compiler/rustc_typeck/src/check/demand.rs

   1 use crate::check::FnCtxt;
   2 use rustc_infer::infer::InferOk;
   3 use rustc_trait_selection::infer::InferCtxtExt as _;
   4 use rustc_trait_selection::traits::ObligationCause;
   5
   6 use rustc_ast::util::parser::PREC_POSTFIX;
   7 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
   8 use rustc_hir as hir;
   9 use rustc_hir::lang_items::LangItem;
  10 use rustc_hir::{is_range_literal, Node};
  11 use rustc_middle::lint::in_external_macro;
  12 use rustc_middle::ty::adjustment::AllowTwoPhase;
  13 use rustc_middle::ty::error::{ExpectedFound, TypeError};
  14 use rustc_middle::ty::print::with_no_trimmed_paths;
  15 use rustc_middle::ty::{self, Article, AssocItem, Ty, TypeAndMut};
  16 use rustc_span::symbol::{sym, Symbol};
  17 use rustc_span::{BytePos, Span};
  18
  19 use super::method::probe;
  20
  21 use std::iter;
  22
  23 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  24     pub fn emit_coerce_suggestions(
  25         &self,
  26         err: &mut Diagnostic,
  27         expr: &hir::Expr<'tcx>,
  28         expr_ty: Ty<'tcx>,
  29         expected: Ty<'tcx>,
  30         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
  31         error: Option<TypeError<'tcx>>,
  32     ) {
  33         self.annotate_expected_due_to_let_ty(err, expr, error);
  34         self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr);
  35         self.suggest_compatible_variants(err, expr, expected, expr_ty);
  36         self.suggest_non_zero_new_unwrap(err, expr, expected, expr_ty);
  37         if self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty) {
  38             return;
  39         }
  40         self.suggest_no_capture_closure(err, expected, expr_ty);
  41         self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
  42         self.suggest_missing_parentheses(err, expr);
  43         self.suggest_block_to_brackets_peeling_refs(err, expr, expr_ty, expected);
  44         self.note_type_is_not_clone(err, expected, expr_ty, expr);
  45         self.note_need_for_fn_pointer(err, expected, expr_ty);
  46         self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
  47         self.report_closure_inferred_return_type(err, expected);
  48     }
  49
  50     // Requires that the two types unify, and prints an error message if
  51     // they don't.
  52     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  53         if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
  54             e.emit();
  55         }
  56     }
  57
  58     pub fn demand_suptype_diag(
  59         &self,
  60         sp: Span,
  61         expected: Ty<'tcx>,
  62         actual: Ty<'tcx>,
  63     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
  64         self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
  65     }
  66
  67     #[instrument(skip(self), level = "debug")]
  68     pub fn demand_suptype_with_origin(
  69         &self,
  70         cause: &ObligationCause<'tcx>,
  71         expected: Ty<'tcx>,
  72         actual: Ty<'tcx>,
  73     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
  74         match self.at(cause, self.param_env).sup(expected, actual) {
  75             Ok(InferOk { obligations, value: () }) => {
  76                 self.register_predicates(obligations);
  77                 None
  78             }
  79             Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
  80         }
  81     }
  82
  83     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  84         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  85             err.emit();
  86         }
  87     }
  88
  89     pub fn demand_eqtype_diag(
  90         &self,
  91         sp: Span,
  92         expected: Ty<'tcx>,
  93         actual: Ty<'tcx>,
  94     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
  95         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  96     }
  97
  98     pub fn demand_eqtype_with_origin(
  99         &self,
 100         cause: &ObligationCause<'tcx>,
 101         expected: Ty<'tcx>,
 102         actual: Ty<'tcx>,
 103     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
 104         match self.at(cause, self.param_env).eq(expected, actual) {
 105             Ok(InferOk { obligations, value: () }) => {
 106                 self.register_predicates(obligations);
 107                 None
 108             }
 109             Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
 110         }
 111     }
 112
 113     pub fn demand_coerce(
 114         &self,
 115         expr: &hir::Expr<'tcx>,
 116         checked_ty: Ty<'tcx>,
 117         expected: Ty<'tcx>,
 118         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 119         allow_two_phase: AllowTwoPhase,
 120     ) -> Ty<'tcx> {
 121         let (ty, err) =
 122             self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
 123         if let Some(mut err) = err {
 124             err.emit();
 125         }
 126         ty
 127     }
 128
 129     /// Checks that the type of `expr` can be coerced to `expected`.
 130     ///
 131     /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
 132     /// will be permitted if the diverges flag is currently "always".
 133     #[tracing::instrument(level = "debug", skip(self, expr, expected_ty_expr, allow_two_phase))]
 134     pub fn demand_coerce_diag(
 135         &self,
 136         expr: &hir::Expr<'tcx>,
 137         checked_ty: Ty<'tcx>,
 138         expected: Ty<'tcx>,
 139         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 140         allow_two_phase: AllowTwoPhase,
 141     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>) {
 142         let expected = self.resolve_vars_with_obligations(expected);
 143
 144         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase, None) {
 145             Ok(ty) => return (ty, None),
 146             Err(e) => e,
 147         };
 148
 149         self.set_tainted_by_errors();
 150         let expr = expr.peel_drop_temps();
 151         let cause = self.misc(expr.span);
 152         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 153         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e.clone());
 154
 155         let is_insufficiently_polymorphic =
 156             matches!(e, TypeError::RegionsInsufficientlyPolymorphic(..));
 157
 158         // FIXME(#73154): For now, we do leak check when coercing function
 159         // pointers in typeck, instead of only during borrowck. This can lead
 160         // to these `RegionsInsufficientlyPolymorphic` errors that aren't helpful.
 161         if !is_insufficiently_polymorphic {
 162             self.emit_coerce_suggestions(
 163                 &mut err,
 164                 expr,
 165                 expr_ty,
 166                 expected,
 167                 expected_ty_expr,
 168                 Some(e),
 169             );
 170         }
 171
 172         (expected, Some(err))
 173     }
 174
 175     fn annotate_expected_due_to_let_ty(
 176         &self,
 177         err: &mut Diagnostic,
 178         expr: &hir::Expr<'_>,
 179         error: Option<TypeError<'_>>,
 180     ) {
 181         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 182         match (self.tcx.hir().find(parent), error) {
 183             (Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })), _)
 184                 if init.hir_id == expr.hir_id =>
 185             {
 186                 // Point at `let` assignment type.
