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: 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, ErrorGuaranteed>> {
  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, ErrorGuaranteed>> {
  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, ErrorGuaranteed>> {
  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, ErrorGuaranteed>> {
 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, ErrorGuaranteed>>) {
 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                 let mut id = expr.hir_id;
 280                 let mut parent;
 281
 282                 // Unroll desugaring, to make sure this works for `for` loops etc.
 283                 loop {
 284                     parent = self.tcx.hir().get_parent_node(id);
 285                     if let Some(parent_span) = self.tcx.hir().opt_span(parent) {
 286                         if parent_span.find_ancestor_inside(expr.span).is_some() {
 287                             // The parent node is part of the same span, so is the result of the
 288                             // same expansion/desugaring and not the 'real' parent node.
 289                             id = parent;
 290                             continue;
 291                         }
 292                     }
 293                     break;
 294                 }
 295
 296                 if let Some(hir::Node::Block(&hir::Block {
 297                     span: block_span, expr: Some(e), ..
 298                 })) = self.tcx.hir().find(parent)
 299                 {
 300                     if e.hir_id == id {
 301                         if let Some(span) = expr.span.find_ancestor_inside(block_span) {
 302                             let return_suggestions = if self
 303                                 .tcx
 304                                 .is_diagnostic_item(sym::Result, expected_adt.did())
 305                             {
 306                                 vec!["Ok(())".to_string()]
 307                             } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did()) {
 308                                 vec!["None".to_string(), "Some(())".to_string()]
 309                             } else {
 310                                 return;
 311                             };
 312                             if let Some(indent) =
 313                                 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
 314                             {
 315                                 // Add a semicolon, except after `}`.
 316                                 let semicolon =
 317                                     match self.tcx.sess.source_map().span_to_snippet(span) {
 318                                         Ok(s) if s.ends_with('}') => "",
 319                                         _ => ";",
 320                                     };
 321                                 err.span_suggestions(
 322                                     span.shrink_to_hi(),
 323                                     "try adding an expression at the end of the block",
 324                                     return_suggestions
 325                                         .into_iter()
 326                                         .map(|r| format!("{}\n{}{}", semicolon, indent, r)),
 327                                     Applicability::MaybeIncorrect,
 328                                 );
 329                             }
 330                             return;
 331                         }
 332                     }
 333                 }
 334             }
 335
 336             let compatible_variants: Vec<String> = expected_adt
 337                 .variants()
 338                 .iter()
 339                 .filter(|variant| variant.fields.len() == 1)
 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                             if let Some((_, path)) = path.split_once("::") {
 349                                 return Some(path.to_string());
 350                             }
 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             },
 639             (_, &ty::Ref(_, _, mutability), _) => {
 640                 // Check if it can work when put into a ref. For example:
 641                 //
 642                 // ```
 643                 // fn bar(x: &mut i32) {}
 644                 //
 645                 // let x = 0u32;
 646                 // bar(&x); // error, expected &mut
 647                 // ```
 648                 let ref_ty = match mutability {
 649                     hir::Mutability::Mut => {
 650                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 651                     }
 652                     hir::Mutability::Not => {
 653                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 654                     }
 655                 };
 656                 if self.can_coerce(ref_ty, expected) {
 657                     let mut sugg_sp = sp;
 658                     if let hir::ExprKind::MethodCall(ref segment, ref args, _) = expr.kind {
 659                         let clone_trait =
 660                             self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
 661                         if let ([arg], Some(true), sym::clone) = (
 662                             &args[..],
 663                             self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
 664                                 |did| {
 665                                     let ai = self.tcx.associated_item(did);
 666                                     ai.container == ty::TraitContainer(clone_trait)
 667                                 },
 668                             ),
 669                             segment.ident.name,
 670                         ) {
 671                             // If this expression had a clone call when suggesting borrowing
 672                             // we want to suggest removing it because it'd now be unnecessary.
