compiler/rustc_hir_typeck/src/demand.rs

   1 use crate::FnCtxt;
   2 use rustc_ast::util::parser::PREC_POSTFIX;
   3 use rustc_data_structures::fx::FxHashMap;
   4 use rustc_errors::MultiSpan;
   5 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
   6 use rustc_hir as hir;
   7 use rustc_hir::def::CtorKind;
   8 use rustc_hir::intravisit::Visitor;
   9 use rustc_hir::lang_items::LangItem;
  10 use rustc_hir::{is_range_literal, Node};
  11 use rustc_infer::infer::InferOk;
  12 use rustc_middle::lint::in_external_macro;
  13 use rustc_middle::middle::stability::EvalResult;
  14 use rustc_middle::ty::adjustment::AllowTwoPhase;
  15 use rustc_middle::ty::error::{ExpectedFound, TypeError};
  16 use rustc_middle::ty::fold::{BottomUpFolder, TypeFolder};
  17 use rustc_middle::ty::print::{with_forced_trimmed_paths, with_no_trimmed_paths};
  18 use rustc_middle::ty::relate::TypeRelation;
  19 use rustc_middle::ty::{self, Article, AssocItem, Ty, TypeAndMut, TypeVisitable};
  20 use rustc_span::symbol::{sym, Symbol};
  21 use rustc_span::{BytePos, Span};
  22 use rustc_trait_selection::infer::InferCtxtExt as _;
  23 use rustc_trait_selection::traits::error_reporting::method_chain::CollectAllMismatches;
  24 use rustc_trait_selection::traits::ObligationCause;
  25
  26 use super::method::probe;
  27
  28 use std::cmp::min;
  29 use std::iter;
  30
  31 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  32     pub fn emit_type_mismatch_suggestions(
  33         &self,
  34         err: &mut Diagnostic,
  35         expr: &hir::Expr<'tcx>,
  36         expr_ty: Ty<'tcx>,
  37         expected: Ty<'tcx>,
  38         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
  39         error: Option<TypeError<'tcx>>,
  40     ) {
  41         if expr_ty == expected {
  42             return;
  43         }
  44
  45         self.annotate_alternative_method_deref(err, expr, error);
  46
  47         // Use `||` to give these suggestions a precedence
  48         let suggested = self.suggest_missing_parentheses(err, expr)
  49             || self.suggest_remove_last_method_call(err, expr, expected)
  50             || self.suggest_associated_const(err, expr, expected)
  51             || self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr)
  52             || self.suggest_option_to_bool(err, expr, expr_ty, expected)
  53             || self.suggest_compatible_variants(err, expr, expected, expr_ty)
  54             || self.suggest_non_zero_new_unwrap(err, expr, expected, expr_ty)
  55             || self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty)
  56             || self.suggest_no_capture_closure(err, expected, expr_ty)
  57             || self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty)
  58             || self.suggest_block_to_brackets_peeling_refs(err, expr, expr_ty, expected)
  59             || self.suggest_copied_or_cloned(err, expr, expr_ty, expected)
  60             || self.suggest_clone_for_ref(err, expr, expr_ty, expected)
  61             || self.suggest_into(err, expr, expr_ty, expected)
  62             || self.suggest_floating_point_literal(err, expr, expected)
  63             || self.note_result_coercion(err, expr, expected, expr_ty);
  64         if !suggested {
  65             self.point_at_expr_source_of_inferred_type(err, expr, expr_ty, expected, expr.span);
  66         }
  67     }
  68
  69     pub fn emit_coerce_suggestions(
  70         &self,
  71         err: &mut Diagnostic,
  72         expr: &hir::Expr<'tcx>,
  73         expr_ty: Ty<'tcx>,
  74         expected: Ty<'tcx>,
  75         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
  76         error: Option<TypeError<'tcx>>,
  77     ) {
  78         if expr_ty == expected {
  79             return;
  80         }
  81
  82         self.annotate_expected_due_to_let_ty(err, expr, error);
  83         self.emit_type_mismatch_suggestions(err, expr, expr_ty, expected, expected_ty_expr, error);
  84         self.note_type_is_not_clone(err, expected, expr_ty, expr);
  85         self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
  86         self.check_for_range_as_method_call(err, expr, expr_ty, expected);
  87         self.check_for_binding_assigned_block_without_tail_expression(err, expr, expr_ty, expected);
  88         self.check_wrong_return_type_due_to_generic_arg(err, expr, expr_ty);
  89     }
  90
  91     /// Requires that the two types unify, and prints an error message if
  92     /// they don't.
  93     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  94         if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
  95             e.emit();
  96         }
  97     }
  98
  99     pub fn demand_suptype_diag(
 100         &self,
 101         sp: Span,
 102         expected: Ty<'tcx>,
 103         actual: Ty<'tcx>,
 104     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
 105         self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
 106     }
 107
 108     #[instrument(skip(self), level = "debug")]
 109     pub fn demand_suptype_with_origin(
 110         &self,
 111         cause: &ObligationCause<'tcx>,
 112         expected: Ty<'tcx>,
 113         actual: Ty<'tcx>,
 114     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
 115         match self.at(cause, self.param_env).sup(expected, actual) {
 116             Ok(InferOk { obligations, value: () }) => {
 117                 self.register_predicates(obligations);
 118                 None
 119             }
 120             Err(e) => Some(self.err_ctxt().report_mismatched_types(&cause, expected, actual, e)),
 121         }
 122     }
 123
 124     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
 125         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
 126             err.emit();
 127         }
 128     }
 129
 130     pub fn demand_eqtype_diag(
 131         &self,
 132         sp: Span,
 133         expected: Ty<'tcx>,
 134         actual: Ty<'tcx>,
 135     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
 136         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
 137     }
 138
 139     pub fn demand_eqtype_with_origin(
 140         &self,
 141         cause: &ObligationCause<'tcx>,
 142         expected: Ty<'tcx>,
 143         actual: Ty<'tcx>,
 144     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
 145         match self.at(cause, self.param_env).eq(expected, actual) {
 146             Ok(InferOk { obligations, value: () }) => {
 147                 self.register_predicates(obligations);
 148                 None
 149             }
 150             Err(e) => Some(self.err_ctxt().report_mismatched_types(cause, expected, actual, e)),
 151         }
 152     }
 153
 154     pub fn demand_coerce(
 155         &self,
 156         expr: &hir::Expr<'tcx>,
 157         checked_ty: Ty<'tcx>,
 158         expected: Ty<'tcx>,
 159         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 160         allow_two_phase: AllowTwoPhase,
 161     ) -> Ty<'tcx> {
 162         let (ty, err) =
 163             self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
 164         if let Some(mut err) = err {
 165             err.emit();
 166         }
 167         ty
 168     }
 169
 170     /// Checks that the type of `expr` can be coerced to `expected`.
 171     ///
 172     /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
 173     /// will be permitted if the diverges flag is currently "always".
 174     #[instrument(level = "debug", skip(self, expr, expected_ty_expr, allow_two_phase))]
 175     pub fn demand_coerce_diag(
 176         &self,
 177         expr: &hir::Expr<'tcx>,
 178         checked_ty: Ty<'tcx>,
 179         expected: Ty<'tcx>,
 180         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 181         allow_two_phase: AllowTwoPhase,
 182     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>) {
 183         let expected = self.resolve_vars_with_obligations(expected);
 184
 185         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase, None) {
 186             Ok(ty) => return (ty, None),
 187             Err(e) => e,
 188         };
 189
 190         self.set_tainted_by_errors(self.tcx.sess.delay_span_bug(
 191             expr.span,
 192             "`TypeError` when attempting coercion but no error emitted",
 193         ));
 194         let expr = expr.peel_drop_temps();
 195         let cause = self.misc(expr.span);
 196         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 197         let mut err = self.err_ctxt().report_mismatched_types(&cause, expected, expr_ty, e);
 198
 199         let is_insufficiently_polymorphic =
 200             matches!(e, TypeError::RegionsInsufficientlyPolymorphic(..));
 201
 202         // FIXME(#73154): For now, we do leak check when coercing function
 203         // pointers in typeck, instead of only during borrowck. This can lead
 204         // to these `RegionsInsufficientlyPolymorphic` errors that aren't helpful.
 205         if !is_insufficiently_polymorphic {
 206             self.emit_coerce_suggestions(
 207                 &mut err,
 208                 expr,
 209                 expr_ty,
 210                 expected,
 211                 expected_ty_expr,
 212                 Some(e),
 213             );
 214         }
 215
 216         (expected, Some(err))
 217     }
 218
 219     pub fn point_at_expr_source_of_inferred_type(
 220         &self,
 221         err: &mut Diagnostic,
 222         expr: &hir::Expr<'_>,
 223         found: Ty<'tcx>,
 224         expected: Ty<'tcx>,
 225         mismatch_span: Span,
 226     ) -> bool {
 227         let map = self.tcx.hir();
 228
 229         let hir::ExprKind::Path(hir::QPath::Resolved(None, p)) = expr.kind else { return false; };
 230         let [hir::PathSegment { ident, args: None, .. }] = p.segments else { return false; };
 231         let hir::def::Res::Local(hir_id) = p.res else { return false; };
 232         let Some(hir::Node::Pat(pat)) = map.find(hir_id) else { return false; };
 233         let Some(hir::Node::Local(hir::Local {
 234             ty: None,
 235             init: Some(init),
 236             ..
 237         })) = map.find_parent(pat.hir_id) else { return false; };
 238         let Some(ty) = self.node_ty_opt(init.hir_id) else { return false; };
 239         if ty.is_closure() || init.span.overlaps(expr.span) || pat.span.from_expansion() {
 240             return false;
 241         }
 242
 243         // Locate all the usages of the relevant binding.
