compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

   1 use super::FnCtxt;
   2
   3 use crate::errors::{AddReturnTypeSuggestion, ExpectedReturnTypeLabel};
   4 use crate::method::probe::{IsSuggestion, Mode, ProbeScope};
   5 use rustc_ast::util::parser::{ExprPrecedence, PREC_POSTFIX};
   6 use rustc_errors::{Applicability, Diagnostic, MultiSpan};
   7 use rustc_hir as hir;
   8 use rustc_hir::def::{CtorOf, DefKind};
   9 use rustc_hir::lang_items::LangItem;
  10 use rustc_hir::{
  11     Expr, ExprKind, GenericBound, Node, Path, QPath, Stmt, StmtKind, TyKind, WherePredicate,
  12 };
  13 use rustc_hir_analysis::astconv::AstConv;
  14 use rustc_infer::infer;
  15 use rustc_infer::traits::{self, StatementAsExpression};
  16 use rustc_middle::lint::in_external_macro;
  17 use rustc_middle::ty::{
  18     self, suggest_constraining_type_params, Binder, DefIdTree, IsSuggestable, ToPredicate, Ty,
  19     TypeVisitable,
  20 };
  21 use rustc_session::errors::ExprParenthesesNeeded;
  22 use rustc_span::source_map::Spanned;
  23 use rustc_span::symbol::{sym, Ident};
  24 use rustc_span::{Span, Symbol};
  25 use rustc_trait_selection::infer::InferCtxtExt;
  26 use rustc_trait_selection::traits::error_reporting::DefIdOrName;
  27 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
  28 use rustc_trait_selection::traits::NormalizeExt;
  29
  30 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  31     pub(crate) fn body_fn_sig(&self) -> Option<ty::FnSig<'tcx>> {
  32         self.typeck_results
  33             .borrow()
  34             .liberated_fn_sigs()
  35             .get(self.tcx.hir().get_parent_node(self.body_id))
  36             .copied()
  37     }
  38
  39     pub(in super::super) fn suggest_semicolon_at_end(&self, span: Span, err: &mut Diagnostic) {
  40         // This suggestion is incorrect for
  41         // fn foo() -> bool { match () { () => true } || match () { () => true } }
  42         err.span_suggestion_short(
  43             span.shrink_to_hi(),
  44             "consider using a semicolon here",
  45             ";",
  46             Applicability::MaybeIncorrect,
  47         );
  48     }
  49
  50     /// On implicit return expressions with mismatched types, provides the following suggestions:
  51     ///
  52     /// - Points out the method's return type as the reason for the expected type.
  53     /// - Possible missing semicolon.
  54     /// - Possible missing return type if the return type is the default, and not `fn main()`.
  55     pub fn suggest_mismatched_types_on_tail(
  56         &self,
  57         err: &mut Diagnostic,
  58         expr: &'tcx hir::Expr<'tcx>,
  59         expected: Ty<'tcx>,
  60         found: Ty<'tcx>,
  61         blk_id: hir::HirId,
  62     ) -> bool {
  63         let expr = expr.peel_drop_temps();
  64         self.suggest_missing_semicolon(err, expr, expected, false);
  65         let mut pointing_at_return_type = false;
  66         if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
  67             let fn_id = self.tcx.hir().get_return_block(blk_id).unwrap();
  68             pointing_at_return_type = self.suggest_missing_return_type(
  69                 err,
  70                 &fn_decl,
  71                 expected,
  72                 found,
  73                 can_suggest,
  74                 fn_id,
  75             );
  76             self.suggest_missing_break_or_return_expr(
  77                 err, expr, &fn_decl, expected, found, blk_id, fn_id,
  78             );
  79         }
  80         pointing_at_return_type
  81     }
  82
  83     /// When encountering an fn-like type, try accessing the output of the type
  84     /// and suggesting calling it if it satisfies a predicate (i.e. if the
  85     /// output has a method or a field):
  86     /// ```compile_fail,E0308
  87     /// fn foo(x: usize) -> usize { x }
  88     /// let x: usize = foo;  // suggest calling the `foo` function: `foo(42)`
  89     /// ```
  90     pub(crate) fn suggest_fn_call(
  91         &self,
  92         err: &mut Diagnostic,
  93         expr: &hir::Expr<'_>,
  94         found: Ty<'tcx>,
  95         can_satisfy: impl FnOnce(Ty<'tcx>) -> bool,
  96     ) -> bool {
  97         let Some((def_id_or_name, output, inputs)) = self.extract_callable_info(expr, found)
  98             else { return false; };
  99         if can_satisfy(output) {
 100             let (sugg_call, mut applicability) = match inputs.len() {
 101                 0 => ("".to_string(), Applicability::MachineApplicable),
 102                 1..=4 => (
 103                     inputs
 104                         .iter()
 105                         .map(|ty| {
 106                             if ty.is_suggestable(self.tcx, false) {
 107                                 format!("/* {ty} */")
 108                             } else {
 109                                 "/* value */".to_string()
 110                             }
 111                         })
 112                         .collect::<Vec<_>>()
 113                         .join(", "),
 114                     Applicability::HasPlaceholders,
 115                 ),
 116                 _ => ("/* ... */".to_string(), Applicability::HasPlaceholders),
 117             };
 118
 119             let msg = match def_id_or_name {
 120                 DefIdOrName::DefId(def_id) => match self.tcx.def_kind(def_id) {
 121                     DefKind::Ctor(CtorOf::Struct, _) => "construct this tuple struct".to_string(),
 122                     DefKind::Ctor(CtorOf::Variant, _) => "construct this tuple variant".to_string(),
 123                     kind => format!("call this {}", kind.descr(def_id)),
 124                 },
 125                 DefIdOrName::Name(name) => format!("call this {name}"),
 126             };
 127
 128             let sugg = match expr.kind {
 129                 hir::ExprKind::Call(..)
 130                 | hir::ExprKind::Path(..)
 131                 | hir::ExprKind::Index(..)
 132                 | hir::ExprKind::Lit(..) => {
 133                     vec![(expr.span.shrink_to_hi(), format!("({sugg_call})"))]
 134                 }
 135                 hir::ExprKind::Closure { .. } => {
 136                     // Might be `{ expr } || { bool }`
 137                     applicability = Applicability::MaybeIncorrect;
 138                     vec![
 139                         (expr.span.shrink_to_lo(), "(".to_string()),
 140                         (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
 141                     ]
 142                 }
 143                 _ => {
 144                     vec![
 145                         (expr.span.shrink_to_lo(), "(".to_string()),
 146                         (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
 147                     ]
 148                 }
 149             };
 150
 151             err.multipart_suggestion_verbose(
 152                 format!("use parentheses to {msg}"),
 153                 sugg,
 154                 applicability,
 155             );
 156             return true;
 157         }
 158         false
 159     }
 160
 161     /// Extracts information about a callable type for diagnostics. This is a
 162     /// heuristic -- it doesn't necessarily mean that a type is always callable,
 163     /// because the callable type must also be well-formed to be called.
 164     pub(in super::super) fn extract_callable_info(
 165         &self,
 166         expr: &Expr<'_>,
 167         found: Ty<'tcx>,
 168     ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)> {
 169         // Autoderef is useful here because sometimes we box callables, etc.
 170         let Some((def_id_or_name, output, inputs)) = self.autoderef(expr.span, found).silence_errors().find_map(|(found, _)| {
 171             match *found.kind() {
 172                 ty::FnPtr(fn_sig) =>
 173                     Some((DefIdOrName::Name("function pointer"), fn_sig.output(), fn_sig.inputs())),
 174                 ty::FnDef(def_id, _) => {
 175                     let fn_sig = found.fn_sig(self.tcx);
 176                     Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs()))
 177                 }
 178                 ty::Closure(def_id, substs) => {
 179                     let fn_sig = substs.as_closure().sig();
 180                     Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs().map_bound(|inputs| &inputs[1..])))