 187                 err.span_label(ty.span, "expected due to this");
 188             }
 189             (
 190                 Some(hir::Node::Expr(hir::Expr {
 191                     kind: hir::ExprKind::Assign(lhs, rhs, _), ..
 192                 })),
 193                 Some(TypeError::Sorts(ExpectedFound { expected, .. })),
 194             ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
 195                 // We ignore closures explicitly because we already point at them elsewhere.
 196                 // Point at the assigned-to binding.
 197                 let mut primary_span = lhs.span;
 198                 let mut secondary_span = lhs.span;
 199                 let mut post_message = "";
 200                 match lhs.kind {
 201                     hir::ExprKind::Path(hir::QPath::Resolved(
 202                         None,
 203                         hir::Path {
 204                             res:
 205                                 hir::def::Res::Def(
 206                                     hir::def::DefKind::Static(_) | hir::def::DefKind::Const,
 207                                     def_id,
 208                                 ),
 209                             ..
 210                         },
 211                     )) => {
 212                         if let Some(hir::Node::Item(hir::Item {
 213                             ident,
 214                             kind: hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..),
 215                             ..
 216                         })) = self.tcx.hir().get_if_local(*def_id)
 217                         {
 218                             primary_span = ty.span;
 219                             secondary_span = ident.span;
 220                             post_message = " type";
 221                         }
 222                     }
 223                     hir::ExprKind::Path(hir::QPath::Resolved(
 224                         None,
 225                         hir::Path { res: hir::def::Res::Local(hir_id), .. },
 226                     )) => {
 227                         if let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(*hir_id) {
 228                             let parent = self.tcx.hir().get_parent_node(pat.hir_id);
 229                             primary_span = pat.span;
 230                             secondary_span = pat.span;
 231                             match self.tcx.hir().find(parent) {
 232                                 Some(hir::Node::Local(hir::Local { ty: Some(ty), .. })) => {
 233                                     primary_span = ty.span;
 234                                     post_message = " type";
 235                                 }
 236                                 Some(hir::Node::Local(hir::Local { init: Some(init), .. })) => {
 237                                     primary_span = init.span;
 238                                     post_message = " value";
 239                                 }
 240                                 Some(hir::Node::Param(hir::Param { ty_span, .. })) => {
 241                                     primary_span = *ty_span;
 242                                     post_message = " parameter type";
 243                                 }
 244                                 _ => {}
 245                             }
 246                         }
 247                     }
 248                     _ => {}
 249                 }
 250
 251                 if primary_span != secondary_span
 252                     && self
 253                         .tcx
 254                         .sess
 255                         .source_map()
 256                         .is_multiline(secondary_span.shrink_to_hi().until(primary_span))
 257                 {
 258                     // We are pointing at the binding's type or initializer value, but it's pattern
 259                     // is in a different line, so we point at both.
 260                     err.span_label(secondary_span, "expected due to the type of this binding");
 261                     err.span_label(primary_span, &format!("expected due to this{post_message}"));
 262                 } else if post_message == "" {
 263                     // We are pointing at either the assignment lhs or the binding def pattern.
 264                     err.span_label(primary_span, "expected due to the type of this binding");
 265                 } else {
 266                     // We are pointing at the binding's type or initializer value.
 267                     err.span_label(primary_span, &format!("expected due to this{post_message}"));
 268                 }
 269
 270                 if !lhs.is_syntactic_place_expr() {
 271                     // We already emitted E0070 "invalid left-hand side of assignment", so we
 272                     // silence this.
 273                     err.downgrade_to_delayed_bug();
 274                 }
 275             }
 276             _ => {}
 277         }
 278     }
 279
 280     /// If the expected type is an enum (Issue #55250) with any variants whose
 281     /// sole field is of the found type, suggest such variants. (Issue #42764)
 282     fn suggest_compatible_variants(
 283         &self,
 284         err: &mut Diagnostic,
 285         expr: &hir::Expr<'_>,
 286         expected: Ty<'tcx>,
 287         expr_ty: Ty<'tcx>,
 288     ) {
 289         if let ty::Adt(expected_adt, substs) = expected.kind() {
 290             if let hir::ExprKind::Field(base, ident) = expr.kind {
 291                 let base_ty = self.typeck_results.borrow().expr_ty(base);
 292                 if self.can_eq(self.param_env, base_ty, expected).is_ok()
 293                     && let Some(base_span) = base.span.find_ancestor_inside(expr.span)
 294                 {
 295                     err.span_suggestion_verbose(
 296                         expr.span.with_lo(base_span.hi()),
 297                         format!("consider removing the tuple struct field `{ident}`"),
 298                         "",
 299                         Applicability::MaybeIncorrect,
 300                     );
 301                     return
 302                 }
 303             }
 304
 305             // If the expression is of type () and it's the return expression of a block,
 306             // we suggest adding a separate return expression instead.
 307             // (To avoid things like suggesting `Ok(while .. { .. })`.)
 308             if expr_ty.is_unit() {
 309                 let mut id = expr.hir_id;
 310                 let mut parent;
 311
 312                 // Unroll desugaring, to make sure this works for `for` loops etc.
 313                 loop {
 314                     parent = self.tcx.hir().get_parent_node(id);
 315                     if let Some(parent_span) = self.tcx.hir().opt_span(parent) {
 316                         if parent_span.find_ancestor_inside(expr.span).is_some() {
 317                             // The parent node is part of the same span, so is the result of the
 318                             // same expansion/desugaring and not the 'real' parent node.
 319                             id = parent;
 320                             continue;
 321                         }
 322                     }
 323                     break;
 324                 }
 325
 326                 if let Some(hir::Node::Block(&hir::Block {
 327                     span: block_span, expr: Some(e), ..
