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