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