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                     .get_attrs(m.def_id)
 411                     .iter()
 412                     // This special internal attribute is used to permit
 413                     // "identity-like" conversion methods to be suggested here.
 414                     //
 415                     // FIXME (#46459 and #46460): ideally
 416                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 417                     // also be `#[rustc_conversion_suggestion]`, if not for
 418                     // method-probing false-positives and -negatives (respectively).
 419                     //
 420                     // FIXME? Other potential candidate methods: `as_ref` and
 421                     // `as_mut`?
 422                     .any(|a| a.has_name(sym::rustc_conversion_suggestion))
 423         });
 424
 425         methods
 426     }
 427
 428     /// This function checks whether the method is not static and does not accept other parameters than `self`.
 429     fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
 430         match method.kind {
 431             ty::AssocKind::Fn => {
 432                 method.fn_has_self_parameter
 433                     && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 434             }
 435             _ => false,
 436         }
 437     }
 438
 439     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 440     ///
 441     /// Given the following code:
 442     /// ```
 443     /// struct Foo;
 444     /// fn takes_ref(_: &Foo) {}
 445     /// let ref opt = Some(Foo);
 446     ///
 447     /// opt.map(|param| takes_ref(param));
 448     /// ```
 449     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 450     ///
 451     /// It only checks for `Option` and `Result` and won't work with
 452     /// ```
 453     /// opt.map(|param| { takes_ref(param) });
 454     /// ```
 455     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 456         let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
 457             return None;
 458         };
 459
 460         let hir::def::Res::Local(local_id) = path.res else {
 461             return None;
 462         };
 463
 464         let local_parent = self.tcx.hir().get_parent_node(local_id);
 465         let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
 466             return None;
 467         };
 468
 469         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 470         let Some(Node::Expr(hir::Expr {
 471             hir_id: expr_hir_id,
 472             kind: hir::ExprKind::Closure(_, closure_fn_decl, ..),
 473             ..
 474         })) = self.tcx.hir().find(param_parent) else {
 475             return None;
 476         };
 477
 478         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 479         let hir = self.tcx.hir().find(expr_parent);
 480         let closure_params_len = closure_fn_decl.inputs.len();
 481         let (
 482             Some(Node::Expr(hir::Expr {
 483                 kind: hir::ExprKind::MethodCall(method_path, method_expr, _),
 484                 ..
 485             })),
 486             1,
 487         ) = (hir, closure_params_len) else {
 488             return None;
 489         };
 490
 491         let self_ty = self.typeck_results.borrow().expr_ty(&method_expr[0]);
 492         let self_ty = format!("{:?}", self_ty);
 493         let name = method_path.ident.name;
 494         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 495             || self_ty.starts_with("&std::result::Result")
 496             || self_ty.starts_with("std::option::Option")
 497             || self_ty.starts_with("std::result::Result"))
 498             && (name == sym::map || name == sym::and_then);
 499         match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
 500             (true, Ok(src)) => {
 501                 let suggestion = format!("as_ref().{}", src);
 502                 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
 503             }
 504             _ => None,
 505         }
 506     }
 507
 508     crate fn maybe_get_struct_pattern_shorthand_field(
 509         &self,
 510         expr: &hir::Expr<'_>,
 511     ) -> Option<Symbol> {
 512         let hir = self.tcx.hir();
 513         let local = match expr {
 514             hir::Expr {
 515                 kind:
 516                     hir::ExprKind::Path(hir::QPath::Resolved(
 517                         None,
 518                         hir::Path {
 519                             res: hir::def::Res::Local(_),
 520                             segments: [hir::PathSegment { ident, .. }],
 521                             ..
 522                         },
 523                     )),
 524                 ..
