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