compiler/rustc_hir_typeck/src/demand.rs

   1 use crate::FnCtxt;
   2 use rustc_ast::util::parser::PREC_POSTFIX;
   3 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
   4 use rustc_hir as hir;
   5 use rustc_hir::lang_items::LangItem;
   6 use rustc_hir::{is_range_literal, Node};
   7 use rustc_infer::infer::InferOk;
   8 use rustc_middle::lint::in_external_macro;
   9 use rustc_middle::middle::stability::EvalResult;
  10 use rustc_middle::ty::adjustment::AllowTwoPhase;
  11 use rustc_middle::ty::error::{ExpectedFound, TypeError};
  12 use rustc_middle::ty::print::with_no_trimmed_paths;
  13 use rustc_middle::ty::{self, Article, AssocItem, Ty, TypeAndMut};
  14 use rustc_span::symbol::{sym, Symbol};
  15 use rustc_span::{BytePos, Span};
  16 use rustc_trait_selection::infer::InferCtxtExt as _;
  17 use rustc_trait_selection::traits::ObligationCause;
  18
  19 use super::method::probe;
  20
  21 use std::iter;
  22
  23 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  24     pub fn emit_coerce_suggestions(
  25         &self,
  26         err: &mut Diagnostic,
  27         expr: &hir::Expr<'tcx>,
  28         expr_ty: Ty<'tcx>,
  29         expected: Ty<'tcx>,
  30         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
  31         error: Option<TypeError<'tcx>>,
  32     ) {
  33         if expr_ty == expected {
  34             return;
  35         }
  36
  37         self.annotate_expected_due_to_let_ty(err, expr, error);
  38
  39         // Use `||` to give these suggestions a precedence
  40         let _ = self.suggest_missing_parentheses(err, expr)
  41             || self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr)
  42             || self.suggest_compatible_variants(err, expr, expected, expr_ty)
  43             || self.suggest_non_zero_new_unwrap(err, expr, expected, expr_ty)
  44             || self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty)
  45             || self.suggest_no_capture_closure(err, expected, expr_ty)
  46             || self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty)
  47             || self.suggest_block_to_brackets_peeling_refs(err, expr, expr_ty, expected)
  48             || self.suggest_copied_or_cloned(err, expr, expr_ty, expected)
  49             || self.suggest_into(err, expr, expr_ty, expected)
  50             || self.suggest_option_to_bool(err, expr, expr_ty, expected)
  51             || self.suggest_floating_point_literal(err, expr, expected);
  52
  53         self.note_type_is_not_clone(err, expected, expr_ty, expr);
  54         self.note_need_for_fn_pointer(err, expected, expr_ty);
  55         self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
  56     }
  57
  58     // Requires that the two types unify, and prints an error message if
  59     // they don't.
  60     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  61         if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
  62             e.emit();
  63         }
  64     }
  65
  66     pub fn demand_suptype_diag(
  67         &self,
  68         sp: Span,
  69         expected: Ty<'tcx>,
  70         actual: Ty<'tcx>,
  71     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
  72         self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
  73     }
  74
  75     #[instrument(skip(self), level = "debug")]
  76     pub fn demand_suptype_with_origin(
  77         &self,
  78         cause: &ObligationCause<'tcx>,
  79         expected: Ty<'tcx>,
  80         actual: Ty<'tcx>,
  81     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
  82         match self.at(cause, self.param_env).sup(expected, actual) {
  83             Ok(InferOk { obligations, value: () }) => {
  84                 self.register_predicates(obligations);
  85                 None
  86             }
  87             Err(e) => Some(self.err_ctxt().report_mismatched_types(&cause, expected, actual, e)),
  88         }
  89     }
  90
  91     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  92         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  93             err.emit();
  94         }
  95     }
  96
  97     pub fn demand_eqtype_diag(
  98         &self,
  99         sp: Span,
 100         expected: Ty<'tcx>,
 101         actual: Ty<'tcx>,
 102     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
 103         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
 104     }
 105
 106     pub fn demand_eqtype_with_origin(
 107         &self,
 108         cause: &ObligationCause<'tcx>,
 109         expected: Ty<'tcx>,
 110         actual: Ty<'tcx>,
 111     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
 112         match self.at(cause, self.param_env).eq(expected, actual) {
 113             Ok(InferOk { obligations, value: () }) => {
 114                 self.register_predicates(obligations);
 115                 None
 116             }
 117             Err(e) => Some(self.err_ctxt().report_mismatched_types(cause, expected, actual, e)),
 118         }
 119     }
 120
 121     pub fn demand_coerce(
 122         &self,
 123         expr: &hir::Expr<'tcx>,
 124         checked_ty: Ty<'tcx>,
 125         expected: Ty<'tcx>,
 126         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 127         allow_two_phase: AllowTwoPhase,
 128     ) -> Ty<'tcx> {
 129         let (ty, err) =
 130             self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
 131         if let Some(mut err) = err {
 132             err.emit();
 133         }
 134         ty
 135     }
 136
 137     /// Checks that the type of `expr` can be coerced to `expected`.
 138     ///
 139     /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
 140     /// will be permitted if the diverges flag is currently "always".
 141     #[instrument(level = "debug", skip(self, expr, expected_ty_expr, allow_two_phase))]
 142     pub fn demand_coerce_diag(
 143         &self,
 144         expr: &hir::Expr<'tcx>,
 145         checked_ty: Ty<'tcx>,
 146         expected: Ty<'tcx>,
 147         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 148         allow_two_phase: AllowTwoPhase,
 149     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>) {
 150         let expected = self.resolve_vars_with_obligations(expected);
 151
 152         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase, None) {
 153             Ok(ty) => return (ty, None),
 154             Err(e) => e,
 155         };
 156
 157         self.set_tainted_by_errors(self.tcx.sess.delay_span_bug(
 158             expr.span,
 159             "`TypeError` when attempting coercion but no error emitted",
 160         ));
 161         let expr = expr.peel_drop_temps();
 162         let cause = self.misc(expr.span);
 163         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 164         let mut err = self.err_ctxt().report_mismatched_types(&cause, expected, expr_ty, e.clone());
 165
 166         let is_insufficiently_polymorphic =
 167             matches!(e, TypeError::RegionsInsufficientlyPolymorphic(..));
 168
 169         // FIXME(#73154): For now, we do leak check when coercing function
 170         // pointers in typeck, instead of only during borrowck. This can lead
 171         // to these `RegionsInsufficientlyPolymorphic` errors that aren't helpful.
