcx.next_ty_var(TypeVariableOrigin {
 808                     kind: TypeVariableOriginKind::MiscVariable,
 809                     span: full_call_span,
 810                 });
 811                 self.point_at_expr_source_of_inferred_type(&mut err, rcvr, expected, callee_ty);
 812             }
 813             // Call out where the function is defined
 814             self.label_fn_like(
 815                 &mut err,
 816                 fn_def_id,
 817                 callee_ty,
 818                 Some(expected_idx.as_usize()),
 819                 is_method,
 820             );
 821             err.emit();
 822             return;
 823         }
 824
 825         let mut err = if formal_and_expected_inputs.len() == provided_args.len() {
 826             struct_span_err!(
 827                 tcx.sess,
 828                 full_call_span,
 829                 E0308,
 830                 "arguments to this {} are incorrect",
 831                 call_name,
 832             )
 833         } else {
 834             tcx.sess.struct_span_err_with_code(
 835                 full_call_span,
 836                 &format!(
 837                     "this {} takes {}{} but {} {} supplied",
 838                     call_name,
 839                     if c_variadic { "at least " } else { "" },
 840                     potentially_plural_count(formal_and_expected_inputs.len(), "argument"),
 841                     potentially_plural_count(provided_args.len(), "argument"),
 842                     pluralize!("was", provided_args.len())
 843                 ),
 844                 DiagnosticId::Error(err_code.to_owned()),
 845             )
 846         };
 847
 848         // As we encounter issues, keep track of what we want to provide for the suggestion
 849         let mut labels = vec![];
 850         // If there is a single error, we give a specific suggestion; otherwise, we change to
 851         // "did you mean" with the suggested function call
 852         enum SuggestionText {
 853             None,
 854             Provide(bool),
 855             Remove(bool),
 856             Swap,
 857             Reorder,
 858             DidYouMean,
 859         }
 860         let mut suggestion_text = SuggestionText::None;
 861
 862         let mut errors = errors.into_iter().peekable();
 863         while let Some(error) = errors.next() {
 864             match error {
 865                 Error::Invalid(provided_idx, expected_idx, compatibility) => {
 866                     let (formal_ty, expected_ty) = formal_and_expected_inputs[expected_idx];
 867                     let (provided_ty, provided_span) = provided_arg_tys[provided_idx];
 868                     if let Compatibility::Incompatible(error) = compatibility {
 869                         let trace = mk_trace(provided_span, (formal_ty, expected_ty), provided_ty);
 870                         if let Some(e) = error {
 871                             self.err_ctxt().note_type_err(
 872                                 &mut err,
 873                                 &trace.cause,
 874                                 None,
 875                                 Some(trace.values),
 876                                 e,
 877                                 false,
 878                                 true,
 879                             );
 880                         }
 881                     }
 882
 883                     self.emit_coerce_suggestions(
 884                         &mut err,
 885                         &provided_args[provided_idx],
 886                         provided_ty,
 887                         Expectation::rvalue_hint(self, expected_ty)
 888                             .only_has_type(self)
 889                             .unwrap_or(formal_ty),
 890                         None,
 891                         None,
 892                     );
 893                 }
 894                 Error::Extra(arg_idx) => {
 895                     let (provided_ty, provided_span) = provided_arg_tys[arg_idx];
 896                     let provided_ty_name = if !has_error_or_infer([provided_ty]) {
 897                         // FIXME: not suggestable, use something else
 898                         format!(" of type `{}`", provided_ty)
 899                     } else {
 900                         "".to_string()
 901                     };
 902                     labels
 903                         .push((provided_span, format!("argument{} unexpected", provided_ty_name)));
 904                     suggestion_text = match suggestion_text {
 905                         SuggestionText::None => SuggestionText::Remove(false),
 906                         SuggestionText::Remove(_) => SuggestionText::Remove(true),
 907                         _ => SuggestionText::DidYouMean,
 908                     };
 909                 }
 910                 Error::Missing(expected_idx) => {
 911                     // If there are multiple missing arguments adjacent to each other,
 912                     // then we can provide a single error.
 913
 914                     let mut missing_idxs = vec![expected_idx];
 915                     while let Some(e) = errors.next_if(|e| {
 916                         matches!(e, Error::Missing(next_expected_idx)
 917                             if *next_expected_idx == *missing_idxs.last().unwrap() + 1)
 918                     }) {
 919                         match e {
 920                             Error::Missing(expected_idx) => missing_idxs.push(expected_idx),
 921                             _ => unreachable!(),
 922                         }
 923                     }
 924
 925                     // NOTE: Because we might be re-arranging arguments, might have extra
 926                     // arguments, etc. it's hard to *really* know where we should provide
 927                     // this error label, so as a heuristic, we point to the provided arg, or
 928                     // to the call if the missing inputs pass the provided args.
 929                     match &missing_idxs[..] {
 930                         &[expected_idx] => {
 931                             let (_, input_ty) = formal_and_expected_inputs[expected_idx];
 932                             let span = if let Some((_, arg_span)) =
 933                                 provided_arg_tys.get(expected_idx.to_provided_idx())
 934                             {
 935                                 *arg_span
 936                             } else {
 937                                 args_span
 938                             };
 939                             let rendered = if !has_error_or_infer([input_ty]) {
 940                                 format!(" of type `{}`", input_ty)
 941                             } else {
 942                                 "".to_string()
 943                             };
 944                             labels.push((span, format!("an argument{} is missing", rendered)));
 945                             suggestion_text = match suggestion_text {
 946                                 SuggestionText::None => SuggestionText::Provide(false),
 947                                 SuggestionText::Provide(_) => SuggestionText::Provide(true),
 948                                 _ => SuggestionText::DidYouMean,
 949                             };
 950                         }
 951                         &[first_idx, second_idx] => {
 952                             let (_, first_expected_ty) = formal_and_expected_inputs[first_idx];
 953                             let (_, second_expected_ty) = formal_and_expected_inputs[second_idx];
 954                             let span = if let (Some((_, first_span)), Some((_, second_span))) = (
 955                                 provided_arg_tys.get(first_idx.to_provided_idx()),
 956                                 provided_arg_tys.get(second_idx.to_provided_idx()),
 957                             ) {
 958                                 first_span.to(*second_span)
 959                             } else {
 960                                 args_span
 961                             };
 962                             let rendered =
 963                                 if !has_error_or_infer([first_expected_ty, second_expected_ty]) {
 964                                     format!(
 965                                         " of type `{}` and `{}`",
 966                                         first_expected_ty, second_expected_ty
 967                                     )
 968                                 } else {
 969                                     "".to_string()
 970                                 };
 971                             labels.push((span, format!("two arguments{} are missing", rendered)));
 972                             suggestion_text = match suggestion_text {
 973                                 SuggestionText::None | SuggestionText::Provide(_) => {
 974                                     SuggestionText::Provide(true)
 975                                 }
 976                                 _ => SuggestionText::DidYouMean,
 977                             };
 978                         }
 979                         &[first_idx, second_idx, third_idx] => {
 980                             let (_, first_expected_ty) = formal_and_expected_inputs[first_idx];
 981                             let (_, second_expected_ty) = formal_and_expected_inputs[second_idx];
 982                             let (_, third_expected_ty) = formal_and_expected_inputs[third_idx];
 983                             let span = if let (Some((_, first_span)), Some((_, third_span))) = (
 984                                 provided_arg_tys.get(first_idx.to_provided_idx()),
 985                                 provided_arg_tys.get(third_idx.to_provided_idx()),
 986                             ) {
 987                                 first_span.to(*third_span)
 988                             } else {
 989                                 args_span
 990                             };
 991                             let rendered = if !has_error_or_infer([
 992                                 first_expected_ty,
 993                                 second_expected_ty,
 994                                 third_expected_ty,
 995                             ]) {
 996                                 format!(
 997                                     " of type `{}`, `{}`, and `{}`",
 998                                     first_expected_ty, second_expected_ty, third_expected_ty
 999                                 )
1000                             } else {
1001                                 "".to_string()
1002                             };
1003                             labels.push((span, format!("three arguments{} are missing", rendered)));
1004                             suggestion_text = match suggestion_text {
1005                                 SuggestionText::None | SuggestionText::Provide(_) => {
1006                                     SuggestionText::Provide(true)
1007                                 }
1008                                 _ => SuggestionText::DidYouMean,
1009                             };
1010                         }
1011                         missing_idxs => {
1012                             let first_idx = *missing_idxs.first().unwrap();
1013                             let last_idx = *missing_idxs.last().unwrap();
1014                             // NOTE: Because we might be re-arranging arguments, might have extra arguments, etc.