 525             } => Some(ident),
 526             _ => None,
 527         }?;
 528
 529         match hir.find(hir.get_parent_node(expr.hir_id))? {
 530             Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) => {
 531                 for field in *fields {
 532                     if field.ident.name == local.name && field.is_shorthand {
 533                         return Some(local.name);
 534                     }
 535                 }
 536             }
 537             _ => {}
 538         }
 539
 540         None
 541     }
 542
 543     /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
 544     crate fn maybe_get_block_expr(&self, expr: &hir::Expr<'tcx>) -> Option<&'tcx hir::Expr<'tcx>> {
 545         match expr {
 546             hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
 547             _ => None,
 548         }
 549     }
 550
 551     /// Returns whether the given expression is an `else if`.
 552     crate fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
 553         if let hir::ExprKind::If(..) = expr.kind {
 554             let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
 555             if let Some(Node::Expr(hir::Expr {
 556                 kind: hir::ExprKind::If(_, _, Some(else_expr)),
 557                 ..
 558             })) = self.tcx.hir().find(parent_id)
 559             {
 560                 return else_expr.hir_id == expr.hir_id;
 561             }
 562         }
 563         false
 564     }
 565
 566     /// This function is used to determine potential "simple" improvements or users' errors and
 567     /// provide them useful help. For example:
 568     ///
 569     /// ```
 570     /// fn some_fn(s: &str) {}
 571     ///
 572     /// let x = "hey!".to_owned();
 573     /// some_fn(x); // error
 574     /// ```
 575     ///
 576     /// No need to find every potential function which could make a coercion to transform a
 577     /// `String` into a `&str` since a `&` would do the trick!
 578     ///
 579     /// In addition of this check, it also checks between references mutability state. If the
 580     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 581     /// `&mut`!".
 582     pub fn check_ref(
 583         &self,
 584         expr: &hir::Expr<'tcx>,
 585         checked_ty: Ty<'tcx>,
 586         expected: Ty<'tcx>,
 587     ) -> Option<(Span, String, String, Applicability, bool /* verbose */)> {
 588         let sess = self.sess();
 589         let sp = expr.span;
 590
 591         // If the span is from an external macro, there's no suggestion we can make.
 592         if in_external_macro(sess, sp) {
 593             return None;
 594         }
 595
 596         let sm = sess.source_map();
 597
 598         let replace_prefix = |s: &str, old: &str, new: &str| {
 599             s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
 600         };
 601
 602         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 603         let expr = expr.peel_drop_temps();
 604
 605         match (&expr.kind, expected.kind(), checked_ty.kind()) {
 606             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
 607                 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
 608                     if let hir::ExprKind::Lit(_) = expr.kind
 609                         && let Ok(src) = sm.span_to_snippet(sp)
 610                         && replace_prefix(&src, "b\"", "\"").is_some()
 611                     {
 612                                 let pos = sp.lo() + BytePos(1);
 613                                 return Some((
 614                                     sp.with_hi(pos),
 615                                     "consider removing the leading `b`".to_string(),
 616                                     String::new(),
 617                                     Applicability::MachineApplicable,
 618                                     true,
 619                                 ));
 620                             }
 621                         }
 622                 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
 623                     if let hir::ExprKind::Lit(_) = expr.kind
 624                         && let Ok(src) = sm.span_to_snippet(sp)
 625                         && replace_prefix(&src, "\"", "b\"").is_some()
 626                     {
 627                                 return Some((
 628                                     sp.shrink_to_lo(),
 629                                     "consider adding a leading `b`".to_string(),
 630                                     "b".to_string(),
 631                                     Applicability::MachineApplicable,
 632                                     true,
 633                                 ));
 634                     }
 635                 }
 636                 _ => {}
 637             },
 638             (_, &ty::Ref(_, _, mutability), _) => {
 639                 // Check if it can work when put into a ref. For example:
 640                 //
 641                 // ```
 642                 // fn bar(x: &mut i32) {}
 643                 //
 644                 // let x = 0u32;
 645                 // bar(&x); // error, expected &mut
 646                 // ```
 647                 let ref_ty = match mutability {
 648                     hir::Mutability::Mut => {
 649                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 650                     }
 651                     hir::Mutability::Not => {
 652                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 653                     }
 654                 };
 655                 if self.can_coerce(ref_ty, expected) {
 656                     let mut sugg_sp = sp;
 657                     if let hir::ExprKind::MethodCall(ref segment, ref args, _) = expr.kind {
 658                         let clone_trait =
 659                             self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
 660                         if let ([arg], Some(true), sym::clone) = (
 661                             &args[..],
 662                             self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
 663                                 |did| {
 664                                     let ai = self.tcx.associated_item(did);
 665                                     ai.container == ty::TraitContainer(clone_trait)
 666                                 },
 667                             ),
 668                             segment.ident.name,
 669                         ) {
 670                             // If this expression had a clone call when suggesting borrowing
 671                             // we want to suggest removing it because it'd now be unnecessary.