 172         if !is_insufficiently_polymorphic {
 173             self.emit_coerce_suggestions(
 174                 &mut err,
 175                 expr,
 176                 expr_ty,
 177                 expected,
 178                 expected_ty_expr,
 179                 Some(e),
 180             );
 181         }
 182
 183         (expected, Some(err))
 184     }
 185
 186     fn annotate_expected_due_to_let_ty(
 187         &self,
 188         err: &mut Diagnostic,
 189         expr: &hir::Expr<'_>,
 190         error: Option<TypeError<'_>>,
 191     ) {
 192         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 193         match (self.tcx.hir().find(parent), error) {
 194             (Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })), _)
 195                 if init.hir_id == expr.hir_id =>
 196             {
 197                 // Point at `let` assignment type.
 198                 err.span_label(ty.span, "expected due to this");
 199             }
 200             (
 201                 Some(hir::Node::Expr(hir::Expr {
 202                     kind: hir::ExprKind::Assign(lhs, rhs, _), ..
 203                 })),
 204                 Some(TypeError::Sorts(ExpectedFound { expected, .. })),
 205             ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
 206                 // We ignore closures explicitly because we already point at them elsewhere.
 207                 // Point at the assigned-to binding.
 208                 let mut primary_span = lhs.span;
 209                 let mut secondary_span = lhs.span;
 210                 let mut post_message = "";
 211                 match lhs.kind {
 212                     hir::ExprKind::Path(hir::QPath::Resolved(
 213                         None,
 214                         hir::Path {
 215                             res:
 216                                 hir::def::Res::Def(
 217                                     hir::def::DefKind::Static(_) | hir::def::DefKind::Const,
 218                                     def_id,
 219                                 ),
 220                             ..
 221                         },
 222                     )) => {
 223                         if let Some(hir::Node::Item(hir::Item {
 224                             ident,
 225                             kind: hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..),
 226                             ..
 227                         })) = self.tcx.hir().get_if_local(*def_id)
 228                         {
 229                             primary_span = ty.span;
 230                             secondary_span = ident.span;
 231                             post_message = " type";
 232                         }
 233                     }
 234                     hir::ExprKind::Path(hir::QPath::Resolved(
 235                         None,
 236                         hir::Path { res: hir::def::Res::Local(hir_id), .. },
 237                     )) => {
 238                         if let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(*hir_id) {
 239                             let parent = self.tcx.hir().get_parent_node(pat.hir_id);
 240                             primary_span = pat.span;
 241                             secondary_span = pat.span;
 242                             match self.tcx.hir().find(parent) {
 243                                 Some(hir::Node::Local(hir::Local { ty: Some(ty), .. })) => {
 244                                     primary_span = ty.span;
 245                                     post_message = " type";
 246                                 }
 247                                 Some(hir::Node::Local(hir::Local { init: Some(init), .. })) => {
 248                                     primary_span = init.span;
 249                                     post_message = " value";
 250                                 }
 251                                 Some(hir::Node::Param(hir::Param { ty_span, .. })) => {
 252                                     primary_span = *ty_span;
 253                                     post_message = " parameter type";
 254                                 }
 255                                 _ => {}
 256                             }
 257                         }
 258                     }
 259                     _ => {}
 260                 }
 261
 262                 if primary_span != secondary_span
 263                     && self
 264                         .tcx
 265                         .sess
 266                         .source_map()
 267                         .is_multiline(secondary_span.shrink_to_hi().until(primary_span))
 268                 {
 269                     // We are pointing at the binding's type or initializer value, but it's pattern
 270                     // is in a different line, so we point at both.
 271                     err.span_label(secondary_span, "expected due to the type of this binding");
 272                     err.span_label(primary_span, &format!("expected due to this{post_message}"));
 273                 } else if post_message == "" {
 274                     // We are pointing at either the assignment lhs or the binding def pattern.
 275                     err.span_label(primary_span, "expected due to the type of this binding");
 276                 } else {
 277                     // We are pointing at the binding's type or initializer value.
 278                     err.span_label(primary_span, &format!("expected due to this{post_message}"));
 279                 }
 280
 281                 if !lhs.is_syntactic_place_expr() {
 282                     // We already emitted E0070 "invalid left-hand side of assignment", so we
 283                     // silence this.
 284                     err.downgrade_to_delayed_bug();
 285                 }
 286             }
 287             _ => {}
 288         }
 289     }
 290
 291     /// If the expected type is an enum (Issue #55250) with any variants whose
 292     /// sole field is of the found type, suggest such variants. (Issue #42764)
 293     fn suggest_compatible_variants(
 294         &self,
 295         err: &mut Diagnostic,
 296         expr: &hir::Expr<'_>,
 297         expected: Ty<'tcx>,
 298         expr_ty: Ty<'tcx>,
 299     ) -> bool {
 300         if let ty::Adt(expected_adt, substs) = expected.kind() {
 301             if let hir::ExprKind::Field(base, ident) = expr.kind {
 302                 let base_ty = self.typeck_results.borrow().expr_ty(base);
 303                 if self.can_eq(self.param_env, base_ty, expected).is_ok()
 304                     && let Some(base_span) = base.span.find_ancestor_inside(expr.span)
 305                 {
 306                     err.span_suggestion_verbose(
 307                         expr.span.with_lo(base_span.hi()),
 308                         format!("consider removing the tuple struct field `{ident}`"),
 309                         "",
 310                         Applicability::MaybeIncorrect,
 311                     );
 312                     return true;
 313                 }
 314             }
 315
 316             // If the expression is of type () and it's the return expression of a block,
 317             // we suggest adding a separate return expression instead.
 318             // (To avoid things like suggesting `Ok(while .. { .. })`.)
 319             if expr_ty.is_unit() {
 320                 let mut id = expr.hir_id;
 321                 let mut parent;
 322
 323                 // Unroll desugaring, to make sure this works for `for` loops etc.
 324                 loop {
 325                     parent = self.tcx.hir().get_parent_node(id);
 326                     if let Some(parent_span) = self.tcx.hir().opt_span(parent) {
 327                         if parent_span.find_ancestor_inside(expr.span).is_some() {
 328                             // The parent node is part of the same span, so is the result of the
 329                             // same expansion/desugaring and not the 'real' parent node.