 181                 }
 182                 ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
 183                     self.tcx.bound_item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
 184                         if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
 185                         && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
 186                         // args tuple will always be substs[1]
 187                         && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
 188                         {
 189                             Some((
 190                                 DefIdOrName::DefId(def_id),
 191                                 pred.kind().rebind(proj.term.ty().unwrap()),
 192                                 pred.kind().rebind(args.as_slice()),
 193                             ))
 194                         } else {
 195                             None
 196                         }
 197                     })
 198                 }
 199                 ty::Dynamic(data, _, ty::Dyn) => {
 200                     data.iter().find_map(|pred| {
 201                         if let ty::ExistentialPredicate::Projection(proj) = pred.skip_binder()
 202                         && Some(proj.def_id) == self.tcx.lang_items().fn_once_output()
 203                         // for existential projection, substs are shifted over by 1
 204                         && let ty::Tuple(args) = proj.substs.type_at(0).kind()
 205                         {
 206                             Some((
 207                                 DefIdOrName::Name("trait object"),
 208                                 pred.rebind(proj.term.ty().unwrap()),
 209                                 pred.rebind(args.as_slice()),
 210                             ))
 211                         } else {
 212                             None
 213                         }
 214                     })
 215                 }
 216                 ty::Param(param) => {
 217                     let def_id = self.tcx.generics_of(self.body_id.owner).type_param(&param, self.tcx).def_id;
 218                     self.tcx.predicates_of(self.body_id.owner).predicates.iter().find_map(|(pred, _)| {
 219                         if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
 220                         && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
 221                         && proj.projection_ty.self_ty() == found
 222                         // args tuple will always be substs[1]
 223                         && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
 224                         {
 225                             Some((
 226                                 DefIdOrName::DefId(def_id),
 227                                 pred.kind().rebind(proj.term.ty().unwrap()),
 228                                 pred.kind().rebind(args.as_slice()),
 229                             ))
 230                         } else {
 231                             None
 232                         }
 233                     })
 234                 }
 235                 _ => None,
 236             }
 237         }) else { return None; };
 238
 239         let output = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, output);
 240         let inputs = inputs
 241             .skip_binder()
 242             .iter()
 243             .map(|ty| {
 244                 self.replace_bound_vars_with_fresh_vars(
 245                     expr.span,
 246                     infer::FnCall,
 247                     inputs.rebind(*ty),
 248                 )
 249             })
 250             .collect();
 251
 252         // We don't want to register any extra obligations, which should be
 253         // implied by wf, but also because that would possibly result in
 254         // erroneous errors later on.
 255         let infer::InferOk { value: output, obligations: _ } =
 256             self.at(&self.misc(expr.span), self.param_env).normalize(output);
 257
 258         if output.is_ty_var() { None } else { Some((def_id_or_name, output, inputs)) }
 259     }
 260
 261     pub fn suggest_two_fn_call(
 262         &self,
 263         err: &mut Diagnostic,
 264         lhs_expr: &'tcx hir::Expr<'tcx>,
 265         lhs_ty: Ty<'tcx>,
 266         rhs_expr: &'tcx hir::Expr<'tcx>,
 267         rhs_ty: Ty<'tcx>,
 268         can_satisfy: impl FnOnce(Ty<'tcx>, Ty<'tcx>) -> bool,
 269     ) -> bool {
 270         let Some((_, lhs_output_ty, lhs_inputs)) = self.extract_callable_info(lhs_expr, lhs_ty)
 271             else { return false; };
 272         let Some((_, rhs_output_ty, rhs_inputs)) = self.extract_callable_info(rhs_expr, rhs_ty)
 273             else { return false; };
 274
 275         if can_satisfy(lhs_output_ty, rhs_output_ty) {
 276             let mut sugg = vec![];
 277             let mut applicability = Applicability::MachineApplicable;
 278
 279             for (expr, inputs) in [(lhs_expr, lhs_inputs), (rhs_expr, rhs_inputs)] {
 280                 let (sugg_call, this_applicability) = match inputs.len() {
 281                     0 => ("".to_string(), Applicability::MachineApplicable),
 282                     1..=4 => (
 283                         inputs
 284                             .iter()
 285                             .map(|ty| {
 286                                 if ty.is_suggestable(self.tcx, false) {
 287                                     format!("/* {ty} */")
 288                                 } else {
 289                                     "/* value */".to_string()
 290                                 }
 291                             })
 292                             .collect::<Vec<_>>()
 293                             .join(", "),
 294                         Applicability::HasPlaceholders,
 295                     ),
 296                     _ => ("/* ... */".to_string(), Applicability::HasPlaceholders),
 297                 };
 298
 299                 applicability = applicability.max(this_applicability);
 300
 301                 match expr.kind {
 302                     hir::ExprKind::Call(..)
 303                     | hir::ExprKind::Path(..)
 304                     | hir::ExprKind::Index(..)
 305                     | hir::ExprKind::Lit(..) => {
 306                         sugg.extend([(expr.span.shrink_to_hi(), format!("({sugg_call})"))]);
 307                     }
 308                     hir::ExprKind::Closure { .. } => {
 309                         // Might be `{ expr } || { bool }`
 310                         applicability = Applicability::MaybeIncorrect;
 311                         sugg.extend([
 312                             (expr.span.shrink_to_lo(), "(".to_string()),
 313                             (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
 314                         ]);
 315                     }
 316                     _ => {
 317                         sugg.extend([
 318                             (expr.span.shrink_to_lo(), "(".to_string()),
 319                             (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
 320                         ]);
 321                     }
 322                 }
 323             }
 324
 325             err.multipart_suggestion_verbose("use parentheses to call these", sugg, applicability);
 326
 327             true
 328         } else {
 329             false
 330         }
 331     }
 332
 333     pub fn suggest_remove_last_method_call(
 334         &self,
 335         err: &mut Diagnostic,
 336         expr: &hir::Expr<'tcx>,
 337         expected: Ty<'tcx>,
 338     ) -> bool {
 339         if let hir::ExprKind::MethodCall(hir::PathSegment { ident: method, .. }, recv_expr, &[], _) = expr.kind &&
 340             let Some(recv_ty) = self.typeck_results.borrow().expr_ty_opt(recv_expr) &&
 341             self.can_coerce(recv_ty, expected) {
 342                 let span = if let Some(recv_span) = recv_expr.span.find_ancestor_inside(expr.span) {
 343                     expr.span.with_lo(recv_span.hi())
 344                 } else {
 345                     expr.span.with_lo(method.span.lo() - rustc_span::BytePos(1))
 346                 };
 347                 err.span_suggestion_verbose(
 348                     span,
 349                     "try removing the method call",
 350                     "",
 351                     Applicability::MachineApplicable,
 352                 );
 353                 return true;
 354             }
 355         false
 356     }
 357
 358     pub fn suggest_deref_ref_or_into(
 359         &self,
 360         err: &mut Diagnostic,
 361         expr: &hir::Expr<'tcx>,
 362         expected: Ty<'tcx>,
 363         found: Ty<'tcx>,
 364         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 365     ) -> bool {
 366         let expr = expr.peel_blocks();
 367         if let Some((sp, msg, suggestion, applicability, verbose, annotation)) =
 368             self.check_ref(expr, found, expected)
 369         {
 370             if verbose {
 371                 err.span_suggestion_verbose(sp, &msg, suggestion, applicability);
 372             } else {
 373                 err.span_suggestion(sp, &msg, suggestion, applicability);
 374             }
 375             if annotation {
 376                 let suggest_annotation = match expr.peel_drop_temps().kind {
 377                     hir::ExprKind::AddrOf(hir::BorrowKind::Ref, mutbl, _) => mutbl.ref_prefix_str(),
 378                     _ => return true,