 328                 })) = self.tcx.hir().find(parent)
 329                 {
 330                     if e.hir_id == id {
 331                         if let Some(span) = expr.span.find_ancestor_inside(block_span) {
 332                             let return_suggestions = if self
 333                                 .tcx
 334                                 .is_diagnostic_item(sym::Result, expected_adt.did())
 335                             {
 336                                 vec!["Ok(())"]
 337                             } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did()) {
 338                                 vec!["None", "Some(())"]
 339                             } else {
 340                                 return;
 341                             };
 342                             if let Some(indent) =
 343                                 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
 344                             {
 345                                 // Add a semicolon, except after `}`.
 346                                 let semicolon =
 347                                     match self.tcx.sess.source_map().span_to_snippet(span) {
 348                                         Ok(s) if s.ends_with('}') => "",
 349                                         _ => ";",
 350                                     };
 351                                 err.span_suggestions(
 352                                     span.shrink_to_hi(),
 353                                     "try adding an expression at the end of the block",
 354                                     return_suggestions
 355                                         .into_iter()
 356                                         .map(|r| format!("{semicolon}\n{indent}{r}")),
 357                                     Applicability::MaybeIncorrect,
 358                                 );
 359                             }
 360                             return;
 361                         }
 362                     }
 363                 }
 364             }
 365
 366             let compatible_variants: Vec<(String, Option<String>)> = expected_adt
 367                 .variants()
 368                 .iter()
 369                 .filter(|variant| {
 370                     variant.fields.len() == 1 && variant.ctor_kind == hir::def::CtorKind::Fn
 371                 })
 372                 .filter_map(|variant| {
 373                     let sole_field = &variant.fields[0];
 374
 375                     let field_is_local = sole_field.did.is_local();
 376                     let field_is_accessible =
 377                         sole_field.vis.is_accessible_from(expr.hir_id.owner.to_def_id(), self.tcx);
 378
 379                     if !field_is_local && !field_is_accessible {
 380                         return None;
 381                     }
 382
 383                     let note_about_variant_field_privacy = (field_is_local && !field_is_accessible)
 384                         .then(|| format!(" (its field is private, but it's local to this crate and its privacy can be changed)"));
 385
 386                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 387                     if self.can_coerce(expr_ty, sole_field_ty) {
 388                         let variant_path =
 389                             with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
 390                         // FIXME #56861: DRYer prelude filtering
 391                         if let Some(path) = variant_path.strip_prefix("std::prelude::")
 392                             && let Some((_, path)) = path.split_once("::")
 393                         {
 394                             return Some((path.to_string(), note_about_variant_field_privacy));
 395                         }
 396                         Some((variant_path, note_about_variant_field_privacy))
 397                     } else {
 398                         None
 399                     }
 400                 })
 401                 .collect();
 402
 403             let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 404                 Some(ident) => format!("{ident}: "),
 405                 None => String::new(),
 406             };
 407
 408             match &compatible_variants[..] {
 409                 [] => { /* No variants to format */ }
 410                 [(variant, note)] => {
 411                     // Just a single matching variant.
 412                     err.multipart_suggestion_verbose(
 413                         &format!(
 414                             "try wrapping the expression in `{variant}`{note}",
 415                             note = note.as_deref().unwrap_or("")
 416                         ),
 417                         vec![
 418                             (expr.span.shrink_to_lo(), format!("{prefix}{variant}(")),
 419                             (expr.span.shrink_to_hi(), ")".to_string()),
 420                         ],
 421                         Applicability::MaybeIncorrect,
 422                     );
 423                 }
 424                 _ => {
 425                     // More than one matching variant.
 426                     err.multipart_suggestions(
 427                         &format!(
 428                             "try wrapping the expression in a variant of `{}`",
 429                             self.tcx.def_path_str(expected_adt.did())
 430                         ),
 431                         compatible_variants.into_iter().map(|(variant, _)| {
 432                             vec![
 433                                 (expr.span.shrink_to_lo(), format!("{prefix}{variant}(")),
 434                                 (expr.span.shrink_to_hi(), ")".to_string()),
 435                             ]
 436                         }),
 437                         Applicability::MaybeIncorrect,
 438                     );
 439                 }
 440             }
 441         }
 442     }
 443
 444     fn suggest_non_zero_new_unwrap(
 445         &self,
 446         err: &mut Diagnostic,
 447         expr: &hir::Expr<'_>,
 448         expected: Ty<'tcx>,
 449         expr_ty: Ty<'tcx>,
 450     ) {
 451         let tcx = self.tcx;
 452         let (adt, unwrap) = match expected.kind() {
 453             // In case Option<NonZero*> is wanted, but * is provided, suggest calling new
 454             ty::Adt(adt, substs) if tcx.is_diagnostic_item(sym::Option, adt.did()) => {
 455                 // Unwrap option
 456                 let ty::Adt(adt, _) = substs.type_at(0).kind() else { return };
 457
 458                 (adt, "")
 459             }
 460             // In case NonZero* is wanted, but * is provided also add `.unwrap()` to satisfy types
 461             ty::Adt(adt, _) => (adt, ".unwrap()"),
 462             _ => return,
 463         };
 464
 465         let map = [
 466             (sym::NonZeroU8, tcx.types.u8),
 467             (sym::NonZeroU16, tcx.types.u16),
 468             (sym::NonZeroU32, tcx.types.u32),
 469             (sym::NonZeroU64, tcx.types.u64),
 470             (sym::NonZeroU128, tcx.types.u128),
 471             (sym::NonZeroI8, tcx.types.i8),
 472             (sym::NonZeroI16, tcx.types.i16),
 473             (sym::NonZeroI32, tcx.types.i32),
 474             (sym::NonZeroI64, tcx.types.i64),
 475             (sym::NonZeroI128, tcx.types.i128),
 476         ];
 477
 478         let Some((s, _)) = map
 479             .iter()
 480             .find(|&&(s, t)| self.tcx.is_diagnostic_item(s, adt.did()) && self.can_coerce(expr_ty, t))
 481             else { return };
 482
 483         let path = self.tcx.def_path_str(adt.non_enum_variant().def_id);
 484
 485         err.multipart_suggestion(
 486             format!("consider calling `{s}::new`"),
 487             vec![
 488                 (expr.span.shrink_to_lo(), format!("{path}::new(")),
 489                 (expr.span.shrink_to_hi(), format!("){unwrap}")),
 490             ],
 491             Applicability::MaybeIncorrect,
 492         );
 493     }
 494
 495     pub fn get_conversion_methods(
 496         &self,
 497         span: Span,
 498         expected: Ty<'tcx>,
 499         checked_ty: Ty<'tcx>,
 500         hir_id: hir::HirId,
 501     ) -> Vec<AssocItem> {
 502         let mut methods =
 503             self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
 504         methods.retain(|m| {
 505             self.has_only_self_parameter(m)
 506                 && self
 507                     .tcx
 508                     // This special internal attribute is used to permit
 509                     // "identity-like" conversion methods to be suggested here.