 244         struct FindExprs<'hir> {
 245             hir_id: hir::HirId,
 246             uses: Vec<&'hir hir::Expr<'hir>>,
 247         }
 248         impl<'v> Visitor<'v> for FindExprs<'v> {
 249             fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
 250                 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = ex.kind
 251                     && let hir::def::Res::Local(hir_id) = path.res
 252                     && hir_id == self.hir_id
 253                 {
 254                     self.uses.push(ex);
 255                 }
 256                 hir::intravisit::walk_expr(self, ex);
 257             }
 258         }
 259
 260         let mut expr_finder = FindExprs { hir_id, uses: vec![] };
 261         let id = map.get_parent_item(hir_id);
 262         let hir_id: hir::HirId = id.into();
 263
 264         let Some(node) = map.find(hir_id) else { return false; };
 265         let Some(body_id) = node.body_id() else { return false; };
 266         let body = map.body(body_id);
 267         expr_finder.visit_expr(body.value);
 268         // Hack to make equality checks on types with inference variables and regions useful.
 269         let mut eraser = BottomUpFolder {
 270             tcx: self.tcx,
 271             lt_op: |_| self.tcx.lifetimes.re_erased,
 272             ct_op: |c| c,
 273             ty_op: |t| match *t.kind() {
 274                 ty::Infer(ty::TyVar(_)) => self.tcx.mk_ty_var(ty::TyVid::from_u32(0)),
 275                 ty::Infer(ty::IntVar(_)) => {
 276                     self.tcx.mk_ty_infer(ty::IntVar(ty::IntVid { index: 0 }))
 277                 }
 278                 ty::Infer(ty::FloatVar(_)) => {
 279                     self.tcx.mk_ty_infer(ty::FloatVar(ty::FloatVid { index: 0 }))
 280                 }
 281                 _ => t,
 282             },
 283         };
 284         let mut prev = eraser.fold_ty(ty);
 285         let mut prev_span: Option<Span> = None;
 286
 287         for binding in expr_finder.uses {
 288             // In every expression where the binding is referenced, we will look at that
 289             // expression's type and see if it is where the incorrect found type was fully
 290             // "materialized" and point at it. We will also try to provide a suggestion there.
 291             if let Some(hir::Node::Expr(expr)
 292             | hir::Node::Stmt(hir::Stmt {
 293                 kind: hir::StmtKind::Expr(expr) | hir::StmtKind::Semi(expr),
 294                 ..
 295             })) = &map.find_parent(binding.hir_id)
 296                 && let hir::ExprKind::MethodCall(segment, rcvr, args, _span) = expr.kind
 297                 && rcvr.hir_id == binding.hir_id
 298                 && let Some(def_id) = self.typeck_results.borrow().type_dependent_def_id(expr.hir_id)
 299             {
 300                 // We special case methods, because they can influence inference through the
 301                 // call's arguments and we can provide a more explicit span.
 302                 let sig = self.tcx.fn_sig(def_id);
 303                 let def_self_ty = sig.input(0).skip_binder();
 304                 let rcvr_ty = self.node_ty(rcvr.hir_id);
 305                 // Get the evaluated type *after* calling the method call, so that the influence
 306                 // of the arguments can be reflected in the receiver type. The receiver
 307                 // expression has the type *before* theis analysis is done.
 308                 let ty = match self.lookup_probe_for_diagnostic(
 309                     segment.ident,
 310                     rcvr_ty,
 311                     expr,
 312                     probe::ProbeScope::TraitsInScope,
 313                     None,
 314                 ) {
 315                     Ok(pick) => pick.self_ty,
 316                     Err(_) => rcvr_ty,
 317                 };
 318                 // Remove one layer of references to account for `&mut self` and
 319                 // `&self`, so that we can compare it against the binding.
 320                 let (ty, def_self_ty) = match (ty.kind(), def_self_ty.kind()) {
 321                     (ty::Ref(_, ty, a), ty::Ref(_, self_ty, b)) if a == b => (*ty, *self_ty),
 322                     _ => (ty, def_self_ty),
 323                 };
 324                 let mut param_args = FxHashMap::default();
 325                 let mut param_expected = FxHashMap::default();
 326                 let mut param_found = FxHashMap::default();
 327                 if self.can_eq(self.param_env, ty, found).is_ok() {
 328                     // We only point at the first place where the found type was inferred.
 329                     for (i, param_ty) in sig.inputs().skip_binder().iter().skip(1).enumerate() {
 330                         if def_self_ty.contains(*param_ty) && let ty::Param(_) = param_ty.kind() {
 331                             // We found an argument that references a type parameter in `Self`,
 332                             // so we assume that this is the argument that caused the found
 333                             // type, which we know already because of `can_eq` above was first
 334                             // inferred in this method call.
 335                             let arg = &args[i];
 336                             let arg_ty = self.node_ty(arg.hir_id);
 337                             if !arg.span.overlaps(mismatch_span) {
 338                                 err.span_label(
 339                                     arg.span,
 340                                     &format!(
 341                                         "this is of type `{arg_ty}`, which causes `{ident}` to be \
 342                                         inferred as `{ty}`",
 343                                     ),
 344                                 );
 345                             }
 346                             param_args.insert(param_ty, (arg, arg_ty));
 347                         }
 348                     }
 349                 }
 350
 351                 // Here we find, for a type param `T`, the type that `T` is in the current
 352                 // method call *and* in the original expected type. That way, we can see if we
 353                 // can give any structured suggestion for the function argument.
 354                 let mut c = CollectAllMismatches {
 355                     infcx: &self.infcx,
 356                     param_env: self.param_env,
 357                     errors: vec![],
 358                 };
 359                 let _ = c.relate(def_self_ty, ty);
 360                 for error in c.errors {
 361                     if let TypeError::Sorts(error) = error {
 362                         param_found.insert(error.expected, error.found);
 363                     }
 364                 }
 365                 c.errors = vec![];
 366                 let _ = c.relate(def_self_ty, expected);
 367                 for error in c.errors {
 368                     if let TypeError::Sorts(error) = error {
 369                         param_expected.insert(error.expected, error.found);
 370                     }
 371                 }
 372                 for (param, (arg, arg_ty)) in param_args.iter() {
 373                     let Some(expected) = param_expected.get(param) else { continue; };
 374                     let Some(found) = param_found.get(param) else { continue; };
 375                     if self.can_eq(self.param_env, *arg_ty, *found).is_err() { continue; }
 376                     self.emit_coerce_suggestions(err, arg, *found, *expected, None, None);
 377                 }
 378
 379                 let ty = eraser.fold_ty(ty);
 380                 if ty.references_error() {
 381                     break;
 382                 }
 383                 if ty != prev
 384                     && param_args.is_empty()
 385                     && self.can_eq(self.param_env, ty, found).is_ok()
 386                 {
 387                     // We only point at the first place where the found type was inferred.
 388                     if !segment.ident.span.overlaps(mismatch_span) {
 389                     err.span_label(
 390                         segment.ident.span,
 391                         with_forced_trimmed_paths!(format!(
 392                             "here the type of `{ident}` is inferred to be `{ty}`",
 393                         )),
 394                     );}
 395                     break;
 396                 } else if !param_args.is_empty() {
 397                     break;
 398                 }
 399                 prev = ty;
 400             } else {
 401                 let ty = eraser.fold_ty(self.node_ty(binding.hir_id));
 402                 if ty.references_error() {
 403                     break;
 404                 }
 405                 if ty != prev
 406                     && let Some(span) = prev_span
 407                     && self.can_eq(self.param_env, ty, found).is_ok()
 408                 {
 409                     // We only point at the first place where the found type was inferred.
 410                     // We use the *previous* span because if the type is known *here* it means
 411                     // it was *evaluated earlier*. We don't do this for method calls because we
 412                     // evaluate the method's self type eagerly, but not in any other case.
 413                     if !span.overlaps(mismatch_span) {
 414                         err.span_label(
 415                             span,
 416                             with_forced_trimmed_paths!(format!(
 417                                 "here the type of `{ident}` is inferred to be `{ty}`",
 418                             )),
 419                         );
 420                     }
 421                     break;
 422                 }
 423                 prev = ty;
 424             }
 425             if binding.hir_id == expr.hir_id {
 426                 // Do not look at expressions that come after the expression we were originally
 427                 // evaluating and had a type error.
 428                 break;
 429             }
 430             prev_span = Some(binding.span);
 431         }
 432         true
 433     }
 434
 435     fn annotate_expected_due_to_let_ty(
 436         &self,
 437         err: &mut Diagnostic,
 438         expr: &hir::Expr<'_>,
 439         error: Option<TypeError<'tcx>>,
 440     ) {
 441         let parent = self.tcx.hir().parent_id(expr.hir_id);
 442         match (self.tcx.hir().find(parent), error) {
 443             (Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })), _)
 444                 if init.hir_id == expr.hir_id =>
 445             {
 446                 // Point at `let` assignment type.
 447                 err.span_label(ty.span, "expected due to this");
 448             }
 449             (
 450                 Some(hir::Node::Expr(hir::Expr {
 451                     kind: hir::ExprKind::Assign(lhs, rhs, _), ..
 452                 })),
 453                 Some(TypeError::Sorts(ExpectedFound { expected, .. })),
 454             ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
 455                 // We ignore closures explicitly because we already point at them elsewhere.
 456                 // Point at the assigned-to binding.
 457                 let mut primary_span = lhs.span;
 458                 let mut secondary_span = lhs.span;
 459                 let mut post_message = "";
 460                 match lhs.kind {
 461                     hir::ExprKind::Path(hir::QPath::Resolved(
 462                         None,
 463                         hir::Path {
 464                             res:
 465                                 hir::def::Res::Def(
 466                                     hir::def::DefKind::Static(_) | hir::def::DefKind::Const,
 467                                     def_id,
 468                                 ),
 469                             ..