1015                             // It's hard to *really* know where we should provide this error label, so this is a
1016                             // decent heuristic
1017                             let span = if let (Some((_, first_span)), Some((_, last_span))) = (
1018                                 provided_arg_tys.get(first_idx.to_provided_idx()),
1019                                 provided_arg_tys.get(last_idx.to_provided_idx()),
1020                             ) {
1021                                 first_span.to(*last_span)
1022                             } else {
1023                                 args_span
1024                             };
1025                             labels.push((span, "multiple arguments are missing".to_string()));
1026                             suggestion_text = match suggestion_text {
1027                                 SuggestionText::None | SuggestionText::Provide(_) => {
1028                                     SuggestionText::Provide(true)
1029                                 }
1030                                 _ => SuggestionText::DidYouMean,
1031                             };
1032                         }
1033                     }
1034                 }
1035                 Error::Swap(
1036                     first_provided_idx,
1037                     second_provided_idx,
1038                     first_expected_idx,
1039                     second_expected_idx,
1040                 ) => {
1041                     let (first_provided_ty, first_span) = provided_arg_tys[first_provided_idx];
1042                     let (_, first_expected_ty) = formal_and_expected_inputs[first_expected_idx];
1043                     let first_provided_ty_name = if !has_error_or_infer([first_provided_ty]) {
1044                         format!(", found `{}`", first_provided_ty)
1045                     } else {
1046                         String::new()
1047                     };
1048                     labels.push((
1049                         first_span,
1050                         format!("expected `{}`{}", first_expected_ty, first_provided_ty_name),
1051                     ));
1052
1053                     let (second_provided_ty, second_span) = provided_arg_tys[second_provided_idx];
1054                     let (_, second_expected_ty) = formal_and_expected_inputs[second_expected_idx];
1055                     let second_provided_ty_name = if !has_error_or_infer([second_provided_ty]) {
1056                         format!(", found `{}`", second_provided_ty)
1057                     } else {
1058                         String::new()
1059                     };
1060                     labels.push((
1061                         second_span,
1062                         format!("expected `{}`{}", second_expected_ty, second_provided_ty_name),
1063                     ));
1064
1065                     suggestion_text = match suggestion_text {
1066                         SuggestionText::None => SuggestionText::Swap,
1067                         _ => SuggestionText::DidYouMean,
1068                     };
1069                 }
1070                 Error::Permutation(args) => {
1071                     for (dst_arg, dest_input) in args {
1072                         let (_, expected_ty) = formal_and_expected_inputs[dst_arg];
1073                         let (provided_ty, provided_span) = provided_arg_tys[dest_input];
1074                         let provided_ty_name = if !has_error_or_infer([provided_ty]) {
1075                             format!(", found `{}`", provided_ty)
1076                         } else {
1077                             String::new()
1078                         };
1079                         labels.push((
1080                             provided_span,
1081                             format!("expected `{}`{}", expected_ty, provided_ty_name),
1082                         ));
1083                     }
1084
1085                     suggestion_text = match suggestion_text {
1086                         SuggestionText::None => SuggestionText::Reorder,
1087                         _ => SuggestionText::DidYouMean,
1088                     };
1089                 }
1090             }
1091         }
1092
1093         // If we have less than 5 things to say, it would be useful to call out exactly what's wrong
1094         if labels.len() <= 5 {
1095             for (span, label) in labels {
1096                 err.span_label(span, label);
1097             }
1098         }
1099
1100         // Call out where the function is defined
1101         self.label_fn_like(&mut err, fn_def_id, callee_ty, None, is_method);
1102
1103         // And add a suggestion block for all of the parameters
1104         let suggestion_text = match suggestion_text {
1105             SuggestionText::None => None,
1106             SuggestionText::Provide(plural) => {
1107                 Some(format!("provide the argument{}", if plural { "s" } else { "" }))
1108             }
1109             SuggestionText::Remove(plural) => {
1110                 Some(format!("remove the extra argument{}", if plural { "s" } else { "" }))
1111             }
1112             SuggestionText::Swap => Some("swap these arguments".to_string()),
1113             SuggestionText::Reorder => Some("reorder these arguments".to_string()),
1114             SuggestionText::DidYouMean => Some("did you mean".to_string()),
1115         };
1116         if let Some(suggestion_text) = suggestion_text {
1117             let source_map = self.sess().source_map();
1118             let (mut suggestion, suggestion_span) =
1119                 if let Some(call_span) = full_call_span.find_ancestor_inside(error_span) {
1120                     ("(".to_string(), call_span.shrink_to_hi().to(error_span.shrink_to_hi()))
1121                 } else {
1122                     (
1123                         format!(
1124                             "{}(",
1125                             source_map.span_to_snippet(full_call_span).unwrap_or_else(|_| {
1126                                 fn_def_id.map_or("".to_string(), |fn_def_id| {
1127                                     tcx.item_name(fn_def_id).to_string()
1128                                 })
1129                             })
1130                         ),
1131                         error_span,
1132                     )
1133                 };
1134             let mut needs_comma = false;
1135             for (expected_idx, provided_idx) in matched_inputs.iter_enumerated() {
1136                 if needs_comma {
1137                     suggestion += ", ";
1138                 } else {
1139                     needs_comma = true;
1140                 }
1141                 let suggestion_text = if let Some(provided_idx) = provided_idx
1142                     && let (_, provided_span) = provided_arg_tys[*provided_idx]
1143                     && let Ok(arg_text) = source_map.span_to_snippet(provided_span)
1144                 {
1145                     arg_text
1146                 } else {
1147                     // Propose a placeholder of the correct type
1148                     let (_, expected_ty) = formal_and_expected_inputs[expected_idx];
1149                     if expected_ty.is_unit() {
1150                         "()".to_string()
1151                     } else if expected_ty.is_suggestable(tcx, false) {
1152                         format!("/* {} */", expected_ty)
1153                     } else if let Some(fn_def_id) = fn_def_id
1154                         && self.tcx.def_kind(fn_def_id).is_fn_like()
1155                         && let self_implicit = matches!(call_expr.kind, hir::ExprKind::MethodCall(..)) as usize
1156                         && let Some(arg) = self.tcx.fn_arg_names(fn_def_id).get(expected_idx.as_usize() + self_implicit)
1157                         && arg.name != kw::SelfLower
1158                     {
1159                         format!("/* {} */", arg.name)
1160                     } else {
1161                         "/* value */".to_string()
1162                     }
1163                 };
1164                 suggestion += &suggestion_text;