 330                             id = parent;
 331                             continue;
 332                         }
 333                     }
 334                     break;
 335                 }
 336
 337                 if let Some(hir::Node::Block(&hir::Block {
 338                     span: block_span, expr: Some(e), ..
 339                 })) = self.tcx.hir().find(parent)
 340                 {
 341                     if e.hir_id == id {
 342                         if let Some(span) = expr.span.find_ancestor_inside(block_span) {
 343                             let return_suggestions = if self
 344                                 .tcx
 345                                 .is_diagnostic_item(sym::Result, expected_adt.did())
 346                             {
 347                                 vec!["Ok(())"]
 348                             } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did()) {
 349                                 vec!["None", "Some(())"]
 350                             } else {
 351                                 return false;
 352                             };
 353                             if let Some(indent) =
 354                                 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
 355                             {
 356                                 // Add a semicolon, except after `}`.
 357                                 let semicolon =
 358                                     match self.tcx.sess.source_map().span_to_snippet(span) {
 359                                         Ok(s) if s.ends_with('}') => "",
 360                                         _ => ";",
 361                                     };
 362                                 err.span_suggestions(
 363                                     span.shrink_to_hi(),
 364                                     "try adding an expression at the end of the block",
 365                                     return_suggestions
 366                                         .into_iter()
 367                                         .map(|r| format!("{semicolon}\n{indent}{r}")),
 368                                     Applicability::MaybeIncorrect,
 369                                 );
 370                             }
 371                             return true;
 372                         }
 373                     }
 374                 }
 375             }
 376
 377             let compatible_variants: Vec<(String, _, _, Option<String>)> = expected_adt
 378                 .variants()
 379                 .iter()
 380                 .filter(|variant| {
 381                     variant.fields.len() == 1
 382                 })
 383                 .filter_map(|variant| {
 384                     let sole_field = &variant.fields[0];
 385
 386                     let field_is_local = sole_field.did.is_local();
 387                     let field_is_accessible =
 388                         sole_field.vis.is_accessible_from(expr.hir_id.owner.def_id, self.tcx)
 389                         // Skip suggestions for unstable public fields (for example `Pin::pointer`)
 390                         && matches!(self.tcx.eval_stability(sole_field.did, None, expr.span, None), EvalResult::Allow | EvalResult::Unmarked);
 391
 392                     if !field_is_local && !field_is_accessible {
 393                         return None;
 394                     }
 395
 396                     let note_about_variant_field_privacy = (field_is_local && !field_is_accessible)
 397                         .then(|| format!(" (its field is private, but it's local to this crate and its privacy can be changed)"));
 398
 399                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 400                     if self.can_coerce(expr_ty, sole_field_ty) {
 401                         let variant_path =
 402                             with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
 403                         // FIXME #56861: DRYer prelude filtering
 404                         if let Some(path) = variant_path.strip_prefix("std::prelude::")
 405                             && let Some((_, path)) = path.split_once("::")
 406                         {
 407                             return Some((path.to_string(), variant.ctor_kind, sole_field.name, note_about_variant_field_privacy));
 408                         }
 409                         Some((variant_path, variant.ctor_kind, sole_field.name, note_about_variant_field_privacy))
 410                     } else {
 411                         None
 412                     }
 413                 })
 414                 .collect();
 415
 416             let suggestions_for = |variant: &_, ctor, field_name| {
 417                 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 418                     Some(ident) => format!("{ident}: "),
 419                     None => String::new(),
 420                 };
 421
 422                 let (open, close) = match ctor {
 423                     hir::def::CtorKind::Fn => ("(".to_owned(), ")"),
 424                     hir::def::CtorKind::Fictive => (format!(" {{ {field_name}: "), " }"),
 425
 426                     // unit variants don't have fields
 427                     hir::def::CtorKind::Const => unreachable!(),
 428                 };
 429
 430                 // Suggest constructor as deep into the block tree as possible.
 431                 // This fixes https://github.com/rust-lang/rust/issues/101065,
 432                 // and also just helps make the most minimal suggestions.
 433                 let mut expr = expr;
 434                 while let hir::ExprKind::Block(block, _) = &expr.kind
 435                     && let Some(expr_) = &block.expr
 436                 {
 437                     expr = expr_
 438                 }
 439
 440                 vec![
 441                     (expr.span.shrink_to_lo(), format!("{prefix}{variant}{open}")),
 442                     (expr.span.shrink_to_hi(), close.to_owned()),
 443                 ]
 444             };
 445
 446             match &compatible_variants[..] {
 447                 [] => { /* No variants to format */ }
 448                 [(variant, ctor_kind, field_name, note)] => {
 449                     // Just a single matching variant.
 450                     err.multipart_suggestion_verbose(
 451                         &format!(
 452                             "try wrapping the expression in `{variant}`{note}",
 453                             note = note.as_deref().unwrap_or("")
 454                         ),
 455                         suggestions_for(&**variant, *ctor_kind, *field_name),
 456                         Applicability::MaybeIncorrect,
 457                     );
 458                     return true;
 459                 }
 460                 _ => {
 461                     // More than one matching variant.