 510                     //
 511                     // FIXME (#46459 and #46460): ideally
 512                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 513                     // also be `#[rustc_conversion_suggestion]`, if not for
 514                     // method-probing false-positives and -negatives (respectively).
 515                     //
 516                     // FIXME? Other potential candidate methods: `as_ref` and
 517                     // `as_mut`?
 518                     .has_attr(m.def_id, sym::rustc_conversion_suggestion)
 519         });
 520
 521         methods
 522     }
 523
 524     /// This function checks whether the method is not static and does not accept other parameters than `self`.
 525     fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
 526         match method.kind {
 527             ty::AssocKind::Fn => {
 528                 method.fn_has_self_parameter
 529                     && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 530             }
 531             _ => false,
 532         }
 533     }
 534
 535     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 536     ///
 537     /// Given the following code:
 538     /// ```compile_fail,E0308
 539     /// struct Foo;
 540     /// fn takes_ref(_: &Foo) {}
 541     /// let ref opt = Some(Foo);
 542     ///
 543     /// opt.map(|param| takes_ref(param));
 544     /// ```
 545     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 546     ///
 547     /// It only checks for `Option` and `Result` and won't work with
 548     /// ```ignore (illustrative)
 549     /// opt.map(|param| { takes_ref(param) });
 550     /// ```
 551     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 552         let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
 553             return None;
 554         };
 555
 556         let hir::def::Res::Local(local_id) = path.res else {
 557             return None;
 558         };
 559
 560         let local_parent = self.tcx.hir().get_parent_node(local_id);
 561         let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
 562             return None;
 563         };
 564
 565         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 566         let Some(Node::Expr(hir::Expr {
 567             hir_id: expr_hir_id,
 568             kind: hir::ExprKind::Closure(hir::Closure { fn_decl: closure_fn_decl, .. }),
 569             ..
 570         })) = self.tcx.hir().find(param_parent) else {
 571             return None;
 572         };
 573
 574         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 575         let hir = self.tcx.hir().find(expr_parent);
 576         let closure_params_len = closure_fn_decl.inputs.len();
 577         let (
 578             Some(Node::Expr(hir::Expr {
 579                 kind: hir::ExprKind::MethodCall(method_path, method_expr, _),
 580                 ..
 581             })),
 582             1,
 583         ) = (hir, closure_params_len) else {
 584             return None;
 585         };
 586
 587         let self_ty = self.typeck_results.borrow().expr_ty(&method_expr[0]);
 588         let self_ty = format!("{:?}", self_ty);
 589         let name = method_path.ident.name;
 590         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 591             || self_ty.starts_with("&std::result::Result")
 592             || self_ty.starts_with("std::option::Option")
 593             || self_ty.starts_with("std::result::Result"))
 594             && (name == sym::map || name == sym::and_then);
 595         match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
 596             (true, Ok(src)) => {
 597                 let suggestion = format!("as_ref().{}", src);
 598                 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
 599             }
 600             _ => None,
 601         }
 602     }
 603
 604     pub(crate) fn maybe_get_struct_pattern_shorthand_field(
 605         &self,
 606         expr: &hir::Expr<'_>,
 607     ) -> Option<Symbol> {
 608         let hir = self.tcx.hir();
 609         let local = match expr {
 610             hir::Expr {
 611                 kind:
 612                     hir::ExprKind::Path(hir::QPath::Resolved(
 613                         None,
 614                         hir::Path {
 615                             res: hir::def::Res::Local(_),
 616                             segments: [hir::PathSegment { ident, .. }],
 617                             ..
 618                         },
 619                     )),
 620                 ..
 621             } => Some(ident),
 622             _ => None,
 623         }?;
 624
 625         match hir.find(hir.get_parent_node(expr.hir_id))? {
 626             Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) => {
 627                 for field in *fields {
 628                     if field.ident.name == local.name && field.is_shorthand {
 629                         return Some(local.name);
 630                     }
 631                 }
 632             }
 633             _ => {}
 634         }
 635
 636         None
 637     }
 638
 639     /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
 640     pub(crate) fn maybe_get_block_expr(
 641         &self,
 642         expr: &hir::Expr<'tcx>,
 643     ) -> Option<&'tcx hir::Expr<'tcx>> {
 644         match expr {
 645             hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
 646             _ => None,
 647         }
 648     }
 649
 650     /// Returns whether the given expression is an `else if`.
 651     pub(crate) fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
 652         if let hir::ExprKind::If(..) = expr.kind {
 653             let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
 654             if let Some(Node::Expr(hir::Expr {
 655                 kind: hir::ExprKind::If(_, _, Some(else_expr)),
 656                 ..
 657             })) = self.tcx.hir().find(parent_id)
 658             {
 659                 return else_expr.hir_id == expr.hir_id;
 660             }
 661         }
 662         false
 663     }
 664
 665     /// This function is used to determine potential "simple" improvements or users' errors and
 666     /// provide them useful help. For example:
 667     ///
 668     /// ```compile_fail,E0308
 669     /// fn some_fn(s: &str) {}
 670     ///
 671     /// let x = "hey!".to_owned();
 672     /// some_fn(x); // error
 673     /// ```
 674     ///
 675     /// No need to find every potential function which could make a coercion to transform a
 676     /// `String` into a `&str` since a `&` would do the trick!
 677     ///
 678     /// In addition of this check, it also checks between references mutability state. If the
 679     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 680     /// `&mut`!".
 681     pub fn check_ref(
 682         &self,
 683         expr: &hir::Expr<'tcx>,
 684         checked_ty: Ty<'tcx>,
 685         expected: Ty<'tcx>,
 686     ) -> Option<(Span, String, String, Applicability, bool /* verbose */)> {
 687         let sess = self.sess();
 688         let sp = expr.span;
 689
 690         // If the span is from an external macro, there's no suggestion we can make.