 672                             sugg_sp = arg.span;
 673                         }
 674                     }
 675                     if let Ok(src) = sm.span_to_snippet(sugg_sp) {
 676                         let needs_parens = match expr.kind {
 677                             // parenthesize if needed (Issue #46756)
 678                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 679                             // parenthesize borrows of range literals (Issue #54505)
 680                             _ if is_range_literal(expr) => true,
 681                             _ => false,
 682                         };
 683                         let sugg_expr = if needs_parens { format!("({src})") } else { src };
 684
 685                         if let Some(sugg) = self.can_use_as_ref(expr) {
 686                             return Some((
 687                                 sugg.0,
 688                                 sugg.1.to_string(),
 689                                 sugg.2,
 690                                 Applicability::MachineApplicable,
 691                                 false,
 692                             ));
 693                         }
 694
 695                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 696                             Some(ident) => format!("{ident}: "),
 697                             None => String::new(),
 698                         };
 699
 700                         if let Some(hir::Node::Expr(hir::Expr {
 701                             kind: hir::ExprKind::Assign(left_expr, ..),
 702                             ..
 703                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 704                         {
 705                             if mutability == hir::Mutability::Mut {
 706                                 // Found the following case:
 707                                 // fn foo(opt: &mut Option<String>){ opt = None }
 708                                 //                                   ---   ^^^^
 709                                 //                                   |     |
 710                                 //    consider dereferencing here: `*opt`  |
 711                                 // expected mutable reference, found enum `Option`
 712                                 if sm.span_to_snippet(left_expr.span).is_ok() {
 713                                     return Some((
 714                                         left_expr.span.shrink_to_lo(),
 715                                         "consider dereferencing here to assign to the mutable \
 716                                          borrowed piece of memory"
 717                                             .to_string(),
 718                                         "*".to_string(),
 719                                         Applicability::MachineApplicable,
 720                                         true,
 721                                     ));
 722                                 }
 723                             }
 724                         }
 725
 726                         return Some(match mutability {
 727                             hir::Mutability::Mut => (
 728                                 sp,
 729                                 "consider mutably borrowing here".to_string(),
 730                                 format!("{prefix}&mut {sugg_expr}"),
 731                                 Applicability::MachineApplicable,
 732                                 false,
 733                             ),
 734                             hir::Mutability::Not => (
 735                                 sp,
 736                                 "consider borrowing here".to_string(),
 737                                 format!("{prefix}&{sugg_expr}"),
 738                                 Applicability::MachineApplicable,
 739                                 false,
 740                             ),
 741                         });
 742                     }
 743                 }
 744             }
 745             (
 746                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 747                 _,
 748                 &ty::Ref(_, checked, _),
 749             ) if self.infcx.can_sub(self.param_env, checked, expected).is_ok() => {
 750                 // We have `&T`, check if what was expected was `T`. If so,
 751                 // we may want to suggest removing a `&`.
 752                 if sm.is_imported(expr.span) {
 753                     // Go through the spans from which this span was expanded,
 754                     // and find the one that's pointing inside `sp`.