 470                         },
 471                     )) => {
 472                         if let Some(hir::Node::Item(hir::Item {
 473                             ident,
 474                             kind: hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..),
 475                             ..
 476                         })) = self.tcx.hir().get_if_local(*def_id)
 477                         {
 478                             primary_span = ty.span;
 479                             secondary_span = ident.span;
 480                             post_message = " type";
 481                         }
 482                     }
 483                     hir::ExprKind::Path(hir::QPath::Resolved(
 484                         None,
 485                         hir::Path { res: hir::def::Res::Local(hir_id), .. },
 486                     )) => {
 487                         if let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(*hir_id) {
 488                             primary_span = pat.span;
 489                             secondary_span = pat.span;
 490                             match self.tcx.hir().find_parent(pat.hir_id) {
 491                                 Some(hir::Node::Local(hir::Local { ty: Some(ty), .. })) => {
 492                                     primary_span = ty.span;
 493                                     post_message = " type";
 494                                 }
 495                                 Some(hir::Node::Local(hir::Local { init: Some(init), .. })) => {
 496                                     primary_span = init.span;
 497                                     post_message = " value";
 498                                 }
 499                                 Some(hir::Node::Param(hir::Param { ty_span, .. })) => {
 500                                     primary_span = *ty_span;
 501                                     post_message = " parameter type";
 502                                 }
 503                                 _ => {}
 504                             }
 505                         }
 506                     }
 507                     _ => {}
 508                 }
 509
 510                 if primary_span != secondary_span
 511                     && self
 512                         .tcx
 513                         .sess
 514                         .source_map()
 515                         .is_multiline(secondary_span.shrink_to_hi().until(primary_span))
 516                 {
 517                     // We are pointing at the binding's type or initializer value, but it's pattern
 518                     // is in a different line, so we point at both.
 519                     err.span_label(secondary_span, "expected due to the type of this binding");
 520                     err.span_label(primary_span, &format!("expected due to this{post_message}"));
 521                 } else if post_message == "" {
 522                     // We are pointing at either the assignment lhs or the binding def pattern.
 523                     err.span_label(primary_span, "expected due to the type of this binding");
 524                 } else {
 525                     // We are pointing at the binding's type or initializer value.
 526                     err.span_label(primary_span, &format!("expected due to this{post_message}"));
 527                 }
 528
 529                 if !lhs.is_syntactic_place_expr() {
 530                     // We already emitted E0070 "invalid left-hand side of assignment", so we
 531                     // silence this.
 532                     err.downgrade_to_delayed_bug();
 533                 }
 534             }
 535             (
 536                 Some(hir::Node::Expr(hir::Expr {
 537                     kind: hir::ExprKind::Binary(_, lhs, rhs), ..
 538                 })),
 539                 Some(TypeError::Sorts(ExpectedFound { expected, .. })),
 540             ) if rhs.hir_id == expr.hir_id
 541                 && self.typeck_results.borrow().expr_ty_adjusted_opt(lhs) == Some(expected) =>
 542             {
 543                 err.span_label(lhs.span, &format!("expected because this is `{expected}`"));
 544             }
 545             _ => {}
 546         }
 547     }
 548
 549     fn annotate_alternative_method_deref(
 550         &self,
 551         err: &mut Diagnostic,
 552         expr: &hir::Expr<'_>,
 553         error: Option<TypeError<'tcx>>,
 554     ) {
 555         let parent = self.tcx.hir().parent_id(expr.hir_id);
 556         let Some(TypeError::Sorts(ExpectedFound { expected, .. })) = error else {return;};
 557         let Some(hir::Node::Expr(hir::Expr {
 558                     kind: hir::ExprKind::Assign(lhs, rhs, _), ..
 559                 })) = self.tcx.hir().find(parent) else {return; };
 560         if rhs.hir_id != expr.hir_id || expected.is_closure() {
 561             return;
 562         }
 563         let hir::ExprKind::Unary(hir::UnOp::Deref, deref) = lhs.kind else { return; };
 564         let hir::ExprKind::MethodCall(path, base, args, _) = deref.kind else { return; };
 565         let Some(self_ty) = self.typeck_results.borrow().expr_ty_adjusted_opt(base) else { return; };
 566
 567         let Ok(pick) = self
 568             .lookup_probe_for_diagnostic(
 569                 path.ident,
 570                 self_ty,
 571                 deref,
 572                 probe::ProbeScope::TraitsInScope,
 573                 None,
 574             ) else {
 575                 return;
 576             };
 577         let in_scope_methods = self.probe_for_name_many(
 578             probe::Mode::MethodCall,
 579             path.ident,
 580             Some(expected),
 581             probe::IsSuggestion(true),
 582             self_ty,
 583             deref.hir_id,
 584             probe::ProbeScope::TraitsInScope,
 585         );
 586         let other_methods_in_scope: Vec<_> =
 587             in_scope_methods.iter().filter(|c| c.item.def_id != pick.item.def_id).collect();
 588
 589         let all_methods = self.probe_for_name_many(
 590             probe::Mode::MethodCall,
 591             path.ident,
 592             Some(expected),
 593             probe::IsSuggestion(true),
 594             self_ty,
 595             deref.hir_id,
 596             probe::ProbeScope::AllTraits,
 597         );
 598         let suggestions: Vec<_> = all_methods
 599             .into_iter()
 600             .filter(|c| c.item.def_id != pick.item.def_id)
 601             .map(|c| {
 602                 let m = c.item;
 603                 let substs = ty::InternalSubsts::for_item(self.tcx, m.def_id, |param, _| {
 604                     self.var_for_def(deref.span, param)
 605                 });
 606                 vec![
 607                     (
 608                         deref.span.until(base.span),
 609                         format!(
 610                             "{}({}",
 611                             with_no_trimmed_paths!(
 612                                 self.tcx.def_path_str_with_substs(m.def_id, substs,)
 613                             ),
 614                             match self.tcx.fn_sig(m.def_id).input(0).skip_binder().kind() {
 615                                 ty::Ref(_, _, hir::Mutability::Mut) => "&mut ",
 616                                 ty::Ref(_, _, _) => "&",
 617                                 _ => "",
 618                             },
 619                         ),
 620                     ),
 621                     match &args[..] {
 622                         [] => (base.span.shrink_to_hi().with_hi(deref.span.hi()), ")".to_string()),
 623                         [first, ..] => (base.span.between(first.span), ", ".to_string()),
 624                     },
 625                 ]
 626             })
 627             .collect();
 628         if suggestions.is_empty() {
 629             return;
 630         }
 631         let mut path_span: MultiSpan = path.ident.span.into();
 632         path_span.push_span_label(
 633             path.ident.span,
 634             with_no_trimmed_paths!(format!(
 635                 "refers to `{}`",
 636                 self.tcx.def_path_str(pick.item.def_id),
 637             )),
 638         );
 639         let container_id = pick.item.container_id(self.tcx);
 640         let container = with_no_trimmed_paths!(self.tcx.def_path_str(container_id));
 641         for def_id in pick.import_ids {
 642             let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
 643             path_span.push_span_label(
 644                 self.tcx.hir().span(hir_id),
 645                 format!("`{container}` imported here"),
 646             );
 647         }
 648         let tail = with_no_trimmed_paths!(match &other_methods_in_scope[..] {
 649             [] => return,
 650             [candidate] => format!(
 651                 "the method of the same name on {} `{}`",
 652                 match candidate.kind {
 653                     probe::CandidateKind::InherentImplCandidate(..) => "the inherent impl for",
 654                     _ => "trait",
 655                 },
 656                 self.tcx.def_path_str(candidate.item.container_id(self.tcx))
 657             ),
 658             [.., last] if other_methods_in_scope.len() < 5 => {
 659                 format!(
 660                     "the methods of the same name on {} and `{}`",
 661                     other_methods_in_scope[..other_methods_in_scope.len() - 1]
 662                         .iter()
 663                         .map(|c| format!(
 664                             "`{}`",
 665                             self.tcx.def_path_str(c.item.container_id(self.tcx))
 666                         ))
 667                         .collect::<Vec<String>>()
 668                         .join(", "),
 669                     self.tcx.def_path_str(last.item.container_id(self.tcx))
 670                 )
 671             }
 672             _ => format!(
 673                 "the methods of the same name on {} other traits",
 674                 other_methods_in_scope.len()
 675             ),
 676         });
 677         err.span_note(
 678             path_span,
 679             &format!(
 680                 "the `{}` call is resolved to the method in `{container}`, shadowing {tail}",
 681                 path.ident,
 682             ),
 683         );
 684         if suggestions.len() > other_methods_in_scope.len() {
 685             err.note(&format!(
 686                 "additionally, there are {} other available methods that aren't in scope",
 687                 suggestions.len() - other_methods_in_scope.len()
 688             ));
 689         }
 690         err.multipart_suggestions(
 691             &format!(
 692                 "you might have meant to call {}; you can use the fully-qualified path to call {} \
 693                  explicitly",
 694                 if suggestions.len() == 1 {
 695                     "the other method"
 696                 } else {
 697                     "one of the other methods"
 698                 },
 699                 if suggestions.len() == 1 { "it" } else { "one of them" },
 700             ),
 701             suggestions,
 702             Applicability::MaybeIncorrect,
 703         );
 704     }
 705
 706     pub(crate) fn note_result_coercion(
 707         &self,
 708         err: &mut Diagnostic,
 709         expr: &hir::Expr<'tcx>,
 710         expected: Ty<'tcx>,
 711         found: Ty<'tcx>,
 712     ) -> bool {
 713         let ty::Adt(e, substs_e) = expected.kind() else { return false; };
 714         let ty::Adt(f, substs_f) = found.kind() else { return false; };
 715         if e.did() != f.did() {
 716             return false;
 717         }
 718         if Some(e.did()) != self.tcx.get_diagnostic_item(sym::Result) {
 719             return false;
 720         }
 721         let map = self.tcx.hir();
 722         if let Some(hir::Node::Expr(expr)) = map.find_parent(expr.hir_id)
 723             && let hir::ExprKind::Ret(_) = expr.kind
 724         {
 725             // `return foo;`
 726         } else if map.get_return_block(expr.hir_id).is_some() {
 727             // Function's tail expression.
