compiler/rustc_hir_analysis/src/check/fn_ctxt/suggestions.rs

   1 use super::FnCtxt;
   2 use crate::astconv::AstConv;
   3 use crate::errors::{AddReturnTypeSuggestion, ExpectedReturnTypeLabel};
   4
   5 use hir::def_id::DefId;
   6 use rustc_ast::util::parser::{ExprPrecedence, PREC_POSTFIX};
   7 use rustc_errors::{Applicability, Diagnostic, MultiSpan};
   8 use rustc_hir as hir;
   9 use rustc_hir::def::{CtorOf, DefKind};
  10 use rustc_hir::lang_items::LangItem;
  11 use rustc_hir::{
  12     Expr, ExprKind, GenericBound, Node, Path, QPath, Stmt, StmtKind, TyKind, WherePredicate,
  13 };
  14 use rustc_infer::infer::{self, TyCtxtInferExt};
  15 use rustc_infer::traits::{self, StatementAsExpression};
  16 use rustc_middle::lint::in_external_macro;
  17 use rustc_middle::ty::{self, Binder, IsSuggestable, ToPredicate, Ty};
  18 use rustc_session::errors::ExprParenthesesNeeded;
  19 use rustc_span::symbol::sym;
  20 use rustc_span::Span;
  21 use rustc_trait_selection::infer::InferCtxtExt;
  22 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
  23
  24 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  25     pub(in super::super) fn suggest_semicolon_at_end(&self, span: Span, err: &mut Diagnostic) {
  26         err.span_suggestion_short(
  27             span.shrink_to_hi(),
  28             "consider using a semicolon here",
  29             ";",
  30             Applicability::MachineApplicable,
  31         );
  32     }
  33
  34     /// On implicit return expressions with mismatched types, provides the following suggestions:
  35     ///
  36     /// - Points out the method's return type as the reason for the expected type.
  37     /// - Possible missing semicolon.
  38     /// - Possible missing return type if the return type is the default, and not `fn main()`.
  39     pub fn suggest_mismatched_types_on_tail(
  40         &self,
  41         err: &mut Diagnostic,
  42         expr: &'tcx hir::Expr<'tcx>,
  43         expected: Ty<'tcx>,
  44         found: Ty<'tcx>,
  45         blk_id: hir::HirId,
  46     ) -> bool {
  47         let expr = expr.peel_drop_temps();
  48         self.suggest_missing_semicolon(err, expr, expected, false);
  49         let mut pointing_at_return_type = false;
  50         if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
  51             let fn_id = self.tcx.hir().get_return_block(blk_id).unwrap();
  52             pointing_at_return_type = self.suggest_missing_return_type(
  53                 err,
  54                 &fn_decl,
  55                 expected,
  56                 found,
  57                 can_suggest,
  58                 fn_id,
  59             );
  60             self.suggest_missing_break_or_return_expr(
  61                 err, expr, &fn_decl, expected, found, blk_id, fn_id,
  62             );
  63         }
  64         pointing_at_return_type
  65     }
  66
  67     /// When encountering an fn-like type, try accessing the output of the type
  68     /// and suggesting calling it if it satisfies a predicate (i.e. if the
  69     /// output has a method or a field):
  70     /// ```compile_fail,E0308
  71     /// fn foo(x: usize) -> usize { x }
  72     /// let x: usize = foo;  // suggest calling the `foo` function: `foo(42)`
  73     /// ```
  74     pub(crate) fn suggest_fn_call(
  75         &self,
  76         err: &mut Diagnostic,
  77         expr: &hir::Expr<'_>,
  78         found: Ty<'tcx>,
  79         can_satisfy: impl FnOnce(Ty<'tcx>) -> bool,
  80     ) -> bool {
  81         let Some((def_id_or_name, output, inputs)) = self.extract_callable_info(expr, found)
  82             else { return false; };
  83         if can_satisfy(output) {
  84             let (sugg_call, mut applicability) = match inputs.len() {
  85                 0 => ("".to_string(), Applicability::MachineApplicable),
  86                 1..=4 => (
  87                     inputs
  88                         .iter()
  89                         .map(|ty| {
  90                             if ty.is_suggestable(self.tcx, false) {
  91                                 format!("/* {ty} */")
  92                             } else {
  93                                 "".to_string()
  94                             }
  95                         })
  96                         .collect::<Vec<_>>()
  97                         .join(", "),
  98                     Applicability::HasPlaceholders,
  99                 ),
 100                 _ => ("/* ... */".to_string(), Applicability::HasPlaceholders),
 101             };
 102
 103             let msg = match def_id_or_name {
 104                 DefIdOrName::DefId(def_id) => match self.tcx.def_kind(def_id) {
 105                     DefKind::Ctor(CtorOf::Struct, _) => "instantiate this tuple struct".to_string(),
 106                     DefKind::Ctor(CtorOf::Variant, _) => {
 107                         "instantiate this tuple variant".to_string()
 108                     }
 109                     kind => format!("call this {}", kind.descr(def_id)),
 110                 },
 111                 DefIdOrName::Name(name) => format!("call this {name}"),
 112             };
 113
 114             let sugg = match expr.kind {
 115                 hir::ExprKind::Call(..)
 116                 | hir::ExprKind::Path(..)
 117                 | hir::ExprKind::Index(..)
 118                 | hir::ExprKind::Lit(..) => {
 119                     vec![(expr.span.shrink_to_hi(), format!("({sugg_call})"))]
 120                 }
 121                 hir::ExprKind::Closure { .. } => {
 122                     // Might be `{ expr } || { bool }`
 123                     applicability = Applicability::MaybeIncorrect;
 124                     vec![
 125                         (expr.span.shrink_to_lo(), "(".to_string()),
 126                         (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
 127                     ]
 128                 }
 129                 _ => {
 130                     vec![
 131                         (expr.span.shrink_to_lo(), "(".to_string()),
 132                         (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
 133                     ]
 134                 }
 135             };
 136
 137             err.multipart_suggestion_verbose(
 138                 format!("use parentheses to {msg}"),
 139                 sugg,
 140                 applicability,
 141             );
 142             return true;
 143         }
 144         false
 145     }
 146
 147     /// Extracts information about a callable type for diagnostics. This is a
 148     /// heuristic -- it doesn't necessarily mean that a type is always callable,
 149     /// because the callable type must also be well-formed to be called.