 379                 };
 380                 let mut tuple_indexes = Vec::new();
 381                 let mut expr_id = expr.hir_id;
 382                 for (parent_id, node) in self.tcx.hir().parent_iter(expr.hir_id) {
 383                     match node {
 384                         Node::Expr(&Expr { kind: ExprKind::Tup(subs), .. }) => {
 385                             tuple_indexes.push(
 386                                 subs.iter()
 387                                     .enumerate()
 388                                     .find(|(_, sub_expr)| sub_expr.hir_id == expr_id)
 389                                     .unwrap()
 390                                     .0,
 391                             );
 392                             expr_id = parent_id;
 393                         }
 394                         Node::Local(local) => {
 395                             if let Some(mut ty) = local.ty {
 396                                 while let Some(index) = tuple_indexes.pop() {
 397                                     match ty.kind {
 398                                         TyKind::Tup(tys) => ty = &tys[index],
 399                                         _ => return true,
 400                                     }
 401                                 }
 402                                 let annotation_span = ty.span;
 403                                 err.span_suggestion(
 404                                     annotation_span.with_hi(annotation_span.lo()),
 405                                     "alternatively, consider changing the type annotation",
 406                                     suggest_annotation,
 407                                     Applicability::MaybeIncorrect,
 408                                 );
 409                             }
 410                             break;
 411                         }
 412                         _ => break,
 413                     }
 414                 }
 415             }
 416             return true;
 417         } else if self.suggest_else_fn_with_closure(err, expr, found, expected) {
 418             return true;
 419         } else if self.suggest_fn_call(err, expr, found, |output| self.can_coerce(output, expected))
 420             && let ty::FnDef(def_id, ..) = &found.kind()
 421             && let Some(sp) = self.tcx.hir().span_if_local(*def_id)
 422         {
 423             err.span_label(sp, format!("{found} defined here"));
 424             return true;
 425         } else if self.check_for_cast(err, expr, found, expected, expected_ty_expr) {
 426             return true;
 427         } else {
 428             let methods = self.get_conversion_methods(expr.span, expected, found, expr.hir_id);
 429             if !methods.is_empty() {
 430                 let mut suggestions = methods.iter()
 431                     .filter_map(|conversion_method| {
 432                         let receiver_method_ident = expr.method_ident();
 433                         if let Some(method_ident) = receiver_method_ident
 434                             && method_ident.name == conversion_method.name
 435                         {
 436                             return None // do not suggest code that is already there (#53348)
 437                         }
 438
 439                         let method_call_list = [sym::to_vec, sym::to_string];
 440                         let mut sugg = if let ExprKind::MethodCall(receiver_method, ..) = expr.kind
 441                             && receiver_method.ident.name == sym::clone
 442                             && method_call_list.contains(&conversion_method.name)
 443                             // If receiver is `.clone()` and found type has one of those methods,
 444                             // we guess that the user wants to convert from a slice type (`&[]` or `&str`)
 445                             // to an owned type (`Vec` or `String`).  These conversions clone internally,
 446                             // so we remove the user's `clone` call.
 447                         {
 448                             vec![(
 449                                 receiver_method.ident.span,
 450                                 conversion_method.name.to_string()
 451                             )]
 452                         } else if expr.precedence().order()
 453                             < ExprPrecedence::MethodCall.order()
 454                         {
 455                             vec![
 456                                 (expr.span.shrink_to_lo(), "(".to_string()),
 457                                 (expr.span.shrink_to_hi(), format!(").{}()", conversion_method.name)),
 458                             ]
 459                         } else {
 460                             vec![(expr.span.shrink_to_hi(), format!(".{}()", conversion_method.name))]
 461                         };
 462                         let struct_pat_shorthand_field = self.maybe_get_struct_pattern_shorthand_field(expr);
 463                         if let Some(name) = struct_pat_shorthand_field {
 464                             sugg.insert(
 465                                 0,
 466                                 (expr.span.shrink_to_lo(), format!("{}: ", name)),
 467                             );
 468                         }
 469                         Some(sugg)
 470                     })
 471                     .peekable();
 472                 if suggestions.peek().is_some() {
 473                     err.multipart_suggestions(
 474                         "try using a conversion method",
 475                         suggestions,
 476                         Applicability::MaybeIncorrect,
 477                     );
 478                     return true;
 479                 }
 480             } else if let ty::Adt(found_adt, found_substs) = found.kind()
 481                 && self.tcx.is_diagnostic_item(sym::Option, found_adt.did())
 482                 && let ty::Adt(expected_adt, expected_substs) = expected.kind()
 483                 && self.tcx.is_diagnostic_item(sym::Option, expected_adt.did())
 484                 && let ty::Ref(_, inner_ty, _) = expected_substs.type_at(0).kind()
 485                 && inner_ty.is_str()
 486             {
 487                 let ty = found_substs.type_at(0);
 488                 let mut peeled = ty;
 489                 let mut ref_cnt = 0;
 490                 while let ty::Ref(_, inner, _) = peeled.kind() {
 491                     peeled = *inner;
 492                     ref_cnt += 1;
 493                 }
 494                 if let ty::Adt(adt, _) = peeled.kind()
 495                     && Some(adt.did()) == self.tcx.lang_items().string()
 496                 {
 497                     err.span_suggestion_verbose(
 498                         expr.span.shrink_to_hi(),
 499                         "try converting the passed type into a `&str`",
 500                         format!(".map(|x| &*{}x)", "*".repeat(ref_cnt)),
 501                         Applicability::MaybeIncorrect,
 502                     );
 503                     return true;
 504                 }
 505             }
 506         }
 507
 508         false
 509     }
 510
 511     /// When encountering the expected boxed value allocated in the stack, suggest allocating it
 512     /// in the heap by calling `Box::new()`.
 513     pub(in super::super) fn suggest_boxing_when_appropriate(
 514         &self,
 515         err: &mut Diagnostic,
 516         expr: &hir::Expr<'_>,
 517         expected: Ty<'tcx>,
 518         found: Ty<'tcx>,
 519     ) -> bool {
 520         if self.tcx.hir().is_inside_const_context(expr.hir_id) {
 521             // Do not suggest `Box::new` in const context.
 522             return false;
 523         }
 524         if !expected.is_box() || found.is_box() {
 525             return false;
 526         }
 527         let boxed_found = self.tcx.mk_box(found);
 528         if self.can_coerce(boxed_found, expected) {
 529             err.multipart_suggestion(
 530                 "store this in the heap by calling `Box::new`",
 531                 vec![
 532                     (expr.span.shrink_to_lo(), "Box::new(".to_string()),
 533                     (expr.span.shrink_to_hi(), ")".to_string()),
 534                 ],
 535                 Applicability::MachineApplicable,
 536             );
 537             err.note(
 538                 "for more on the distinction between the stack and the heap, read \
 539                  https://doc.rust-lang.org/book/ch15-01-box.html, \
 540                  https://doc.rust-lang.org/rust-by-example/std/box.html, and \
 541                  https://doc.rust-lang.org/std/boxed/index.html",
 542             );
 543             true
 544         } else {
 545             false
 546         }
 547     }
 548
 549     /// When encountering a closure that captures variables, where a FnPtr is expected,
 550     /// suggest a non-capturing closure
 551     pub(in super::super) fn suggest_no_capture_closure(
 552         &self,
 553         err: &mut Diagnostic,
 554         expected: Ty<'tcx>,
 555         found: Ty<'tcx>,
 556     ) -> bool {
 557         if let (ty::FnPtr(_), ty::Closure(def_id, _)) = (expected.kind(), found.kind()) {
 558             if let Some(upvars) = self.tcx.upvars_mentioned(*def_id) {
 559                 // Report upto four upvars being captured to reduce the amount error messages
 560                 // reported back to the user.