1165             }
1166             suggestion += ")";
1167             err.span_suggestion_verbose(
1168                 suggestion_span,
1169                 &suggestion_text,
1170                 suggestion,
1171                 Applicability::HasPlaceholders,
1172             );
1173         }
1174
1175         err.emit();
1176     }
1177
1178     // AST fragment checking
1179     pub(in super::super) fn check_lit(
1180         &self,
1181         lit: &hir::Lit,
1182         expected: Expectation<'tcx>,
1183     ) -> Ty<'tcx> {
1184         let tcx = self.tcx;
1185
1186         match lit.node {
1187             ast::LitKind::Str(..) => tcx.mk_static_str(),
1188             ast::LitKind::ByteStr(ref v, _) => {
1189                 tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_array(tcx.types.u8, v.len() as u64))
1190             }
1191             ast::LitKind::Byte(_) => tcx.types.u8,
1192             ast::LitKind::Char(_) => tcx.types.char,
1193             ast::LitKind::Int(_, ast::LitIntType::Signed(t)) => tcx.mk_mach_int(ty::int_ty(t)),
1194             ast::LitKind::Int(_, ast::LitIntType::Unsigned(t)) => tcx.mk_mach_uint(ty::uint_ty(t)),
1195             ast::LitKind::Int(_, ast::LitIntType::Unsuffixed) => {
1196                 let opt_ty = expected.to_option(self).and_then(|ty| match ty.kind() {
1197                     ty::Int(_) | ty::Uint(_) => Some(ty),
1198                     ty::Char => Some(tcx.types.u8),
1199                     ty::RawPtr(..) => Some(tcx.types.usize),
1200                     ty::FnDef(..) | ty::FnPtr(_) => Some(tcx.types.usize),
1201                     _ => None,
1202                 });
1203                 opt_ty.unwrap_or_else(|| self.next_int_var())
1204             }
1205             ast::LitKind::Float(_, ast::LitFloatType::Suffixed(t)) => {
1206                 tcx.mk_mach_float(ty::float_ty(t))
1207             }
1208             ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) => {
1209                 let opt_ty = expected.to_option(self).and_then(|ty| match ty.kind() {
1210                     ty::Float(_) => Some(ty),
1211                     _ => None,
1212                 });
1213                 opt_ty.unwrap_or_else(|| self.next_float_var())
1214             }
1215             ast::LitKind::Bool(_) => tcx.types.bool,
1216             ast::LitKind::Err => tcx.ty_error(),
1217         }
1218     }
1219
1220     pub fn check_struct_path(
1221         &self,
1222         qpath: &QPath<'_>,
1223         hir_id: hir::HirId,
1224     ) -> Option<(&'tcx ty::VariantDef, Ty<'tcx>)> {
1225         let path_span = qpath.span();
1226         let (def, ty) = self.finish_resolving_struct_path(qpath, path_span, hir_id);
1227         let variant = match def {
1228             Res::Err => {
1229                 self.set_tainted_by_errors(
1230                     self.tcx.sess.delay_span_bug(path_span, "`Res::Err` but no error emitted"),
1231                 );
1232                 return None;
1233             }
1234             Res::Def(DefKind::Variant, _) => match ty.normalized.ty_adt_def() {
1235                 Some(adt) => {
1236                     Some((adt.variant_of_res(def), adt.did(), Self::user_substs_for_adt(ty)))
1237                 }
1238                 _ => bug!("unexpected type: {:?}", ty.normalized),
1239             },
1240             Res::Def(DefKind::Struct | DefKind::Union | DefKind::TyAlias | DefKind::AssocTy, _)
1241             | Res::SelfTyParam { .. }
1242             | Res::SelfTyAlias { .. } => match ty.normalized.ty_adt_def() {
1243                 Some(adt) if !adt.is_enum() => {
1244                     Some((adt.non_enum_variant(), adt.did(), Self::user_substs_for_adt(ty)))
1245                 }
1246                 _ => None,
1247             },
1248             _ => bug!("unexpected definition: {:?}", def),
1249         };
1250
1251         if let Some((variant, did, ty::UserSubsts { substs, user_self_ty })) = variant {
1252             debug!("check_struct_path: did={:?} substs={:?}", did, substs);
1253
1254             // Register type annotation.
1255             self.write_user_type_annotation_from_substs(hir_id, did, substs, user_self_ty);
1256
1257             // Check bounds on type arguments used in the path.
1258             self.add_required_obligations_for_hir(path_span, did, substs, hir_id);
1259
1260             Some((variant, ty.normalized))
1261         } else {
1262             match ty.normalized.kind() {
1263                 ty::Error(_) => {
1264                     // E0071 might be caused by a spelling error, which will have
1265                     // already caused an error message and probably a suggestion
1266                     // elsewhere. Refrain from emitting more unhelpful errors here
1267                     // (issue #88844).
1268                 }
1269                 _ => {
1270                     struct_span_err!(
1271                         self.tcx.sess,
1272                         path_span,
1273                         E0071,
1274                         "expected struct, variant or union type, found {}",
1275                         ty.normalized.sort_string(self.tcx)
1276                     )
1277                     .span_label(path_span, "not a struct")
1278                     .emit();
1279                 }
1280             }
1281             None
1282         }
1283     }
1284
1285     pub fn check_decl_initializer(
1286         &self,
1287         hir_id: hir::HirId,
1288         pat: &'tcx hir::Pat<'tcx>,
1289         init: &'tcx hir::Expr<'tcx>,
1290     ) -> Ty<'tcx> {
1291         // FIXME(tschottdorf): `contains_explicit_ref_binding()` must be removed
1292         // for #42640 (default match binding modes).
1293         //
1294         // See #44848.
1295         let ref_bindings = pat.contains_explicit_ref_binding();
1296
1297         let local_ty = self.local_ty(init.span, hir_id).revealed_ty;
1298         if let Some(m) = ref_bindings {
1299             // Somewhat subtle: if we have a `ref` binding in the pattern,
1300             // we want to avoid introducing coercions for the RHS. This is
1301             // both because it helps preserve sanity and, in the case of
1302             // ref mut, for soundness (issue #23116). In particular, in
1303             // the latter case, we need to be clear that the type of the
1304             // referent for the reference that results is *equal to* the
1305             // type of the place it is referencing, and not some
1306             // supertype thereof.
1307             let init_ty = self.check_expr_with_needs(init, Needs::maybe_mut_place(m));
1308             self.demand_eqtype(init.span, local_ty, init_ty);
1309             init_ty
1310         } else {
1311             self.check_expr_coercable_to_type(init, local_ty, None)
1312         }
1313     }
1314
1315     pub(in super::super) fn check_decl(&self, decl: Declaration<'tcx>) {
1316         // Determine and write the type which we'll check the pattern against.
1317         let decl_ty = self.local_ty(decl.span, decl.hir_id).decl_ty;
1318         self.write_ty(decl.hir_id, decl_ty);
1319
1320         // Type check the initializer.
1321         if let Some(ref init) = decl.init {
1322             let init_ty = self.check_decl_initializer(decl.hir_id, decl.pat, &init);
1323             self.overwrite_local_ty_if_err(decl.hir_id, decl.pat, init_ty);
1324         }
1325
1326         // Does the expected pattern type originate from an expression and what is the span?
1327         let (origin_expr, ty_span) = match (decl.ty, decl.init) {
1328             (Some(ty), _) => (false, Some(ty.span)), // Bias towards the explicit user type.
1329             (_, Some(init)) => {
1330                 (true, Some(init.span.find_ancestor_inside(decl.span).unwrap_or(init.span)))
1331             } // No explicit type; so use the scrutinee.
1332             _ => (false, None), // We have `let $pat;`, so the expected type is unconstrained.
1333         };
1334
1335         // Type check the pattern. Override if necessary to avoid knock-on errors.