 755                     //
 756                     // E.g. for `&format!("")`, where we want the span to the
 757                     // `format!()` invocation instead of its expansion.
 758                     if let Some(call_span) =
 759                         iter::successors(Some(expr.span), |s| s.parent_callsite())
 760                             .find(|&s| sp.contains(s))
 761                         && sm.span_to_snippet(call_span).is_ok()
 762                     {
 763                         return Some((
 764                             sp.with_hi(call_span.lo()),
 765                             "consider removing the borrow".to_string(),
 766                             String::new(),
 767                             Applicability::MachineApplicable,
 768                             true,
 769                         ));
 770                     }
 771                     return None;
 772                 }
 773                 if sp.contains(expr.span)
 774                     && sm.span_to_snippet(expr.span).is_ok()
 775                 {
 776                     return Some((
 777                         sp.with_hi(expr.span.lo()),
 778                         "consider removing the borrow".to_string(),
 779                         String::new(),
 780                         Applicability::MachineApplicable,
 781                         true,
 782                     ));
 783                 }
 784             }
 785             (
 786                 _,
 787                 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
 788                 &ty::Ref(_, ty_a, mutbl_a),
 789             ) => {
 790                 if let Some(steps) = self.deref_steps(ty_a, ty_b)
 791                     // Only suggest valid if dereferencing needed.
 792                     && steps > 0
 793                     // The pointer type implements `Copy` trait so the suggestion is always valid.
 794                     && let Ok(src) = sm.span_to_snippet(sp)
 795                 {
 796                     let derefs = "*".repeat(steps);
 797                     if let Some((span, src, applicability)) = match mutbl_b {
 798                         hir::Mutability::Mut => {
 799                             let new_prefix = "&mut ".to_owned() + &derefs;
 800                             match mutbl_a {
 801                                 hir::Mutability::Mut => {
 802                                     replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
 803                                         let pos = sp.lo() + BytePos(5);
 804                                         let sp = sp.with_lo(pos).with_hi(pos);
 805                                         (sp, derefs, Applicability::MachineApplicable)
 806                                     })
 807                                 }
 808                                 hir::Mutability::Not => {
 809                                     replace_prefix(&src, "&", &new_prefix).map(|_| {
 810                                         let pos = sp.lo() + BytePos(1);
 811                                         let sp = sp.with_lo(pos).with_hi(pos);
 812                                         (
 813                                             sp,
 814                                             format!("mut {derefs}"),
 815                                             Applicability::Unspecified,
 816                                         )
 817                                     })
 818                                 }
 819                             }
 820                         }
 821                         hir::Mutability::Not => {
 822                             let new_prefix = "&".to_owned() + &derefs;
 823                             match mutbl_a {
 824                                 hir::Mutability::Mut => {
 825                                     replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
 826                                         let lo = sp.lo() + BytePos(1);
 827                                         let hi = sp.lo() + BytePos(5);
 828                                         let sp = sp.with_lo(lo).with_hi(hi);
 829                                         (sp, derefs, Applicability::MachineApplicable)
 830                                     })
 831                                 }
 832                                 hir::Mutability::Not => {
 833                                     replace_prefix(&src, "&", &new_prefix).map(|_| {
 834                                         let pos = sp.lo() + BytePos(1);
 835                                         let sp = sp.with_lo(pos).with_hi(pos);
 836                                         (sp, derefs, Applicability::MachineApplicable)
 837                                     })
 838                                 }
 839                             }
 840                         }
 841                     } {
 842                         return Some((
 843                             span,
 844                             "consider dereferencing".to_string(),
 845                             src,
 846                             applicability,
 847                             true,
 848                         ));
 849                     }
 850                 }
 851             }
 852             _ if sp == expr.span => {
 853                 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
 854                     let mut expr = expr.peel_blocks();
 855                     let mut prefix_span = expr.span.shrink_to_lo();
 856                     let mut remove = String::new();
 857
 858                     // Try peeling off any existing `&` and `&mut` to reach our target type
 859                     while steps > 0 {
 860                         if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
 861                             // If the expression has `&`, removing it would fix the error
 862                             prefix_span = prefix_span.with_hi(inner.span.lo());
 863                             expr = inner;
 864                             remove += match mutbl {
 865                                 hir::Mutability::Not => "&",
 866                                 hir::Mutability::Mut => "&mut ",
 867                             };
 868                             steps -= 1;
 869                         } else {
 870                             break;
 871                         }
 872                     }
 873                     // If we've reached our target type with just removing `&`, then just print now.