 728         } else {
 729             return false;
 730         }
 731         let e = substs_e.type_at(1);
 732         let f = substs_f.type_at(1);
 733         if self
 734             .infcx
 735             .type_implements_trait(
 736                 self.tcx.get_diagnostic_item(sym::Into).unwrap(),
 737                 [f, e],
 738                 self.param_env,
 739             )
 740             .must_apply_modulo_regions()
 741         {
 742             err.multipart_suggestion(
 743                 "use `?` to coerce and return an appropriate `Err`, and wrap the resulting value \
 744                  in `Ok` so the expression remains of type `Result`",
 745                 vec![
 746                     (expr.span.shrink_to_lo(), "Ok(".to_string()),
 747                     (expr.span.shrink_to_hi(), "?)".to_string()),
 748                 ],
 749                 Applicability::MaybeIncorrect,
 750             );
 751             return true;
 752         }
 753         false
 754     }
 755
 756     /// If the expected type is an enum (Issue #55250) with any variants whose
 757     /// sole field is of the found type, suggest such variants. (Issue #42764)
 758     fn suggest_compatible_variants(
 759         &self,
 760         err: &mut Diagnostic,
 761         expr: &hir::Expr<'_>,
 762         expected: Ty<'tcx>,
 763         expr_ty: Ty<'tcx>,
 764     ) -> bool {
 765         if let ty::Adt(expected_adt, substs) = expected.kind() {
 766             if let hir::ExprKind::Field(base, ident) = expr.kind {
 767                 let base_ty = self.typeck_results.borrow().expr_ty(base);
 768                 if self.can_eq(self.param_env, base_ty, expected).is_ok()
 769                     && let Some(base_span) = base.span.find_ancestor_inside(expr.span)
 770                 {
 771                     err.span_suggestion_verbose(
 772                         expr.span.with_lo(base_span.hi()),
 773                         format!("consider removing the tuple struct field `{ident}`"),
 774                         "",
 775                         Applicability::MaybeIncorrect,
 776                     );
 777                     return true;
 778                 }
 779             }
 780
 781             // If the expression is of type () and it's the return expression of a block,
 782             // we suggest adding a separate return expression instead.
 783             // (To avoid things like suggesting `Ok(while .. { .. })`.)
 784             if expr_ty.is_unit() {
 785                 let mut id = expr.hir_id;
 786                 let mut parent;
 787
 788                 // Unroll desugaring, to make sure this works for `for` loops etc.
 789                 loop {
 790                     parent = self.tcx.hir().parent_id(id);
 791                     if let Some(parent_span) = self.tcx.hir().opt_span(parent) {
 792                         if parent_span.find_ancestor_inside(expr.span).is_some() {
 793                             // The parent node is part of the same span, so is the result of the
 794                             // same expansion/desugaring and not the 'real' parent node.
 795                             id = parent;
 796                             continue;
 797                         }
 798                     }
 799                     break;
 800                 }
 801
 802                 if let Some(hir::Node::Block(&hir::Block {
 803                     span: block_span, expr: Some(e), ..
 804                 })) = self.tcx.hir().find(parent)
 805                 {
 806                     if e.hir_id == id {
 807                         if let Some(span) = expr.span.find_ancestor_inside(block_span) {
 808                             let return_suggestions = if self
 809                                 .tcx
 810                                 .is_diagnostic_item(sym::Result, expected_adt.did())
 811                             {
 812                                 vec!["Ok(())"]
 813                             } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did()) {
 814                                 vec!["None", "Some(())"]
 815                             } else {
 816                                 return false;
 817                             };
 818                             if let Some(indent) =
 819                                 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
 820                             {
 821                                 // Add a semicolon, except after `}`.
 822                                 let semicolon =
 823                                     match self.tcx.sess.source_map().span_to_snippet(span) {
 824                                         Ok(s) if s.ends_with('}') => "",
 825                                         _ => ";",
 826                                     };
 827                                 err.span_suggestions(
 828                                     span.shrink_to_hi(),
 829                                     "try adding an expression at the end of the block",
 830                                     return_suggestions
 831                                         .into_iter()
 832                                         .map(|r| format!("{semicolon}\n{indent}{r}")),
 833                                     Applicability::MaybeIncorrect,
 834                                 );
 835                             }
 836                             return true;
 837                         }
 838                     }
 839                 }
 840             }
 841
 842             let compatible_variants: Vec<(String, _, _, Option<String>)> = expected_adt
 843                 .variants()
 844                 .iter()
 845                 .filter(|variant| {
 846                     variant.fields.len() == 1
 847                 })
 848                 .filter_map(|variant| {
 849                     let sole_field = &variant.fields[0];
 850
 851                     let field_is_local = sole_field.did.is_local();
 852                     let field_is_accessible =
 853                         sole_field.vis.is_accessible_from(expr.hir_id.owner.def_id, self.tcx)
 854                         // Skip suggestions for unstable public fields (for example `Pin::pointer`)
 855                         && matches!(self.tcx.eval_stability(sole_field.did, None, expr.span, None), EvalResult::Allow | EvalResult::Unmarked);
 856
 857                     if !field_is_local && !field_is_accessible {
 858                         return None;
 859                     }
 860
 861                     let note_about_variant_field_privacy = (field_is_local && !field_is_accessible)
 862                         .then(|| " (its field is private, but it's local to this crate and its privacy can be changed)".to_string());
 863
 864                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 865                     if self.can_coerce(expr_ty, sole_field_ty) {
 866                         let variant_path =
 867                             with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
 868                         // FIXME #56861: DRYer prelude filtering
 869                         if let Some(path) = variant_path.strip_prefix("std::prelude::")
 870                             && let Some((_, path)) = path.split_once("::")
 871                         {
 872                             return Some((path.to_string(), variant.ctor_kind(), sole_field.name, note_about_variant_field_privacy));
 873                         }
 874                         Some((variant_path, variant.ctor_kind(), sole_field.name, note_about_variant_field_privacy))
 875                     } else {
 876                         None
 877                     }
 878                 })
 879                 .collect();
 880
 881             let suggestions_for = |variant: &_, ctor_kind, field_name| {
 882                 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 883                     Some(ident) => format!("{ident}: "),
 884                     None => String::new(),
 885                 };
 886
 887                 let (open, close) = match ctor_kind {
 888                     Some(CtorKind::Fn) => ("(".to_owned(), ")"),
 889                     None => (format!(" {{ {field_name}: "), " }"),
 890
 891                     // unit variants don't have fields
 892                     Some(CtorKind::Const) => unreachable!(),
 893                 };
 894
 895                 // Suggest constructor as deep into the block tree as possible.
 896                 // This fixes https://github.com/rust-lang/rust/issues/101065,
 897                 // and also just helps make the most minimal suggestions.
 898                 let mut expr = expr;
 899                 while let hir::ExprKind::Block(block, _) = &expr.kind
 900                     && let Some(expr_) = &block.expr
 901                 {
 902                     expr = expr_
 903                 }
 904
 905                 vec![
 906                     (expr.span.shrink_to_lo(), format!("{prefix}{variant}{open}")),
 907                     (expr.span.shrink_to_hi(), close.to_owned()),
 908                 ]
 909             };
 910
 911             match &compatible_variants[..] {
 912                 [] => { /* No variants to format */ }
 913                 [(variant, ctor_kind, field_name, note)] => {
 914                     // Just a single matching variant.
 915                     err.multipart_suggestion_verbose(
 916                         &format!(
 917                             "try wrapping the expression in `{variant}`{note}",
 918                             note = note.as_deref().unwrap_or("")
 919                         ),
 920                         suggestions_for(&**variant, *ctor_kind, *field_name),
 921                         Applicability::MaybeIncorrect,
 922                     );
 923                     return true;
 924                 }
 925                 _ => {
 926                     // More than one matching variant.