 462                     err.multipart_suggestions(
 463                         &format!(
 464                             "try wrapping the expression in a variant of `{}`",
 465                             self.tcx.def_path_str(expected_adt.did())
 466                         ),
 467                         compatible_variants.into_iter().map(
 468                             |(variant, ctor_kind, field_name, _)| {
 469                                 suggestions_for(&variant, ctor_kind, field_name)
 470                             },
 471                         ),
 472                         Applicability::MaybeIncorrect,
 473                     );
 474                     return true;
 475                 }
 476             }
 477         }
 478
 479         false
 480     }
 481
 482     fn suggest_non_zero_new_unwrap(
 483         &self,
 484         err: &mut Diagnostic,
 485         expr: &hir::Expr<'_>,
 486         expected: Ty<'tcx>,
 487         expr_ty: Ty<'tcx>,
 488     ) -> bool {
 489         let tcx = self.tcx;
 490         let (adt, unwrap) = match expected.kind() {
 491             // In case Option<NonZero*> is wanted, but * is provided, suggest calling new
 492             ty::Adt(adt, substs) if tcx.is_diagnostic_item(sym::Option, adt.did()) => {
 493                 // Unwrap option
 494                 let ty::Adt(adt, _) = substs.type_at(0).kind() else { return false; };
 495
 496                 (adt, "")
 497             }
 498             // In case NonZero* is wanted, but * is provided also add `.unwrap()` to satisfy types
 499             ty::Adt(adt, _) => (adt, ".unwrap()"),
 500             _ => return false,
 501         };
 502
 503         let map = [
 504             (sym::NonZeroU8, tcx.types.u8),
 505             (sym::NonZeroU16, tcx.types.u16),
 506             (sym::NonZeroU32, tcx.types.u32),
 507             (sym::NonZeroU64, tcx.types.u64),
 508             (sym::NonZeroU128, tcx.types.u128),
 509             (sym::NonZeroI8, tcx.types.i8),
 510             (sym::NonZeroI16, tcx.types.i16),
 511             (sym::NonZeroI32, tcx.types.i32),
 512             (sym::NonZeroI64, tcx.types.i64),
 513             (sym::NonZeroI128, tcx.types.i128),
 514         ];
 515
 516         let Some((s, _)) = map
 517             .iter()
 518             .find(|&&(s, t)| self.tcx.is_diagnostic_item(s, adt.did()) && self.can_coerce(expr_ty, t))
 519             else { return false; };
 520
 521         let path = self.tcx.def_path_str(adt.non_enum_variant().def_id);
 522
 523         err.multipart_suggestion(
 524             format!("consider calling `{s}::new`"),
 525             vec![
 526                 (expr.span.shrink_to_lo(), format!("{path}::new(")),
 527                 (expr.span.shrink_to_hi(), format!("){unwrap}")),
 528             ],
 529             Applicability::MaybeIncorrect,
 530         );
 531
 532         true
 533     }
 534
 535     pub fn get_conversion_methods(
 536         &self,
 537         span: Span,
 538         expected: Ty<'tcx>,
 539         checked_ty: Ty<'tcx>,
 540         hir_id: hir::HirId,
 541     ) -> Vec<AssocItem> {
 542         let methods = self.probe_for_return_type(
 543             span,
 544             probe::Mode::MethodCall,
 545             expected,
 546             checked_ty,
 547             hir_id,
 548             |m| {
 549                 self.has_only_self_parameter(m)
 550                     && self
 551                         .tcx
 552                         // This special internal attribute is used to permit
 553                         // "identity-like" conversion methods to be suggested here.
 554                         //
 555                         // FIXME (#46459 and #46460): ideally
 556                         // `std::convert::Into::into` and `std::borrow:ToOwned` would
 557                         // also be `#[rustc_conversion_suggestion]`, if not for
 558                         // method-probing false-positives and -negatives (respectively).
 559                         //
 560                         // FIXME? Other potential candidate methods: `as_ref` and
 561                         // `as_mut`?
 562                         .has_attr(m.def_id, sym::rustc_conversion_suggestion)
 563             },
 564         );
 565
 566         methods
 567     }
 568
 569     /// This function checks whether the method is not static and does not accept other parameters than `self`.
 570     fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
 571         match method.kind {
 572             ty::AssocKind::Fn => {
 573                 method.fn_has_self_parameter
 574                     && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 575             }
 576             _ => false,
 577         }
 578     }
 579
 580     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 581     ///
 582     /// Given the following code:
 583     /// ```compile_fail,E0308
 584     /// struct Foo;
 585     /// fn takes_ref(_: &Foo) {}
 586     /// let ref opt = Some(Foo);
 587     ///
 588     /// opt.map(|param| takes_ref(param));
 589     /// ```
 590     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 591     ///
 592     /// It only checks for `Option` and `Result` and won't work with
 593     /// ```ignore (illustrative)
 594     /// opt.map(|param| { takes_ref(param) });
 595     /// ```
 596     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 597         let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
 598             return None;
 599         };
 600
 601         let hir::def::Res::Local(local_id) = path.res else {
 602             return None;
 603         };
 604
 605         let local_parent = self.tcx.hir().get_parent_node(local_id);
 606         let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
 607             return None;
 608         };
 609
 610         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 611         let Some(Node::Expr(hir::Expr {
 612             hir_id: expr_hir_id,
 613             kind: hir::ExprKind::Closure(hir::Closure { fn_decl: closure_fn_decl, .. }),
 614             ..
 615         })) = self.tcx.hir().find(param_parent) else {
 616             return None;
 617         };
 618
 619         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 620         let hir = self.tcx.hir().find(expr_parent);
 621         let closure_params_len = closure_fn_decl.inputs.len();
 622         let (
 623             Some(Node::Expr(hir::Expr {
 624                 kind: hir::ExprKind::MethodCall(method_path, receiver, ..),
 625                 ..
 626             })),
 627             1,
 628         ) = (hir, closure_params_len) else {
 629             return None;
 630         };
 631
 632         let self_ty = self.typeck_results.borrow().expr_ty(receiver);
 633         let name = method_path.ident.name;
 634         let is_as_ref_able = match self_ty.peel_refs().kind() {
 635             ty::Adt(def, _) => {
 636                 (self.tcx.is_diagnostic_item(sym::Option, def.did())
 637                     || self.tcx.is_diagnostic_item(sym::Result, def.did()))
 638                     && (name == sym::map || name == sym::and_then)
 639             }
 640             _ => false,
 641         };
 642         match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
 643             (true, Ok(src)) => {
 644                 let suggestion = format!("as_ref().{}", src);
 645                 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
 646             }
 647             _ => None,
 648         }
 649     }
 650
 651     pub(crate) fn maybe_get_struct_pattern_shorthand_field(
 652         &self,
 653         expr: &hir::Expr<'_>,
 654     ) -> Option<Symbol> {
 655         let hir = self.tcx.hir();
 656         let local = match expr {
 657             hir::Expr {
 658                 kind:
 659                     hir::ExprKind::Path(hir::QPath::Resolved(
 660                         None,
 661                         hir::Path {
 662                             res: hir::def::Res::Local(_),
 663                             segments: [hir::PathSegment { ident, .. }],
 664                             ..
 665                         },
 666                     )),
 667                 ..
 668             } => Some(ident),
 669             _ => None,
 670         }?;
 671
 672         match hir.find(hir.get_parent_node(expr.hir_id))? {
 673             Node::ExprField(field) => {
 674                 if field.ident.name == local.name && field.is_shorthand {
 675                     return Some(local.name);
 676                 }
 677             }
 678             _ => {}
 679         }
 680
 681         None
 682     }
 683
 684     /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
 685     pub(crate) fn maybe_get_block_expr(
 686         &self,
 687         expr: &hir::Expr<'tcx>,
 688     ) -> Option<&'tcx hir::Expr<'tcx>> {
 689         match expr {
 690             hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
 691             _ => None,
 692         }
 693     }
 694
 695     /// Returns whether the given expression is an `else if`.