 874                     if steps == 0 {
 875                         return Some((
 876                             prefix_span,
 877                             format!("consider removing the `{}`", remove.trim()),
 878                             String::new(),
 879                             // Do not remove `&&` to get to bool, because it might be something like
 880                             // { a } && b, which we have a separate fixup suggestion that is more
 881                             // likely correct...
 882                             if remove.trim() == "&&" && expected == self.tcx.types.bool {
 883                                 Applicability::MaybeIncorrect
 884                             } else {
 885                                 Applicability::MachineApplicable
 886                             },
 887                             true,
 888                         ));
 889                     }
 890
 891                     // For this suggestion to make sense, the type would need to be `Copy`,
 892                     // or we have to be moving out of a `Box<T>`
 893                     if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp)
 894                         // FIXME(compiler-errors): We can actually do this if the checked_ty is
 895                         // `steps` layers of boxes, not just one, but this is easier and most likely.
 896                         || (checked_ty.is_box() && steps == 1)
 897                     {
 898                         let deref_kind = if checked_ty.is_box() {
 899                             "unboxing the value"
 900                         } else if checked_ty.is_region_ptr() {
 901                             "dereferencing the borrow"
 902                         } else {
 903                             "dereferencing the type"
 904                         };
 905
 906                         // Suggest removing `&` if we have removed any, otherwise suggest just
 907                         // dereferencing the remaining number of steps.
 908                         let message = if remove.is_empty() {
 909                             format!("consider {deref_kind}")
 910                         } else {
 911                             format!(
 912                                 "consider removing the `{}` and {} instead",
 913                                 remove.trim(),
 914                                 deref_kind
 915                             )
 916                         };
 917
 918                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 919                             Some(ident) => format!("{ident}: "),
 920                             None => String::new(),
 921                         };
 922
 923                         let (span, suggestion) = if self.is_else_if_block(expr) {
 924                             // Don't suggest nonsense like `else *if`
 925                             return None;
 926                         } else if let Some(expr) = self.maybe_get_block_expr(expr) {
 927                             // prefix should be empty here..
 928                             (expr.span.shrink_to_lo(), "*".to_string())
 929                         } else {
 930                             (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
 931                         };
 932
 933                         return Some((
 934                             span,
 935                             message,
 936                             suggestion,
 937                             Applicability::MachineApplicable,
 938                             true,
 939                         ));
 940                     }
 941                 }
 942             }
 943             _ => {}
 944         }
 945         None
 946     }
 947
 948     pub fn check_for_cast(
 949         &self,
 950         err: &mut Diagnostic,
 951         expr: &hir::Expr<'_>,
 952         checked_ty: Ty<'tcx>,
 953         expected_ty: Ty<'tcx>,
 954         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 955     ) -> bool {
 956         if self.tcx.sess.source_map().is_imported(expr.span) {
 957             // Ignore if span is from within a macro.
 958             return false;
 959         }
 960
 961         let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
 962             return false;
 963         };
 964
 965         // If casting this expression to a given numeric type would be appropriate in case of a type
 966         // mismatch.
 967         //
 968         // We want to minimize the amount of casting operations that are suggested, as it can be a
 969         // lossy operation with potentially bad side effects, so we only suggest when encountering
 970         // an expression that indicates that the original type couldn't be directly changed.
 971         //
 972         // For now, don't suggest casting with `as`.