 691         if in_external_macro(sess, sp) {
 692             return None;
 693         }
 694
 695         let sm = sess.source_map();
 696
 697         let replace_prefix = |s: &str, old: &str, new: &str| {
 698             s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
 699         };
 700
 701         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 702         let expr = expr.peel_drop_temps();
 703
 704         match (&expr.kind, expected.kind(), checked_ty.kind()) {
 705             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
 706                 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
 707                     if let hir::ExprKind::Lit(_) = expr.kind
 708                         && let Ok(src) = sm.span_to_snippet(sp)
 709                         && replace_prefix(&src, "b\"", "\"").is_some()
 710                     {
 711                                 let pos = sp.lo() + BytePos(1);
 712                                 return Some((
 713                                     sp.with_hi(pos),
 714                                     "consider removing the leading `b`".to_string(),
 715                                     String::new(),
 716                                     Applicability::MachineApplicable,
 717                                     true,
 718                                 ));
 719                             }
 720                         }
 721                 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
 722                     if let hir::ExprKind::Lit(_) = expr.kind
 723                         && let Ok(src) = sm.span_to_snippet(sp)
 724                         && replace_prefix(&src, "\"", "b\"").is_some()
 725                     {
 726                                 return Some((
 727                                     sp.shrink_to_lo(),
 728                                     "consider adding a leading `b`".to_string(),
 729                                     "b".to_string(),
 730                                     Applicability::MachineApplicable,
 731                                     true,
 732                                 ));
 733                     }
 734                 }
 735                 _ => {}
 736             },
 737             (_, &ty::Ref(_, _, mutability), _) => {
 738                 // Check if it can work when put into a ref. For example:
 739                 //
 740                 // ```
 741                 // fn bar(x: &mut i32) {}
 742                 //
 743                 // let x = 0u32;
 744                 // bar(&x); // error, expected &mut
 745                 // ```
 746                 let ref_ty = match mutability {
 747                     hir::Mutability::Mut => {
 748                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 749                     }
 750                     hir::Mutability::Not => {
 751                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 752                     }
 753                 };
 754                 if self.can_coerce(ref_ty, expected) {
 755                     let mut sugg_sp = sp;
 756                     if let hir::ExprKind::MethodCall(ref segment, ref args, _) = expr.kind {
 757                         let clone_trait =
 758                             self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
 759                         if let ([arg], Some(true), sym::clone) = (
 760                             &args[..],
 761                             self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
 762                                 |did| {
 763                                     let ai = self.tcx.associated_item(did);
 764                                     ai.container == ty::TraitContainer(clone_trait)
 765                                 },
 766                             ),
 767                             segment.ident.name,
 768                         ) {
 769                             // If this expression had a clone call when suggesting borrowing
 770                             // we want to suggest removing it because it'd now be unnecessary.
 771                             sugg_sp = arg.span;
 772                         }
 773                     }
 774                     if let Ok(src) = sm.span_to_snippet(sugg_sp) {
 775                         let needs_parens = match expr.kind {
 776                             // parenthesize if needed (Issue #46756)
 777                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 778                             // parenthesize borrows of range literals (Issue #54505)
 779                             _ if is_range_literal(expr) => true,
 780                             _ => false,
 781                         };
 782                         let sugg_expr = if needs_parens { format!("({src})") } else { src };
 783
 784                         if let Some(sugg) = self.can_use_as_ref(expr) {
 785                             return Some((
 786                                 sugg.0,
 787                                 sugg.1.to_string(),
 788                                 sugg.2,
 789                                 Applicability::MachineApplicable,
 790                                 false,
 791                             ));
 792                         }
 793
 794                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 795                             Some(ident) => format!("{ident}: "),
 796                             None => String::new(),
 797                         };
 798
 799                         if let Some(hir::Node::Expr(hir::Expr {
 800                             kind: hir::ExprKind::Assign(..),
 801                             ..
 802                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 803                         {
 804                             if mutability == hir::Mutability::Mut {
 805                                 // Suppressing this diagnostic, we'll properly print it in `check_expr_assign`
 806                                 return None;
 807                             }
 808                         }
 809
 810                         return Some(match mutability {
 811                             hir::Mutability::Mut => (
 812                                 sp,
 813                                 "consider mutably borrowing here".to_string(),
 814                                 format!("{prefix}&mut {sugg_expr}"),
 815                                 Applicability::MachineApplicable,
 816                                 false,
 817                             ),
 818                             hir::Mutability::Not => (
 819                                 sp,
 820                                 "consider borrowing here".to_string(),
 821                                 format!("{prefix}&{sugg_expr}"),
 822                                 Applicability::MachineApplicable,
 823                                 false,
 824                             ),
 825                         });
 826                     }
 827                 }
 828             }
 829             (
 830                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 831                 _,
 832                 &ty::Ref(_, checked, _),
 833             ) if self.can_sub(self.param_env, checked, expected).is_ok() => {
 834                 // We have `&T`, check if what was expected was `T`. If so,
 835                 // we may want to suggest removing a `&`.
 836                 if sm.is_imported(expr.span) {
 837                     // Go through the spans from which this span was expanded,
 838                     // and find the one that's pointing inside `sp`.
 839                     //
 840                     // E.g. for `&format!("")`, where we want the span to the
 841                     // `format!()` invocation instead of its expansion.
 842                     if let Some(call_span) =
 843                         iter::successors(Some(expr.span), |s| s.parent_callsite())
 844                             .find(|&s| sp.contains(s))
 845                         && sm.is_span_accessible(call_span)
 846                     {
 847                         return Some((
 848                             sp.with_hi(call_span.lo()),
 849                             "consider removing the borrow".to_string(),
 850                             String::new(),
 851                             Applicability::MachineApplicable,
 852                             true,
 853                         ));
 854                     }
 855                     return None;
 856                 }
 857                 if sp.contains(expr.span)
 858                     && sm.is_span_accessible(expr.span)
 859                 {
 860                     return Some((
 861                         sp.with_hi(expr.span.lo()),
 862                         "consider removing the borrow".to_string(),
 863                         String::new(),
 864                         Applicability::MachineApplicable,
 865                         true,
 866                     ));
 867                 }
 868             }
 869             (
 870                 _,
 871                 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
 872                 &ty::Ref(_, ty_a, mutbl_a),
 873             ) => {
 874                 if let Some(steps) = self.deref_steps(ty_a, ty_b)
 875                     // Only suggest valid if dereferencing needed.