 696     pub(crate) fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
 697         if let hir::ExprKind::If(..) = expr.kind {
 698             let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
 699             if let Some(Node::Expr(hir::Expr {
 700                 kind: hir::ExprKind::If(_, _, Some(else_expr)),
 701                 ..
 702             })) = self.tcx.hir().find(parent_id)
 703             {
 704                 return else_expr.hir_id == expr.hir_id;
 705             }
 706         }
 707         false
 708     }
 709
 710     /// This function is used to determine potential "simple" improvements or users' errors and
 711     /// provide them useful help. For example:
 712     ///
 713     /// ```compile_fail,E0308
 714     /// fn some_fn(s: &str) {}
 715     ///
 716     /// let x = "hey!".to_owned();
 717     /// some_fn(x); // error
 718     /// ```
 719     ///
 720     /// No need to find every potential function which could make a coercion to transform a
 721     /// `String` into a `&str` since a `&` would do the trick!
 722     ///
 723     /// In addition of this check, it also checks between references mutability state. If the
 724     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 725     /// `&mut`!".
 726     pub fn check_ref(
 727         &self,
 728         expr: &hir::Expr<'tcx>,
 729         checked_ty: Ty<'tcx>,
 730         expected: Ty<'tcx>,
 731     ) -> Option<(
 732         Span,
 733         String,
 734         String,
 735         Applicability,
 736         bool, /* verbose */
 737         bool, /* suggest `&` or `&mut` type annotation */
 738     )> {
 739         let sess = self.sess();
 740         let sp = expr.span;
 741
 742         // If the span is from an external macro, there's no suggestion we can make.
 743         if in_external_macro(sess, sp) {
 744             return None;
 745         }
 746
 747         let sm = sess.source_map();
 748
 749         let replace_prefix = |s: &str, old: &str, new: &str| {
 750             s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
 751         };
 752
 753         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 754         let expr = expr.peel_drop_temps();
 755
 756         match (&expr.kind, expected.kind(), checked_ty.kind()) {
 757             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
 758                 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
 759                     if let hir::ExprKind::Lit(_) = expr.kind
 760                         && let Ok(src) = sm.span_to_snippet(sp)
 761                         && replace_prefix(&src, "b\"", "\"").is_some()
 762                     {
 763                                 let pos = sp.lo() + BytePos(1);
 764                                 return Some((
 765                                     sp.with_hi(pos),
 766                                     "consider removing the leading `b`".to_string(),
 767                                     String::new(),
 768                                     Applicability::MachineApplicable,
 769                                     true,
 770                                     false,
 771                                 ));
 772                             }
 773                         }
 774                 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
 775                     if let hir::ExprKind::Lit(_) = expr.kind
 776                         && let Ok(src) = sm.span_to_snippet(sp)
 777                         && replace_prefix(&src, "\"", "b\"").is_some()
 778                     {
 779                                 return Some((
 780                                     sp.shrink_to_lo(),
 781                                     "consider adding a leading `b`".to_string(),
 782                                     "b".to_string(),
 783                                     Applicability::MachineApplicable,
 784                                     true,
 785                                     false,
 786                                 ));
 787                     }
 788                 }
 789                 _ => {}
 790             },
 791             (_, &ty::Ref(_, _, mutability), _) => {
 792                 // Check if it can work when put into a ref. For example:
 793                 //
 794                 // ```
 795                 // fn bar(x: &mut i32) {}
 796                 //
 797                 // let x = 0u32;
 798                 // bar(&x); // error, expected &mut
 799                 // ```
 800                 let ref_ty = match mutability {
 801                     hir::Mutability::Mut => {
 802                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 803                     }
 804                     hir::Mutability::Not => {
 805                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 806                     }
 807                 };
 808                 if self.can_coerce(ref_ty, expected) {
 809                     let mut sugg_sp = sp;
 810                     if let hir::ExprKind::MethodCall(ref segment, receiver, args, _) = expr.kind {
 811                         let clone_trait =
 812                             self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
 813                         if args.is_empty()
 814                             && self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
 815                                 |did| {
 816                                     let ai = self.tcx.associated_item(did);
 817                                     ai.trait_container(self.tcx) == Some(clone_trait)
 818                                 },
 819                             ) == Some(true)
 820                             && segment.ident.name == sym::clone
 821                         {
 822                             // If this expression had a clone call when suggesting borrowing
 823                             // we want to suggest removing it because it'd now be unnecessary.
 824                             sugg_sp = receiver.span;
 825                         }
 826                     }
 827                     if let Ok(src) = sm.span_to_snippet(sugg_sp) {
 828                         let needs_parens = match expr.kind {
 829                             // parenthesize if needed (Issue #46756)
 830                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 831                             // parenthesize borrows of range literals (Issue #54505)
 832                             _ if is_range_literal(expr) => true,
 833                             _ => false,
 834                         };
 835
 836                         if let Some(sugg) = self.can_use_as_ref(expr) {
 837                             return Some((
 838                                 sugg.0,
 839                                 sugg.1.to_string(),
 840                                 sugg.2,
 841                                 Applicability::MachineApplicable,
 842                                 false,
 843                                 false,
 844                             ));
 845                         }
 846
 847                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
 848                             Some(ident) => format!("{ident}: "),
 849                             None => String::new(),
 850                         };
 851
 852                         if let Some(hir::Node::Expr(hir::Expr {
 853                             kind: hir::ExprKind::Assign(..),
 854                             ..
 855                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 856                         {
 857                             if mutability == hir::Mutability::Mut {
 858                                 // Suppressing this diagnostic, we'll properly print it in `check_expr_assign`
 859                                 return None;
 860                             }
 861                         }
 862
 863                         let sugg_expr = if needs_parens { format!("({src})") } else { src };
 864                         return Some(match mutability {
 865                             hir::Mutability::Mut => (
 866                                 sp,
 867                                 "consider mutably borrowing here".to_string(),
 868                                 format!("{prefix}&mut {sugg_expr}"),
 869                                 Applicability::MachineApplicable,
 870                                 false,
 871                                 false,
 872                             ),
 873                             hir::Mutability::Not => (
 874                                 sp,
 875                                 "consider borrowing here".to_string(),
 876                                 format!("{prefix}&{sugg_expr}"),
 877                                 Applicability::MachineApplicable,
 878                                 false,
 879                                 false,
 880                             ),
 881                         });
 882                     }
 883                 }
 884             }
 885             (
 886                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 887                 _,
 888                 &ty::Ref(_, checked, _),
 889             ) if self.can_sub(self.param_env, checked, expected).is_ok() => {
 890                 // We have `&T`, check if what was expected was `T`. If so,
 891                 // we may want to suggest removing a `&`.