 673                             sugg_sp = arg.span;
 674                         }
 675                     }
 676                     if let Ok(src) = sm.span_to_snippet(sugg_sp) {
 677                         let needs_parens = match expr.kind {
 678                             // parenthesize if needed (Issue #46756)
 679                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 680                             // parenthesize borrows of range literals (Issue #54505)
 681                             _ if is_range_literal(expr) => true,
 682                             _ => false,
 683                         };
 684                         let sugg_expr = if needs_parens { format!("({})", src) } else { src };
 685
 686                         if let Some(sugg) = self.can_use_as_ref(expr) {
 687                             return Some((
 688                                 sugg.0,
 689                                 sugg.1.to_string(),
 690                                 sugg.2,
 691                                 Applicability::MachineApplicable,
 692                                 false,
 693                             ));
 694                         }
 695
 696                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 697                             Some(ident) => format!("{}: ", ident),
 698                             None => String::new(),
 699                         };
 700
 701                         if let Some(hir::Node::Expr(hir::Expr {
 702                             kind: hir::ExprKind::Assign(left_expr, ..),
 703                             ..
 704                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 705                         {
 706                             if mutability == hir::Mutability::Mut {
 707                                 // Found the following case:
 708                                 // fn foo(opt: &mut Option<String>){ opt = None }
 709                                 //                                   ---   ^^^^
 710                                 //                                   |     |
 711                                 //    consider dereferencing here: `*opt`  |
 712                                 // expected mutable reference, found enum `Option`
 713                                 if sm.span_to_snippet(left_expr.span).is_ok() {
 714                                     return Some((
 715                                         left_expr.span.shrink_to_lo(),
 716                                         "consider dereferencing here to assign to the mutable \
 717                                          borrowed piece of memory"
 718                                             .to_string(),
 719                                         "*".to_string(),
 720                                         Applicability::MachineApplicable,
 721                                         true,
 722                                     ));
 723                                 }
 724                             }
 725                         }
 726
 727                         return Some(match mutability {
 728                             hir::Mutability::Mut => (
 729                                 sp,
 730                                 "consider mutably borrowing here".to_string(),
 731                                 format!("{}&mut {}", prefix, sugg_expr),
 732                                 Applicability::MachineApplicable,
 733                                 false,
 734                             ),
 735                             hir::Mutability::Not => (
 736                                 sp,
 737                                 "consider borrowing here".to_string(),
 738                                 format!("{}&{}", prefix, sugg_expr),
 739                                 Applicability::MachineApplicable,
 740                                 false,
 741                             ),
 742                         });
 743                     }
 744                 }
 745             }
 746             (
 747                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 748                 _,
 749                 &ty::Ref(_, checked, _),
 750             ) if self.infcx.can_sub(self.param_env, checked, expected).is_ok() => {
 751                 // We have `&T`, check if what was expected was `T`. If so,
 752                 // we may want to suggest removing a `&`.
 753                 if sm.is_imported(expr.span) {
 754                     // Go through the spans from which this span was expanded,
 755                     // and find the one that's pointing inside `sp`.
 756                     //
 757                     // E.g. for `&format!("")`, where we want the span to the
 758                     // `format!()` invocation instead of its expansion.
 759                     if let Some(call_span) =
 760                         iter::successors(Some(expr.span), |s| s.parent_callsite())
 761                             .find(|&s| sp.contains(s))
 762                     {
 763                         if sm.span_to_snippet(call_span).is_ok() {
 764                             return Some((
 765                                 sp.with_hi(call_span.lo()),
 766                                 "consider removing the borrow".to_string(),
 767                                 String::new(),
 768                                 Applicability::MachineApplicable,
 769                                 true,
 770                             ));
 771                         }
 772                     }
 773                     return None;
 774                 }
 775                 if sp.contains(expr.span) {
 776                     if sm.span_to_snippet(expr.span).is_ok() {
 777                         return Some((
 778                             sp.with_hi(expr.span.lo()),
 779                             "consider removing the borrow".to_string(),
 780                             String::new(),
 781                             Applicability::MachineApplicable,
 782                             true,
 783                         ));
 784                     }
 785                 }
 786             }
 787             (
 788                 _,
 789                 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
 790                 &ty::Ref(_, ty_a, mutbl_a),
 791             ) => {
 792                 if let Some(steps) = self.deref_steps(ty_a, ty_b) {
 793                     // Only suggest valid if dereferencing needed.