 876                     && steps > 0
 877                     // The pointer type implements `Copy` trait so the suggestion is always valid.
 878                     && let Ok(src) = sm.span_to_snippet(sp)
 879                 {
 880                     let derefs = "*".repeat(steps);
 881                     if let Some((span, src, applicability)) = match mutbl_b {
 882                         hir::Mutability::Mut => {
 883                             let new_prefix = "&mut ".to_owned() + &derefs;
 884                             match mutbl_a {
 885                                 hir::Mutability::Mut => {
 886                                     replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
 887                                         let pos = sp.lo() + BytePos(5);
 888                                         let sp = sp.with_lo(pos).with_hi(pos);
 889                                         (sp, derefs, Applicability::MachineApplicable)
 890                                     })
 891                                 }
 892                                 hir::Mutability::Not => {
 893                                     replace_prefix(&src, "&", &new_prefix).map(|_| {
 894                                         let pos = sp.lo() + BytePos(1);
 895                                         let sp = sp.with_lo(pos).with_hi(pos);
 896                                         (
 897                                             sp,
 898                                             format!("mut {derefs}"),
 899                                             Applicability::Unspecified,
 900                                         )
 901                                     })
 902                                 }
 903                             }
 904                         }
 905                         hir::Mutability::Not => {
 906                             let new_prefix = "&".to_owned() + &derefs;
 907                             match mutbl_a {
 908                                 hir::Mutability::Mut => {
 909                                     replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
 910                                         let lo = sp.lo() + BytePos(1);
 911                                         let hi = sp.lo() + BytePos(5);
 912                                         let sp = sp.with_lo(lo).with_hi(hi);
 913                                         (sp, derefs, Applicability::MachineApplicable)
 914                                     })
 915                                 }
 916                                 hir::Mutability::Not => {
 917                                     replace_prefix(&src, "&", &new_prefix).map(|_| {
 918                                         let pos = sp.lo() + BytePos(1);
 919                                         let sp = sp.with_lo(pos).with_hi(pos);
 920                                         (sp, derefs, Applicability::MachineApplicable)
 921                                     })
 922                                 }
 923                             }
 924                         }
 925                     } {
 926                         return Some((
 927                             span,
 928                             "consider dereferencing".to_string(),
 929                             src,
 930                             applicability,
 931                             true,
 932                         ));
 933                     }
 934                 }
 935             }
 936             _ if sp == expr.span => {
 937                 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
 938                     let mut expr = expr.peel_blocks();
 939                     let mut prefix_span = expr.span.shrink_to_lo();
 940                     let mut remove = String::new();
 941
 942                     // Try peeling off any existing `&` and `&mut` to reach our target type
 943                     while steps > 0 {
 944                         if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
 945                             // If the expression has `&`, removing it would fix the error
 946                             prefix_span = prefix_span.with_hi(inner.span.lo());
 947                             expr = inner;
 948                             remove += match mutbl {
 949                                 hir::Mutability::Not => "&",
 950                                 hir::Mutability::Mut => "&mut ",
 951                             };
 952                             steps -= 1;
 953                         } else {
 954                             break;
 955                         }
 956                     }
 957                     // If we've reached our target type with just removing `&`, then just print now.
 958                     if steps == 0 {
 959                         return Some((
 960                             prefix_span,
 961                             format!("consider removing the `{}`", remove.trim()),
 962                             String::new(),
 963                             // Do not remove `&&` to get to bool, because it might be something like
 964                             // { a } && b, which we have a separate fixup suggestion that is more
 965                             // likely correct...
 966                             if remove.trim() == "&&" && expected == self.tcx.types.bool {
 967                                 Applicability::MaybeIncorrect
 968                             } else {
 969                                 Applicability::MachineApplicable
 970                             },
 971                             true,
 972                         ));
 973                     }
 974
 975                     // For this suggestion to make sense, the type would need to be `Copy`,
 976                     // or we have to be moving out of a `Box<T>`
 977                     if self.type_is_copy_modulo_regions(self.param_env, expected, sp)
 978                         // FIXME(compiler-errors): We can actually do this if the checked_ty is
 979                         // `steps` layers of boxes, not just one, but this is easier and most likely.
 980                         || (checked_ty.is_box() && steps == 1)
 981                     {
 982                         let deref_kind = if checked_ty.is_box() {
 983                             "unboxing the value"
 984                         } else if checked_ty.is_region_ptr() {
 985                             "dereferencing the borrow"
 986                         } else {
 987                             "dereferencing the type"
 988                         };
 989
 990                         // Suggest removing `&` if we have removed any, otherwise suggest just
 991                         // dereferencing the remaining number of steps.
 992                         let message = if remove.is_empty() {
 993                             format!("consider {deref_kind}")
 994                         } else {
 995                             format!(
 996                                 "consider removing the `{}` and {} instead",
 997                                 remove.trim(),
 998                                 deref_kind
 999                             )
1000                         };
1001
1002                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
1003                             Some(ident) => format!("{ident}: "),
1004                             None => String::new(),
1005                         };
1006
1007                         let (span, suggestion) = if self.is_else_if_block(expr) {
1008                             // Don't suggest nonsense like `else *if`
1009                             return None;
1010                         } else if let Some(expr) = self.maybe_get_block_expr(expr) {
1011                             // prefix should be empty here..
1012                             (expr.span.shrink_to_lo(), "*".to_string())
1013                         } else {
1014                             (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
1015                         };
1016
1017                         return Some((
1018                             span,
1019                             message,
1020                             suggestion,
1021                             Applicability::MachineApplicable,
1022                             true,
1023                         ));
1024                     }
1025                 }
1026             }
1027             _ => {}
1028         }
1029         None
1030     }
1031
1032     pub fn check_for_cast(
1033         &self,
1034         err: &mut Diagnostic,
1035         expr: &hir::Expr<'_>,
1036         checked_ty: Ty<'tcx>,
1037         expected_ty: Ty<'tcx>,
1038         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
1039     ) -> bool {
1040         if self.tcx.sess.source_map().is_imported(expr.span) {
1041             // Ignore if span is from within a macro.