 561                 let spans_and_labels = upvars
 562                     .iter()
 563                     .take(4)
 564                     .map(|(var_hir_id, upvar)| {
 565                         let var_name = self.tcx.hir().name(*var_hir_id).to_string();
 566                         let msg = format!("`{}` captured here", var_name);
 567                         (upvar.span, msg)
 568                     })
 569                     .collect::<Vec<_>>();
 570
 571                 let mut multi_span: MultiSpan =
 572                     spans_and_labels.iter().map(|(sp, _)| *sp).collect::<Vec<_>>().into();
 573                 for (sp, label) in spans_and_labels {
 574                     multi_span.push_span_label(sp, label);
 575                 }
 576                 err.span_note(
 577                     multi_span,
 578                     "closures can only be coerced to `fn` types if they do not capture any variables"
 579                 );
 580                 return true;
 581             }
 582         }
 583         false
 584     }
 585
 586     /// When encountering an `impl Future` where `BoxFuture` is expected, suggest `Box::pin`.
 587     #[instrument(skip(self, err))]
 588     pub(in super::super) fn suggest_calling_boxed_future_when_appropriate(
 589         &self,
 590         err: &mut Diagnostic,
 591         expr: &hir::Expr<'_>,
 592         expected: Ty<'tcx>,
 593         found: Ty<'tcx>,
 594     ) -> bool {
 595         // Handle #68197.
 596
 597         if self.tcx.hir().is_inside_const_context(expr.hir_id) {
 598             // Do not suggest `Box::new` in const context.
 599             return false;
 600         }
 601         let pin_did = self.tcx.lang_items().pin_type();
 602         // This guards the `unwrap` and `mk_box` below.
 603         if pin_did.is_none() || self.tcx.lang_items().owned_box().is_none() {
 604             return false;
 605         }
 606         let box_found = self.tcx.mk_box(found);
 607         let pin_box_found = self.tcx.mk_lang_item(box_found, LangItem::Pin).unwrap();
 608         let pin_found = self.tcx.mk_lang_item(found, LangItem::Pin).unwrap();
 609         match expected.kind() {
 610             ty::Adt(def, _) if Some(def.did()) == pin_did => {
 611                 if self.can_coerce(pin_box_found, expected) {
 612                     debug!("can coerce {:?} to {:?}, suggesting Box::pin", pin_box_found, expected);
 613                     match found.kind() {
 614                         ty::Adt(def, _) if def.is_box() => {
 615                             err.help("use `Box::pin`");
 616                         }
 617                         _ => {
 618                             err.multipart_suggestion(
 619                                 "you need to pin and box this expression",
 620                                 vec![
 621                                     (expr.span.shrink_to_lo(), "Box::pin(".to_string()),
 622                                     (expr.span.shrink_to_hi(), ")".to_string()),
 623                                 ],
 624                                 Applicability::MaybeIncorrect,
 625                             );
 626                         }
 627                     }
 628                     true
 629                 } else if self.can_coerce(pin_found, expected) {
 630                     match found.kind() {
 631                         ty::Adt(def, _) if def.is_box() => {
 632                             err.help("use `Box::pin`");
 633                             true
 634                         }
 635                         _ => false,
 636                     }
 637                 } else {
 638                     false
 639                 }
 640             }
 641             ty::Adt(def, _) if def.is_box() && self.can_coerce(box_found, expected) => {
 642                 // Check if the parent expression is a call to Pin::new.  If it
 643                 // is and we were expecting a Box, ergo Pin<Box<expected>>, we
 644                 // can suggest Box::pin.
 645                 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 646                 let Some(Node::Expr(Expr { kind: ExprKind::Call(fn_name, _), .. })) = self.tcx.hir().find(parent) else {
 647                     return false;
 648                 };
 649                 match fn_name.kind {
 650                     ExprKind::Path(QPath::TypeRelative(
 651                         hir::Ty {
 652                             kind: TyKind::Path(QPath::Resolved(_, Path { res: recv_ty, .. })),
 653                             ..
 654                         },
 655                         method,
 656                     )) if recv_ty.opt_def_id() == pin_did && method.ident.name == sym::new => {
 657                         err.span_suggestion(
 658                             fn_name.span,
 659                             "use `Box::pin` to pin and box this expression",
 660                             "Box::pin",
 661                             Applicability::MachineApplicable,
 662                         );
 663                         true
 664                     }
 665                     _ => false,
 666                 }
 667             }
 668             _ => false,
 669         }
 670     }
 671
 672     /// A common error is to forget to add a semicolon at the end of a block, e.g.,
 673     ///
 674     /// ```compile_fail,E0308
 675     /// # fn bar_that_returns_u32() -> u32 { 4 }
 676     /// fn foo() {
 677     ///     bar_that_returns_u32()
 678     /// }
 679     /// ```
 680     ///
 681     /// This routine checks if the return expression in a block would make sense on its own as a
 682     /// statement and the return type has been left as default or has been specified as `()`. If so,
 683     /// it suggests adding a semicolon.
 684     ///
 685     /// If the expression is the expression of a closure without block (`|| expr`), a
 686     /// block is needed to be added too (`|| { expr; }`). This is denoted by `needs_block`.
 687     pub fn suggest_missing_semicolon(
 688         &self,
 689         err: &mut Diagnostic,
 690         expression: &'tcx hir::Expr<'tcx>,
 691         expected: Ty<'tcx>,
 692         needs_block: bool,
 693     ) {
 694         if expected.is_unit() {
 695             // `BlockTailExpression` only relevant if the tail expr would be
 696             // useful on its own.
 697             match expression.kind {
 698                 ExprKind::Call(..)
 699                 | ExprKind::MethodCall(..)
 700                 | ExprKind::Loop(..)
 701                 | ExprKind::If(..)
 702                 | ExprKind::Match(..)
 703                 | ExprKind::Block(..)
 704                     if expression.can_have_side_effects()
 705                         // If the expression is from an external macro, then do not suggest
 706                         // adding a semicolon, because there's nowhere to put it.
 707                         // See issue #81943.
 708                         && !in_external_macro(self.tcx.sess, expression.span) =>
 709                 {
 710                     if needs_block {
 711                         err.multipart_suggestion(
 712                             "consider using a semicolon here",
 713                             vec![
 714                                 (expression.span.shrink_to_lo(), "{ ".to_owned()),
 715                                 (expression.span.shrink_to_hi(), "; }".to_owned()),
 716                             ],
 717                             Applicability::MachineApplicable,
 718                         );
 719                     } else {
 720                         err.span_suggestion(
 721                             expression.span.shrink_to_hi(),
 722                             "consider using a semicolon here",
 723                             ";",
 724                             Applicability::MachineApplicable,
 725                         );
 726                     }
 727                 }
 728                 _ => (),
 729             }
 730         }
 731     }
 732
 733     /// A possible error is to forget to add a return type that is needed:
 734     ///
 735     /// ```compile_fail,E0308
 736     /// # fn bar_that_returns_u32() -> u32 { 4 }
 737     /// fn foo() {
 738     ///     bar_that_returns_u32()
 739     /// }
 740     /// ```
 741     ///
 742     /// This routine checks if the return type is left as default, the method is not part of an
 743     /// `impl` block and that it isn't the `main` method. If so, it suggests setting the return
 744     /// type.