 794                     if steps > 0 {
 795                         // The pointer type implements `Copy` trait so the suggestion is always valid.
 796                         if let Ok(src) = sm.span_to_snippet(sp) {
 797                             let derefs = "*".repeat(steps);
 798                             if let Some((span, src, applicability)) = match mutbl_b {
 799                                 hir::Mutability::Mut => {
 800                                     let new_prefix = "&mut ".to_owned() + &derefs;
 801                                     match mutbl_a {
 802                                         hir::Mutability::Mut => {
 803                                             replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
 804                                                 let pos = sp.lo() + BytePos(5);
 805                                                 let sp = sp.with_lo(pos).with_hi(pos);
 806                                                 (sp, derefs, Applicability::MachineApplicable)
 807                                             })
 808                                         }
 809                                         hir::Mutability::Not => {
 810                                             replace_prefix(&src, "&", &new_prefix).map(|_| {
 811                                                 let pos = sp.lo() + BytePos(1);
 812                                                 let sp = sp.with_lo(pos).with_hi(pos);
 813                                                 (
 814                                                     sp,
 815                                                     format!("mut {}", derefs),
 816                                                     Applicability::Unspecified,
 817                                                 )
 818                                             })
 819                                         }
 820                                     }
 821                                 }
 822                                 hir::Mutability::Not => {
 823                                     let new_prefix = "&".to_owned() + &derefs;
 824                                     match mutbl_a {
 825                                         hir::Mutability::Mut => {
 826                                             replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
 827                                                 let lo = sp.lo() + BytePos(1);
 828                                                 let hi = sp.lo() + BytePos(5);
 829                                                 let sp = sp.with_lo(lo).with_hi(hi);
 830                                                 (sp, derefs, Applicability::MachineApplicable)
 831                                             })
 832                                         }
 833                                         hir::Mutability::Not => {
 834                                             replace_prefix(&src, "&", &new_prefix).map(|_| {
 835                                                 let pos = sp.lo() + BytePos(1);
 836                                                 let sp = sp.with_lo(pos).with_hi(pos);
 837                                                 (sp, derefs, Applicability::MachineApplicable)
 838                                             })
 839                                         }
 840                                     }
 841                                 }
 842                             } {
 843                                 return Some((
 844                                     span,
 845                                     "consider dereferencing".to_string(),
 846                                     src,
 847                                     applicability,
 848                                     true,
 849                                 ));
 850                             }
 851                         }
 852                     }
 853                 }
 854             }
 855             _ if sp == expr.span => {
 856                 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
 857                     let mut expr = expr.peel_blocks();
 858                     let mut prefix_span = expr.span.shrink_to_lo();
 859                     let mut remove = String::new();
 860
 861                     // Try peeling off any existing `&` and `&mut` to reach our target type
 862                     while steps > 0 {
 863                         if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
 864                             // If the expression has `&`, removing it would fix the error
 865                             prefix_span = prefix_span.with_hi(inner.span.lo());
 866                             expr = inner;
 867                             remove += match mutbl {
 868                                 hir::Mutability::Not => "&",
 869                                 hir::Mutability::Mut => "&mut ",
 870                             };
 871                             steps -= 1;
 872                         } else {
 873                             break;
 874                         }
 875                     }
 876                     // If we've reached our target type with just removing `&`, then just print now.
 877                     if steps == 0 {
 878                         return Some((
 879                             prefix_span,
 880                             format!("consider removing the `{}`", remove.trim()),
 881                             String::new(),
 882                             // Do not remove `&&` to get to bool, because it might be something like
 883                             // { a } && b, which we have a separate fixup suggestion that is more
 884                             // likely correct...