 150     pub(in super::super) fn extract_callable_info(
 151         &self,
 152         expr: &Expr<'_>,
 153         found: Ty<'tcx>,
 154     ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)> {
 155         // Autoderef is useful here because sometimes we box callables, etc.
 156         let Some((def_id_or_name, output, inputs)) = self.autoderef(expr.span, found).silence_errors().find_map(|(found, _)| {
 157             match *found.kind() {
 158                 ty::FnPtr(fn_sig) =>
 159                     Some((DefIdOrName::Name("function pointer"), fn_sig.output(), fn_sig.inputs())),
 160                 ty::FnDef(def_id, _) => {
 161                     let fn_sig = found.fn_sig(self.tcx);
 162                     Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs()))
 163                 }
 164                 ty::Closure(def_id, substs) => {
 165                     let fn_sig = substs.as_closure().sig();
 166                     Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs().map_bound(|inputs| &inputs[1..])))
 167                 }
 168                 ty::Opaque(def_id, substs) => {
 169                     self.tcx.bound_item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
 170                         if let ty::PredicateKind::Projection(proj) = pred.kind().skip_binder()
 171                         && Some(proj.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output()
 172                         // args tuple will always be substs[1]
 173                         && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
 174                         {
 175                             Some((
 176                                 DefIdOrName::DefId(def_id),
 177                                 pred.kind().rebind(proj.term.ty().unwrap()),
 178                                 pred.kind().rebind(args.as_slice()),
 179                             ))
 180                         } else {
 181                             None
 182                         }
 183                     })
 184                 }
 185                 ty::Dynamic(data, _, ty::Dyn) => {
 186                     data.iter().find_map(|pred| {
 187                         if let ty::ExistentialPredicate::Projection(proj) = pred.skip_binder()
 188                         && Some(proj.item_def_id) == self.tcx.lang_items().fn_once_output()
 189                         // for existential projection, substs are shifted over by 1
 190                         && let ty::Tuple(args) = proj.substs.type_at(0).kind()
 191                         {
 192                             Some((
 193                                 DefIdOrName::Name("trait object"),
 194                                 pred.rebind(proj.term.ty().unwrap()),
 195                                 pred.rebind(args.as_slice()),
 196                             ))
 197                         } else {
 198                             None
 199                         }
 200                     })
 201                 }
 202                 ty::Param(param) => {
 203                     let def_id = self.tcx.generics_of(self.body_id.owner).type_param(&param, self.tcx).def_id;
 204                     self.tcx.predicates_of(self.body_id.owner).predicates.iter().find_map(|(pred, _)| {
 205                         if let ty::PredicateKind::Projection(proj) = pred.kind().skip_binder()
 206                         && Some(proj.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output()
 207                         && proj.projection_ty.self_ty() == found
 208                         // args tuple will always be substs[1]
 209                         && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
 210                         {
 211                             Some((
 212                                 DefIdOrName::DefId(def_id),
 213                                 pred.kind().rebind(proj.term.ty().unwrap()),
 214                                 pred.kind().rebind(args.as_slice()),
 215                             ))
 216                         } else {
 217                             None
 218                         }
 219                     })
 220                 }
 221                 _ => None,
 222             }
 223         }) else { return None; };
 224
 225         let output = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, output);
 226         let inputs = inputs
 227             .skip_binder()
 228             .iter()
 229             .map(|ty| {
 230                 self.replace_bound_vars_with_fresh_vars(
 231                     expr.span,
 232                     infer::FnCall,
 233                     inputs.rebind(*ty),
 234                 )
 235             })
 236             .collect();
 237
 238         // We don't want to register any extra obligations, which should be
 239         // implied by wf, but also because that would possibly result in
 240         // erroneous errors later on.
 241         let infer::InferOk { value: output, obligations: _ } =
 242             self.normalize_associated_types_in_as_infer_ok(expr.span, output);
 243
 244         if output.is_ty_var() { None } else { Some((def_id_or_name, output, inputs)) }
 245     }
 246
 247     pub fn suggest_two_fn_call(
 248         &self,
 249         err: &mut Diagnostic,
 250         lhs_expr: &'tcx hir::Expr<'tcx>,
 251         lhs_ty: Ty<'tcx>,
 252         rhs_expr: &'tcx hir::Expr<'tcx>,
 253         rhs_ty: Ty<'tcx>,
 254         can_satisfy: impl FnOnce(Ty<'tcx>, Ty<'tcx>) -> bool,
 255     ) -> bool {
 256         let Some((_, lhs_output_ty, lhs_inputs)) = self.extract_callable_info(lhs_expr, lhs_ty)
 257             else { return false; };
 258         let Some((_, rhs_output_ty, rhs_inputs)) = self.extract_callable_info(rhs_expr, rhs_ty)
 259             else { return false; };
 260
 261         if can_satisfy(lhs_output_ty, rhs_output_ty) {
 262             let mut sugg = vec![];
 263             let mut applicability = Applicability::MachineApplicable;
 264
 265             for (expr, inputs) in [(lhs_expr, lhs_inputs), (rhs_expr, rhs_inputs)] {
 266                 let (sugg_call, this_applicability) = match inputs.len() {
 267                     0 => ("".to_string(), Applicability::MachineApplicable),
 268                     1..=4 => (
 269                         inputs
 270                             .iter()
 271                             .map(|ty| {
 272                                 if ty.is_suggestable(self.tcx, false) {
 273                                     format!("/* {ty} */")
 274                                 } else {
 275                                     "/* value */".to_string()
 276                                 }
 277                             })
 278                             .collect::<Vec<_>>()
 279                             .join(", "),
 280                         Applicability::HasPlaceholders,
 281                     ),
 282                     _ => ("/* ... */".to_string(), Applicability::HasPlaceholders),
 283                 };
 284
 285                 applicability = applicability.max(this_applicability);
 286
 287                 match expr.kind {
 288                     hir::ExprKind::Call(..)
 289                     | hir::ExprKind::Path(..)
 290                     | hir::ExprKind::Index(..)