 745     pub(in super::super) fn suggest_missing_return_type(
 746         &self,
 747         err: &mut Diagnostic,
 748         fn_decl: &hir::FnDecl<'_>,
 749         expected: Ty<'tcx>,
 750         found: Ty<'tcx>,
 751         can_suggest: bool,
 752         fn_id: hir::HirId,
 753     ) -> bool {
 754         let found =
 755             self.resolve_numeric_literals_with_default(self.resolve_vars_if_possible(found));
 756         // Only suggest changing the return type for methods that
 757         // haven't set a return type at all (and aren't `fn main()` or an impl).
 758         match &fn_decl.output {
 759             &hir::FnRetTy::DefaultReturn(span) if expected.is_unit() && !can_suggest => {
 760                 // `fn main()` must return `()`, do not suggest changing return type
 761                 err.subdiagnostic(ExpectedReturnTypeLabel::Unit { span });
 762                 return true;
 763             }
 764             &hir::FnRetTy::DefaultReturn(span) if expected.is_unit() => {
 765                 if found.is_suggestable(self.tcx, false) {
 766                     err.subdiagnostic(AddReturnTypeSuggestion::Add { span, found: found.to_string() });
 767                     return true;
 768                 } else if let ty::Closure(_, substs) = found.kind()
 769                     // FIXME(compiler-errors): Get better at printing binders...
 770                     && let closure = substs.as_closure()
 771                     && closure.sig().is_suggestable(self.tcx, false)
 772                 {
 773                     err.subdiagnostic(AddReturnTypeSuggestion::Add { span, found: closure.print_as_impl_trait().to_string() });
 774                     return true;
 775                 } else {
 776                     // FIXME: if `found` could be `impl Iterator` we should suggest that.
 777                     err.subdiagnostic(AddReturnTypeSuggestion::MissingHere { span });
 778                     return true
 779                 }
 780             }
 781             hir::FnRetTy::Return(ty) => {
 782                 // Only point to return type if the expected type is the return type, as if they
 783                 // are not, the expectation must have been caused by something else.
 784                 debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
 785                 let span = ty.span;
 786                 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
 787                 debug!("suggest_missing_return_type: return type {:?}", ty);
 788                 debug!("suggest_missing_return_type: expected type {:?}", ty);
 789                 let bound_vars = self.tcx.late_bound_vars(fn_id);
 790                 let ty = Binder::bind_with_vars(ty, bound_vars);
 791                 let ty = self.normalize(span, ty);
 792                 let ty = self.tcx.erase_late_bound_regions(ty);
 793                 if self.can_coerce(expected, ty) {
 794                     err.subdiagnostic(ExpectedReturnTypeLabel::Other { span, expected });
 795                     self.try_suggest_return_impl_trait(err, expected, ty, fn_id);
 796                     return true;
 797                 }
 798             }
 799             _ => {}
 800         }
 801         false
 802     }
 803
 804     /// check whether the return type is a generic type with a trait bound
 805     /// only suggest this if the generic param is not present in the arguments
 806     /// if this is true, hint them towards changing the return type to `impl Trait`
 807     /// ```compile_fail,E0308
 808     /// fn cant_name_it<T: Fn() -> u32>() -> T {
 809     ///     || 3
 810     /// }
 811     /// ```
 812     fn try_suggest_return_impl_trait(
 813         &self,
 814         err: &mut Diagnostic,
 815         expected: Ty<'tcx>,
 816         found: Ty<'tcx>,
 817         fn_id: hir::HirId,
 818     ) {
 819         // Only apply the suggestion if:
 820         //  - the return type is a generic parameter
 821         //  - the generic param is not used as a fn param
 822         //  - the generic param has at least one bound
 823         //  - the generic param doesn't appear in any other bounds where it's not the Self type
 824         // Suggest:
 825         //  - Changing the return type to be `impl <all bounds>`
 826
 827         debug!("try_suggest_return_impl_trait, expected = {:?}, found = {:?}", expected, found);
 828
 829         let ty::Param(expected_ty_as_param) = expected.kind() else { return };
 830
 831         let fn_node = self.tcx.hir().find(fn_id);
 832
 833         let Some(hir::Node::Item(hir::Item {
 834             kind:
 835                 hir::ItemKind::Fn(
 836                     hir::FnSig { decl: hir::FnDecl { inputs: fn_parameters, output: fn_return, .. }, .. },
 837                     hir::Generics { params, predicates, .. },
 838                     _body_id,
 839                 ),
 840             ..
 841         })) = fn_node else { return };
 842
 843         if params.get(expected_ty_as_param.index as usize).is_none() {
 844             return;
 845         };
 846
 847         // get all where BoundPredicates here, because they are used in to cases below
 848         let where_predicates = predicates
 849             .iter()
 850             .filter_map(|p| match p {
 851                 WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
 852                     bounds,
 853                     bounded_ty,
 854                     ..
 855                 }) => {
 856                     // FIXME: Maybe these calls to `ast_ty_to_ty` can be removed (and the ones below)
 857                     let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, bounded_ty);
 858                     Some((ty, bounds))
 859                 }
 860                 _ => None,
 861             })
 862             .map(|(ty, bounds)| match ty.kind() {
 863                 ty::Param(param_ty) if param_ty == expected_ty_as_param => Ok(Some(bounds)),
 864                 // check whether there is any predicate that contains our `T`, like `Option<T>: Send`
 865                 _ => match ty.contains(expected) {
 866                     true => Err(()),
 867                     false => Ok(None),
 868                 },
 869             })
 870             .collect::<Result<Vec<_>, _>>();
 871
 872         let Ok(where_predicates) = where_predicates else { return };
 873
 874         // now get all predicates in the same types as the where bounds, so we can chain them
 875         let predicates_from_where =
 876             where_predicates.iter().flatten().flat_map(|bounds| bounds.iter());
 877
 878         // extract all bounds from the source code using their spans
 879         let all_matching_bounds_strs = predicates_from_where
 880             .filter_map(|bound| match bound {
 881                 GenericBound::Trait(_, _) => {
 882                     self.tcx.sess.source_map().span_to_snippet(bound.span()).ok()
 883                 }
 884                 _ => None,
 885             })
 886             .collect::<Vec<String>>();
 887
 888         if all_matching_bounds_strs.len() == 0 {
 889             return;
 890         }
 891
 892         let all_bounds_str = all_matching_bounds_strs.join(" + ");
 893
 894         let ty_param_used_in_fn_params = fn_parameters.iter().any(|param| {
 895                 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, param);
 896                 matches!(ty.kind(), ty::Param(fn_param_ty_param) if expected_ty_as_param == fn_param_ty_param)
 897             });
 898
 899         if ty_param_used_in_fn_params {
 900             return;
 901         }
 902
 903         err.span_suggestion(
 904             fn_return.span(),
 905             "consider using an impl return type",
 906             format!("impl {}", all_bounds_str),
 907             Applicability::MaybeIncorrect,
 908         );
 909     }
 910
 911     pub(in super::super) fn suggest_missing_break_or_return_expr(
 912         &self,
 913         err: &mut Diagnostic,
 914         expr: &'tcx hir::Expr<'tcx>,
 915         fn_decl: &hir::FnDecl<'_>,
 916         expected: Ty<'tcx>,