 885                             if remove.trim() == "&&" && expected == self.tcx.types.bool {
 886                                 Applicability::MaybeIncorrect
 887                             } else {
 888                                 Applicability::MachineApplicable
 889                             },
 890                             true,
 891                         ));
 892                     }
 893
 894                     // For this suggestion to make sense, the type would need to be `Copy`,
 895                     // or we have to be moving out of a `Box<T>`
 896                     if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp)
 897                         // FIXME(compiler-errors): We can actually do this if the checked_ty is
 898                         // `steps` layers of boxes, not just one, but this is easier and most likely.
 899                         || (checked_ty.is_box() && steps == 1)
 900                     {
 901                         let deref_kind = if checked_ty.is_box() {
 902                             "unboxing the value"
 903                         } else if checked_ty.is_region_ptr() {
 904                             "dereferencing the borrow"
 905                         } else {
 906                             "dereferencing the type"
 907                         };
 908
 909                         // Suggest removing `&` if we have removed any, otherwise suggest just
 910                         // dereferencing the remaining number of steps.
 911                         let message = if remove.is_empty() {
 912                             format!("consider {}", deref_kind)
 913                         } else {
 914                             format!(
 915                                 "consider removing the `{}` and {} instead",
 916                                 remove.trim(),
 917                                 deref_kind
 918                             )
 919                         };
 920
 921                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 922                             Some(ident) => format!("{}: ", ident),
 923                             None => String::new(),
 924                         };
 925
 926                         let (span, suggestion) = if self.is_else_if_block(expr) {
 927                             // Don't suggest nonsense like `else *if`
 928                             return None;
 929                         } else if let Some(expr) = self.maybe_get_block_expr(expr) {
 930                             // prefix should be empty here..
 931                             (expr.span.shrink_to_lo(), "*".to_string())
 932                         } else {
 933                             (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
 934                         };
 935
 936                         return Some((
 937                             span,
 938                             message,
 939                             suggestion,
 940                             Applicability::MachineApplicable,
 941                             true,
 942                         ));
 943                     }
 944                 }
 945             }
 946             _ => {}
 947         }
 948         None
 949     }
 950
 951     pub fn check_for_cast(
 952         &self,
 953         err: &mut Diagnostic,
 954         expr: &hir::Expr<'_>,
 955         checked_ty: Ty<'tcx>,
 956         expected_ty: Ty<'tcx>,
 957         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 958     ) -> bool {
 959         if self.tcx.sess.source_map().is_imported(expr.span) {
 960             // Ignore if span is from within a macro.
 961             return false;
 962         }
 963
 964         let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
 965             return false;
 966         };
 967
 968         // If casting this expression to a given numeric type would be appropriate in case of a type
 969         // mismatch.
 970         //
 971         // We want to minimize the amount of casting operations that are suggested, as it can be a
 972         // lossy operation with potentially bad side effects, so we only suggest when encountering
 973         // an expression that indicates that the original type couldn't be directly changed.
 974         //
 975         // For now, don't suggest casting with `as`.
 976         let can_cast = false;
 977
 978         let mut sugg = vec![];
 979
 980         if let Some(hir::Node::Expr(hir::Expr {
 981             kind: hir::ExprKind::Struct(_, fields, _), ..