 973         let can_cast = false;
 974
 975         let mut sugg = vec![];
 976
 977         if let Some(hir::Node::Expr(hir::Expr {
 978             kind: hir::ExprKind::Struct(_, fields, _), ..
 979         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 980         {
 981             // `expr` is a literal field for a struct, only suggest if appropriate
 982             match (*fields)
 983                 .iter()
 984                 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
 985             {
 986                 // This is a field literal
 987                 Some(field) => {
 988                     sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
 989                 }
 990                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 991                 None => return false,
 992             }
 993         };
 994
 995         if let hir::ExprKind::Call(path, args) = &expr.kind
 996             && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
 997                 (&path.kind, args.len())
 998             // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 999             && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1000                 (&base_ty.kind, path_segment.ident.name)
1001         {
1002             if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1003                 match ident.name {
1004                     sym::i128
1005                     | sym::i64
1006                     | sym::i32
1007                     | sym::i16
1008                     | sym::i8
1009                     | sym::u128
1010                     | sym::u64
1011                     | sym::u32
1012                     | sym::u16
1013                     | sym::u8
1014                     | sym::isize
1015                     | sym::usize
1016                         if base_ty_path.segments.len() == 1 =>
1017                     {
1018                         return false;
1019                     }
1020                     _ => {}
1021                 }
1022             }
1023         }
1024
1025         let msg = format!(
1026             "you can convert {} `{}` to {} `{}`",
1027             checked_ty.kind().article(),
1028             checked_ty,
1029             expected_ty.kind().article(),
1030             expected_ty,
1031         );
1032         let cast_msg = format!(
1033             "you can cast {} `{}` to {} `{}`",
1034             checked_ty.kind().article(),
1035             checked_ty,
1036             expected_ty.kind().article(),
1037             expected_ty,
1038         );
1039         let lit_msg = format!(
1040             "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1041         );
1042
1043         let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1044             sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1045             ")"
1046         } else {
1047             ""
1048         };
1049
1050         let mut cast_suggestion = sugg.clone();
1051         cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1052         let mut into_suggestion = sugg.clone();
1053         into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1054         let mut suffix_suggestion = sugg.clone();
1055         suffix_suggestion.push((
1056             if matches!(
1057                 (&expected_ty.kind(), &checked_ty.kind()),
1058                 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1059             ) {
1060                 // Remove fractional part from literal, for example `42.0f32` into `42`
1061                 let src = src.trim_end_matches(&checked_ty.to_string());
1062                 let len = src.split('.').next().unwrap().len();
1063                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1064             } else {
1065                 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1066                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1067             },
1068             if expr.precedence().order() < PREC_POSTFIX {
1069                 // Readd `)`
1070                 format!("{expected_ty})")
1071             } else {
1072                 expected_ty.to_string()
1073             },
1074         ));
1075         let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1076             if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1077         };
1078         let is_negative_int =
1079             |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1080         let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1081
1082         let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1083
1084         let suggest_fallible_into_or_lhs_from =
1085             |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1086                 // If we know the expression the expected type is derived from, we might be able
1087                 // to suggest a widening conversion rather than a narrowing one (which may
1088                 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1089                 //   x > y
1090                 // can be given the suggestion "u32::from(x) > y" rather than
1091                 // "x > y.try_into().unwrap()".