 291                     | hir::ExprKind::Lit(..) => {
 292                         sugg.extend([(expr.span.shrink_to_hi(), format!("({sugg_call})"))]);
 293                     }
 294                     hir::ExprKind::Closure { .. } => {
 295                         // Might be `{ expr } || { bool }`
 296                         applicability = Applicability::MaybeIncorrect;
 297                         sugg.extend([
 298                             (expr.span.shrink_to_lo(), "(".to_string()),
 299                             (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
 300                         ]);
 301                     }
 302                     _ => {
 303                         sugg.extend([
 304                             (expr.span.shrink_to_lo(), "(".to_string()),
 305                             (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
 306                         ]);
 307                     }
 308                 }
 309             }
 310
 311             err.multipart_suggestion_verbose(
 312                 format!("use parentheses to call these"),
 313                 sugg,
 314                 applicability,
 315             );
 316
 317             true
 318         } else {
 319             false
 320         }
 321     }
 322
 323     pub fn suggest_deref_ref_or_into(
 324         &self,
 325         err: &mut Diagnostic,
 326         expr: &hir::Expr<'tcx>,
 327         expected: Ty<'tcx>,
 328         found: Ty<'tcx>,
 329         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 330     ) -> bool {
 331         let expr = expr.peel_blocks();
 332         if let Some((sp, msg, suggestion, applicability, verbose)) =
 333             self.check_ref(expr, found, expected)
 334         {
 335             if verbose {
 336                 err.span_suggestion_verbose(sp, &msg, suggestion, applicability);
 337             } else {
 338                 err.span_suggestion(sp, &msg, suggestion, applicability);
 339             }
 340             return true;
 341         } else if self.suggest_else_fn_with_closure(err, expr, found, expected)
 342         {
 343             return true;
 344         } else if self.suggest_fn_call(err, expr, found, |output| self.can_coerce(output, expected))
 345             && let ty::FnDef(def_id, ..) = &found.kind()
 346             && let Some(sp) = self.tcx.hir().span_if_local(*def_id)
 347         {
 348             err.span_label(sp, format!("{found} defined here"));
 349             return true;
 350         } else if self.check_for_cast(err, expr, found, expected, expected_ty_expr) {
 351             return true;
 352         } else {
 353             let methods = self.get_conversion_methods(expr.span, expected, found, expr.hir_id);
 354             if !methods.is_empty() {
 355                 let mut suggestions = methods.iter()
 356                     .filter_map(|conversion_method| {
 357                         let receiver_method_ident = expr.method_ident();
 358                         if let Some(method_ident) = receiver_method_ident
 359                             && method_ident.name == conversion_method.name
 360                         {
 361                             return None // do not suggest code that is already there (#53348)
 362                         }
 363
 364                         let method_call_list = [sym::to_vec, sym::to_string];
 365                         let mut sugg = if let ExprKind::MethodCall(receiver_method, ..) = expr.kind
 366                             && receiver_method.ident.name == sym::clone
 367                             && method_call_list.contains(&conversion_method.name)
 368                             // If receiver is `.clone()` and found type has one of those methods,
 369                             // we guess that the user wants to convert from a slice type (`&[]` or `&str`)
 370                             // to an owned type (`Vec` or `String`).  These conversions clone internally,
 371                             // so we remove the user's `clone` call.
 372                         {
 373                             vec![(
 374                                 receiver_method.ident.span,
 375                                 conversion_method.name.to_string()
 376                             )]
 377                         } else if expr.precedence().order()
 378                             < ExprPrecedence::MethodCall.order()
 379                         {
 380                             vec![
 381                                 (expr.span.shrink_to_lo(), "(".to_string()),
 382                                 (expr.span.shrink_to_hi(), format!(").{}()", conversion_method.name)),
 383                             ]
 384                         } else {
 385                             vec![(expr.span.shrink_to_hi(), format!(".{}()", conversion_method.name))]
 386                         };
 387                         let struct_pat_shorthand_field = self.maybe_get_struct_pattern_shorthand_field(expr);
 388                         if let Some(name) = struct_pat_shorthand_field {
 389                             sugg.insert(
 390                                 0,
 391                                 (expr.span.shrink_to_lo(), format!("{}: ", name)),
 392                             );
 393                         }
 394                         Some(sugg)
 395                     })
 396                     .peekable();
 397                 if suggestions.peek().is_some() {
 398                     err.multipart_suggestions(
 399                         "try using a conversion method",
 400                         suggestions,
 401                         Applicability::MaybeIncorrect,
 402                     );
 403                     return true;
 404                 }
 405             } else if let ty::Adt(found_adt, found_substs) = found.kind()
 406                 && self.tcx.is_diagnostic_item(sym::Option, found_adt.did())
 407                 && let ty::Adt(expected_adt, expected_substs) = expected.kind()
 408                 && self.tcx.is_diagnostic_item(sym::Option, expected_adt.did())
 409                 && let ty::Ref(_, inner_ty, _) = expected_substs.type_at(0).kind()
 410                 && inner_ty.is_str()
 411             {
 412                 let ty = found_substs.type_at(0);
 413                 let mut peeled = ty;
 414                 let mut ref_cnt = 0;
 415                 while let ty::Ref(_, inner, _) = peeled.kind() {
 416                     peeled = *inner;
 417                     ref_cnt += 1;
 418                 }
 419                 if let ty::Adt(adt, _) = peeled.kind()
 420                     && self.tcx.is_diagnostic_item(sym::String, adt.did())
 421                 {
 422                     err.span_suggestion_verbose(
 423                         expr.span.shrink_to_hi(),
 424                         "try converting the passed type into a `&str`",
 425                         format!(".map(|x| &*{}x)", "*".repeat(ref_cnt)),
 426                         Applicability::MaybeIncorrect,
 427                     );
 428                     return true;
 429                 }
 430             }
 431         }
 432
 433         false
 434     }
 435
 436     /// When encountering the expected boxed value allocated in the stack, suggest allocating it
 437     /// in the heap by calling `Box::new()`.
 438     pub(in super::super) fn suggest_boxing_when_appropriate(
 439         &self,
 440         err: &mut Diagnostic,
 441         expr: &hir::Expr<'_>,
 442         expected: Ty<'tcx>,
 443         found: Ty<'tcx>,
 444     ) -> bool {
 445         if self.tcx.hir().is_inside_const_context(expr.hir_id) {
 446             // Do not suggest `Box::new` in const context.