 982         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 983         {
 984             // `expr` is a literal field for a struct, only suggest if appropriate
 985             match (*fields)
 986                 .iter()
 987                 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
 988             {
 989                 // This is a field literal
 990                 Some(field) => {
 991                     sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
 992                 }
 993                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 994                 None => return false,
 995             }
 996         };
 997
 998         if let hir::ExprKind::Call(path, args) = &expr.kind {
 999             if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
1000                 (&path.kind, args.len())
1001             {
1002                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1003                 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1004                     (&base_ty.kind, path_segment.ident.name)
1005                 {
1006                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1007                         match ident.name {
1008                             sym::i128
1009                             | sym::i64
1010                             | sym::i32
1011                             | sym::i16
1012                             | sym::i8
1013                             | sym::u128
1014                             | sym::u64
1015                             | sym::u32
1016                             | sym::u16
1017                             | sym::u8
1018                             | sym::isize
1019                             | sym::usize
1020                                 if base_ty_path.segments.len() == 1 =>
1021                             {
1022                                 return false;
1023                             }
1024                             _ => {}
1025                         }
1026                     }
1027                 }
1028             }
1029         }
1030
1031         let msg = format!(
1032             "you can convert {} `{}` to {} `{}`",
1033             checked_ty.kind().article(),
1034             checked_ty,
1035             expected_ty.kind().article(),
1036             expected_ty,
1037         );
1038         let cast_msg = format!(
1039             "you can cast {} `{}` to {} `{}`",
1040             checked_ty.kind().article(),
1041             checked_ty,
1042             expected_ty.kind().article(),
1043             expected_ty,
1044         );
1045         let lit_msg = format!(
1046             "change the type of the numeric literal from `{}` to `{}`",
1047             checked_ty, expected_ty,
1048         );
1049
1050         let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1051             sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1052             ")"
1053         } else {
1054             ""
1055         };
1056
1057         let mut cast_suggestion = sugg.clone();
1058         cast_suggestion
1059             .push((expr.span.shrink_to_hi(), format!("{} as {}", close_paren, expected_ty)));
1060         let mut into_suggestion = sugg.clone();
1061         into_suggestion.push((expr.span.shrink_to_hi(), format!("{}.into()", close_paren)));
1062         let mut suffix_suggestion = sugg.clone();
1063         suffix_suggestion.push((
1064             if matches!(
1065                 (&expected_ty.kind(), &checked_ty.kind()),
1066                 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1067             ) {
1068                 // Remove fractional part from literal, for example `42.0f32` into `42`
1069                 let src = src.trim_end_matches(&checked_ty.to_string());
1070                 let len = src.split('.').next().unwrap().len();
1071                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1072             } else {
1073                 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1074                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1075             },
1076             if expr.precedence().order() < PREC_POSTFIX {
1077                 // Readd `)`
1078                 format!("{})", expected_ty)
1079             } else {
1080                 expected_ty.to_string()
1081             },
1082         ));
1083         let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1084             if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1085         };
1086         let is_negative_int =
1087             |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1088         let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1089
1090         let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1091
1092         let suggest_fallible_into_or_lhs_from =
1093             |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1094                 // If we know the expression the expected type is derived from, we might be able
1095                 // to suggest a widening conversion rather than a narrowing one (which may
1096                 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1097                 //   x > y
1098                 // can be given the suggestion "u32::from(x) > y" rather than
1099                 // "x > y.try_into().unwrap()".
1100                 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1101                     self.tcx
1102                         .sess
1103                         .source_map()
1104                         .span_to_snippet(expr.span)
1105                         .ok()
1106                         .map(|src| (expr, src))
1107                 });
1108                 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1109                     (lhs_expr_and_src, exp_to_found_is_fallible)
1110                 {
1111                     let msg = format!(
1112                         "you can convert `{}` from `{}` to `{}`, matching the type of `{}`",
1113                         lhs_src, expected_ty, checked_ty, src
1114                     );
1115                     let suggestion = vec![
1116                         (lhs_expr.span.shrink_to_lo(), format!("{}::from(", checked_ty)),
1117                         (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1118                     ];
1119                     (msg, suggestion)
1120                 } else {
1121                     let msg = format!("{} and panic if the converted value doesn't fit", msg);
1122                     let mut suggestion = sugg.clone();
1123                     suggestion.push((
1124                         expr.span.shrink_to_hi(),
1125                         format!("{}.try_into().unwrap()", close_paren),
1126                     ));
1127                     (msg, suggestion)
1128                 };
1129                 err.multipart_suggestion_verbose(
1130                     &msg,
1131                     suggestion,
1132                     Applicability::MachineApplicable,
1133                 );
1134             };
1135
1136         let suggest_to_change_suffix_or_into =
1137             |err: &mut Diagnostic,
1138              found_to_exp_is_fallible: bool,
1139              exp_to_found_is_fallible: bool| {
1140                 let exp_is_lhs =
1141                     expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1142
1143                 if exp_is_lhs {
1144                     return;
1145                 }
1146
1147                 let always_fallible = found_to_exp_is_fallible
1148                     && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1149                 let msg = if literal_is_ty_suffixed(expr) {
1150                     &lit_msg
1151                 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1152                     // We now know that converting either the lhs or rhs is fallible. Before we
1153                     // suggest a fallible conversion, check if the value can never fit in the
1154                     // expected type.