1042             return false;
1043         }
1044
1045         let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
1046             return false;
1047         };
1048
1049         // If casting this expression to a given numeric type would be appropriate in case of a type
1050         // mismatch.
1051         //
1052         // We want to minimize the amount of casting operations that are suggested, as it can be a
1053         // lossy operation with potentially bad side effects, so we only suggest when encountering
1054         // an expression that indicates that the original type couldn't be directly changed.
1055         //
1056         // For now, don't suggest casting with `as`.
1057         let can_cast = false;
1058
1059         let mut sugg = vec![];
1060
1061         if let Some(hir::Node::Expr(hir::Expr {
1062             kind: hir::ExprKind::Struct(_, fields, _), ..
1063         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
1064         {
1065             // `expr` is a literal field for a struct, only suggest if appropriate
1066             match (*fields)
1067                 .iter()
1068                 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
1069             {
1070                 // This is a field literal
1071                 Some(field) => {
1072                     sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
1073                 }
1074                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
1075                 None => return false,
1076             }
1077         };
1078
1079         if let hir::ExprKind::Call(path, args) = &expr.kind
1080             && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
1081                 (&path.kind, args.len())
1082             // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1083             && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1084                 (&base_ty.kind, path_segment.ident.name)
1085         {
1086             if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1087                 match ident.name {
1088                     sym::i128
1089                     | sym::i64
1090                     | sym::i32
1091                     | sym::i16
1092                     | sym::i8
1093                     | sym::u128
1094                     | sym::u64
1095                     | sym::u32
1096                     | sym::u16
1097                     | sym::u8
1098                     | sym::isize
1099                     | sym::usize
1100                         if base_ty_path.segments.len() == 1 =>
1101                     {
1102                         return false;
1103                     }
1104                     _ => {}
1105                 }
1106             }
1107         }
1108
1109         let msg = format!(
1110             "you can convert {} `{}` to {} `{}`",
1111             checked_ty.kind().article(),
1112             checked_ty,
1113             expected_ty.kind().article(),
1114             expected_ty,
1115         );
1116         let cast_msg = format!(
1117             "you can cast {} `{}` to {} `{}`",
1118             checked_ty.kind().article(),
1119             checked_ty,
1120             expected_ty.kind().article(),
1121             expected_ty,
1122         );
1123         let lit_msg = format!(
1124             "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1125         );
1126
1127         let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1128             sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1129             ")"
1130         } else {
1131             ""
1132         };
1133
1134         let mut cast_suggestion = sugg.clone();
1135         cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1136         let mut into_suggestion = sugg.clone();
1137         into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1138         let mut suffix_suggestion = sugg.clone();
1139         suffix_suggestion.push((
1140             if matches!(
1141                 (&expected_ty.kind(), &checked_ty.kind()),
1142                 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1143             ) {
1144                 // Remove fractional part from literal, for example `42.0f32` into `42`
1145                 let src = src.trim_end_matches(&checked_ty.to_string());
1146                 let len = src.split('.').next().unwrap().len();
1147                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1148             } else {
1149                 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1150                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1151             },
1152             if expr.precedence().order() < PREC_POSTFIX {
1153                 // Readd `)`
1154                 format!("{expected_ty})")
1155             } else {
1156                 expected_ty.to_string()
1157             },
1158         ));
1159         let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1160             if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1161         };
1162         let is_negative_int =
1163             |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1164         let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1165
1166         let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1167
1168         let suggest_fallible_into_or_lhs_from =
1169             |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1170                 // If we know the expression the expected type is derived from, we might be able
1171                 // to suggest a widening conversion rather than a narrowing one (which may
1172                 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1173                 //   x > y
1174                 // can be given the suggestion "u32::from(x) > y" rather than
1175                 // "x > y.try_into().unwrap()".
1176                 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1177                     self.tcx
1178                         .sess
1179                         .source_map()
1180                         .span_to_snippet(expr.span)
1181                         .ok()
1182                         .map(|src| (expr, src))
1183                 });
1184                 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1185                     (lhs_expr_and_src, exp_to_found_is_fallible)
1186                 {
1187                     let msg = format!(
1188                         "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1189                     );
1190                     let suggestion = vec![
1191                         (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1192                         (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1193                     ];
1194                     (msg, suggestion)
1195                 } else {
1196                     let msg = format!("{msg} and panic if the converted value doesn't fit");
1197                     let mut suggestion = sugg.clone();
1198                     suggestion.push((
1199                         expr.span.shrink_to_hi(),
1200                         format!("{close_paren}.try_into().unwrap()"),
1201                     ));
1202                     (msg, suggestion)
1203                 };
1204                 err.multipart_suggestion_verbose(
1205                     &msg,
1206                     suggestion,
1207                     Applicability::MachineApplicable,
1208                 );
1209             };
1210
1211         let suggest_to_change_suffix_or_into =
1212             |err: &mut Diagnostic,
1213              found_to_exp_is_fallible: bool,
1214              exp_to_found_is_fallible: bool| {
1215                 let exp_is_lhs =
1216                     expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1217
1218                 if exp_is_lhs {
1219                     return;
1220                 }
1221
1222                 let always_fallible = found_to_exp_is_fallible
1223                     && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1224                 let msg = if literal_is_ty_suffixed(expr) {
1225                     &lit_msg
1226                 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1227                     // We now know that converting either the lhs or rhs is fallible. Before we
1228                     // suggest a fallible conversion, check if the value can never fit in the
1229                     // expected type.
1230                     let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1231                     err.note(&msg);
1232                     return;
1233                 } else if in_const_context {
1234                     // Do not recommend `into` or `try_into` in const contexts.