1336         self.check_pat_top(&decl.pat, decl_ty, ty_span, origin_expr);
1337         let pat_ty = self.node_ty(decl.pat.hir_id);
1338         self.overwrite_local_ty_if_err(decl.hir_id, decl.pat, pat_ty);
1339
1340         if let Some(blk) = decl.els {
1341             let previous_diverges = self.diverges.get();
1342             let else_ty = self.check_block_with_expected(blk, NoExpectation);
1343             let cause = self.cause(blk.span, ObligationCauseCode::LetElse);
1344             if let Some(mut err) =
1345                 self.demand_eqtype_with_origin(&cause, self.tcx.types.never, else_ty)
1346             {
1347                 err.emit();
1348             }
1349             self.diverges.set(previous_diverges);
1350         }
1351     }
1352
1353     /// Type check a `let` statement.
1354     pub fn check_decl_local(&self, local: &'tcx hir::Local<'tcx>) {
1355         self.check_decl(local.into());
1356     }
1357
1358     pub fn check_stmt(&self, stmt: &'tcx hir::Stmt<'tcx>, is_last: bool) {
1359         // Don't do all the complex logic below for `DeclItem`.
1360         match stmt.kind {
1361             hir::StmtKind::Item(..) => return,
1362             hir::StmtKind::Local(..) | hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => {}
1363         }
1364
1365         self.warn_if_unreachable(stmt.hir_id, stmt.span, "statement");
1366
1367         // Hide the outer diverging and `has_errors` flags.
1368         let old_diverges = self.diverges.replace(Diverges::Maybe);
1369
1370         match stmt.kind {
1371             hir::StmtKind::Local(l) => {
1372                 self.check_decl_local(l);
1373             }
1374             // Ignore for now.
1375             hir::StmtKind::Item(_) => {}
1376             hir::StmtKind::Expr(ref expr) => {
1377                 // Check with expected type of `()`.
1378                 self.check_expr_has_type_or_error(&expr, self.tcx.mk_unit(), |err| {
1379                     if expr.can_have_side_effects() {
1380                         self.suggest_semicolon_at_end(expr.span, err);
1381                     }
1382                 });
1383             }
1384             hir::StmtKind::Semi(ref expr) => {
1385                 // All of this is equivalent to calling `check_expr`, but it is inlined out here
1386                 // in order to capture the fact that this `match` is the last statement in its
1387                 // function. This is done for better suggestions to remove the `;`.
1388                 let expectation = match expr.kind {
1389                     hir::ExprKind::Match(..) if is_last => IsLast(stmt.span),
1390                     _ => NoExpectation,
1391                 };
1392                 self.check_expr_with_expectation(expr, expectation);
1393             }
1394         }
1395
1396         // Combine the diverging and `has_error` flags.
1397         self.diverges.set(self.diverges.get() | old_diverges);
1398     }
1399
1400     pub fn check_block_no_value(&self, blk: &'tcx hir::Block<'tcx>) {
1401         let unit = self.tcx.mk_unit();
1402         let ty = self.check_block_with_expected(blk, ExpectHasType(unit));
1403
1404         // if the block produces a `!` value, that can always be
1405         // (effectively) coerced to unit.
1406         if !ty.is_never() {
1407             self.demand_suptype(blk.span, unit, ty);
1408         }
1409     }
1410
1411     pub(in super::super) fn check_block_with_expected(
1412         &self,
1413         blk: &'tcx hir::Block<'tcx>,
1414         expected: Expectation<'tcx>,
1415     ) -> Ty<'tcx> {
1416         // In some cases, blocks have just one exit, but other blocks
1417         // can be targeted by multiple breaks. This can happen both
1418         // with labeled blocks as well as when we desugar
1419         // a `try { ... }` expression.
1420         //
1421         // Example 1:
1422         //
1423         //    'a: { if true { break 'a Err(()); } Ok(()) }
1424         //
1425         // Here we would wind up with two coercions, one from
1426         // `Err(())` and the other from the tail expression
1427         // `Ok(())`. If the tail expression is omitted, that's a
1428         // "forced unit" -- unless the block diverges, in which
1429         // case we can ignore the tail expression (e.g., `'a: {
1430         // break 'a 22; }` would not force the type of the block
1431         // to be `()`).
1432         let tail_expr = blk.expr.as_ref();
1433         let coerce_to_ty = expected.coercion_target_type(self, blk.span);
1434         let coerce = if blk.targeted_by_break {
1435             CoerceMany::new(coerce_to_ty)
1436         } else {
1437             let tail_expr: &[&hir::Expr<'_>] = match tail_expr {
1438                 Some(e) => slice::from_ref(e),
1439                 None => &[],
1440             };
1441             CoerceMany::with_coercion_sites(coerce_to_ty, tail_expr)
1442         };
1443
1444         let prev_diverges = self.diverges.get();
1445         let ctxt = BreakableCtxt { coerce: Some(coerce), may_break: false };
1446
1447         let (ctxt, ()) = self.with_breakable_ctxt(blk.hir_id, ctxt, || {
1448             for (pos, s) in blk.stmts.iter().enumerate() {
1449                 self.check_stmt(s, blk.stmts.len() - 1 == pos);
1450             }
1451
1452             // check the tail expression **without** holding the
1453             // `enclosing_breakables` lock below.
1454             let tail_expr_ty = tail_expr.map(|t| self.check_expr_with_expectation(t, expected));
1455
1456             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
1457             let ctxt = enclosing_breakables.find_breakable(blk.hir_id);
1458             let coerce = ctxt.coerce.as_mut().unwrap();
1459             if let Some(tail_expr_ty) = tail_expr_ty {
1460                 let tail_expr = tail_expr.unwrap();
1461                 let span = self.get_expr_coercion_span(tail_expr);
1462                 let cause = self.cause(span, ObligationCauseCode::BlockTailExpression(blk.hir_id));
1463                 let ty_for_diagnostic = coerce.merged_ty();
1464                 // We use coerce_inner here because we want to augment the error
1465                 // suggesting to wrap the block in square brackets if it might've
1466                 // been mistaken array syntax
1467                 coerce.coerce_inner(
1468                     self,
1469                     &cause,
1470                     Some(tail_expr),
1471                     tail_expr_ty,
1472                     Some(&mut |diag: &mut Diagnostic| {
1473                         self.suggest_block_to_brackets(diag, blk, tail_expr_ty, ty_for_diagnostic);
1474                     }),
1475                     false,
1476                 );
1477             } else {
1478                 // Subtle: if there is no explicit tail expression,
1479                 // that is typically equivalent to a tail expression
1480                 // of `()` -- except if the block diverges. In that
1481                 // case, there is no value supplied from the tail
1482                 // expression (assuming there are no other breaks,
1483                 // this implies that the type of the block will be
1484                 // `!`).
1485                 //
1486                 // #41425 -- label the implicit `()` as being the
1487                 // "found type" here, rather than the "expected type".
1488                 if !self.diverges.get().is_always() {
1489                     // #50009 -- Do not point at the entire fn block span, point at the return type
1490                     // span, as it is the cause of the requirement, and
1491                     // `consider_hint_about_removing_semicolon` will point at the last expression
1492                     // if it were a relevant part of the error. This improves usability in editors
1493                     // that highlight errors inline.
1494                     let mut sp = blk.span;
1495                     let mut fn_span = None;
1496                     if let Some((decl, ident)) = self.get_parent_fn_decl(blk.hir_id) {
1497                         let ret_sp = decl.output.span();
1498                         if let Some(block_sp) = self.parent_item_span(blk.hir_id) {
1499                             // HACK: on some cases (`ui/liveness/liveness-issue-2163.rs`) the
1500                             // output would otherwise be incorrect and even misleading. Make sure
1501                             // the span we're aiming at correspond to a `fn` body.