1155                     let msg = format!("`{}` cannot fit into type `{}`", src, expected_ty);
1156                     err.note(&msg);
1157                     return;
1158                 } else if in_const_context {
1159                     // Do not recommend `into` or `try_into` in const contexts.
1160                     return;
1161                 } else if found_to_exp_is_fallible {
1162                     return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1163                 } else {
1164                     &msg
1165                 };
1166                 let suggestion = if literal_is_ty_suffixed(expr) {
1167                     suffix_suggestion.clone()
1168                 } else {
1169                     into_suggestion.clone()
1170                 };
1171                 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1172             };
1173
1174         match (&expected_ty.kind(), &checked_ty.kind()) {
1175             (&ty::Int(ref exp), &ty::Int(ref found)) => {
1176                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1177                 {
1178                     (Some(exp), Some(found)) if exp < found => (true, false),
1179                     (Some(exp), Some(found)) if exp > found => (false, true),
1180                     (None, Some(8 | 16)) => (false, true),
1181                     (Some(8 | 16), None) => (true, false),
1182                     (None, _) | (_, None) => (true, true),
1183                     _ => (false, false),
1184                 };
1185                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1186                 true
1187             }
1188             (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1189                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1190                 {
1191                     (Some(exp), Some(found)) if exp < found => (true, false),
1192                     (Some(exp), Some(found)) if exp > found => (false, true),
1193                     (None, Some(8 | 16)) => (false, true),
1194                     (Some(8 | 16), None) => (true, false),
1195                     (None, _) | (_, None) => (true, true),
1196                     _ => (false, false),
1197                 };
1198                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1199                 true
1200             }
1201             (&ty::Int(exp), &ty::Uint(found)) => {
1202                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1203                 {
1204                     (Some(exp), Some(found)) if found < exp => (false, true),
1205                     (None, Some(8)) => (false, true),
1206                     _ => (true, true),
1207                 };
1208                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1209                 true
1210             }
1211             (&ty::Uint(exp), &ty::Int(found)) => {
1212                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1213                 {
1214                     (Some(exp), Some(found)) if found > exp => (true, false),
1215                     (Some(8), None) => (true, false),
1216                     _ => (true, true),
1217                 };
1218                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1219                 true
1220             }
1221             (&ty::Float(ref exp), &ty::Float(ref found)) => {
1222                 if found.bit_width() < exp.bit_width() {
1223                     suggest_to_change_suffix_or_into(err, false, true);
1224                 } else if literal_is_ty_suffixed(expr) {
1225                     err.multipart_suggestion_verbose(
1226                         &lit_msg,
1227                         suffix_suggestion,
1228                         Applicability::MachineApplicable,
1229                     );
1230                 } else if can_cast {
1231                     // Missing try_into implementation for `f64` to `f32`
1232                     err.multipart_suggestion_verbose(
1233                         &format!("{}, producing the closest possible value", cast_msg),
1234                         cast_suggestion,
1235                         Applicability::MaybeIncorrect, // lossy conversion
1236                     );
1237                 }
1238                 true
1239             }
1240             (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1241                 if literal_is_ty_suffixed(expr) {
1242                     err.multipart_suggestion_verbose(
1243                         &lit_msg,
1244                         suffix_suggestion,
1245                         Applicability::MachineApplicable,
1246                     );
1247                 } else if can_cast {
1248                     // Missing try_into implementation for `{float}` to `{integer}`
1249                     err.multipart_suggestion_verbose(
1250                         &format!("{}, rounding the float towards zero", msg),
1251                         cast_suggestion,