 447             return false;
 448         }
 449         if !expected.is_box() || found.is_box() {
 450             return false;
 451         }
 452         let boxed_found = self.tcx.mk_box(found);
 453         if self.can_coerce(boxed_found, expected) {
 454             err.multipart_suggestion(
 455                 "store this in the heap by calling `Box::new`",
 456                 vec![
 457                     (expr.span.shrink_to_lo(), "Box::new(".to_string()),
 458                     (expr.span.shrink_to_hi(), ")".to_string()),
 459                 ],
 460                 Applicability::MachineApplicable,
 461             );
 462             err.note(
 463                 "for more on the distinction between the stack and the heap, read \
 464                  https://doc.rust-lang.org/book/ch15-01-box.html, \
 465                  https://doc.rust-lang.org/rust-by-example/std/box.html, and \
 466                  https://doc.rust-lang.org/std/boxed/index.html",
 467             );
 468             true
 469         } else {
 470             false
 471         }
 472     }
 473
 474     /// When encountering a closure that captures variables, where a FnPtr is expected,
 475     /// suggest a non-capturing closure
 476     pub(in super::super) fn suggest_no_capture_closure(
 477         &self,
 478         err: &mut Diagnostic,
 479         expected: Ty<'tcx>,
 480         found: Ty<'tcx>,
 481     ) -> bool {
 482         if let (ty::FnPtr(_), ty::Closure(def_id, _)) = (expected.kind(), found.kind()) {
 483             if let Some(upvars) = self.tcx.upvars_mentioned(*def_id) {
 484                 // Report upto four upvars being captured to reduce the amount error messages
 485                 // reported back to the user.
 486                 let spans_and_labels = upvars
 487                     .iter()
 488                     .take(4)
 489                     .map(|(var_hir_id, upvar)| {
 490                         let var_name = self.tcx.hir().name(*var_hir_id).to_string();
 491                         let msg = format!("`{}` captured here", var_name);
 492                         (upvar.span, msg)
 493                     })
 494                     .collect::<Vec<_>>();
 495
 496                 let mut multi_span: MultiSpan =
 497                     spans_and_labels.iter().map(|(sp, _)| *sp).collect::<Vec<_>>().into();
 498                 for (sp, label) in spans_and_labels {
 499                     multi_span.push_span_label(sp, label);
 500                 }
 501                 err.span_note(
 502                     multi_span,
 503                     "closures can only be coerced to `fn` types if they do not capture any variables"
 504                 );
 505                 return true;
 506             }
 507         }
 508         false
 509     }
 510
 511     /// When encountering an `impl Future` where `BoxFuture` is expected, suggest `Box::pin`.
 512     #[instrument(skip(self, err))]
 513     pub(in super::super) fn suggest_calling_boxed_future_when_appropriate(
 514         &self,
 515         err: &mut Diagnostic,
 516         expr: &hir::Expr<'_>,
 517         expected: Ty<'tcx>,
 518         found: Ty<'tcx>,
 519     ) -> bool {
 520         // Handle #68197.
 521
 522         if self.tcx.hir().is_inside_const_context(expr.hir_id) {
 523             // Do not suggest `Box::new` in const context.
 524             return false;
 525         }
 526         let pin_did = self.tcx.lang_items().pin_type();
 527         // This guards the `unwrap` and `mk_box` below.
 528         if pin_did.is_none() || self.tcx.lang_items().owned_box().is_none() {
 529             return false;
 530         }
 531         let box_found = self.tcx.mk_box(found);
 532         let pin_box_found = self.tcx.mk_lang_item(box_found, LangItem::Pin).unwrap();
 533         let pin_found = self.tcx.mk_lang_item(found, LangItem::Pin).unwrap();
 534         match expected.kind() {
 535             ty::Adt(def, _) if Some(def.did()) == pin_did => {
 536                 if self.can_coerce(pin_box_found, expected) {
 537                     debug!("can coerce {:?} to {:?}, suggesting Box::pin", pin_box_found, expected);
 538                     match found.kind() {
 539                         ty::Adt(def, _) if def.is_box() => {
 540                             err.help("use `Box::pin`");
 541                         }
 542                         _ => {
 543                             err.multipart_suggestion(
 544                                 "you need to pin and box this expression",
 545                                 vec![
 546                                     (expr.span.shrink_to_lo(), "Box::pin(".to_string()),
 547                                     (expr.span.shrink_to_hi(), ")".to_string()),
 548                                 ],
 549                                 Applicability::MaybeIncorrect,
 550                             );
 551                         }
 552                     }
 553                     true
 554                 } else if self.can_coerce(pin_found, expected) {
 555                     match found.kind() {
 556                         ty::Adt(def, _) if def.is_box() => {
 557                             err.help("use `Box::pin`");
 558                             true
 559                         }
 560                         _ => false,
 561                     }
 562                 } else {
 563                     false
 564                 }
 565             }
 566             ty::Adt(def, _) if def.is_box() && self.can_coerce(box_found, expected) => {
 567                 // Check if the parent expression is a call to Pin::new.  If it
 568                 // is and we were expecting a Box, ergo Pin<Box<expected>>, we
 569                 // can suggest Box::pin.
 570                 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 571                 let Some(Node::Expr(Expr { kind: ExprKind::Call(fn_name, _), .. })) = self.tcx.hir().find(parent) else {
 572                     return false;
 573                 };
 574                 match fn_name.kind {
 575                     ExprKind::Path(QPath::TypeRelative(
 576                         hir::Ty {
 577                             kind: TyKind::Path(QPath::Resolved(_, Path { res: recv_ty, .. })),
 578                             ..
 579                         },
 580                         method,
 581                     )) if recv_ty.opt_def_id() == pin_did && method.ident.name == sym::new => {
 582                         err.span_suggestion(
 583                             fn_name.span,
 584                             "use `Box::pin` to pin and box this expression",
 585                             "Box::pin",
 586                             Applicability::MachineApplicable,
 587                         );
 588                         true
 589                     }
 590                     _ => false,
 591                 }
 592             }
 593             _ => false,
 594         }
 595     }
 596
 597     /// A common error is to forget to add a semicolon at the end of a block, e.g.,
 598     ///
 599     /// ```compile_fail,E0308
 600     /// # fn bar_that_returns_u32() -> u32 { 4 }
 601     /// fn foo() {
 602     ///     bar_that_returns_u32()
 603     /// }
 604     /// ```
 605     ///
 606     /// This routine checks if the return expression in a block would make sense on its own as a
 607     /// statement and the return type has been left as default or has been specified as `()`. If so,
 608     /// it suggests adding a semicolon.