1502                             if block_sp == blk.span {
1503                                 sp = ret_sp;
1504                                 fn_span = Some(ident.span);
1505                             }
1506                         }
1507                     }
1508                     coerce.coerce_forced_unit(
1509                         self,
1510                         &self.misc(sp),
1511                         &mut |err| {
1512                             if let Some(expected_ty) = expected.only_has_type(self) {
1513                                 if !self.consider_removing_semicolon(blk, expected_ty, err) {
1514                                     self.err_ctxt().consider_returning_binding(
1515                                         blk,
1516                                         expected_ty,
1517                                         err,
1518                                     );
1519                                 }
1520                                 if expected_ty == self.tcx.types.bool {
1521                                     // If this is caused by a missing `let` in a `while let`,
1522                                     // silence this redundant error, as we already emit E0070.
1523
1524                                     // Our block must be a `assign desugar local; assignment`
1525                                     if let Some(hir::Node::Block(hir::Block {
1526                                         stmts:
1527                                             [
1528                                                 hir::Stmt {
1529                                                     kind:
1530                                                         hir::StmtKind::Local(hir::Local {
1531                                                             source:
1532                                                                 hir::LocalSource::AssignDesugar(_),
1533                                                             ..
1534                                                         }),
1535                                                     ..
1536                                                 },
1537                                                 hir::Stmt {
1538                                                     kind:
1539                                                         hir::StmtKind::Expr(hir::Expr {
1540                                                             kind: hir::ExprKind::Assign(..),
1541                                                             ..
1542                                                         }),
1543                                                     ..
1544                                                 },
1545                                             ],
1546                                         ..
1547                                     })) = self.tcx.hir().find(blk.hir_id)
1548                                     {
1549                                         self.comes_from_while_condition(blk.hir_id, |_| {
1550                                             err.downgrade_to_delayed_bug();
1551                                         })
1552                                     }
1553                                 }
1554                             }
1555                             if let Some(fn_span) = fn_span {
1556                                 err.span_label(
1557                                     fn_span,
1558                                     "implicitly returns `()` as its body has no tail or `return` \
1559                                      expression",
1560                                 );
1561                             }
1562                         },
1563                         false,
1564                     );
1565                 }
1566             }
1567         });
1568
1569         if ctxt.may_break {
1570             // If we can break from the block, then the block's exit is always reachable
1571             // (... as long as the entry is reachable) - regardless of the tail of the block.
1572             self.diverges.set(prev_diverges);
1573         }
1574
1575         let ty = ctxt.coerce.unwrap().complete(self);
1576
1577         self.write_ty(blk.hir_id, ty);
1578
1579         ty
1580     }
1581
1582     fn parent_item_span(&self, id: hir::HirId) -> Option<Span> {
1583         let node = self.tcx.hir().get_by_def_id(self.tcx.hir().get_parent_item(id).def_id);
1584         match node {
1585             Node::Item(&hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })
1586             | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(_, body_id), .. }) => {
1587                 let body = self.tcx.hir().body(body_id);
1588                 if let ExprKind::Block(block, _) = &body.value.kind {
1589                     return Some(block.span);
1590                 }
1591             }
1592             _ => {}
1593         }
1594         None
1595     }
1596
1597     /// Given a function block's `HirId`, returns its `FnDecl` if it exists, or `None` otherwise.
1598     fn get_parent_fn_decl(&self, blk_id: hir::HirId) -> Option<(&'tcx hir::FnDecl<'tcx>, Ident)> {
1599         let parent = self.tcx.hir().get_by_def_id(self.tcx.hir().get_parent_item(blk_id).def_id);
1600         self.get_node_fn_decl(parent).map(|(fn_decl, ident, _)| (fn_decl, ident))
1601     }
1602
1603     /// If `expr` is a `match` expression that has only one non-`!` arm, use that arm's tail
1604     /// expression's `Span`, otherwise return `expr.span`. This is done to give better errors
1605     /// when given code like the following:
1606     /// ```text
1607     /// if false { return 0i32; } else { 1u32 }
1608     /// //                               ^^^^ point at this instead of the whole `if` expression
1609     /// ```
1610     fn get_expr_coercion_span(&self, expr: &hir::Expr<'_>) -> rustc_span::Span {
1611         let check_in_progress = |elem: &hir::Expr<'_>| {
1612             self.typeck_results.borrow().node_type_opt(elem.hir_id).filter(|ty| !ty.is_never()).map(
1613                 |_| match elem.kind {
1614                     // Point at the tail expression when possible.
1615                     hir::ExprKind::Block(block, _) => block.expr.map_or(block.span, |e| e.span),
1616                     _ => elem.span,
1617                 },
1618             )
1619         };
1620
1621         if let hir::ExprKind::If(_, _, Some(el)) = expr.kind {
1622             if let Some(rslt) = check_in_progress(el) {
1623                 return rslt;
1624             }
1625         }
1626
1627         if let hir::ExprKind::Match(_, arms, _) = expr.kind {
1628             let mut iter = arms.iter().filter_map(|arm| check_in_progress(arm.body));
1629             if let Some(span) = iter.next() {
1630                 if iter.next().is_none() {
1631                     return span;
1632                 }
1633             }
1634         }
1635
1636         expr.span
1637     }
1638
1639     fn overwrite_local_ty_if_err(
1640         &self,
1641         hir_id: hir::HirId,
1642         pat: &'tcx hir::Pat<'tcx>,
1643         ty: Ty<'tcx>,
1644     ) {
1645         if ty.references_error() {
1646             // Override the types everywhere with `err()` to avoid knock on errors.
1647             let err = self.tcx.ty_error();
1648             self.write_ty(hir_id, err);
1649             self.write_ty(pat.hir_id, err);
1650             let local_ty = LocalTy { decl_ty: err, revealed_ty: err };
1651             self.locals.borrow_mut().insert(hir_id, local_ty);
1652             self.locals.borrow_mut().insert(pat.hir_id, local_ty);
1653         }
1654     }
1655
1656     // Finish resolving a path in a struct expression or pattern `S::A { .. }` if necessary.
1657     // The newly resolved definition is written into `type_dependent_defs`.
1658     fn finish_resolving_struct_path(
1659         &self,
1660         qpath: &QPath<'_>,
1661         path_span: Span,
1662         hir_id: hir::HirId,
1663     ) -> (Res, RawTy<'tcx>) {
1664         match *qpath {
1665             QPath::Resolved(ref maybe_qself, ref path) => {
1666                 let self_ty = maybe_qself.as_ref().map(|qself| self.to_ty(qself).raw);
1667                 let ty = self.astconv().res_to_ty(self_ty, path, true);
1668                 (path.res, self.handle_raw_ty(path_span, ty))
1669             }
1670             QPath::TypeRelative(ref qself, ref segment) => {
1671                 let ty = self.to_ty(qself);
1672
1673                 let result = self
1674                     .astconv()
1675                     .associated_path_to_ty(hir_id, path_span, ty.raw, qself, segment, true);
1676                 let ty = result.map(|(ty, _, _)| ty).unwrap_or_else(|_| self.tcx().ty_error());
1677                 let ty = self.handle_raw_ty(path_span, ty);
1678                 let result = result.map(|(_, kind, def_id)| (kind, def_id));
1679
1680                 // Write back the new resolution.
1681                 self.write_resolution(hir_id, result);
1682
1683                 (result.map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id)), ty)
1684             }
1685             QPath::LangItem(lang_item, span, id) => {
1686                 let (res, ty) = self.resolve_lang_item_path(lang_item, span, hir_id, id);
1687                 (res, self.handle_raw_ty(path_span, ty))
1688             }
1689         }
1690     }
1691
1692     /// Given a vector of fulfillment errors, try to adjust the spans of the
1693     /// errors to more accurately point at the cause of the failure.