1092                 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1093                     self.tcx
1094                         .sess
1095                         .source_map()
1096                         .span_to_snippet(expr.span)
1097                         .ok()
1098                         .map(|src| (expr, src))
1099                 });
1100                 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1101                     (lhs_expr_and_src, exp_to_found_is_fallible)
1102                 {
1103                     let msg = format!(
1104                         "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1105                     );
1106                     let suggestion = vec![
1107                         (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1108                         (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1109                     ];
1110                     (msg, suggestion)
1111                 } else {
1112                     let msg = format!("{msg} and panic if the converted value doesn't fit");
1113                     let mut suggestion = sugg.clone();
1114                     suggestion.push((
1115                         expr.span.shrink_to_hi(),
1116                         format!("{close_paren}.try_into().unwrap()"),
1117                     ));
1118                     (msg, suggestion)
1119                 };
1120                 err.multipart_suggestion_verbose(
1121                     &msg,
1122                     suggestion,
1123                     Applicability::MachineApplicable,
1124                 );
1125             };
1126
1127         let suggest_to_change_suffix_or_into =
1128             |err: &mut Diagnostic,
1129              found_to_exp_is_fallible: bool,
1130              exp_to_found_is_fallible: bool| {
1131                 let exp_is_lhs =
1132                     expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1133
1134                 if exp_is_lhs {
1135                     return;
1136                 }
1137
1138                 let always_fallible = found_to_exp_is_fallible
1139                     && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1140                 let msg = if literal_is_ty_suffixed(expr) {
1141                     &lit_msg
1142                 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1143                     // We now know that converting either the lhs or rhs is fallible. Before we
1144                     // suggest a fallible conversion, check if the value can never fit in the
1145                     // expected type.
1146                     let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1147                     err.note(&msg);
1148                     return;
1149                 } else if in_const_context {
1150                     // Do not recommend `into` or `try_into` in const contexts.
1151                     return;
1152                 } else if found_to_exp_is_fallible {
1153                     return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1154                 } else {
1155                     &msg
1156                 };
1157                 let suggestion = if literal_is_ty_suffixed(expr) {
1158                     suffix_suggestion.clone()
1159                 } else {
1160                     into_suggestion.clone()
1161                 };
1162                 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1163             };
1164
1165         match (&expected_ty.kind(), &checked_ty.kind()) {
1166             (&ty::Int(ref exp), &ty::Int(ref found)) => {
1167                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1168                 {
1169                     (Some(exp), Some(found)) if exp < found => (true, false),
1170                     (Some(exp), Some(found)) if exp > found => (false, true),
1171                     (None, Some(8 | 16)) => (false, true),
1172                     (Some(8 | 16), None) => (true, false),
1173                     (None, _) | (_, None) => (true, true),
1174                     _ => (false, false),
1175                 };
1176                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1177                 true
1178             }
1179             (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1180                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1181                 {
1182                     (Some(exp), Some(found)) if exp < found => (true, false),
1183                     (Some(exp), Some(found)) if exp > found => (false, true),
1184                     (None, Some(8 | 16)) => (false, true),
1185                     (Some(8 | 16), None) => (true, false),
1186                     (None, _) | (_, None) => (true, true),
1187                     _ => (false, false),
1188                 };
1189                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1190                 true
1191             }
1192             (&ty::Int(exp), &ty::Uint(found)) => {
1193                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1194                 {
1195                     (Some(exp), Some(found)) if found < exp => (false, true),
1196                     (None, Some(8)) => (false, true),
1197                     _ => (true, true),
1198                 };
1199                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1200                 true
1201             }
1202             (&ty::Uint(exp), &ty::Int(found)) => {
1203                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1204                 {
1205                     (Some(exp), Some(found)) if found > exp => (true, false),
1206                     (Some(8), None) => (true, false),
1207                     _ => (true, true),
1208                 };
1209                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1210                 true
1211             }
1212             (&ty::Float(ref exp), &ty::Float(ref found)) => {
1213                 if found.bit_width() < exp.bit_width() {
1214                     suggest_to_change_suffix_or_into(err, false, true);
1215                 } else if literal_is_ty_suffixed(expr) {
1216                     err.multipart_suggestion_verbose(