1235                     return;
1236                 } else if found_to_exp_is_fallible {
1237                     return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1238                 } else {
1239                     &msg
1240                 };
1241                 let suggestion = if literal_is_ty_suffixed(expr) {
1242                     suffix_suggestion.clone()
1243                 } else {
1244                     into_suggestion.clone()
1245                 };
1246                 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1247             };
1248
1249         match (&expected_ty.kind(), &checked_ty.kind()) {
1250             (&ty::Int(ref exp), &ty::Int(ref found)) => {
1251                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1252                 {
1253                     (Some(exp), Some(found)) if exp < found => (true, false),
1254                     (Some(exp), Some(found)) if exp > found => (false, true),
1255                     (None, Some(8 | 16)) => (false, true),
1256                     (Some(8 | 16), None) => (true, false),
1257                     (None, _) | (_, None) => (true, true),
1258                     _ => (false, false),
1259                 };
1260                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1261                 true
1262             }
1263             (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1264                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1265                 {
1266                     (Some(exp), Some(found)) if exp < found => (true, false),
1267                     (Some(exp), Some(found)) if exp > found => (false, true),
1268                     (None, Some(8 | 16)) => (false, true),
1269                     (Some(8 | 16), None) => (true, false),
1270                     (None, _) | (_, None) => (true, true),
1271                     _ => (false, false),
1272                 };
1273                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1274                 true
1275             }
1276             (&ty::Int(exp), &ty::Uint(found)) => {
1277                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1278                 {
1279                     (Some(exp), Some(found)) if found < exp => (false, true),
1280                     (None, Some(8)) => (false, true),
1281                     _ => (true, true),
1282                 };
1283                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1284                 true
1285             }
1286             (&ty::Uint(exp), &ty::Int(found)) => {
1287                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1288                 {
1289                     (Some(exp), Some(found)) if found > exp => (true, false),
1290                     (Some(8), None) => (true, false),
1291                     _ => (true, true),
1292                 };
1293                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1294                 true
1295             }
1296             (&ty::Float(ref exp), &ty::Float(ref found)) => {
1297                 if found.bit_width() < exp.bit_width() {
1298                     suggest_to_change_suffix_or_into(err, false, true);
1299                 } else if literal_is_ty_suffixed(expr) {
1300                     err.multipart_suggestion_verbose(
1301                         &lit_msg,
1302                         suffix_suggestion,
1303                         Applicability::MachineApplicable,
1304                     );
1305                 } else if can_cast {
1306                     // Missing try_into implementation for `f64` to `f32`
1307                     err.multipart_suggestion_verbose(
1308                         &format!("{cast_msg}, producing the closest possible value"),
1309                         cast_suggestion,
1310                         Applicability::MaybeIncorrect, // lossy conversion
1311                     );
1312                 }
1313                 true
1314             }
1315             (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1316                 if literal_is_ty_suffixed(expr) {
1317                     err.multipart_suggestion_verbose(
1318                         &lit_msg,
1319                         suffix_suggestion,
1320                         Applicability::MachineApplicable,
1321                     );
1322                 } else if can_cast {
1323                     // Missing try_into implementation for `{float}` to `{integer}`
1324                     err.multipart_suggestion_verbose(
1325                         &format!("{msg}, rounding the float towards zero"),
1326                         cast_suggestion,
1327                         Applicability::MaybeIncorrect, // lossy conversion
1328                     );
1329                 }
1330                 true
1331             }
1332             (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1333                 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1334                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1335                     err.multipart_suggestion_verbose(
1336                         &format!(
1337                             "{msg}, producing the floating point representation of the integer",
1338                         ),
1339                         into_suggestion,
1340                         Applicability::MachineApplicable,
1341                     );
1342                 } else if literal_is_ty_suffixed(expr) {
1343                     err.multipart_suggestion_verbose(
1344                         &lit_msg,
1345                         suffix_suggestion,
1346                         Applicability::MachineApplicable,
1347                     );
1348                 } else {
1349                     // Missing try_into implementation for `{integer}` to `{float}`
1350                     err.multipart_suggestion_verbose(
1351                         &format!(
1352                             "{cast_msg}, producing the floating point representation of the integer, \
1353                                  rounded if necessary",
1354                         ),
1355                         cast_suggestion,
1356                         Applicability::MaybeIncorrect, // lossy conversion
1357                     );
1358                 }
1359                 true
1360             }
1361             (&ty::Float(ref exp), &ty::Int(ref found)) => {
1362                 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1363                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1364                     err.multipart_suggestion_verbose(
1365                         &format!(
1366                             "{}, producing the floating point representation of the integer",
1367                             &msg,
1368                         ),
1369                         into_suggestion,
1370                         Applicability::MachineApplicable,
1371                     );
1372                 } else if literal_is_ty_suffixed(expr) {
1373                     err.multipart_suggestion_verbose(
1374                         &lit_msg,
1375                         suffix_suggestion,
1376                         Applicability::MachineApplicable,
1377                     );
1378                 } else {
1379                     // Missing try_into implementation for `{integer}` to `{float}`
1380                     err.multipart_suggestion_verbose(
1381                         &format!(
1382                             "{}, producing the floating point representation of the integer, \
1383                                 rounded if necessary",
1384                             &msg,
1385                         ),
1386                         cast_suggestion,
1387                         Applicability::MaybeIncorrect, // lossy conversion
1388                     );
1389                 }
1390                 true
1391             }
1392             (
1393                 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1394                 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1395                 &ty::Char,
1396             ) => {
1397                 err.multipart_suggestion_verbose(
1398                     &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1399                     cast_suggestion,
1400                     Applicability::MachineApplicable,
1401                 );
1402                 true
1403             }
1404             _ => false,
1405         }
1406     }
1407
1408     // Report the type inferred by the return statement.
1409     fn report_closure_inferred_return_type(&self, err: &mut Diagnostic, expected: Ty<'tcx>) {
1410         if let Some(sp) = self.ret_coercion_span.get()
1411             // If the closure has an explicit return type annotation, or if
1412             // the closure's return type has been inferred from outside
1413             // requirements (such as an Fn* trait bound), then a type error
1414             // may occur at the first return expression we see in the closure
1415             // (if it conflicts with the declared return type). Skip adding a
1416             // note in this case, since it would be incorrect.
1417             && !self.return_type_pre_known
1418         {
1419             err.span_note(
1420                 sp,
1421                 &format!(
1422                     "return type inferred to be `{}` here",
1423                     self.resolve_vars_if_possible(expected)
1424                 ),
1425             );
1426         }
1427     }
1428 }