 609     ///
 610     /// If the expression is the expression of a closure without block (`|| expr`), a
 611     /// block is needed to be added too (`|| { expr; }`). This is denoted by `needs_block`.
 612     pub fn suggest_missing_semicolon(
 613         &self,
 614         err: &mut Diagnostic,
 615         expression: &'tcx hir::Expr<'tcx>,
 616         expected: Ty<'tcx>,
 617         needs_block: bool,
 618     ) {
 619         if expected.is_unit() {
 620             // `BlockTailExpression` only relevant if the tail expr would be
 621             // useful on its own.
 622             match expression.kind {
 623                 ExprKind::Call(..)
 624                 | ExprKind::MethodCall(..)
 625                 | ExprKind::Loop(..)
 626                 | ExprKind::If(..)
 627                 | ExprKind::Match(..)
 628                 | ExprKind::Block(..)
 629                     if expression.can_have_side_effects()
 630                         // If the expression is from an external macro, then do not suggest
 631                         // adding a semicolon, because there's nowhere to put it.
 632                         // See issue #81943.
 633                         && !in_external_macro(self.tcx.sess, expression.span) =>
 634                 {
 635                     if needs_block {
 636                         err.multipart_suggestion(
 637                             "consider using a semicolon here",
 638                             vec![
 639                                 (expression.span.shrink_to_lo(), "{ ".to_owned()),
 640                                 (expression.span.shrink_to_hi(), "; }".to_owned()),
 641                             ],
 642                             Applicability::MachineApplicable,
 643                         );
 644                     } else {
 645                         err.span_suggestion(
 646                             expression.span.shrink_to_hi(),
 647                             "consider using a semicolon here",
 648                             ";",
 649                             Applicability::MachineApplicable,
 650                         );
 651                     }
 652                 }
 653                 _ => (),
 654             }
 655         }
 656     }
 657
 658     /// A possible error is to forget to add a return type that is needed:
 659     ///
 660     /// ```compile_fail,E0308
 661     /// # fn bar_that_returns_u32() -> u32 { 4 }
 662     /// fn foo() {
 663     ///     bar_that_returns_u32()
 664     /// }
 665     /// ```
 666     ///
 667     /// This routine checks if the return type is left as default, the method is not part of an
 668     /// `impl` block and that it isn't the `main` method. If so, it suggests setting the return
 669     /// type.
 670     pub(in super::super) fn suggest_missing_return_type(
 671         &self,
 672         err: &mut Diagnostic,
 673         fn_decl: &hir::FnDecl<'_>,
 674         expected: Ty<'tcx>,
 675         found: Ty<'tcx>,
 676         can_suggest: bool,
 677         fn_id: hir::HirId,
 678     ) -> bool {
 679         let found =
 680             self.resolve_numeric_literals_with_default(self.resolve_vars_if_possible(found));
 681         // Only suggest changing the return type for methods that
 682         // haven't set a return type at all (and aren't `fn main()` or an impl).
 683         match &fn_decl.output {
 684             &hir::FnRetTy::DefaultReturn(span) if expected.is_unit() && !can_suggest => {
 685                 // `fn main()` must return `()`, do not suggest changing return type
 686                 err.subdiagnostic(ExpectedReturnTypeLabel::Unit { span });
 687                 return true;
 688             }
 689             &hir::FnRetTy::DefaultReturn(span) if expected.is_unit() => {
 690                 if found.is_suggestable(self.tcx, false) {
 691                     err.subdiagnostic(AddReturnTypeSuggestion::Add { span, found: found.to_string() });
 692                     return true;
 693                 } else if let ty::Closure(_, substs) = found.kind()
 694                     // FIXME(compiler-errors): Get better at printing binders...
 695                     && let closure = substs.as_closure()
 696                     && closure.sig().is_suggestable(self.tcx, false)
 697                 {
 698                     err.subdiagnostic(AddReturnTypeSuggestion::Add { span, found: closure.print_as_impl_trait().to_string() });
 699                     return true;
 700                 } else {
 701                     // FIXME: if `found` could be `impl Iterator` we should suggest that.
 702                     err.subdiagnostic(AddReturnTypeSuggestion::MissingHere { span });
 703                     return true
 704                 }
 705             }
 706             &hir::FnRetTy::Return(ref ty) => {
 707                 // Only point to return type if the expected type is the return type, as if they
 708                 // are not, the expectation must have been caused by something else.
 709                 debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
 710                 let span = ty.span;
 711                 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
 712                 debug!("suggest_missing_return_type: return type {:?}", ty);
 713                 debug!("suggest_missing_return_type: expected type {:?}", ty);
 714                 let bound_vars = self.tcx.late_bound_vars(fn_id);
 715                 let ty = Binder::bind_with_vars(ty, bound_vars);
 716                 let ty = self.normalize_associated_types_in(span, ty);
 717                 let ty = self.tcx.erase_late_bound_regions(ty);
 718                 if self.can_coerce(expected, ty) {
 719                     err.subdiagnostic(ExpectedReturnTypeLabel::Other { span, expected });
 720                     self.try_suggest_return_impl_trait(err, expected, ty, fn_id);
 721                     return true;
 722                 }
 723             }
 724             _ => {}
 725         }
 726         false
 727     }
 728
 729     /// check whether the return type is a generic type with a trait bound
 730     /// only suggest this if the generic param is not present in the arguments
 731     /// if this is true, hint them towards changing the return type to `impl Trait`
 732     /// ```compile_fail,E0308
 733     /// fn cant_name_it<T: Fn() -> u32>() -> T {
 734     ///     || 3
 735     /// }
 736     /// ```
 737     fn try_suggest_return_impl_trait(
 738         &self,
 739         err: &mut Diagnostic,
 740         expected: Ty<'tcx>,
 741         found: Ty<'tcx>,
 742         fn_id: hir::HirId,
 743     ) {
 744         // Only apply the suggestion if:
 745         //  - the return type is a generic parameter
 746         //  - the generic param is not used as a fn param
 747         //  - the generic param has at least one bound
 748         //  - the generic param doesn't appear in any other bounds where it's not the Self type
 749         // Suggest:
 750         //  - Changing the return type to be `impl <all bounds>`
 751
 752         debug!("try_suggest_return_impl_trait, expected = {:?}, found = {:?}", expected, found);
 753
 754         let ty::Param(expected_ty_as_param) = expected.kind() else { return };
 755
 756         let fn_node = self.tcx.hir().find(fn_id);
 757
 758         let Some(hir::Node::Item(hir::Item {
 759             kind:
 760                 hir::ItemKind::Fn(
 761                     hir::FnSig { decl: hir::FnDecl { inputs: fn_parameters, output: fn_return, .. }, .. },
 762                     hir::Generics { params, predicates, .. },
 763                     _body_id,
 764                 ),
 765             ..