 892                 if sm.is_imported(expr.span) {
 893                     // Go through the spans from which this span was expanded,
 894                     // and find the one that's pointing inside `sp`.
 895                     //
 896                     // E.g. for `&format!("")`, where we want the span to the
 897                     // `format!()` invocation instead of its expansion.
 898                     if let Some(call_span) =
 899                         iter::successors(Some(expr.span), |s| s.parent_callsite())
 900                             .find(|&s| sp.contains(s))
 901                         && sm.is_span_accessible(call_span)
 902                     {
 903                         return Some((
 904                             sp.with_hi(call_span.lo()),
 905                             "consider removing the borrow".to_string(),
 906                             String::new(),
 907                             Applicability::MachineApplicable,
 908                             true,
 909                             true
 910                         ));
 911                     }
 912                     return None;
 913                 }
 914                 if sp.contains(expr.span)
 915                     && sm.is_span_accessible(expr.span)
 916                 {
 917                     return Some((
 918                         sp.with_hi(expr.span.lo()),
 919                         "consider removing the borrow".to_string(),
 920                         String::new(),
 921                         Applicability::MachineApplicable,
 922                         true,
 923                         true,
 924                     ));
 925                 }
 926             }
 927             (
 928                 _,
 929                 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
 930                 &ty::Ref(_, ty_a, mutbl_a),
 931             ) => {
 932                 if let Some(steps) = self.deref_steps(ty_a, ty_b)
 933                     // Only suggest valid if dereferencing needed.
 934                     && steps > 0
 935                     // The pointer type implements `Copy` trait so the suggestion is always valid.
 936                     && let Ok(src) = sm.span_to_snippet(sp)
 937                 {
 938                     let derefs = "*".repeat(steps);
 939                     if let Some((span, src, applicability)) = match mutbl_b {
 940                         hir::Mutability::Mut => {
 941                             let new_prefix = "&mut ".to_owned() + &derefs;
 942                             match mutbl_a {
 943                                 hir::Mutability::Mut => {
 944                                     replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
 945                                         let pos = sp.lo() + BytePos(5);
 946                                         let sp = sp.with_lo(pos).with_hi(pos);
 947                                         (sp, derefs, Applicability::MachineApplicable)
 948                                     })
 949                                 }
 950                                 hir::Mutability::Not => {
 951                                     replace_prefix(&src, "&", &new_prefix).map(|_| {
 952                                         let pos = sp.lo() + BytePos(1);
 953                                         let sp = sp.with_lo(pos).with_hi(pos);
 954                                         (
 955                                             sp,
 956                                             format!("mut {derefs}"),
 957                                             Applicability::Unspecified,
 958                                         )
 959                                     })
 960                                 }
 961                             }
 962                         }
 963                         hir::Mutability::Not => {
 964                             let new_prefix = "&".to_owned() + &derefs;
 965                             match mutbl_a {
 966                                 hir::Mutability::Mut => {
 967                                     replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
 968                                         let lo = sp.lo() + BytePos(1);
 969                                         let hi = sp.lo() + BytePos(5);
 970                                         let sp = sp.with_lo(lo).with_hi(hi);
 971                                         (sp, derefs, Applicability::MachineApplicable)
 972                                     })
 973                                 }
 974                                 hir::Mutability::Not => {
 975                                     replace_prefix(&src, "&", &new_prefix).map(|_| {
 976                                         let pos = sp.lo() + BytePos(1);
 977                                         let sp = sp.with_lo(pos).with_hi(pos);
 978                                         (sp, derefs, Applicability::MachineApplicable)
 979                                     })
 980                                 }
 981                             }
 982                         }
 983                     } {
 984                         return Some((
 985                             span,
 986                             "consider dereferencing".to_string(),
 987                             src,
 988                             applicability,
 989                             true,
 990                             false,
 991                         ));
 992                     }
 993                 }
 994             }
 995             _ if sp == expr.span => {
 996                 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
 997                     let mut expr = expr.peel_blocks();
 998                     let mut prefix_span = expr.span.shrink_to_lo();
 999                     let mut remove = String::new();
1000
1001                     // Try peeling off any existing `&` and `&mut` to reach our target type
1002                     while steps > 0 {
1003                         if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
1004                             // If the expression has `&`, removing it would fix the error
1005                             prefix_span = prefix_span.with_hi(inner.span.lo());
1006                             expr = inner;
1007                             remove += match mutbl {
1008                                 hir::Mutability::Not => "&",
1009                                 hir::Mutability::Mut => "&mut ",
1010                             };
1011                             steps -= 1;
1012                         } else {
1013                             break;
1014                         }
1015                     }
1016                     // If we've reached our target type with just removing `&`, then just print now.
1017                     if steps == 0 {
1018                         return Some((
1019                             prefix_span,
1020                             format!("consider removing the `{}`", remove.trim()),
1021                             String::new(),
1022                             // Do not remove `&&` to get to bool, because it might be something like
1023                             // { a } && b, which we have a separate fixup suggestion that is more
1024                             // likely correct...
1025                             if remove.trim() == "&&" && expected == self.tcx.types.bool {
1026                                 Applicability::MaybeIncorrect
1027                             } else {
1028                                 Applicability::MachineApplicable
1029                             },
1030                             true,
1031                             false,
1032                         ));
1033                     }
1034
1035                     // For this suggestion to make sense, the type would need to be `Copy`,
1036                     // or we have to be moving out of a `Box<T>`
1037                     if self.type_is_copy_modulo_regions(self.param_env, expected, sp)
1038                         // FIXME(compiler-errors): We can actually do this if the checked_ty is
1039                         // `steps` layers of boxes, not just one, but this is easier and most likely.
1040                         || (checked_ty.is_box() && steps == 1)
1041                     {
1042                         let deref_kind = if checked_ty.is_box() {
1043                             "unboxing the value"
1044                         } else if checked_ty.is_region_ptr() {
1045                             "dereferencing the borrow"
1046                         } else {
1047                             "dereferencing the type"
1048                         };
1049
1050                         // Suggest removing `&` if we have removed any, otherwise suggest just
1051                         // dereferencing the remaining number of steps.