1694     ///
1695     /// This applies to calls, methods, and struct expressions. This will also
1696     /// try to deduplicate errors that are due to the same cause but might
1697     /// have been created with different [`ObligationCause`][traits::ObligationCause]s.
1698     pub(super) fn adjust_fulfillment_errors_for_expr_obligation(
1699         &self,
1700         errors: &mut Vec<traits::FulfillmentError<'tcx>>,
1701     ) {
1702         // Store a mapping from `(Span, Predicate) -> ObligationCause`, so that
1703         // other errors that have the same span and predicate can also get fixed,
1704         // even if their `ObligationCauseCode` isn't an `Expr*Obligation` kind.
1705         // This is important since if we adjust one span but not the other, then
1706         // we will have "duplicated" the error on the UI side.
1707         let mut remap_cause = FxIndexSet::default();
1708         let mut not_adjusted = vec![];
1709
1710         for error in errors {
1711             let before_span = error.obligation.cause.span;
1712             if self.adjust_fulfillment_error_for_expr_obligation(error)
1713                 || before_span != error.obligation.cause.span
1714             {
1715                 // Store both the predicate and the predicate *without constness*
1716                 // since sometimes we instantiate and check both of these in a
1717                 // method call, for example.
1718                 remap_cause.insert((
1719                     before_span,
1720                     error.obligation.predicate,
1721                     error.obligation.cause.clone(),
1722                 ));
1723                 remap_cause.insert((
1724                     before_span,
1725                     error.obligation.predicate.without_const(self.tcx),
1726                     error.obligation.cause.clone(),
1727                 ));
1728             } else {
1729                 // If it failed to be adjusted once around, it may be adjusted
1730                 // via the "remap cause" mapping the second time...
1731                 not_adjusted.push(error);
1732             }
1733         }
1734
1735         // Adjust any other errors that come from other cause codes, when these
1736         // errors are of the same predicate as one we successfully adjusted, and
1737         // when their spans overlap (suggesting they're due to the same root cause).
1738         //
1739         // This is because due to normalization, we often register duplicate
1740         // obligations with misc obligations that are basically impossible to
1741         // line back up with a useful ExprBindingObligation.
1742         for error in not_adjusted {
1743             for (span, predicate, cause) in &remap_cause {
1744                 if *predicate == error.obligation.predicate
1745                     && span.contains(error.obligation.cause.span)
1746                 {
1747                     error.obligation.cause = cause.clone();
1748                     continue;
1749                 }
1750             }
1751         }
1752     }
1753
1754     fn adjust_fulfillment_error_for_expr_obligation(
1755         &self,
1756         error: &mut traits::FulfillmentError<'tcx>,
1757     ) -> bool {
1758         let (traits::ExprItemObligation(def_id, hir_id, idx) | traits::ExprBindingObligation(def_id, _, hir_id, idx))
1759             = *error.obligation.cause.code().peel_derives() else { return false; };
1760         let hir = self.tcx.hir();
1761         let hir::Node::Expr(expr) = hir.get(hir_id) else { return false; };
1762
1763         let Some(unsubstituted_pred) =
1764             self.tcx.predicates_of(def_id).instantiate_identity(self.tcx).predicates.into_iter().nth(idx)
1765             else { return false; };
1766
1767         let generics = self.tcx.generics_of(def_id);
1768         let predicate_substs = match unsubstituted_pred.kind().skip_binder() {
1769             ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => pred.trait_ref.substs,
1770             ty::PredicateKind::Clause(ty::Clause::Projection(pred)) => pred.projection_ty.substs,
1771             _ => ty::List::empty(),
1772         };
1773
1774         let find_param_matching = |matches: &dyn Fn(&ty::ParamTy) -> bool| {
1775             predicate_substs.types().find_map(|ty| {
1776                 ty.walk().find_map(|arg| {
1777                     if let ty::GenericArgKind::Type(ty) = arg.unpack()
1778                         && let ty::Param(param_ty) = ty.kind()
1779                         && matches(param_ty)
1780                     {
1781                         Some(arg)
1782                     } else {
1783                         None
1784                     }
1785                 })
1786             })
1787         };
1788
1789         // Prefer generics that are local to the fn item, since these are likely
1790         // to be the cause of the unsatisfied predicate.
1791         let mut param_to_point_at = find_param_matching(&|param_ty| {
1792             self.tcx.parent(generics.type_param(param_ty, self.tcx).def_id) == def_id
1793         });
1794         // Fall back to generic that isn't local to the fn item. This will come
1795         // from a trait or impl, for example.
1796         let mut fallback_param_to_point_at = find_param_matching(&|param_ty| {
1797             self.tcx.parent(generics.type_param(param_ty, self.tcx).def_id) != def_id
1798                 && param_ty.name != rustc_span::symbol::kw::SelfUpper
1799         });
1800         // Finally, the `Self` parameter is possibly the reason that the predicate
1801         // is unsatisfied. This is less likely to be true for methods, because
1802         // method probe means that we already kinda check that the predicates due
1803         // to the `Self` type are true.
1804         let mut self_param_to_point_at =
1805             find_param_matching(&|param_ty| param_ty.name == rustc_span::symbol::kw::SelfUpper);
1806
1807         // Finally, for ambiguity-related errors, we actually want to look
1808         // for a parameter that is the source of the inference type left
1809         // over in this predicate.
1810         if let traits::FulfillmentErrorCode::CodeAmbiguity = error.code {
1811             fallback_param_to_point_at = None;
1812             self_param_to_point_at = None;
1813             param_to_point_at =
1814                 self.find_ambiguous_parameter_in(def_id, error.root_obligation.predicate);
1815         }
1816
1817         if self.closure_span_overlaps_error(error, expr.span) {
1818             return false;
1819         }
1820
1821         match &expr.kind {
1822             hir::ExprKind::Path(qpath) => {
1823                 if let hir::Node::Expr(hir::Expr {
1824                     kind: hir::ExprKind::Call(callee, args),
1825                     hir_id: call_hir_id,
1826                     span: call_span,
1827                     ..
1828                 }) = hir.get_parent(expr.hir_id)
1829                     && callee.hir_id == expr.hir_id
1830                 {
1831                     if self.closure_span_overlaps_error(error, *call_span) {
1832                         return false;
1833                     }
1834
1835                     for param in
1836                         [param_to_point_at, fallback_param_to_point_at, self_param_to_point_at]
1837                         .into_iter()
1838                         .flatten()
1839                     {
1840                         if self.point_at_arg_if_possible(
1841                                 error,
1842                                 def_id,
1843                                 param,
1844                                 *call_hir_id,
1845                                 callee.span,
1846                                 None,
1847                                 args,
1848                             )
1849                         {
1850                             return true;
1851                         }
1852                     }
1853                 }
1854                 // Notably, we only point to params that are local to the
1855                 // item we're checking, since those are the ones we are able
1856                 // to look in the final `hir::PathSegment` for. Everything else
1857                 // would require a deeper search into the `qpath` than I think
1858                 // is worthwhile.