 927                     err.multipart_suggestions(
 928                         &format!(
 929                             "try wrapping the expression in a variant of `{}`",
 930                             self.tcx.def_path_str(expected_adt.did())
 931                         ),
 932                         compatible_variants.into_iter().map(
 933                             |(variant, ctor_kind, field_name, _)| {
 934                                 suggestions_for(&variant, ctor_kind, field_name)
 935                             },
 936                         ),
 937                         Applicability::MaybeIncorrect,
 938                     );
 939                     return true;
 940                 }
 941             }
 942         }
 943
 944         false
 945     }
 946
 947     fn suggest_non_zero_new_unwrap(
 948         &self,
 949         err: &mut Diagnostic,
 950         expr: &hir::Expr<'_>,
 951         expected: Ty<'tcx>,
 952         expr_ty: Ty<'tcx>,
 953     ) -> bool {
 954         let tcx = self.tcx;
 955         let (adt, unwrap) = match expected.kind() {
 956             // In case Option<NonZero*> is wanted, but * is provided, suggest calling new
 957             ty::Adt(adt, substs) if tcx.is_diagnostic_item(sym::Option, adt.did()) => {
 958                 // Unwrap option
 959                 let ty::Adt(adt, _) = substs.type_at(0).kind() else { return false; };
 960
 961                 (adt, "")
 962             }
 963             // In case NonZero* is wanted, but * is provided also add `.unwrap()` to satisfy types
 964             ty::Adt(adt, _) => (adt, ".unwrap()"),
 965             _ => return false,
 966         };
 967
 968         let map = [
 969             (sym::NonZeroU8, tcx.types.u8),
 970             (sym::NonZeroU16, tcx.types.u16),
 971             (sym::NonZeroU32, tcx.types.u32),
 972             (sym::NonZeroU64, tcx.types.u64),
 973             (sym::NonZeroU128, tcx.types.u128),
 974             (sym::NonZeroI8, tcx.types.i8),
 975             (sym::NonZeroI16, tcx.types.i16),
 976             (sym::NonZeroI32, tcx.types.i32),
 977             (sym::NonZeroI64, tcx.types.i64),
 978             (sym::NonZeroI128, tcx.types.i128),
 979         ];
 980
 981         let Some((s, _)) = map
 982             .iter()
 983             .find(|&&(s, t)| self.tcx.is_diagnostic_item(s, adt.did()) && self.can_coerce(expr_ty, t))
 984             else { return false; };
 985
 986         let path = self.tcx.def_path_str(adt.non_enum_variant().def_id);
 987
 988         err.multipart_suggestion(
 989             format!("consider calling `{s}::new`"),
 990             vec![
 991                 (expr.span.shrink_to_lo(), format!("{path}::new(")),
 992                 (expr.span.shrink_to_hi(), format!("){unwrap}")),
 993             ],
 994             Applicability::MaybeIncorrect,
 995         );
 996
 997         true
 998     }
 999
1000     pub fn get_conversion_methods(
1001         &self,
1002         span: Span,
1003         expected: Ty<'tcx>,
1004         checked_ty: Ty<'tcx>,
1005         hir_id: hir::HirId,
1006     ) -> Vec<AssocItem> {
1007         let methods = self.probe_for_return_type(
1008             span,
1009             probe::Mode::MethodCall,
1010             expected,
1011             checked_ty,
1012             hir_id,
1013             |m| {
1014                 self.has_only_self_parameter(m)
1015                     && self
1016                         .tcx
1017                         // This special internal attribute is used to permit
1018                         // "identity-like" conversion methods to be suggested here.
1019                         //
1020                         // FIXME (#46459 and #46460): ideally
1021                         // `std::convert::Into::into` and `std::borrow:ToOwned` would
1022                         // also be `#[rustc_conversion_suggestion]`, if not for
1023                         // method-probing false-positives and -negatives (respectively).
1024                         //
1025                         // FIXME? Other potential candidate methods: `as_ref` and
1026                         // `as_mut`?
1027                         .has_attr(m.def_id, sym::rustc_conversion_suggestion)
1028             },
1029         );
1030
1031         methods
1032     }
1033
1034     /// This function checks whether the method is not static and does not accept other parameters than `self`.
1035     fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
1036         match method.kind {
1037             ty::AssocKind::Fn => {
1038                 method.fn_has_self_parameter
1039                     && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
1040             }
1041             _ => false,
1042         }
1043     }
1044
1045     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
1046     ///
1047     /// Given the following code:
1048     /// ```compile_fail,E0308
1049     /// struct Foo;
1050     /// fn takes_ref(_: &Foo) {}
1051     /// let ref opt = Some(Foo);
1052     ///
1053     /// opt.map(|param| takes_ref(param));
1054     /// ```
1055     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
1056     ///
1057     /// It only checks for `Option` and `Result` and won't work with
1058     /// ```ignore (illustrative)
1059     /// opt.map(|param| { takes_ref(param) });
1060     /// ```
1061     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
1062         let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
1063             return None;
1064         };
1065
1066         let hir::def::Res::Local(local_id) = path.res else {
1067             return None;
1068         };
1069
1070         let local_parent = self.tcx.hir().parent_id(local_id);
1071         let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
1072             return None;
1073         };
1074
1075         let param_parent = self.tcx.hir().parent_id(*param_hir_id);
1076         let Some(Node::Expr(hir::Expr {
1077             hir_id: expr_hir_id,
1078             kind: hir::ExprKind::Closure(hir::Closure { fn_decl: closure_fn_decl, .. }),
1079             ..
1080         })) = self.tcx.hir().find(param_parent) else {
1081             return None;
1082         };
1083
1084         let expr_parent = self.tcx.hir().parent_id(*expr_hir_id);
1085         let hir = self.tcx.hir().find(expr_parent);
1086         let closure_params_len = closure_fn_decl.inputs.len();
1087         let (
1088             Some(Node::Expr(hir::Expr {
1089                 kind: hir::ExprKind::MethodCall(method_path, receiver, ..),
1090                 ..
1091             })),
1092             1,
1093         ) = (hir, closure_params_len) else {
1094             return None;
1095         };
1096
1097         let self_ty = self.typeck_results.borrow().expr_ty(receiver);
1098         let name = method_path.ident.name;
1099         let is_as_ref_able = match self_ty.peel_refs().kind() {
1100             ty::Adt(def, _) => {
1101                 (self.tcx.is_diagnostic_item(sym::Option, def.did())
1102                     || self.tcx.is_diagnostic_item(sym::Result, def.did()))
1103                     && (name == sym::map || name == sym::and_then)
1104             }
1105             _ => false,
1106         };
1107         match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
1108             (true, Ok(src)) => {
1109                 let suggestion = format!("as_ref().{}", src);
1110                 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
1111             }
1112             _ => None,
1113         }
1114     }
1115
1116     pub(crate) fn maybe_get_struct_pattern_shorthand_field(
1117         &self,
1118         expr: &hir::Expr<'_>,
1119     ) -> Option<Symbol> {
1120         let hir = self.tcx.hir();
1121         let local = match expr {
1122             hir::Expr {
1123                 kind:
1124                     hir::ExprKind::Path(hir::QPath::Resolved(
1125                         None,
1126                         hir::Path {
1127                             res: hir::def::Res::Local(_),
1128                             segments: [hir::PathSegment { ident, .. }],
1129                             ..
1130                         },
1131                     )),
1132                 ..
1133             } => Some(ident),
1134             _ => None,
1135         }?;
1136
1137         match hir.find_parent(expr.hir_id)? {
1138             Node::ExprField(field) => {
1139                 if field.ident.name == local.name && field.is_shorthand {
1140                     return Some(local.name);
1141                 }
1142             }
1143             _ => {}
1144         }
1145
1146         None
1147     }
1148
1149     /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
1150     pub(crate) fn maybe_get_block_expr(
1151         &self,
1152         expr: &hir::Expr<'tcx>,
1153     ) -> Option<&'tcx hir::Expr<'tcx>> {
1154         match expr {
1155             hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
1156             _ => None,
1157         }
1158     }
1159
1160     /// Returns whether the given expression is an `else if`.
1161     pub(crate) fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
1162         if let hir::ExprKind::If(..) = expr.kind {
1163             let parent_id = self.tcx.hir().parent_id(expr.hir_id);
1164             if let Some(Node::Expr(hir::Expr {
1165                 kind: hir::ExprKind::If(_, _, Some(else_expr)),
1166                 ..
1167             })) = self.tcx.hir().find(parent_id)
1168             {
1169                 return else_expr.hir_id == expr.hir_id;
1170             }
1171         }
1172         false
1173     }
1174
1175     /// This function is used to determine potential "simple" improvements or users' errors and
1176     /// provide them useful help. For example:
1177     ///
1178     /// ```compile_fail,E0308
1179     /// fn some_fn(s: &str) {}
1180     ///
1181     /// let x = "hey!".to_owned();
1182     /// some_fn(x); // error
1183     /// ```
1184     ///
1185     /// No need to find every potential function which could make a coercion to transform a
1186     /// `String` into a `&str` since a `&` would do the trick!
1187     ///
1188     /// In addition of this check, it also checks between references mutability state. If the
1189     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
1190     /// `&mut`!".
1191     pub fn check_ref(
1192         &self,
1193         expr: &hir::Expr<'tcx>,
1194         checked_ty: Ty<'tcx>,
1195         expected: Ty<'tcx>,
1196     ) -> Option<(
1197         Span,
1198         String,
1199         String,
1200         Applicability,
1201         bool, /* verbose */
1202         bool, /* suggest `&` or `&mut` type annotation */
1203     )> {
1204         let sess = self.sess();
1205         let sp = expr.span;
1206
1207         // If the span is from an external macro, there's no suggestion we can make.
1208         if in_external_macro(sess, sp) {
1209             return None;
1210         }
1211
1212         let sm = sess.source_map();
1213
1214         let replace_prefix = |s: &str, old: &str, new: &str| {
1215             s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
1216         };
1217
1218         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
1219         let expr = expr.peel_drop_temps();
1220
1221         match (&expr.kind, expected.kind(), checked_ty.kind()) {
1222             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
1223                 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
1224                     if let hir::ExprKind::Lit(_) = expr.kind
1225                         && let Ok(src) = sm.span_to_snippet(sp)
1226                         && replace_prefix(&src, "b\"", "\"").is_some()
1227                     {
1228                                 let pos = sp.lo() + BytePos(1);
1229                                 return Some((
1230                                     sp.with_hi(pos),
1231                                     "consider removing the leading `b`".to_string(),
1232                                     String::new(),
1233                                     Applicability::MachineApplicable,
1234                                     true,
1235                                     false,
1236                                 ));
1237                             }
1238                         }
1239                 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
1240                     if let hir::ExprKind::Lit(_) = expr.kind
1241                         && let Ok(src) = sm.span_to_snippet(sp)
1242                         && replace_prefix(&src, "\"", "b\"").is_some()
1243                     {
1244                                 return Some((
1245                                     sp.shrink_to_lo(),
1246                                     "consider adding a leading `b`".to_string(),
1247                                     "b".to_string(),
1248                                     Applicability::MachineApplicable,
1249                                     true,
1250                                     false,
1251                                 ));
1252                     }
1253                 }
1254                 _ => {}
1255             },
1256             (_, &ty::Ref(_, _, mutability), _) => {
1257                 // Check if it can work when put into a ref. For example:
1258                 //
1259                 // ```
1260                 // fn bar(x: &mut i32) {}
1261                 //
1262                 // let x = 0u32;
1263                 // bar(&x); // error, expected &mut
1264                 // ```
1265                 let ref_ty = match mutability {
1266                     hir::Mutability::Mut => {
1267                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
1268                     }
1269                     hir::Mutability::Not => {
1270                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
1271                     }
1272                 };
1273                 if self.can_coerce(ref_ty, expected) {
1274                     let mut sugg_sp = sp;
1275                     if let hir::ExprKind::MethodCall(ref segment, receiver, args, _) = expr.kind {
1276                         let clone_trait =
1277                             self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
1278                         if args.is_empty()
1279                             && self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
1280                                 |did| {
1281                                     let ai = self.tcx.associated_item(did);
1282                                     ai.trait_container(self.tcx) == Some(clone_trait)
1283                                 },
1284                             ) == Some(true)
1285                             && segment.ident.name == sym::clone
1286                         {
1287                             // If this expression had a clone call when suggesting borrowing
1288                             // we want to suggest removing it because it'd now be unnecessary.
