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