1859                 if let Some(param_to_point_at) = param_to_point_at
1860                     && self.point_at_path_if_possible(error, def_id, param_to_point_at, qpath)
1861                 {
1862                     return true;
1863                 }
1864             }
1865             hir::ExprKind::MethodCall(segment, receiver, args, ..) => {
1866                 for param in [param_to_point_at, fallback_param_to_point_at, self_param_to_point_at]
1867                     .into_iter()
1868                     .flatten()
1869                 {
1870                     if self.point_at_arg_if_possible(
1871                         error,
1872                         def_id,
1873                         param,
1874                         hir_id,
1875                         segment.ident.span,
1876                         Some(receiver),
1877                         args,
1878                     ) {
1879                         return true;
1880                     }
1881                 }
1882                 if let Some(param_to_point_at) = param_to_point_at
1883                     && self.point_at_generic_if_possible(error, def_id, param_to_point_at, segment)
1884                 {
1885                     return true;
1886                 }
1887             }
1888             hir::ExprKind::Struct(qpath, fields, ..) => {
1889                 if let Res::Def(DefKind::Struct | DefKind::Variant, variant_def_id) =
1890                     self.typeck_results.borrow().qpath_res(qpath, hir_id)
1891                 {
1892                     for param in
1893                         [param_to_point_at, fallback_param_to_point_at, self_param_to_point_at]
1894                     {
1895                         if let Some(param) = param
1896                             && self.point_at_field_if_possible(
1897                                 error,
1898                                 def_id,
1899                                 param,
1900                                 variant_def_id,
1901                                 fields,
1902                             )
1903                         {
1904                             return true;
1905                         }
1906                     }
1907                 }
1908                 if let Some(param_to_point_at) = param_to_point_at
1909                     && self.point_at_path_if_possible(error, def_id, param_to_point_at, qpath)
1910                 {
1911                     return true;
1912                 }
1913             }
1914             _ => {}
1915         }
1916
1917         false
1918     }
1919
1920     fn closure_span_overlaps_error(
1921         &self,
1922         error: &traits::FulfillmentError<'tcx>,
1923         span: Span,
1924     ) -> bool {
1925         if let traits::FulfillmentErrorCode::CodeSelectionError(
1926             traits::SelectionError::OutputTypeParameterMismatch(_, expected, _),
1927         ) = error.code
1928             && let ty::Closure(def_id, _) | ty::Generator(def_id, ..) = expected.skip_binder().self_ty().kind()
1929             && span.overlaps(self.tcx.def_span(*def_id))
1930         {
1931             true
1932         } else {
1933             false
1934         }
1935     }
1936
1937     fn point_at_arg_if_possible(
1938         &self,
1939         error: &mut traits::FulfillmentError<'tcx>,
1940         def_id: DefId,
1941         param_to_point_at: ty::GenericArg<'tcx>,
1942         call_hir_id: hir::HirId,
1943         callee_span: Span,
1944         receiver: Option<&'tcx hir::Expr<'tcx>>,
1945         args: &'tcx [hir::Expr<'tcx>],
1946     ) -> bool {
1947         let ty = self.tcx.type_of(def_id);
1948         if !ty.is_fn() {
1949             return false;
1950         }
1951         let sig = ty.fn_sig(self.tcx).skip_binder();
1952         let args_referencing_param: Vec<_> = sig
1953             .inputs()
1954             .iter()
1955             .enumerate()
1956             .filter(|(_, ty)| find_param_in_ty(**ty, param_to_point_at))
1957             .collect();
1958         // If there's one field that references the given generic, great!
1959         if let [(idx, _)] = args_referencing_param.as_slice()
1960             && let Some(arg) = receiver
1961                 .map_or(args.get(*idx), |rcvr| if *idx == 0 { Some(rcvr) } else { args.get(*idx - 1) }) {
1962             error.obligation.cause.span = arg.span.find_ancestor_in_same_ctxt(error.obligation.cause.span).unwrap_or(arg.span);
1963             error.obligation.cause.map_code(|parent_code| {
1964                 ObligationCauseCode::FunctionArgumentObligation {
1965                     arg_hir_id: arg.hir_id,
1966                     call_hir_id,
1967                     parent_code,
1968                 }
1969             });
1970             return true;
1971         } else if args_referencing_param.len() > 0 {
1972             // If more than one argument applies, then point to the callee span at least...
1973             // We have chance to fix this up further in `point_at_generics_if_possible`
1974             error.obligation.cause.span = callee_span;
1975         }
1976
1977         false
1978     }
1979
1980     fn point_at_field_if_possible(
1981         &self,
1982         error: &mut traits::FulfillmentError<'tcx>,
1983         def_id: DefId,
1984         param_to_point_at: ty::GenericArg<'tcx>,
1985         variant_def_id: DefId,
1986         expr_fields: &[hir::ExprField<'tcx>],
1987     ) -> bool {
1988         let def = self.tcx.adt_def(def_id);
1989
1990         let identity_substs = ty::InternalSubsts::identity_for_item(self.tcx, def_id);
1991         let fields_referencing_param: Vec<_> = def
1992             .variant_with_id(variant_def_id)
1993             .fields
1994             .iter()
1995             .filter(|field| {
1996                 let field_ty = field.ty(self.tcx, identity_substs);
1997                 find_param_in_ty(field_ty, param_to_point_at)
1998             })
1999             .collect();
2000
2001         if let [field] = fields_referencing_param.as_slice() {
2002             for expr_field in expr_fields {
2003                 // Look for the ExprField that matches the field, using the
2004                 // same rules that check_expr_struct uses for macro hygiene.
2005                 if self.tcx.adjust_ident(expr_field.ident, variant_def_id) == field.ident(self.tcx)
2006                 {
2007                     error.obligation.cause.span = expr_field
2008                         .expr
2009                         .span
2010                         .find_ancestor_in_same_ctxt(error.obligation.cause.span)
2011                         .unwrap_or(expr_field.span);
2012                     return true;
2013                 }
2014             }
2015         }
2016
2017         false
2018     }
2019
2020     fn point_at_path_if_possible(
2021         &self,
2022         error: &mut traits::FulfillmentError<'tcx>,
2023         def_id: DefId,
2024         param: ty::GenericArg<'tcx>,
2025         qpath: &QPath<'tcx>,
2026     ) -> bool {
2027         match qpath {
2028             hir::QPath::Resolved(_, path) => {
2029                 if let Some(segment) = path.segments.last()
2030                     && self.point_at_generic_if_possible(error, def_id, param, segment)
2031                 {
2032                     return true;
2033                 }
2034             }
2035             hir::QPath::TypeRelative(_, segment) => {
2036                 if self.point_at_generic_if_possible(error, def_id, param, segment) {
2037                     return true;
2038                 }
2039             }
2040             _ => {}
2041         }
2042
2043         false
2044     }
2045
2046     fn point_at_generic_if_possible(
2047         &self,
2048         error: &mut traits::FulfillmentError<'tcx>,
2049         def_id: DefId,
2050         param_to_point_at: ty::GenericArg<'tcx>,
2051         segment: &hir::PathSegment<'tcx>,
2052     ) -> bool {
2053         let own_substs = self
2054             .tcx
2055             .generics_of(def_id)
2056             .own_substs(ty::InternalSubsts::identity_for_item(self.tcx, def_id));
2057         let Some((index, _)) = own_substs
2058             .iter()
2059             .filter(|arg| matches!(arg.unpack(), ty::GenericArgKind::Type(_)))
2060             .enumerate()
2061             .find(|(_, arg)| **arg == param_to_point_at) else { return false };
2062         let Some(arg) = segment
2063             .args()
2064             .args
2065             .iter()
2066             .filter(|arg| matches!(arg, hir::GenericArg::Type(_)))
2067             .nth(index) else { return false; };
2068         error.obligation.cause.span = arg
2069             .span()
2070             .find_ancestor_in_same_ctxt(error.obligation.cause.span)
2071             .unwrap_or(arg.span());
2072         true
2073     }
2074
2075     fn find_ambiguous_parameter_in<T: TypeVisitable<'tcx>>(
2076         &self,
2077         item_def_id: DefId,
2078         t: T,
2079     ) -> Option<ty::GenericArg<'tcx>> {
2080         struct FindAmbiguousParameter<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, DefId);
2081         impl<'tcx> TypeVisitor<'tcx> for FindAmbiguousParameter<'_, 'tcx> {
2082             type BreakTy = ty::GenericArg<'tcx>;
2083             fn visit_ty(&mut self, ty: Ty<'tcx>) -> std::ops::ControlFlow<Self::BreakTy> {
2084                 if let Some(origin) = self.0.type_var_origin(ty)
2085                     && let TypeVariableOriginKind::TypeParameterDefinition(_, Some(def_id)) =
2086                         origin.kind
2087                     && let generics = self.0.tcx.generics_of(self.1)
2088                     && let Some(index) = generics.param_def_id_to_index(self.0.tcx, def_id)
2089                     && let Some(subst) = ty::InternalSubsts::identity_for_item(self.0.tcx, self.1)
2090                         .get(index as usize)
2091                 {
2092                     ControlFlow::Break(*subst)
2093                 } else {
2094                     ty.super_visit_with(self)
2095                 }
2096             }
2097         }
2098         t.visit_with(&mut FindAmbiguousParameter(self, item_def_id)).break_value()
2099     }
2100
2101     fn label_fn_like(
2102         &self,
2103         err: &mut Diagnostic,
2104         callable_def_id: Option<DefId>,
2105         callee_ty: Option<Ty<'tcx>>,
2106         // A specific argument should be labeled, instead of all of them
2107         expected_idx: Option<usize>,
2108         is_method: bool,
2109     ) {
2110         let Some(mut def_id) = callable_def_id else {
2111             return;
2112         };
2113
2114         if let Some(assoc_item) = self.tcx.opt_associated_item(def_id)
2115             // Possibly points at either impl or trait item, so try to get it
2116             // to point to trait item, then get the parent.