1217                         &lit_msg,
1218                         suffix_suggestion,
1219                         Applicability::MachineApplicable,
1220                     );
1221                 } else if can_cast {
1222                     // Missing try_into implementation for `f64` to `f32`
1223                     err.multipart_suggestion_verbose(
1224                         &format!("{cast_msg}, producing the closest possible value"),
1225                         cast_suggestion,
1226                         Applicability::MaybeIncorrect, // lossy conversion
1227                     );
1228                 }
1229                 true
1230             }
1231             (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1232                 if literal_is_ty_suffixed(expr) {
1233                     err.multipart_suggestion_verbose(
1234                         &lit_msg,
1235                         suffix_suggestion,
1236                         Applicability::MachineApplicable,
1237                     );
1238                 } else if can_cast {
1239                     // Missing try_into implementation for `{float}` to `{integer}`
1240                     err.multipart_suggestion_verbose(
1241                         &format!("{msg}, rounding the float towards zero"),
1242                         cast_suggestion,
1243                         Applicability::MaybeIncorrect, // lossy conversion
1244                     );
1245                 }
1246                 true
1247             }
1248             (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1249                 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1250                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1251                     err.multipart_suggestion_verbose(
1252                         &format!(
1253                             "{msg}, producing the floating point representation of the integer",
1254                         ),
1255                         into_suggestion,
1256                         Applicability::MachineApplicable,
1257                     );
1258                 } else if literal_is_ty_suffixed(expr) {
1259                     err.multipart_suggestion_verbose(
1260                         &lit_msg,
1261                         suffix_suggestion,
1262                         Applicability::MachineApplicable,
1263                     );
1264                 } else {
1265                     // Missing try_into implementation for `{integer}` to `{float}`
1266                     err.multipart_suggestion_verbose(
1267                         &format!(
1268                             "{cast_msg}, producing the floating point representation of the integer, \
1269                                  rounded if necessary",
1270                         ),
1271                         cast_suggestion,
1272                         Applicability::MaybeIncorrect, // lossy conversion
1273                     );
1274                 }
1275                 true
1276             }
1277             (&ty::Float(ref exp), &ty::Int(ref found)) => {
1278                 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1279                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1280                     err.multipart_suggestion_verbose(
1281                         &format!(
1282                             "{}, producing the floating point representation of the integer",
1283                             &msg,
1284                         ),
1285                         into_suggestion,
1286                         Applicability::MachineApplicable,
1287                     );
1288                 } else if literal_is_ty_suffixed(expr) {
1289                     err.multipart_suggestion_verbose(
1290                         &lit_msg,
1291                         suffix_suggestion,
1292                         Applicability::MachineApplicable,
1293                     );
1294                 } else {
1295                     // Missing try_into implementation for `{integer}` to `{float}`
1296                     err.multipart_suggestion_verbose(
1297                         &format!(
1298                             "{}, producing the floating point representation of the integer, \
1299                                 rounded if necessary",
1300                             &msg,
1301                         ),
1302                         cast_suggestion,
1303                         Applicability::MaybeIncorrect, // lossy conversion
1304                     );
1305                 }
1306                 true
1307             }
1308             (
1309                 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1310                 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1311                 &ty::Char,
1312             ) => {
1313                 err.multipart_suggestion_verbose(
1314                     &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1315                     cast_suggestion,
1316                     Applicability::MachineApplicable,
1317                 );
1318                 true
1319             }
1320             _ => false,
1321         }
1322     }
1323
1324     // Report the type inferred by the return statement.
1325     fn report_closure_inferred_return_type(&self, err: &mut Diagnostic, expected: Ty<'tcx>) {
1326         if let Some(sp) = self.ret_coercion_span.get()
1327             // If the closure has an explicit return type annotation, or if
1328             // the closure's return type has been inferred from outside
1329             // requirements (such as an Fn* trait bound), then a type error
1330             // may occur at the first return expression we see in the closure
1331             // (if it conflicts with the declared return type). Skip adding a
1332             // note in this case, since it would be incorrect.
1333             && !self.return_type_pre_known
1334         {
1335             err.span_note(
1336                 sp,
1337                 &format!(
1338                     "return type inferred to be `{}` here",
1339                     self.resolve_vars_if_possible(expected)
1340                 ),
1341             );
1342         }
1343     }
1344 }