 766         })) = fn_node else { return };
 767
 768         if params.get(expected_ty_as_param.index as usize).is_none() {
 769             return;
 770         };
 771
 772         // get all where BoundPredicates here, because they are used in to cases below
 773         let where_predicates = predicates
 774             .iter()
 775             .filter_map(|p| match p {
 776                 WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
 777                     bounds,
 778                     bounded_ty,
 779                     ..
 780                 }) => {
 781                     // FIXME: Maybe these calls to `ast_ty_to_ty` can be removed (and the ones below)
 782                     let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, bounded_ty);
 783                     Some((ty, bounds))
 784                 }
 785                 _ => None,
 786             })
 787             .map(|(ty, bounds)| match ty.kind() {
 788                 ty::Param(param_ty) if param_ty == expected_ty_as_param => Ok(Some(bounds)),
 789                 // check whether there is any predicate that contains our `T`, like `Option<T>: Send`
 790                 _ => match ty.contains(expected) {
 791                     true => Err(()),
 792                     false => Ok(None),
 793                 },
 794             })
 795             .collect::<Result<Vec<_>, _>>();
 796
 797         let Ok(where_predicates) = where_predicates else { return };
 798
 799         // now get all predicates in the same types as the where bounds, so we can chain them
 800         let predicates_from_where =
 801             where_predicates.iter().flatten().flat_map(|bounds| bounds.iter());
 802
 803         // extract all bounds from the source code using their spans
 804         let all_matching_bounds_strs = predicates_from_where
 805             .filter_map(|bound| match bound {
 806                 GenericBound::Trait(_, _) => {
 807                     self.tcx.sess.source_map().span_to_snippet(bound.span()).ok()
 808                 }
 809                 _ => None,
 810             })
 811             .collect::<Vec<String>>();
 812
 813         if all_matching_bounds_strs.len() == 0 {
 814             return;
 815         }
 816
 817         let all_bounds_str = all_matching_bounds_strs.join(" + ");
 818
 819         let ty_param_used_in_fn_params = fn_parameters.iter().any(|param| {
 820                 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, param);
 821                 matches!(ty.kind(), ty::Param(fn_param_ty_param) if expected_ty_as_param == fn_param_ty_param)
 822             });
 823
 824         if ty_param_used_in_fn_params {
 825             return;
 826         }
 827
 828         err.span_suggestion(
 829             fn_return.span(),
 830             "consider using an impl return type",
 831             format!("impl {}", all_bounds_str),
 832             Applicability::MaybeIncorrect,
 833         );
 834     }
 835
 836     pub(in super::super) fn suggest_missing_break_or_return_expr(
 837         &self,
 838         err: &mut Diagnostic,
 839         expr: &'tcx hir::Expr<'tcx>,
 840         fn_decl: &hir::FnDecl<'_>,
 841         expected: Ty<'tcx>,
 842         found: Ty<'tcx>,
 843         id: hir::HirId,
 844         fn_id: hir::HirId,
 845     ) {
 846         if !expected.is_unit() {
 847             return;
 848         }
 849         let found = self.resolve_vars_with_obligations(found);
 850
 851         let in_loop = self.is_loop(id)
 852             || self.tcx.hir().parent_iter(id).any(|(parent_id, _)| self.is_loop(parent_id));
 853
 854         let in_local_statement = self.is_local_statement(id)
 855             || self
 856                 .tcx
 857                 .hir()
 858                 .parent_iter(id)
 859                 .any(|(parent_id, _)| self.is_local_statement(parent_id));
 860
 861         if in_loop && in_local_statement {
 862             err.multipart_suggestion(
 863                 "you might have meant to break the loop with this value",
 864                 vec![
 865                     (expr.span.shrink_to_lo(), "break ".to_string()),
 866                     (expr.span.shrink_to_hi(), ";".to_string()),
 867                 ],
 868                 Applicability::MaybeIncorrect,
 869             );
 870             return;
 871         }
 872
 873         if let hir::FnRetTy::Return(ty) = fn_decl.output {
 874             let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
 875             let bound_vars = self.tcx.late_bound_vars(fn_id);
 876             let ty = self.tcx.erase_late_bound_regions(Binder::bind_with_vars(ty, bound_vars));
 877             let ty = self.normalize_associated_types_in(expr.span, ty);
 878             let ty = match self.tcx.asyncness(fn_id.owner) {
 879                 hir::IsAsync::Async => {
 880                     let infcx = self.tcx.infer_ctxt().build();
 881                     infcx
 882                         .get_impl_future_output_ty(ty)
 883                         .unwrap_or_else(|| {
 884                             span_bug!(
 885                                 fn_decl.output.span(),
 886                                 "failed to get output type of async function"
 887                             )
 888                         })
 889                         .skip_binder()
 890                 }
 891                 hir::IsAsync::NotAsync => ty,
 892             };
 893             if self.can_coerce(found, ty) {
 894                 err.multipart_suggestion(
 895                     "you might have meant to return this value",
 896                     vec![
 897                         (expr.span.shrink_to_lo(), "return ".to_string()),
 898                         (expr.span.shrink_to_hi(), ";".to_string()),
 899                     ],
 900                     Applicability::MaybeIncorrect,
 901                 );
 902             }
 903         }
 904     }
 905
 906     pub(in super::super) fn suggest_missing_parentheses(
 907         &self,
 908         err: &mut Diagnostic,
 909         expr: &hir::Expr<'_>,
 910     ) -> bool {
 911         let sp = self.tcx.sess.source_map().start_point(expr.span);
 912         if let Some(sp) = self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp) {
 913             // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
 914             err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
 915             true
 916         } else {
 917             false
 918         }
 919     }
 920
 921     /// Given an expression type mismatch, peel any `&` expressions until we get to
 922     /// a block expression, and then suggest replacing the braces with square braces
 923     /// if it was possibly mistaken array syntax.