1052                         let message = if remove.is_empty() {
1053                             format!("consider {deref_kind}")
1054                         } else {
1055                             format!(
1056                                 "consider removing the `{}` and {} instead",
1057                                 remove.trim(),
1058                                 deref_kind
1059                             )
1060                         };
1061
1062                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
1063                             Some(ident) => format!("{ident}: "),
1064                             None => String::new(),
1065                         };
1066
1067                         let (span, suggestion) = if self.is_else_if_block(expr) {
1068                             // Don't suggest nonsense like `else *if`
1069                             return None;
1070                         } else if let Some(expr) = self.maybe_get_block_expr(expr) {
1071                             // prefix should be empty here..
1072                             (expr.span.shrink_to_lo(), "*".to_string())
1073                         } else {
1074                             (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
1075                         };
1076
1077                         return Some((
1078                             span,
1079                             message,
1080                             suggestion,
1081                             Applicability::MachineApplicable,
1082                             true,
1083                             false,
1084                         ));
1085                     }
1086                 }
1087             }
1088             _ => {}
1089         }
1090         None
1091     }
1092
1093     pub fn check_for_cast(
1094         &self,
1095         err: &mut Diagnostic,
1096         expr: &hir::Expr<'_>,
1097         checked_ty: Ty<'tcx>,
1098         expected_ty: Ty<'tcx>,
1099         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
1100     ) -> bool {
1101         if self.tcx.sess.source_map().is_imported(expr.span) {
1102             // Ignore if span is from within a macro.
1103             return false;
1104         }
1105
1106         let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
1107             return false;
1108         };
1109
1110         // If casting this expression to a given numeric type would be appropriate in case of a type
1111         // mismatch.
1112         //
1113         // We want to minimize the amount of casting operations that are suggested, as it can be a
1114         // lossy operation with potentially bad side effects, so we only suggest when encountering
1115         // an expression that indicates that the original type couldn't be directly changed.
1116         //
1117         // For now, don't suggest casting with `as`.
1118         let can_cast = false;
1119
1120         let mut sugg = vec![];
1121
1122         if let Some(hir::Node::ExprField(field)) =
1123             self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
1124         {
1125             // `expr` is a literal field for a struct, only suggest if appropriate
1126             if field.is_shorthand {
1127                 // This is a field literal
1128                 sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
1129             } else {
1130                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
1131                 return false;
1132             }
1133         };
1134
1135         if let hir::ExprKind::Call(path, args) = &expr.kind
1136             && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
1137                 (&path.kind, args.len())
1138             // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1139             && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1140                 (&base_ty.kind, path_segment.ident.name)
1141         {
1142             if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1143                 match ident.name {
1144                     sym::i128
1145                     | sym::i64
1146                     | sym::i32
1147                     | sym::i16
1148                     | sym::i8
1149                     | sym::u128
1150                     | sym::u64
1151                     | sym::u32
1152                     | sym::u16
1153                     | sym::u8
1154                     | sym::isize
1155                     | sym::usize
1156                         if base_ty_path.segments.len() == 1 =>
1157                     {
1158                         return false;
1159                     }
1160                     _ => {}
1161                 }
1162             }
1163         }
1164
1165         let msg = format!(
1166             "you can convert {} `{}` to {} `{}`",
1167             checked_ty.kind().article(),
1168             checked_ty,
1169             expected_ty.kind().article(),
1170             expected_ty,
1171         );
1172         let cast_msg = format!(
1173             "you can cast {} `{}` to {} `{}`",
1174             checked_ty.kind().article(),
1175             checked_ty,
1176             expected_ty.kind().article(),
1177             expected_ty,
1178         );
1179         let lit_msg = format!(
1180             "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1181         );
1182
1183         let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1184             sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1185             ")"
1186         } else {
1187             ""
1188         };
1189
1190         let mut cast_suggestion = sugg.clone();
1191         cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1192         let mut into_suggestion = sugg.clone();
1193         into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1194         let mut suffix_suggestion = sugg.clone();
1195         suffix_suggestion.push((
1196             if matches!(
1197                 (&expected_ty.kind(), &checked_ty.kind()),
1198                 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1199             ) {
1200                 // Remove fractional part from literal, for example `42.0f32` into `42`
1201                 let src = src.trim_end_matches(&checked_ty.to_string());
1202                 let len = src.split('.').next().unwrap().len();
1203                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1204             } else {
1205                 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1206                 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1207             },
1208             if expr.precedence().order() < PREC_POSTFIX {
1209                 // Readd `)`
1210                 format!("{expected_ty})")
1211             } else {
1212                 expected_ty.to_string()
1213             },
1214         ));
1215         let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1216             if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1217         };
1218         let is_negative_int =
1219             |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1220         let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1221
1222         let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1223
1224         let suggest_fallible_into_or_lhs_from =
1225             |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1226                 // If we know the expression the expected type is derived from, we might be able
1227                 // to suggest a widening conversion rather than a narrowing one (which may
1228                 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1229                 //   x > y
1230                 // can be given the suggestion "u32::from(x) > y" rather than
1231                 // "x > y.try_into().unwrap()".
1232                 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1233                     self.tcx
1234                         .sess
1235                         .source_map()
1236                         .span_to_snippet(expr.span)
1237                         .ok()
1238                         .map(|src| (expr, src))
1239                 });
1240                 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1241                     (lhs_expr_and_src, exp_to_found_is_fallible)
1242                 {
1243                     let msg = format!(
1244                         "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1245                     );
1246                     let suggestion = vec![
1247                         (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1248                         (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1249                     ];
1250                     (msg, suggestion)
1251                 } else {
1252                     let msg = format!("{msg} and panic if the converted value doesn't fit");
1253                     let mut suggestion = sugg.clone();
1254                     suggestion.push((
1255                         expr.span.shrink_to_hi(),
1256                         format!("{close_paren}.try_into().unwrap()"),
1257                     ));
1258                     (msg, suggestion)
1259                 };
1260                 err.multipart_suggestion_verbose(
1261                     &msg,
1262                     suggestion,
1263                     Applicability::MachineApplicable,
1264                 );
1265             };
1266
1267         let suggest_to_change_suffix_or_into =
1268             |err: &mut Diagnostic,
1269              found_to_exp_is_fallible: bool,
1270              exp_to_found_is_fallible: bool| {
1271                 let exp_is_lhs =
1272                     expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1273
1274                 if exp_is_lhs {
1275                     return;
1276                 }
1277
1278                 let always_fallible = found_to_exp_is_fallible
1279                     && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1280                 let msg = if literal_is_ty_suffixed(expr) {
1281                     &lit_msg
1282                 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1283                     // We now know that converting either the lhs or rhs is fallible. Before we
1284                     // suggest a fallible conversion, check if the value can never fit in the
1285                     // expected type.