 917         found: Ty<'tcx>,
 918         id: hir::HirId,
 919         fn_id: hir::HirId,
 920     ) {
 921         if !expected.is_unit() {
 922             return;
 923         }
 924         let found = self.resolve_vars_with_obligations(found);
 925
 926         let in_loop = self.is_loop(id)
 927             || self.tcx.hir().parent_iter(id).any(|(parent_id, _)| self.is_loop(parent_id));
 928
 929         let in_local_statement = self.is_local_statement(id)
 930             || self
 931                 .tcx
 932                 .hir()
 933                 .parent_iter(id)
 934                 .any(|(parent_id, _)| self.is_local_statement(parent_id));
 935
 936         if in_loop && in_local_statement {
 937             err.multipart_suggestion(
 938                 "you might have meant to break the loop with this value",
 939                 vec![
 940                     (expr.span.shrink_to_lo(), "break ".to_string()),
 941                     (expr.span.shrink_to_hi(), ";".to_string()),
 942                 ],
 943                 Applicability::MaybeIncorrect,
 944             );
 945             return;
 946         }
 947
 948         if let hir::FnRetTy::Return(ty) = fn_decl.output {
 949             let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
 950             let bound_vars = self.tcx.late_bound_vars(fn_id);
 951             let ty = self.tcx.erase_late_bound_regions(Binder::bind_with_vars(ty, bound_vars));
 952             let ty = match self.tcx.asyncness(fn_id.owner) {
 953                 hir::IsAsync::Async => self.get_impl_future_output_ty(ty).unwrap_or_else(|| {
 954                     span_bug!(fn_decl.output.span(), "failed to get output type of async function")
 955                 }),
 956                 hir::IsAsync::NotAsync => ty,
 957             };
 958             let ty = self.normalize(expr.span, ty);
 959             if self.can_coerce(found, ty) {
 960                 err.multipart_suggestion(
 961                     "you might have meant to return this value",
 962                     vec![
 963                         (expr.span.shrink_to_lo(), "return ".to_string()),
 964                         (expr.span.shrink_to_hi(), ";".to_string()),
 965                     ],
 966                     Applicability::MaybeIncorrect,
 967                 );
 968             }
 969         }
 970     }
 971
 972     pub(in super::super) fn suggest_missing_parentheses(
 973         &self,
 974         err: &mut Diagnostic,
 975         expr: &hir::Expr<'_>,
 976     ) -> bool {
 977         let sp = self.tcx.sess.source_map().start_point(expr.span).with_parent(None);
 978         if let Some(sp) = self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp) {
 979             // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
 980             err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
 981             true
 982         } else {
 983             false
 984         }
 985     }
 986
 987     /// Given an expression type mismatch, peel any `&` expressions until we get to
 988     /// a block expression, and then suggest replacing the braces with square braces
 989     /// if it was possibly mistaken array syntax.
 990     pub(crate) fn suggest_block_to_brackets_peeling_refs(
 991         &self,
 992         diag: &mut Diagnostic,
 993         mut expr: &hir::Expr<'_>,
 994         mut expr_ty: Ty<'tcx>,
 995         mut expected_ty: Ty<'tcx>,
 996     ) -> bool {
 997         loop {
 998             match (&expr.kind, expr_ty.kind(), expected_ty.kind()) {
 999                 (
1000                     hir::ExprKind::AddrOf(_, _, inner_expr),
1001                     ty::Ref(_, inner_expr_ty, _),
1002                     ty::Ref(_, inner_expected_ty, _),
1003                 ) => {
1004                     expr = *inner_expr;
1005                     expr_ty = *inner_expr_ty;
1006                     expected_ty = *inner_expected_ty;
1007                 }
1008                 (hir::ExprKind::Block(blk, _), _, _) => {
1009                     self.suggest_block_to_brackets(diag, *blk, expr_ty, expected_ty);
1010                     break true;
1011                 }
1012                 _ => break false,
1013             }
1014         }
1015     }
1016
1017     pub(crate) fn suggest_copied_or_cloned(
1018         &self,
1019         diag: &mut Diagnostic,
1020         expr: &hir::Expr<'_>,
1021         expr_ty: Ty<'tcx>,
1022         expected_ty: Ty<'tcx>,
1023     ) -> bool {
1024         let ty::Adt(adt_def, substs) = expr_ty.kind() else { return false; };
1025         let ty::Adt(expected_adt_def, expected_substs) = expected_ty.kind() else { return false; };
1026         if adt_def != expected_adt_def {
1027             return false;
1028         }
1029
1030         let mut suggest_copied_or_cloned = || {
1031             let expr_inner_ty = substs.type_at(0);
1032             let expected_inner_ty = expected_substs.type_at(0);
1033             if let ty::Ref(_, ty, hir::Mutability::Not) = expr_inner_ty.kind()
1034                 && self.can_eq(self.param_env, *ty, expected_inner_ty).is_ok()
1035             {
1036                 let def_path = self.tcx.def_path_str(adt_def.did());
1037                 if self.type_is_copy_modulo_regions(self.param_env, *ty, expr.span) {
1038                     diag.span_suggestion_verbose(
1039                         expr.span.shrink_to_hi(),
1040                         format!(
1041                             "use `{def_path}::copied` to copy the value inside the `{def_path}`"
1042                         ),
1043                         ".copied()",
1044                         Applicability::MachineApplicable,
1045                     );
1046                     return true;
1047                 } else if let Some(clone_did) = self.tcx.lang_items().clone_trait()
1048                     && rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions(
1049                         self,
1050                         self.param_env,
1051                         *ty,
1052                         clone_did,
1053                         expr.span
1054                     )
1055                 {
1056                     diag.span_suggestion_verbose(
1057                         expr.span.shrink_to_hi(),
1058                         format!(
1059                             "use `{def_path}::cloned` to clone the value inside the `{def_path}`"
1060                         ),
1061                         ".cloned()",
1062                         Applicability::MachineApplicable,
1063                     );
1064                     return true;
1065                 }
1066             }
1067             false
1068         };
1069
1070         if let Some(result_did) = self.tcx.get_diagnostic_item(sym::Result)
1071             && adt_def.did() == result_did
1072             // Check that the error types are equal
1073             && self.can_eq(self.param_env, substs.type_at(1), expected_substs.type_at(1)).is_ok()
1074         {
1075             return suggest_copied_or_cloned();
1076         } else if let Some(option_did) = self.tcx.get_diagnostic_item(sym::Option)
1077             && adt_def.did() == option_did
1078         {
1079             return suggest_copied_or_cloned();
1080         }
1081
1082         false
1083     }
1084
1085     pub(crate) fn suggest_into(
1086         &self,
1087         diag: &mut Diagnostic,
1088         expr: &hir::Expr<'_>,
1089         expr_ty: Ty<'tcx>,
1090         expected_ty: Ty<'tcx>,
1091     ) -> bool {
1092         let expr = expr.peel_blocks();
1093
1094         // We have better suggestions for scalar interconversions...
1095         if expr_ty.is_scalar() && expected_ty.is_scalar() {
1096             return false;
1097         }
1098
1099         // Don't suggest turning a block into another type (e.g. `{}.into()`)
1100         if matches!(expr.kind, hir::ExprKind::Block(..)) {
1101             return false;
1102         }
1103
1104         // We'll later suggest `.as_ref` when noting the type error,
1105         // so skip if we will suggest that instead.