 924     pub(crate) fn suggest_block_to_brackets_peeling_refs(
 925         &self,
 926         diag: &mut Diagnostic,
 927         mut expr: &hir::Expr<'_>,
 928         mut expr_ty: Ty<'tcx>,
 929         mut expected_ty: Ty<'tcx>,
 930     ) -> bool {
 931         loop {
 932             match (&expr.kind, expr_ty.kind(), expected_ty.kind()) {
 933                 (
 934                     hir::ExprKind::AddrOf(_, _, inner_expr),
 935                     ty::Ref(_, inner_expr_ty, _),
 936                     ty::Ref(_, inner_expected_ty, _),
 937                 ) => {
 938                     expr = *inner_expr;
 939                     expr_ty = *inner_expr_ty;
 940                     expected_ty = *inner_expected_ty;
 941                 }
 942                 (hir::ExprKind::Block(blk, _), _, _) => {
 943                     self.suggest_block_to_brackets(diag, *blk, expr_ty, expected_ty);
 944                     break true;
 945                 }
 946                 _ => break false,
 947             }
 948         }
 949     }
 950
 951     pub(crate) fn suggest_copied_or_cloned(
 952         &self,
 953         diag: &mut Diagnostic,
 954         expr: &hir::Expr<'_>,
 955         expr_ty: Ty<'tcx>,
 956         expected_ty: Ty<'tcx>,
 957     ) -> bool {
 958         let ty::Adt(adt_def, substs) = expr_ty.kind() else { return false; };
 959         let ty::Adt(expected_adt_def, expected_substs) = expected_ty.kind() else { return false; };
 960         if adt_def != expected_adt_def {
 961             return false;
 962         }
 963
 964         let mut suggest_copied_or_cloned = || {
 965             let expr_inner_ty = substs.type_at(0);
 966             let expected_inner_ty = expected_substs.type_at(0);
 967             if let ty::Ref(_, ty, hir::Mutability::Not) = expr_inner_ty.kind()
 968                 && self.can_eq(self.param_env, *ty, expected_inner_ty).is_ok()
 969             {
 970                 let def_path = self.tcx.def_path_str(adt_def.did());
 971                 if self.type_is_copy_modulo_regions(self.param_env, *ty, expr.span) {
 972                     diag.span_suggestion_verbose(
 973                         expr.span.shrink_to_hi(),
 974                         format!(
 975                             "use `{def_path}::copied` to copy the value inside the `{def_path}`"
 976                         ),
 977                         ".copied()",
 978                         Applicability::MachineApplicable,
 979                     );
 980                     return true;
 981                 } else if let Some(clone_did) = self.tcx.lang_items().clone_trait()
 982                     && rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions(
 983                         self,
 984                         self.param_env,
 985                         *ty,
 986                         clone_did,
 987                         expr.span
 988                     )
 989                 {
 990                     diag.span_suggestion_verbose(
 991                         expr.span.shrink_to_hi(),
 992                         format!(
 993                             "use `{def_path}::cloned` to clone the value inside the `{def_path}`"
 994                         ),
 995                         ".cloned()",
 996                         Applicability::MachineApplicable,
 997                     );
 998                     return true;
 999                 }
1000             }
1001             false
1002         };
1003
1004         if let Some(result_did) = self.tcx.get_diagnostic_item(sym::Result)
1005             && adt_def.did() == result_did
1006             // Check that the error types are equal
1007             && self.can_eq(self.param_env, substs.type_at(1), expected_substs.type_at(1)).is_ok()
1008         {
1009             return suggest_copied_or_cloned();
1010         } else if let Some(option_did) = self.tcx.get_diagnostic_item(sym::Option)
1011             && adt_def.did() == option_did
1012         {
1013             return suggest_copied_or_cloned();
1014         }
1015
1016         false
1017     }
1018
1019     pub(crate) fn suggest_into(
1020         &self,
1021         diag: &mut Diagnostic,
1022         expr: &hir::Expr<'_>,
1023         expr_ty: Ty<'tcx>,
1024         expected_ty: Ty<'tcx>,
1025     ) -> bool {
1026         let expr = expr.peel_blocks();
1027
1028         // We have better suggestions for scalar interconversions...
1029         if expr_ty.is_scalar() && expected_ty.is_scalar() {
1030             return false;
1031         }
1032
1033         // Don't suggest turning a block into another type (e.g. `{}.into()`)
1034         if matches!(expr.kind, hir::ExprKind::Block(..)) {
1035             return false;
1036         }
1037
1038         // We'll later suggest `.as_ref` when noting the type error,
1039         // so skip if we will suggest that instead.
1040         if self.err_ctxt().should_suggest_as_ref(expected_ty, expr_ty).is_some() {
1041             return false;
1042         }
1043
1044         if let Some(into_def_id) = self.tcx.get_diagnostic_item(sym::Into)
1045             && self.predicate_must_hold_modulo_regions(&traits::Obligation::new(
1046                 self.misc(expr.span),
1047                 self.param_env,
1048                 ty::Binder::dummy(ty::TraitRef {
1049                     def_id: into_def_id,
1050                     substs: self.tcx.mk_substs_trait(expr_ty, &[expected_ty.into()]),
1051                 })
1052                 .to_poly_trait_predicate()
1053                 .to_predicate(self.tcx),
1054             ))
1055         {
1056             let sugg = if expr.precedence().order() >= PREC_POSTFIX {
1057                 vec![(expr.span.shrink_to_hi(), ".into()".to_owned())]
1058             } else {
1059                 vec![(expr.span.shrink_to_lo(), "(".to_owned()), (expr.span.shrink_to_hi(), ").into()".to_owned())]
1060             };
1061             diag.multipart_suggestion(
1062                 format!("call `Into::into` on this expression to convert `{expr_ty}` into `{expected_ty}`"),
1063                 sugg,
1064                 Applicability::MaybeIncorrect
1065             );
1066             return true;
1067         }
1068
1069         false
1070     }
1071
1072     /// Suggest wrapping the block in square brackets instead of curly braces
1073     /// in case the block was mistaken array syntax, e.g. `{ 1 }` -> `[ 1 ]`.