1252                         Applicability::MaybeIncorrect, // lossy conversion
1253                     );
1254                 }
1255                 true
1256             }
1257             (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1258                 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1259                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1260                     err.multipart_suggestion_verbose(
1261                         &format!(
1262                             "{}, producing the floating point representation of the integer",
1263                             msg,
1264                         ),
1265                         into_suggestion,
1266                         Applicability::MachineApplicable,
1267                     );
1268                 } else if literal_is_ty_suffixed(expr) {
1269                     err.multipart_suggestion_verbose(
1270                         &lit_msg,
1271                         suffix_suggestion,
1272                         Applicability::MachineApplicable,
1273                     );
1274                 } else {
1275                     // Missing try_into implementation for `{integer}` to `{float}`
1276                     err.multipart_suggestion_verbose(
1277                         &format!(
1278                             "{}, producing the floating point representation of the integer, \
1279                                  rounded if necessary",
1280                             cast_msg,
1281                         ),
1282                         cast_suggestion,
1283                         Applicability::MaybeIncorrect, // lossy conversion
1284                     );
1285                 }
1286                 true
1287             }
1288             (&ty::Float(ref exp), &ty::Int(ref found)) => {
1289                 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1290                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1291                     err.multipart_suggestion_verbose(
1292                         &format!(
1293                             "{}, producing the floating point representation of the integer",
1294                             &msg,
1295                         ),
1296                         into_suggestion,
1297                         Applicability::MachineApplicable,
1298                     );
1299                 } else if literal_is_ty_suffixed(expr) {
1300                     err.multipart_suggestion_verbose(
1301                         &lit_msg,
1302                         suffix_suggestion,
1303                         Applicability::MachineApplicable,
1304                     );
1305                 } else {
1306                     // Missing try_into implementation for `{integer}` to `{float}`
1307                     err.multipart_suggestion_verbose(
1308                         &format!(
1309                             "{}, producing the floating point representation of the integer, \
1310                                 rounded if necessary",
1311                             &msg,
1312                         ),
1313                         cast_suggestion,
1314                         Applicability::MaybeIncorrect, // lossy conversion
1315                     );
1316                 }
1317                 true
1318             }
1319             (
1320                 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1321                 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1322                 &ty::Char,
1323             ) => {
1324                 err.multipart_suggestion_verbose(
1325                     &format!("{}, since a `char` always occupies 4 bytes", cast_msg,),
1326                     cast_suggestion,
1327                     Applicability::MachineApplicable,
1328                 );
1329                 true
1330             }
1331             _ => false,
1332         }
1333     }
1334
1335     // Report the type inferred by the return statement.
1336     fn report_closure_inferred_return_type(&self, err: &mut Diagnostic, expected: Ty<'tcx>) {
1337         if let Some(sp) = self.ret_coercion_span.get() {
1338             // If the closure has an explicit return type annotation, or if
1339             // the closure's return type has been inferred from outside
1340             // requirements (such as an Fn* trait bound), then a type error
1341             // may occur at the first return expression we see in the closure
1342             // (if it conflicts with the declared return type). Skip adding a
1343             // note in this case, since it would be incorrect.
1344             if !self.return_type_pre_known {
1345                 err.span_note(
1346                     sp,
1347                     &format!(
1348                         "return type inferred to be `{}` here",
1349                         self.resolve_vars_if_possible(expected)
1350                     ),
1351                 );
1352             }
1353         }
1354     }
1355 }