1289                             sugg_sp = receiver.span;
1290                         }
1291                     }
1292
1293                     if let hir::ExprKind::Unary(hir::UnOp::Deref, ref inner) = expr.kind
1294                         && let Some(1) = self.deref_steps(expected, checked_ty) {
1295                         // We have `*&T`, check if what was expected was `&T`.
1296                         // If so, we may want to suggest removing a `*`.
1297                         sugg_sp = sugg_sp.with_hi(inner.span.lo());
1298                         return Some((
1299                             sugg_sp,
1300                             "consider removing deref here".to_string(),
1301                             "".to_string(),
1302                             Applicability::MachineApplicable,
1303                             true,
1304                             false,
1305                         ));
1306                     }
1307
1308                     if let Ok(src) = sm.span_to_snippet(sugg_sp) {
1309                         let needs_parens = match expr.kind {
1310                             // parenthesize if needed (Issue #46756)
1311                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
1312                             // parenthesize borrows of range literals (Issue #54505)
1313                             _ if is_range_literal(expr) => true,
1314                             _ => false,
1315                         };
1316
1317                         if let Some(sugg) = self.can_use_as_ref(expr) {
1318                             return Some((
1319                                 sugg.0,
1320                                 sugg.1.to_string(),
1321                                 sugg.2,
1322                                 Applicability::MachineApplicable,
1323                                 false,
1324                                 false,
1325                             ));
1326                         }
1327
1328                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
1329                             Some(ident) => format!("{ident}: "),
1330                             None => String::new(),
1331                         };
1332
1333                         if let Some(hir::Node::Expr(hir::Expr {
1334                             kind: hir::ExprKind::Assign(..),
1335                             ..
1336                         })) = self.tcx.hir().find_parent(expr.hir_id)
1337                         {
1338                             if mutability.is_mut() {
1339                                 // Suppressing this diagnostic, we'll properly print it in `check_expr_assign`
1340                                 return None;
1341                             }
1342                         }
1343
1344                         let sugg_expr = if needs_parens { format!("({src})") } else { src };
1345                         return Some((
1346                             sp,
1347                             format!("consider {}borrowing here", mutability.mutably_str()),
1348                             format!("{prefix}{}{sugg_expr}", mutability.ref_prefix_str()),
1349                             Applicability::MachineApplicable,
1350                             false,
1351                             false,
1352                         ));
1353                     }
1354                 }
1355             }
1356             (
1357                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
1358                 _,
1359                 &ty::Ref(_, checked, _),
1360             ) if self.can_sub(self.param_env, checked, expected).is_ok() => {
1361                 // We have `&T`, check if what was expected was `T`. If so,
1362                 // we may want to suggest removing a `&`.
1363                 if sm.is_imported(expr.span) {
1364                     // Go through the spans from which this span was expanded,
1365                     // and find the one that's pointing inside `sp`.
1366                     //
1367                     // E.g. for `&format!("")`, where we want the span to the
1368                     // `format!()` invocation instead of its expansion.
1369                     if let Some(call_span) =
1370                         iter::successors(Some(expr.span), |s| s.parent_callsite())
1371                             .find(|&s| sp.contains(s))
1372                         && sm.is_span_accessible(call_span)
1373                     {
1374                         return Some((
1375                             sp.with_hi(call_span.lo()),
1376                             "consider removing the borrow".to_string(),
1377                             String::new(),
1378                             Applicability::MachineApplicable,
1379                             true,
1380                             true
1381                         ));
1382                     }
1383                     return None;
1384                 }
1385                 if sp.contains(expr.span)
1386                     && sm.is_span_accessible(expr.span)
1387                 {
1388                     return Some((
1389                         sp.with_hi(expr.span.lo()),
1390                         "consider removing the borrow".to_string(),
1391                         String::new(),
1392                         Applicability::MachineApplicable,
1393                         true,
1394                         true,
1395                     ));
1396                 }
1397             }
1398             (
1399                 _,
1400                 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
1401                 &ty::Ref(_, ty_a, mutbl_a),
1402             ) => {
1403                 if let Some(steps) = self.deref_steps(ty_a, ty_b)
1404                     // Only suggest valid if dereferencing needed.
1405                     && steps > 0
1406                     // The pointer type implements `Copy` trait so the suggestion is always valid.
1407                     && let Ok(src) = sm.span_to_snippet(sp)
1408                 {
1409                     let derefs = "*".repeat(steps);
1410                     let old_prefix = mutbl_a.ref_prefix_str();
1411                     let new_prefix = mutbl_b.ref_prefix_str().to_owned() + &derefs;
1412
1413                     let suggestion = replace_prefix(&src, old_prefix, &new_prefix).map(|_| {
1414                         // skip `&` or `&mut ` if both mutabilities are mutable
1415                         let lo = sp.lo() + BytePos(min(old_prefix.len(), mutbl_b.ref_prefix_str().len()) as _);
1416                         // skip `&` or `&mut `
1417                         let hi = sp.lo() + BytePos(old_prefix.len() as _);
1418                         let sp = sp.with_lo(lo).with_hi(hi);
1419
1420                         (
1421                             sp,
1422                             format!("{}{derefs}", if mutbl_a != mutbl_b { mutbl_b.prefix_str() } else { "" }),
1423                             if mutbl_b <= mutbl_a { Applicability::MachineApplicable } else { Applicability::MaybeIncorrect }
1424                         )
1425                     });
1426
1427                     if let Some((span, src, applicability)) = suggestion {
1428                         return Some((
1429                             span,
1430                             "consider dereferencing".to_string(),
1431                             src,
1432                             applicability,
1433                             true,
1434                             false,
1435                         ));
1436                     }
1437                 }
1438             }
1439             _ if sp == expr.span => {
1440                 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
1441                     let mut expr = expr.peel_blocks();
1442                     let mut prefix_span = expr.span.shrink_to_lo();
1443                     let mut remove = String::new();
1444
1445                     // Try peeling off any existing `&` and `&mut` to reach our target type
1446                     while steps > 0 {
1447                         if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
1448                             // If the expression has `&`, removing it would fix the error
1449                             prefix_span = prefix_span.with_hi(inner.span.lo());
1450                             expr = inner;
1451                             remove.push_str(mutbl.ref_prefix_str());
1452                             steps -= 1;
1453                         } else {
1454                             break;
1455                         }
1456                     }
1457                     // If we've reached our target type with just removing `&`, then just print now.
1458                     if steps == 0 && !remove.trim().is_empty() {
1459                         return Some((
1460                             prefix_span,
1461                             format!("consider removing the `{}`", remove.trim()),
1462                             String::new(),
1463                             // Do not remove `&&` to get to bool, because it might be something like
1464                             // { a } && b, which we have a separate fixup suggestion that is more
1465                             // likely correct...
1466                             if remove.trim() == "&&" && expected == self.tcx.types.bool {
1467                                 Applicability::MaybeIncorrect
1468                             } else {
1469                                 Applicability::MachineApplicable
1470                             },
1471                             true,
1472                             false,
1473                         ));
1474                     }
1475
1476                     // For this suggestion to make sense, the type would need to be `Copy`,
1477                     // or we have to be moving out of a `Box<T>`
1478                     if self.type_is_copy_modulo_regions(self.param_env, expected, sp)
1479                         // FIXME(compiler-errors): We can actually do this if the checked_ty is
1480                         // `steps` layers of boxes, not just one, but this is easier and most likely.
1481                         || (checked_ty.is_box() && steps == 1)
1482                     {
1483                         let deref_kind = if checked_ty.is_box() {
1484                             "unboxing the value"
1485                         } else if checked_ty.is_region_ptr() {
1486                             "dereferencing the borrow"
1487                         } else {
1488                             "dereferencing the type"
1489                         };
1490
1491                         // Suggest removing `&` if we have removed any, otherwise suggest just
1492                         // dereferencing the remaining number of steps.
1493                         let message = if remove.is_empty() {
1494                             format!("consider {deref_kind}")
1495                         } else {
1496                             format!(
1497                                 "consider removing the `{}` and {} instead",
1498                                 remove.trim(),
1499                                 deref_kind
1500                             )
1501                         };
1502
1503                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
1504                             Some(ident) => format!("{ident}: "),
1505                             None => String::new(),
1506                         };
1507
1508                         let (span, suggestion) = if self.is_else_if_block(expr) {
1509                             // Don't suggest nonsense like `else *if`
1510                             return None;
1511                         } else if let Some(expr) = self.maybe_get_block_expr(expr) {
1512                             // prefix should be empty here..