1074     pub(crate) fn suggest_block_to_brackets(
1075         &self,
1076         diag: &mut Diagnostic,
1077         blk: &hir::Block<'_>,
1078         blk_ty: Ty<'tcx>,
1079         expected_ty: Ty<'tcx>,
1080     ) {
1081         if let ty::Slice(elem_ty) | ty::Array(elem_ty, _) = expected_ty.kind() {
1082             if self.can_coerce(blk_ty, *elem_ty)
1083                 && blk.stmts.is_empty()
1084                 && blk.rules == hir::BlockCheckMode::DefaultBlock
1085             {
1086                 let source_map = self.tcx.sess.source_map();
1087                 if let Ok(snippet) = source_map.span_to_snippet(blk.span) {
1088                     if snippet.starts_with('{') && snippet.ends_with('}') {
1089                         diag.multipart_suggestion_verbose(
1090                             "to create an array, use square brackets instead of curly braces",
1091                             vec![
1092                                 (
1093                                     blk.span
1094                                         .shrink_to_lo()
1095                                         .with_hi(rustc_span::BytePos(blk.span.lo().0 + 1)),
1096                                     "[".to_string(),
1097                                 ),
1098                                 (
1099                                     blk.span
1100                                         .shrink_to_hi()
1101                                         .with_lo(rustc_span::BytePos(blk.span.hi().0 - 1)),
1102                                     "]".to_string(),
1103                                 ),
1104                             ],
1105                             Applicability::MachineApplicable,
1106                         );
1107                     }
1108                 }
1109             }
1110         }
1111     }
1112
1113     fn is_loop(&self, id: hir::HirId) -> bool {
1114         let node = self.tcx.hir().get(id);
1115         matches!(node, Node::Expr(Expr { kind: ExprKind::Loop(..), .. }))
1116     }
1117
1118     fn is_local_statement(&self, id: hir::HirId) -> bool {
1119         let node = self.tcx.hir().get(id);
1120         matches!(node, Node::Stmt(Stmt { kind: StmtKind::Local(..), .. }))
1121     }
1122
1123     /// Suggest that `&T` was cloned instead of `T` because `T` does not implement `Clone`,
1124     /// which is a side-effect of autoref.
1125     pub(crate) fn note_type_is_not_clone(
1126         &self,
1127         diag: &mut Diagnostic,
1128         expected_ty: Ty<'tcx>,
1129         found_ty: Ty<'tcx>,
1130         expr: &hir::Expr<'_>,
1131     ) {
1132         let hir::ExprKind::MethodCall(segment, callee_expr, &[], _) = expr.kind else { return; };
1133         let Some(clone_trait_did) = self.tcx.lang_items().clone_trait() else { return; };
1134         let ty::Ref(_, pointee_ty, _) = found_ty.kind() else { return };
1135         let results = self.typeck_results.borrow();
1136         // First, look for a `Clone::clone` call
1137         if segment.ident.name == sym::clone
1138             && results.type_dependent_def_id(expr.hir_id).map_or(
1139                 false,
1140                 |did| {
1141                     let assoc_item = self.tcx.associated_item(did);
1142                     assoc_item.container == ty::AssocItemContainer::TraitContainer
1143                         && assoc_item.container_id(self.tcx) == clone_trait_did
1144                 },
1145             )
1146             // If that clone call hasn't already dereferenced the self type (i.e. don't give this
1147             // diagnostic in cases where we have `(&&T).clone()` and we expect `T`).
1148             && !results.expr_adjustments(callee_expr).iter().any(|adj| matches!(adj.kind, ty::adjustment::Adjust::Deref(..)))
1149             // Check that we're in fact trying to clone into the expected type
1150             && self.can_coerce(*pointee_ty, expected_ty)
1151             // And the expected type doesn't implement `Clone`
1152             && !self.predicate_must_hold_considering_regions(&traits::Obligation {
1153                 cause: traits::ObligationCause::dummy(),
1154                 param_env: self.param_env,
1155                 recursion_depth: 0,
1156                 predicate: ty::Binder::dummy(ty::TraitRef {
1157                     def_id: clone_trait_did,
1158                     substs: self.tcx.mk_substs([expected_ty.into()].iter()),
1159                 })
1160                 .without_const()
1161                 .to_predicate(self.tcx),
1162             })
1163         {
1164             diag.span_note(
1165                 callee_expr.span,
1166                 &format!(
1167                     "`{expected_ty}` does not implement `Clone`, so `{found_ty}` was cloned instead"
1168                 ),
1169             );
1170         }
1171     }
1172
1173     /// A common error is to add an extra semicolon:
1174     ///
1175     /// ```compile_fail,E0308
1176     /// fn foo() -> usize {
1177     ///     22;
1178     /// }
1179     /// ```
1180     ///
1181     /// This routine checks if the final statement in a block is an
1182     /// expression with an explicit semicolon whose type is compatible
1183     /// with `expected_ty`. If so, it suggests removing the semicolon.
1184     pub(crate) fn consider_removing_semicolon(
1185         &self,
1186         blk: &'tcx hir::Block<'tcx>,
1187         expected_ty: Ty<'tcx>,
1188         err: &mut Diagnostic,
1189     ) -> bool {
1190         if let Some((span_semi, boxed)) = self.err_ctxt().could_remove_semicolon(blk, expected_ty) {
1191             if let StatementAsExpression::NeedsBoxing = boxed {
1192                 err.span_suggestion_verbose(
1193                     span_semi,
1194                     "consider removing this semicolon and boxing the expression",
1195                     "",
1196                     Applicability::HasPlaceholders,
1197                 );
1198             } else {
1199                 err.span_suggestion_short(
1200                     span_semi,
1201                     "remove this semicolon to return this value",
1202                     "",
1203                     Applicability::MachineApplicable,
1204                 );
1205             }
1206             true
1207         } else {
1208             false
1209         }
1210     }
1211 }
1212
1213 pub enum DefIdOrName {
1214     DefId(DefId),
1215     Name(&'static str),
1216 }