1106         if self.err_ctxt().should_suggest_as_ref(expected_ty, expr_ty).is_some() {
1107             return false;
1108         }
1109
1110         if let Some(into_def_id) = self.tcx.get_diagnostic_item(sym::Into)
1111             && self.predicate_must_hold_modulo_regions(&traits::Obligation::new(
1112                 self.tcx,
1113                 self.misc(expr.span),
1114                 self.param_env,
1115                 ty::Binder::dummy(self.tcx.mk_trait_ref(
1116                     into_def_id,
1117                     [expr_ty, expected_ty]
1118                 )),
1119             ))
1120         {
1121             let sugg = if expr.precedence().order() >= PREC_POSTFIX {
1122                 vec![(expr.span.shrink_to_hi(), ".into()".to_owned())]
1123             } else {
1124                 vec![(expr.span.shrink_to_lo(), "(".to_owned()), (expr.span.shrink_to_hi(), ").into()".to_owned())]
1125             };
1126             diag.multipart_suggestion(
1127                 format!("call `Into::into` on this expression to convert `{expr_ty}` into `{expected_ty}`"),
1128                 sugg,
1129                 Applicability::MaybeIncorrect
1130             );
1131             return true;
1132         }
1133
1134         false
1135     }
1136
1137     /// When expecting a `bool` and finding an `Option`, suggests using `let Some(..)` or `.is_some()`
1138     pub(crate) fn suggest_option_to_bool(
1139         &self,
1140         diag: &mut Diagnostic,
1141         expr: &hir::Expr<'_>,
1142         expr_ty: Ty<'tcx>,
1143         expected_ty: Ty<'tcx>,
1144     ) -> bool {
1145         if !expected_ty.is_bool() {
1146             return false;
1147         }
1148
1149         let ty::Adt(def, _) = expr_ty.peel_refs().kind() else { return false; };
1150         if !self.tcx.is_diagnostic_item(sym::Option, def.did()) {
1151             return false;
1152         }
1153
1154         let hir = self.tcx.hir();
1155         let cond_parent = hir.parent_iter(expr.hir_id).find(|(_, node)| {
1156             !matches!(node, hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Binary(op, _, _), .. }) if op.node == hir::BinOpKind::And)
1157         });
1158         // Don't suggest:
1159         //     `let Some(_) = a.is_some() && b`
1160         //                     ++++++++++
1161         // since the user probably just misunderstood how `let else`
1162         // and `&&` work together.
1163         if let Some((_, hir::Node::Local(local))) = cond_parent
1164             && let hir::PatKind::Path(qpath) | hir::PatKind::TupleStruct(qpath, _, _) = &local.pat.kind
1165             && let hir::QPath::Resolved(None, path) = qpath
1166             && let Some(did) = path.res.opt_def_id()
1167                 .and_then(|did| self.tcx.opt_parent(did))
1168                 .and_then(|did| self.tcx.opt_parent(did))
1169             && self.tcx.is_diagnostic_item(sym::Option, did)
1170         {
1171             return false;
1172         }
1173
1174         diag.span_suggestion(
1175             expr.span.shrink_to_hi(),
1176             "use `Option::is_some` to test if the `Option` has a value",
1177             ".is_some()",
1178             Applicability::MachineApplicable,
1179         );
1180
1181         true
1182     }
1183
1184     /// Suggest wrapping the block in square brackets instead of curly braces
1185     /// in case the block was mistaken array syntax, e.g. `{ 1 }` -> `[ 1 ]`.
1186     pub(crate) fn suggest_block_to_brackets(
1187         &self,
1188         diag: &mut Diagnostic,
1189         blk: &hir::Block<'_>,
1190         blk_ty: Ty<'tcx>,
1191         expected_ty: Ty<'tcx>,
1192     ) {
1193         if let ty::Slice(elem_ty) | ty::Array(elem_ty, _) = expected_ty.kind() {
1194             if self.can_coerce(blk_ty, *elem_ty)
1195                 && blk.stmts.is_empty()
1196                 && blk.rules == hir::BlockCheckMode::DefaultBlock
1197             {
1198                 let source_map = self.tcx.sess.source_map();
1199                 if let Ok(snippet) = source_map.span_to_snippet(blk.span) {
1200                     if snippet.starts_with('{') && snippet.ends_with('}') {
1201                         diag.multipart_suggestion_verbose(
1202                             "to create an array, use square brackets instead of curly braces",
1203                             vec![
1204                                 (
1205                                     blk.span
1206                                         .shrink_to_lo()
1207                                         .with_hi(rustc_span::BytePos(blk.span.lo().0 + 1)),
1208                                     "[".to_string(),
1209                                 ),
1210                                 (
1211                                     blk.span
1212                                         .shrink_to_hi()
1213                                         .with_lo(rustc_span::BytePos(blk.span.hi().0 - 1)),
1214                                     "]".to_string(),
1215                                 ),
1216                             ],
1217                             Applicability::MachineApplicable,
1218                         );
1219                     }
1220                 }
1221             }
1222         }
1223     }
1224
1225     #[instrument(skip(self, err))]
1226     pub(crate) fn suggest_floating_point_literal(
1227         &self,
1228         err: &mut Diagnostic,
1229         expr: &hir::Expr<'_>,
1230         expected_ty: Ty<'tcx>,
1231     ) -> bool {
1232         if !expected_ty.is_floating_point() {
1233             return false;
1234         }
1235         match expr.kind {
1236             ExprKind::Struct(QPath::LangItem(LangItem::Range, ..), [start, end], _) => {
1237                 err.span_suggestion_verbose(
1238                     start.span.shrink_to_hi().with_hi(end.span.lo()),
1239                     "remove the unnecessary `.` operator for a floating point literal",
1240                     '.',
1241                     Applicability::MaybeIncorrect,
1242                 );
1243                 true
1244             }
1245             ExprKind::Struct(QPath::LangItem(LangItem::RangeFrom, ..), [start], _) => {
1246                 err.span_suggestion_verbose(
1247                     expr.span.with_lo(start.span.hi()),
1248                     "remove the unnecessary `.` operator for a floating point literal",
1249                     '.',
1250                     Applicability::MaybeIncorrect,
1251                 );
1252                 true
1253             }
1254             ExprKind::Struct(QPath::LangItem(LangItem::RangeTo, ..), [end], _) => {
1255                 err.span_suggestion_verbose(
1256                     expr.span.until(end.span),
1257                     "remove the unnecessary `.` operator and add an integer part for a floating point literal",
1258                     "0.",
1259                     Applicability::MaybeIncorrect,
1260                 );
1261                 true
1262             }
1263             ExprKind::Lit(Spanned {
1264                 node: rustc_ast::LitKind::Int(lit, rustc_ast::LitIntType::Unsuffixed),
1265                 span,
1266             }) => {
1267                 let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) else { return false; };
1268                 if !(snippet.starts_with("0x") || snippet.starts_with("0X")) {
1269                     return false;
1270                 }
1271                 if snippet.len() <= 5 || !snippet.is_char_boundary(snippet.len() - 3) {
1272                     return false;
1273                 }
1274                 let (_, suffix) = snippet.split_at(snippet.len() - 3);
1275                 let value = match suffix {
1276                     "f32" => (lit - 0xf32) / (16 * 16 * 16),
1277                     "f64" => (lit - 0xf64) / (16 * 16 * 16),
1278                     _ => return false,
1279                 };
1280                 err.span_suggestions(
1281                     expr.span,
1282                     "rewrite this as a decimal floating point literal, or use `as` to turn a hex literal into a float",
1283                     [format!("0x{value:X} as {suffix}"), format!("{value}_{suffix}")],
1284                     Applicability::MaybeIncorrect,
1285                 );
1286                 true
1287             }
1288             _ => false,
1289         }
1290     }
1291
1292     pub(crate) fn suggest_associated_const(
1293         &self,
1294         err: &mut Diagnostic,
1295         expr: &hir::Expr<'_>,
1296         expected_ty: Ty<'tcx>,
1297     ) -> bool {
1298         let Some((DefKind::AssocFn, old_def_id)) = self.typeck_results.borrow().type_dependent_def(expr.hir_id) else {
1299             return false;
1300         };
1301         let old_item_name = self.tcx.item_name(old_def_id);
1302         let capitalized_name = Symbol::intern(&old_item_name.as_str().to_uppercase());
1303         if old_item_name == capitalized_name {
1304             return false;
1305         }
1306         let (item, segment) = match expr.kind {
1307             hir::ExprKind::Path(QPath::Resolved(
1308                 Some(ty),
1309                 hir::Path { segments: [segment], .. },
1310             ))
1311             | hir::ExprKind::Path(QPath::TypeRelative(ty, segment)) => {
1312                 let self_ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
1313                 if let Ok(pick) = self.probe_for_name(
1314                     Mode::Path,
1315                     Ident::new(capitalized_name, segment.ident.span),
1316                     IsSuggestion(true),
1317                     self_ty,
1318                     expr.hir_id,
1319                     ProbeScope::TraitsInScope,
1320                 ) {
1321                     (pick.item, segment)
1322                 } else {
1323                     return false;
1324                 }
1325             }
1326             hir::ExprKind::Path(QPath::Resolved(
1327                 None,
1328                 hir::Path { segments: [.., segment], .. },
1329             )) => {
1330                 // we resolved through some path that doesn't end in the item name,
1331                 // better not do a bad suggestion by accident.