1513                             (expr.span.shrink_to_lo(), "*".to_string())
1514                         } else {
1515                             (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
1516                         };
1517                         if suggestion.trim().is_empty() {
1518                             return None;
1519                         }
1520
1521                         return Some((
1522                             span,
1523                             message,
1524                             suggestion,
1525                             Applicability::MachineApplicable,
1526                             true,
1527                             false,
1528                         ));
1529                     }
1530                 }
1531             }
1532             _ => {}
1533         }
1534         None
1535     }
1536
1537     pub fn check_for_cast(
1538         &self,
1539         err: &mut Diagnostic,
1540         expr: &hir::Expr<'_>,
1541         checked_ty: Ty<'tcx>,
1542         expected_ty: Ty<'tcx>,
1543         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
1544     ) -> bool {
1545         if self.tcx.sess.source_map().is_imported(expr.span) {
1546             // Ignore if span is from within a macro.
1547             return false;
1548         }
1549
1550         let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
1551             return false;
1552         };
1553
1554         // If casting this expression to a given numeric type would be appropriate in case of a type
1555         // mismatch.
1556         //
1557         // We want to minimize the amount of casting operations that are suggested, as it can be a
1558         // lossy operation with potentially bad side effects, so we only suggest when encountering
1559         // an expression that indicates that the original type couldn't be directly changed.
1560         //
1561         // For now, don't suggest casting with `as`.
1562         let can_cast = false;
1563
1564         let mut sugg = vec![];
1565
1566         if let Some(hir::Node::ExprField(field)) = self.tcx.hir().find_parent(expr.hir_id) {
1567             // `expr` is a literal field for a struct, only suggest if appropriate
1568             if field.is_shorthand {
1569                 // This is a field literal
1570                 sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
1571             } else {
1572                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
1573                 return false;
1574             }
1575         };
1576
1577         if let hir::ExprKind::Call(path, args) = &expr.kind
1578             && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
1579                 (&path.kind, args.len())
1580             // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1581             && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1582                 (&base_ty.kind, path_segment.ident.name)
1583         {
1584             if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1585                 match ident.name {
1586                     sym::i128
1587                     | sym::i64
1588                     | sym::i32
1589                     | sym::i16
1590                     | sym::i8
1591                     | sym::u128
1592                     | sym::u64
1593                     | sym::u32
1594                     | sym::u16
1595                     | sym::u8
1596                     | sym::isize
1597                     | sym::usize
1598                         if base_ty_path.segments.len() == 1 =>
1599                     {
1600                         return false;
1601                     }
1602                     _ => {}
1603                 }
1604             }
1605         }
1606
1607         let msg = format!(
1608             "you can convert {} `{}` to {} `{}`",
1609             checked_ty.kind().article(),
1610             checked_ty,
1611             expected_ty.kind().article(),
1612             expected_ty,
1613         );
1614         let cast_msg = format!(
1615             "you can cast {} `{}` to {} `{}`",
1616             checked_ty.kind().article(),
1617             checked_ty,
1618             expected_ty.kind().article(),
1619             expected_ty,
1620         );
1621         let lit_msg = format!(
1622             "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1623         );
1624
1625         let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1626             sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1627             ")"
1628         } else {
1629             ""
1630         };
1631
1632         let mut cast_suggestion = sugg.clone();
1633         cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1634         let mut into_suggestion = sugg.clone();
1635         into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1636         let mut suffix_suggestion = sugg.clone();
1637         suffix_suggestion.push((
1638             if matches!(
1639                 (&expected_ty.kind(), &checked_ty.kind()),
1640                 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1641             ) {
1642                 // Remove fractional part from literal, for example `42.0f32` into `42`
1643                 let src = src.trim_end_matches(&checked_ty.to_string());
1644                 let len = src.split('.').next().unwrap().len();
1645                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1646             } else {
1647                 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1648                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1649             },
1650             if expr.precedence().order() < PREC_POSTFIX {
1651                 // Readd `)`
1652                 format!("{expected_ty})")
1653             } else {
1654                 expected_ty.to_string()
1655             },
1656         ));
1657         let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1658             if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1659         };
1660         let is_negative_int =
1661             |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1662         let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1663
1664         let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1665
1666         let suggest_fallible_into_or_lhs_from =
1667             |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1668                 // If we know the expression the expected type is derived from, we might be able
1669                 // to suggest a widening conversion rather than a narrowing one (which may
1670                 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1671                 //   x > y
1672                 // can be given the suggestion "u32::from(x) > y" rather than
1673                 // "x > y.try_into().unwrap()".
1674                 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1675                     self.tcx
1676                         .sess
1677                         .source_map()
1678                         .span_to_snippet(expr.span)
1679                         .ok()
1680                         .map(|src| (expr, src))
1681                 });
1682                 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1683                     (lhs_expr_and_src, exp_to_found_is_fallible)
1684                 {
1685                     let msg = format!(
1686                         "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1687                     );
1688                     let suggestion = vec![
1689                         (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1690                         (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1691                     ];
1692                     (msg, suggestion)
1693                 } else {
1694                     let msg = format!("{msg} and panic if the converted value doesn't fit");
1695                     let mut suggestion = sugg.clone();
1696                     suggestion.push((
1697                         expr.span.shrink_to_hi(),
1698                         format!("{close_paren}.try_into().unwrap()"),
1699                     ));
1700                     (msg, suggestion)
1701                 };
1702                 err.multipart_suggestion_verbose(
1703                     &msg,
1704                     suggestion,
1705                     Applicability::MachineApplicable,
1706                 );
1707             };
1708
1709         let suggest_to_change_suffix_or_into =
1710             |err: &mut Diagnostic,
1711              found_to_exp_is_fallible: bool,
1712              exp_to_found_is_fallible: bool| {
1713                 let exp_is_lhs =
1714                     expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1715
1716                 if exp_is_lhs {
1717                     return;
1718                 }
1719
1720                 let always_fallible = found_to_exp_is_fallible
1721                     && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1722                 let msg = if literal_is_ty_suffixed(expr) {
1723                     &lit_msg
1724                 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1725                     // We now know that converting either the lhs or rhs is fallible. Before we
1726                     // suggest a fallible conversion, check if the value can never fit in the
1727                     // expected type.
1728                     let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1729                     err.note(&msg);
1730                     return;
1731                 } else if in_const_context {
1732                     // Do not recommend `into` or `try_into` in const contexts.
1733                     return;
1734                 } else if found_to_exp_is_fallible {
1735                     return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1736                 } else {
1737                     &msg
1738                 };
1739                 let suggestion = if literal_is_ty_suffixed(expr) {
1740                     suffix_suggestion.clone()
1741                 } else {
1742                     into_suggestion.clone()
1743                 };
1744                 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1745             };
1746
1747         match (&expected_ty.kind(), &checked_ty.kind()) {
1748             (ty::Int(exp), ty::Int(found)) => {
1749                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1750                 {
1751                     (Some(exp), Some(found)) if exp < found => (true, false),
1752                     (Some(exp), Some(found)) if exp > found => (false, true),
1753                     (None, Some(8 | 16)) => (false, true),
1754                     (Some(8 | 16), None) => (true, false),
1755                     (None, _) | (_, None) => (true, true),
1756                     _ => (false, false),
1757                 };
1758                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1759                 true
1760             }
1761             (ty::Uint(exp), ty::Uint(found)) => {
1762                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1763                 {
1764                     (Some(exp), Some(found)) if exp < found => (true, false),
1765                     (Some(exp), Some(found)) if exp > found => (false, true),
1766                     (None, Some(8 | 16)) => (false, true),
1767                     (Some(8 | 16), None) => (true, false),
1768                     (None, _) | (_, None) => (true, true),
1769                     _ => (false, false),
1770                 };
1771                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1772                 true
1773             }
1774             (&ty::Int(exp), &ty::Uint(found)) => {
1775                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1776                 {
1777                     (Some(exp), Some(found)) if found < exp => (false, true),
1778                     (None, Some(8)) => (false, true),
1779                     _ => (true, true),
1780                 };
1781                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1782                 true
1783             }
1784             (&ty::Uint(exp), &ty::Int(found)) => {
1785                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1786                 {
1787                     (Some(exp), Some(found)) if found > exp => (true, false),
1788                     (Some(8), None) => (true, false),
1789                     _ => (true, true),
1790                 };
1791                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1792                 true
1793             }
1794             (ty::Float(exp), ty::Float(found)) => {
1795                 if found.bit_width() < exp.bit_width() {
1796                     suggest_to_change_suffix_or_into(err, false, true);
1797                 } else if literal_is_ty_suffixed(expr) {
1798                     err.multipart_suggestion_verbose(
1799                         &lit_msg,
1800                         suffix_suggestion,
1801                         Applicability::MachineApplicable,
1802                     );
1803                 } else if can_cast {
1804                     // Missing try_into implementation for `f64` to `f32`
1805                     err.multipart_suggestion_verbose(
1806                         &format!("{cast_msg}, producing the closest possible value"),
1807                         cast_suggestion,
1808                         Applicability::MaybeIncorrect, // lossy conversion
1809                     );
1810                 }
1811                 true
1812             }
1813             (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1814                 if literal_is_ty_suffixed(expr) {
1815                     err.multipart_suggestion_verbose(
1816                         &lit_msg,
1817                         suffix_suggestion,
1818                         Applicability::MachineApplicable,
1819                     );
1820                 } else if can_cast {
1821                     // Missing try_into implementation for `{float}` to `{integer}`
1822                     err.multipart_suggestion_verbose(
1823                         &format!("{msg}, rounding the float towards zero"),
1824                         cast_suggestion,
1825                         Applicability::MaybeIncorrect, // lossy conversion
1826                     );
1827                 }
1828                 true
1829             }
1830             (ty::Float(exp), ty::Uint(found)) => {
1831                 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1832                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1833                     err.multipart_suggestion_verbose(
1834                         &format!(
1835                             "{msg}, producing the floating point representation of the integer",
1836                         ),
1837                         into_suggestion,
1838                         Applicability::MachineApplicable,
1839                     );
1840                 } else if literal_is_ty_suffixed(expr) {
1841                     err.multipart_suggestion_verbose(
1842                         &lit_msg,
1843                         suffix_suggestion,
1844                         Applicability::MachineApplicable,
1845                     );
1846                 } else {
1847                     // Missing try_into implementation for `{integer}` to `{float}`
1848                     err.multipart_suggestion_verbose(
1849                         &format!(
1850                             "{cast_msg}, producing the floating point representation of the integer, \
1851                                  rounded if necessary",
1852                         ),
1853                         cast_suggestion,
1854                         Applicability::MaybeIncorrect, // lossy conversion
1855                     );
1856                 }
1857                 true
1858             }
1859             (ty::Float(exp), ty::Int(found)) => {
1860                 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1861                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1862                     err.multipart_suggestion_verbose(
1863                         &format!(
1864                             "{}, producing the floating point representation of the integer",
1865                             &msg,
1866                         ),
1867                         into_suggestion,
1868                         Applicability::MachineApplicable,
1869                     );
1870                 } else if literal_is_ty_suffixed(expr) {
1871                     err.multipart_suggestion_verbose(
1872                         &lit_msg,
1873                         suffix_suggestion,
1874                         Applicability::MachineApplicable,
1875                     );
1876                 } else {
1877                     // Missing try_into implementation for `{integer}` to `{float}`
1878                     err.multipart_suggestion_verbose(
1879                         &format!(
1880                             "{}, producing the floating point representation of the integer, \
1881                                 rounded if necessary",
1882                             &msg,
1883                         ),
1884                         cast_suggestion,
1885                         Applicability::MaybeIncorrect, // lossy conversion
1886                     );
1887                 }
1888                 true
1889             }
1890             (
1891                 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1892                 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1893                 &ty::Char,
1894             ) => {
1895                 err.multipart_suggestion_verbose(
1896                     &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1897                     cast_suggestion,
1898                     Applicability::MachineApplicable,
1899                 );
1900                 true
1901             }
1902             _ => false,
1903         }
1904     }
1905
1906     /// Identify when the user has written `foo..bar()` instead of `foo.bar()`.