1286                     let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1287                     err.note(&msg);
1288                     return;
1289                 } else if in_const_context {
1290                     // Do not recommend `into` or `try_into` in const contexts.
1291                     return;
1292                 } else if found_to_exp_is_fallible {
1293                     return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1294                 } else {
1295                     &msg
1296                 };
1297                 let suggestion = if literal_is_ty_suffixed(expr) {
1298                     suffix_suggestion.clone()
1299                 } else {
1300                     into_suggestion.clone()
1301                 };
1302                 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1303             };
1304
1305         match (&expected_ty.kind(), &checked_ty.kind()) {
1306             (&ty::Int(ref exp), &ty::Int(ref found)) => {
1307                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1308                 {
1309                     (Some(exp), Some(found)) if exp < found => (true, false),
1310                     (Some(exp), Some(found)) if exp > found => (false, true),
1311                     (None, Some(8 | 16)) => (false, true),
1312                     (Some(8 | 16), None) => (true, false),
1313                     (None, _) | (_, None) => (true, true),
1314                     _ => (false, false),
1315                 };
1316                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1317                 true
1318             }
1319             (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1320                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1321                 {
1322                     (Some(exp), Some(found)) if exp < found => (true, false),
1323                     (Some(exp), Some(found)) if exp > found => (false, true),
1324                     (None, Some(8 | 16)) => (false, true),
1325                     (Some(8 | 16), None) => (true, false),
1326                     (None, _) | (_, None) => (true, true),
1327                     _ => (false, false),
1328                 };
1329                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1330                 true
1331             }
1332             (&ty::Int(exp), &ty::Uint(found)) => {
1333                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1334                 {
1335                     (Some(exp), Some(found)) if found < exp => (false, true),
1336                     (None, Some(8)) => (false, true),
1337                     _ => (true, true),
1338                 };
1339                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1340                 true
1341             }
1342             (&ty::Uint(exp), &ty::Int(found)) => {
1343                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1344                 {
1345                     (Some(exp), Some(found)) if found > exp => (true, false),
1346                     (Some(8), None) => (true, false),
1347                     _ => (true, true),
1348                 };
1349                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1350                 true
1351             }
1352             (&ty::Float(ref exp), &ty::Float(ref found)) => {
1353                 if found.bit_width() < exp.bit_width() {
1354                     suggest_to_change_suffix_or_into(err, false, true);
1355                 } else if literal_is_ty_suffixed(expr) {
1356                     err.multipart_suggestion_verbose(
1357                         &lit_msg,
1358                         suffix_suggestion,
1359                         Applicability::MachineApplicable,
1360                     );
1361                 } else if can_cast {
1362                     // Missing try_into implementation for `f64` to `f32`
1363                     err.multipart_suggestion_verbose(
1364                         &format!("{cast_msg}, producing the closest possible value"),
1365                         cast_suggestion,
1366                         Applicability::MaybeIncorrect, // lossy conversion
1367                     );
1368                 }
1369                 true
1370             }
1371             (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1372                 if literal_is_ty_suffixed(expr) {
1373                     err.multipart_suggestion_verbose(
1374                         &lit_msg,
1375                         suffix_suggestion,
1376                         Applicability::MachineApplicable,
1377                     );
1378                 } else if can_cast {
1379                     // Missing try_into implementation for `{float}` to `{integer}`
1380                     err.multipart_suggestion_verbose(
1381                         &format!("{msg}, rounding the float towards zero"),
1382                         cast_suggestion,
1383                         Applicability::MaybeIncorrect, // lossy conversion
1384                     );
1385                 }
1386                 true
1387             }
1388             (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1389                 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1390                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1391                     err.multipart_suggestion_verbose(
1392                         &format!(
1393                             "{msg}, producing the floating point representation of the integer",
1394                         ),
1395                         into_suggestion,
1396                         Applicability::MachineApplicable,
1397                     );
1398                 } else if literal_is_ty_suffixed(expr) {
1399                     err.multipart_suggestion_verbose(
1400                         &lit_msg,
1401                         suffix_suggestion,
1402                         Applicability::MachineApplicable,
1403                     );
1404                 } else {
1405                     // Missing try_into implementation for `{integer}` to `{float}`
1406                     err.multipart_suggestion_verbose(
1407                         &format!(
1408                             "{cast_msg}, producing the floating point representation of the integer, \
1409                                  rounded if necessary",
1410                         ),
1411                         cast_suggestion,
1412                         Applicability::MaybeIncorrect, // lossy conversion
1413                     );
1414                 }
1415                 true
1416             }
1417             (&ty::Float(ref exp), &ty::Int(ref found)) => {
1418                 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1419                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1420                     err.multipart_suggestion_verbose(
1421                         &format!(
1422                             "{}, producing the floating point representation of the integer",
1423                             &msg,
1424                         ),
1425                         into_suggestion,
1426                         Applicability::MachineApplicable,
1427                     );
1428                 } else if literal_is_ty_suffixed(expr) {
1429                     err.multipart_suggestion_verbose(
1430                         &lit_msg,
1431                         suffix_suggestion,
1432                         Applicability::MachineApplicable,
1433                     );
1434                 } else {
1435                     // Missing try_into implementation for `{integer}` to `{float}`
1436                     err.multipart_suggestion_verbose(
1437                         &format!(
1438                             "{}, producing the floating point representation of the integer, \
1439                                 rounded if necessary",
1440                             &msg,
1441                         ),
1442                         cast_suggestion,
1443                         Applicability::MaybeIncorrect, // lossy conversion
1444                     );
1445                 }
1446                 true
1447             }
1448             (
1449                 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1450                 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1451                 &ty::Char,
1452             ) => {
1453                 err.multipart_suggestion_verbose(
1454                     &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1455                     cast_suggestion,
1456                     Applicability::MachineApplicable,
1457                 );
1458                 true
1459             }
1460             _ => false,
1461         }
1462     }
1463 }