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