1907     pub fn check_for_range_as_method_call(
1908         &self,
1909         err: &mut Diagnostic,
1910         expr: &hir::Expr<'tcx>,
1911         checked_ty: Ty<'tcx>,
1912         expected_ty: Ty<'tcx>,
1913     ) {
1914         if !hir::is_range_literal(expr) {
1915             return;
1916         }
1917         let hir::ExprKind::Struct(
1918             hir::QPath::LangItem(LangItem::Range, ..),
1919             [start, end],
1920             _,
1921         ) = expr.kind else { return; };
1922         let parent = self.tcx.hir().parent_id(expr.hir_id);
1923         if let Some(hir::Node::ExprField(_)) = self.tcx.hir().find(parent) {
1924             // Ignore `Foo { field: a..Default::default() }`
1925             return;
1926         }
1927         let mut expr = end.expr;
1928         let mut expectation = Some(expected_ty);
1929         while let hir::ExprKind::MethodCall(_, rcvr, ..) = expr.kind {
1930             // Getting to the root receiver and asserting it is a fn call let's us ignore cases in
1931             // `tests/ui/methods/issues/issue-90315.stderr`.
1932             expr = rcvr;
1933             // If we have more than one layer of calls, then the expected ty
1934             // cannot guide the method probe.
1935             expectation = None;
1936         }
1937         let hir::ExprKind::Call(method_name, _) = expr.kind else { return; };
1938         let ty::Adt(adt, _) = checked_ty.kind() else { return; };
1939         if self.tcx.lang_items().range_struct() != Some(adt.did()) {
1940             return;
1941         }
1942         if let ty::Adt(adt, _) = expected_ty.kind()
1943             && self.tcx.lang_items().range_struct() == Some(adt.did())
1944         {
1945             return;
1946         }
1947         // Check if start has method named end.
1948         let hir::ExprKind::Path(hir::QPath::Resolved(None, p)) = method_name.kind else { return; };
1949         let [hir::PathSegment { ident, .. }] = p.segments else { return; };
1950         let self_ty = self.typeck_results.borrow().expr_ty(start.expr);
1951         let Ok(_pick) = self.lookup_probe_for_diagnostic(
1952             *ident,
1953             self_ty,
1954             expr,
1955             probe::ProbeScope::AllTraits,
1956             expectation,
1957         ) else { return; };
1958         let mut sugg = ".";
1959         let mut span = start.expr.span.between(end.expr.span);
1960         if span.lo() + BytePos(2) == span.hi() {
1961             // There's no space between the start, the range op and the end, suggest removal which
1962             // will be more noticeable than the replacement of `..` with `.`.
1963             span = span.with_lo(span.lo() + BytePos(1));
1964             sugg = "";
1965         }
1966         err.span_suggestion_verbose(
1967             span,
1968             "you likely meant to write a method call instead of a range",
1969             sugg,
1970             Applicability::MachineApplicable,
1971         );
1972     }
1973
1974     /// Identify when the type error is because `()` is found in a binding that was assigned a
1975     /// block without a tail expression.
1976     fn check_for_binding_assigned_block_without_tail_expression(
1977         &self,
1978         err: &mut Diagnostic,
1979         expr: &hir::Expr<'_>,
1980         checked_ty: Ty<'tcx>,
1981         expected_ty: Ty<'tcx>,
1982     ) {
1983         if !checked_ty.is_unit() {
1984             return;
1985         }
1986         let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind else { return; };
1987         let hir::def::Res::Local(hir_id) = path.res else { return; };
1988         let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(hir_id) else {
1989             return;
1990         };
1991         let Some(hir::Node::Local(hir::Local {
1992             ty: None,
1993             init: Some(init),
1994             ..
1995         })) = self.tcx.hir().find_parent(pat.hir_id) else { return; };
1996         let hir::ExprKind::Block(block, None) = init.kind else { return; };
1997         if block.expr.is_some() {
1998             return;
1999         }
2000         let [.., stmt] = block.stmts else {
2001             err.span_label(block.span, "this empty block is missing a tail expression");
2002             return;
2003         };
2004         let hir::StmtKind::Semi(tail_expr) = stmt.kind else { return; };
2005         let Some(ty) = self.node_ty_opt(tail_expr.hir_id) else { return; };
2006         if self.can_eq(self.param_env, expected_ty, ty).is_ok() {
2007             err.span_suggestion_short(
2008                 stmt.span.with_lo(tail_expr.span.hi()),
2009                 "remove this semicolon",
2010                 "",
2011                 Applicability::MachineApplicable,
2012             );
2013         } else {
2014             err.span_label(block.span, "this block is missing a tail expression");
2015         }
2016     }
2017
2018     fn check_wrong_return_type_due_to_generic_arg(
2019         &self,
2020         err: &mut Diagnostic,
2021         expr: &hir::Expr<'_>,
2022         checked_ty: Ty<'tcx>,
2023     ) {
2024         let Some(hir::Node::Expr(parent_expr)) = self.tcx.hir().find_parent(expr.hir_id) else { return; };
2025         enum CallableKind {
2026             Function,
2027             Method,
2028             Constructor,
2029         }
2030         let mut maybe_emit_help = |def_id: hir::def_id::DefId,
2031                                    callable: rustc_span::symbol::Ident,
2032                                    args: &[hir::Expr<'_>],
2033                                    kind: CallableKind| {
2034             let arg_idx = args.iter().position(|a| a.hir_id == expr.hir_id).unwrap();
2035             let fn_ty = self.tcx.bound_type_of(def_id).0;
2036             if !fn_ty.is_fn() {
2037                 return;
2038             }
2039             let fn_sig = fn_ty.fn_sig(self.tcx).skip_binder();
2040             let Some(&arg) = fn_sig.inputs().get(arg_idx + if matches!(kind, CallableKind::Method) { 1 } else { 0 }) else { return; };
2041             if matches!(arg.kind(), ty::Param(_))
2042                 && fn_sig.output().contains(arg)
2043                 && self.node_ty(args[arg_idx].hir_id) == checked_ty
2044             {
2045                 let mut multi_span: MultiSpan = parent_expr.span.into();
2046                 multi_span.push_span_label(
2047                     args[arg_idx].span,
2048                     format!(
2049                         "this argument influences the {} of `{}`",
2050                         if matches!(kind, CallableKind::Constructor) {
2051                             "type"
2052                         } else {
2053                             "return type"
2054                         },
2055                         callable
2056                     ),
2057                 );
2058                 err.span_help(
2059                     multi_span,
2060                     format!(
2061                         "the {} `{}` due to the type of the argument passed",
2062                         match kind {
2063                             CallableKind::Function => "return type of this call is",
2064                             CallableKind::Method => "return type of this call is",
2065                             CallableKind::Constructor => "type constructed contains",
2066                         },
2067                         checked_ty
2068                     ),
2069                 );
2070             }
2071         };
2072         match parent_expr.kind {
2073             hir::ExprKind::Call(fun, args) => {
2074                 let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = fun.kind else { return; };
2075                 let hir::def::Res::Def(kind, def_id) = path.res else { return; };
2076                 let callable_kind = if matches!(kind, hir::def::DefKind::Ctor(_, _)) {
2077                     CallableKind::Constructor
2078                 } else {
2079                     CallableKind::Function
2080                 };
2081                 maybe_emit_help(def_id, path.segments[0].ident, args, callable_kind);
2082             }
2083             hir::ExprKind::MethodCall(method, _receiver, args, _span) => {
2084                 let Some(def_id) = self.typeck_results.borrow().type_dependent_def_id(parent_expr.hir_id) else { return; };
2085                 maybe_emit_help(def_id, method.ident, args, CallableKind::Method)
2086             }
2087             _ => return,
2088         }
2089     }
2090 }