2117             // This parent might be an impl in the case of an inherent function,
2118             // but the next check will fail.
2119             && let maybe_trait_item_def_id = assoc_item.trait_item_def_id.unwrap_or(def_id)
2120             && let maybe_trait_def_id = self.tcx.parent(maybe_trait_item_def_id)
2121             // Just an easy way to check "trait_def_id == Fn/FnMut/FnOnce"
2122             && let Some(call_kind) = self.tcx.fn_trait_kind_from_def_id(maybe_trait_def_id)
2123             && let Some(callee_ty) = callee_ty
2124         {
2125             let callee_ty = callee_ty.peel_refs();
2126             match *callee_ty.kind() {
2127                 ty::Param(param) => {
2128                     let param =
2129                         self.tcx.generics_of(self.body_id).type_param(&param, self.tcx);
2130                     if param.kind.is_synthetic() {
2131                         // if it's `impl Fn() -> ..` then just fall down to the def-id based logic
2132                         def_id = param.def_id;
2133                     } else {
2134                         // Otherwise, find the predicate that makes this generic callable,
2135                         // and point at that.
2136                         let instantiated = self
2137                             .tcx
2138                             .explicit_predicates_of(self.body_id)
2139                             .instantiate_identity(self.tcx);
2140                         // FIXME(compiler-errors): This could be problematic if something has two
2141                         // fn-like predicates with different args, but callable types really never
2142                         // do that, so it's OK.
2143                         for (predicate, span) in instantiated
2144                         {
2145                             if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = predicate.kind().skip_binder()
2146                                 && pred.self_ty().peel_refs() == callee_ty
2147                                 && self.tcx.is_fn_trait(pred.def_id())
2148                             {
2149                                 err.span_note(span, "callable defined here");
2150                                 return;
2151                             }
2152                         }
2153                     }
2154                 }
2155                 ty::Alias(ty::Opaque, ty::AliasTy { def_id: new_def_id, .. })
2156                 | ty::Closure(new_def_id, _)
2157                 | ty::FnDef(new_def_id, _) => {
2158                     def_id = new_def_id;
2159                 }
2160                 _ => {
2161                     // Look for a user-provided impl of a `Fn` trait, and point to it.
2162                     let new_def_id = self.probe(|_| {
2163                         let trait_ref = self.tcx.mk_trait_ref(
2164                             call_kind.to_def_id(self.tcx),
2165                             [
2166                                 callee_ty,
2167                                 self.next_ty_var(TypeVariableOrigin {
2168                                     kind: TypeVariableOriginKind::MiscVariable,
2169                                     span: rustc_span::DUMMY_SP,
2170                                 }),
2171                             ],
2172                         );
2173                         let obligation = traits::Obligation::new(
2174                             self.tcx,
2175                             traits::ObligationCause::dummy(),
2176                             self.param_env,
2177                             ty::Binder::dummy(trait_ref),
2178                         );
2179                         match SelectionContext::new(&self).select(&obligation) {
2180                             Ok(Some(traits::ImplSource::UserDefined(impl_source))) => {
2181                                 Some(impl_source.impl_def_id)
2182                             }
2183                             _ => None,
2184                         }
2185                     });
2186                     if let Some(new_def_id) = new_def_id {
2187                         def_id = new_def_id;
2188                     } else {
2189                         return;
2190                     }
2191                 }
2192             }
2193         }
2194
2195         if let Some(def_span) = self.tcx.def_ident_span(def_id) && !def_span.is_dummy() {
2196             let mut spans: MultiSpan = def_span.into();
2197
2198             let params = self
2199                 .tcx
2200                 .hir()
2201                 .get_if_local(def_id)
2202                 .and_then(|node| node.body_id())
2203                 .into_iter()
2204                 .flat_map(|id| self.tcx.hir().body(id).params)
2205                 .skip(if is_method { 1 } else { 0 });
2206
2207             for (_, param) in params
2208                 .into_iter()
2209                 .enumerate()
2210                 .filter(|(idx, _)| expected_idx.map_or(true, |expected_idx| expected_idx == *idx))
2211             {
2212                 spans.push_span_label(param.span, "");
2213             }
2214
2215             let def_kind = self.tcx.def_kind(def_id);
2216             err.span_note(spans, &format!("{} defined here", def_kind.descr(def_id)));
2217         } else if let Some(hir::Node::Expr(e)) = self.tcx.hir().get_if_local(def_id)
2218             && let hir::ExprKind::Closure(hir::Closure { body, .. }) = &e.kind
2219         {
2220             let param = expected_idx
2221                 .and_then(|expected_idx| self.tcx.hir().body(*body).params.get(expected_idx));
2222             let (kind, span) = if let Some(param) = param {
2223                 ("closure parameter", param.span)
2224             } else {
2225                 ("closure", self.tcx.def_span(def_id))
2226             };
2227             err.span_note(span, &format!("{} defined here", kind));
2228         } else {
2229             let def_kind = self.tcx.def_kind(def_id);
2230             err.span_note(
2231                 self.tcx.def_span(def_id),
2232                 &format!("{} defined here", def_kind.descr(def_id)),
2233             );
2234         }
2235     }
2236 }
2237
2238 fn find_param_in_ty<'tcx>(ty: Ty<'tcx>, param_to_point_at: ty::GenericArg<'tcx>) -> bool {
2239     let mut walk = ty.walk();
2240     while let Some(arg) = walk.next() {
2241         if arg == param_to_point_at {
2242             return true;
2243         } else if let ty::GenericArgKind::Type(ty) = arg.unpack()
2244             && let ty::Alias(ty::Projection, ..) = ty.kind()
2245         {
2246             // This logic may seem a bit strange, but typically when
2247             // we have a projection type in a function signature, the
2248             // argument that's being passed into that signature is
2249             // not actually constraining that projection's substs in
2250             // a meaningful way. So we skip it, and see improvements
2251             // in some UI tests.
2252             walk.skip_current_subtree();
2253         }
2254     }
2255     false
2256 }