1332                 if old_item_name != segment.ident.name {
1333                     return false;
1334                 }
1335                 if let Some(item) = self
1336                     .tcx
1337                     .associated_items(self.tcx.parent(old_def_id))
1338                     .filter_by_name_unhygienic(capitalized_name)
1339                     .next()
1340                 {
1341                     (*item, segment)
1342                 } else {
1343                     return false;
1344                 }
1345             }
1346             _ => return false,
1347         };
1348         if item.def_id == old_def_id || self.tcx.def_kind(item.def_id) != DefKind::AssocConst {
1349             // Same item
1350             return false;
1351         }
1352         let item_ty = self.tcx.type_of(item.def_id);
1353         // FIXME(compiler-errors): This check is *so* rudimentary
1354         if item_ty.needs_subst() {
1355             return false;
1356         }
1357         if self.can_coerce(item_ty, expected_ty) {
1358             err.span_suggestion_verbose(
1359                 segment.ident.span,
1360                 format!("try referring to the associated const `{capitalized_name}` instead",),
1361                 capitalized_name,
1362                 Applicability::MachineApplicable,
1363             );
1364             true
1365         } else {
1366             false
1367         }
1368     }
1369
1370     fn is_loop(&self, id: hir::HirId) -> bool {
1371         let node = self.tcx.hir().get(id);
1372         matches!(node, Node::Expr(Expr { kind: ExprKind::Loop(..), .. }))
1373     }
1374
1375     fn is_local_statement(&self, id: hir::HirId) -> bool {
1376         let node = self.tcx.hir().get(id);
1377         matches!(node, Node::Stmt(Stmt { kind: StmtKind::Local(..), .. }))
1378     }
1379
1380     /// Suggest that `&T` was cloned instead of `T` because `T` does not implement `Clone`,
1381     /// which is a side-effect of autoref.
1382     pub(crate) fn note_type_is_not_clone(
1383         &self,
1384         diag: &mut Diagnostic,
1385         expected_ty: Ty<'tcx>,
1386         found_ty: Ty<'tcx>,
1387         expr: &hir::Expr<'_>,
1388     ) {
1389         let hir::ExprKind::MethodCall(segment, callee_expr, &[], _) = expr.kind else { return; };
1390         let Some(clone_trait_did) = self.tcx.lang_items().clone_trait() else { return; };
1391         let ty::Ref(_, pointee_ty, _) = found_ty.kind() else { return };
1392         let results = self.typeck_results.borrow();
1393         // First, look for a `Clone::clone` call
1394         if segment.ident.name == sym::clone
1395             && results.type_dependent_def_id(expr.hir_id).map_or(
1396                 false,
1397                 |did| {
1398                     let assoc_item = self.tcx.associated_item(did);
1399                     assoc_item.container == ty::AssocItemContainer::TraitContainer
1400                         && assoc_item.container_id(self.tcx) == clone_trait_did
1401                 },
1402             )
1403             // If that clone call hasn't already dereferenced the self type (i.e. don't give this
1404             // diagnostic in cases where we have `(&&T).clone()` and we expect `T`).
1405             && !results.expr_adjustments(callee_expr).iter().any(|adj| matches!(adj.kind, ty::adjustment::Adjust::Deref(..)))
1406             // Check that we're in fact trying to clone into the expected type
1407             && self.can_coerce(*pointee_ty, expected_ty)
1408             && let trait_ref = ty::Binder::dummy(self.tcx.mk_trait_ref(clone_trait_did, [expected_ty]))
1409             // And the expected type doesn't implement `Clone`
1410             && !self.predicate_must_hold_considering_regions(&traits::Obligation::new(
1411                 self.tcx,
1412                 traits::ObligationCause::dummy(),
1413                 self.param_env,
1414                 trait_ref,
1415             ))
1416         {
1417             diag.span_note(
1418                 callee_expr.span,
1419                 &format!(
1420                     "`{expected_ty}` does not implement `Clone`, so `{found_ty}` was cloned instead"
1421                 ),
1422             );
1423             let owner = self.tcx.hir().enclosing_body_owner(expr.hir_id);
1424             if let ty::Param(param) = expected_ty.kind()
1425                 && let Some(generics) = self.tcx.hir().get_generics(owner)
1426             {
1427                 suggest_constraining_type_params(
1428                     self.tcx,
1429                     generics,
1430                     diag,
1431                     vec![(param.name.as_str(), "Clone", Some(clone_trait_did))].into_iter(),
1432                 );
1433             } else {
1434                 self.suggest_derive(diag, &[(trait_ref.to_predicate(self.tcx), None, None)]);
1435             }
1436         }
1437     }
1438
1439     /// A common error is to add an extra semicolon:
1440     ///
1441     /// ```compile_fail,E0308
1442     /// fn foo() -> usize {
1443     ///     22;
1444     /// }
1445     /// ```
1446     ///
1447     /// This routine checks if the final statement in a block is an
1448     /// expression with an explicit semicolon whose type is compatible
1449     /// with `expected_ty`. If so, it suggests removing the semicolon.
1450     pub(crate) fn consider_removing_semicolon(
1451         &self,
1452         blk: &'tcx hir::Block<'tcx>,
1453         expected_ty: Ty<'tcx>,
1454         err: &mut Diagnostic,
1455     ) -> bool {
1456         if let Some((span_semi, boxed)) = self.err_ctxt().could_remove_semicolon(blk, expected_ty) {
1457             if let StatementAsExpression::NeedsBoxing = boxed {
1458                 err.span_suggestion_verbose(
1459                     span_semi,
1460                     "consider removing this semicolon and boxing the expression",
1461                     "",
1462                     Applicability::HasPlaceholders,
1463                 );
1464             } else {
1465                 err.span_suggestion_short(
1466                     span_semi,
1467                     "remove this semicolon to return this value",
1468                     "",
1469                     Applicability::MachineApplicable,
1470                 );
1471             }
1472             true
1473         } else {
1474             false
1475         }
1476     }
1477 }