src/librustc_typeck/check/demand.rs

   1 use crate::check::FnCtxt;
   2 use rustc_infer::infer::InferOk;
   3 use rustc_trait_selection::infer::InferCtxtExt as _;
   4 use rustc_trait_selection::traits::ObligationCause;
   5
   6 use rustc_ast::util::parser::PREC_POSTFIX;
   7 use rustc_errors::{Applicability, DiagnosticBuilder};
   8 use rustc_hir as hir;
   9 use rustc_hir::lang_items::CloneTraitLangItem;
  10 use rustc_hir::{is_range_literal, Node};
  11 use rustc_middle::ty::adjustment::AllowTwoPhase;
  12 use rustc_middle::ty::{self, AssocItem, Ty, TypeAndMut};
  13 use rustc_span::symbol::sym;
  14 use rustc_span::Span;
  15
  16 use super::method::probe;
  17
  18 use std::fmt;
  19
  20 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  21     pub fn emit_coerce_suggestions(
  22         &self,
  23         err: &mut DiagnosticBuilder<'_>,
  24         expr: &hir::Expr<'_>,
  25         expr_ty: Ty<'tcx>,
  26         expected: Ty<'tcx>,
  27         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
  28     ) {
  29         self.annotate_expected_due_to_let_ty(err, expr);
  30         self.suggest_compatible_variants(err, expr, expected, expr_ty);
  31         self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr);
  32         if self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty) {
  33             return;
  34         }
  35         self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
  36         self.suggest_missing_await(err, expr, expected, expr_ty);
  37         self.suggest_missing_parentheses(err, expr);
  38         self.note_need_for_fn_pointer(err, expected, expr_ty);
  39     }
  40
  41     // Requires that the two types unify, and prints an error message if
  42     // they don't.
  43     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  44         if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
  45             e.emit();
  46         }
  47     }
  48
  49     pub fn demand_suptype_diag(
  50         &self,
  51         sp: Span,
  52         expected: Ty<'tcx>,
  53         actual: Ty<'tcx>,
  54     ) -> Option<DiagnosticBuilder<'tcx>> {
  55         self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
  56     }
  57
  58     pub fn demand_suptype_with_origin(
  59         &self,
  60         cause: &ObligationCause<'tcx>,
  61         expected: Ty<'tcx>,
  62         actual: Ty<'tcx>,
  63     ) -> Option<DiagnosticBuilder<'tcx>> {
  64         match self.at(cause, self.param_env).sup(expected, actual) {
  65             Ok(InferOk { obligations, value: () }) => {
  66                 self.register_predicates(obligations);
  67                 None
  68             }
  69             Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
  70         }
  71     }
  72
  73     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  74         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  75             err.emit();
  76         }
  77     }
  78
  79     pub fn demand_eqtype_diag(
  80         &self,
  81         sp: Span,
  82         expected: Ty<'tcx>,
  83         actual: Ty<'tcx>,
  84     ) -> Option<DiagnosticBuilder<'tcx>> {
  85         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  86     }
  87
  88     pub fn demand_eqtype_with_origin(
  89         &self,
  90         cause: &ObligationCause<'tcx>,
  91         expected: Ty<'tcx>,
  92         actual: Ty<'tcx>,
  93     ) -> Option<DiagnosticBuilder<'tcx>> {
  94         match self.at(cause, self.param_env).eq(expected, actual) {
  95             Ok(InferOk { obligations, value: () }) => {
  96                 self.register_predicates(obligations);
  97                 None
  98             }
  99             Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
 100         }
 101     }
 102
 103     pub fn demand_coerce(
 104         &self,
 105         expr: &hir::Expr<'_>,
 106         checked_ty: Ty<'tcx>,
 107         expected: Ty<'tcx>,
 108         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 109         allow_two_phase: AllowTwoPhase,
 110     ) -> Ty<'tcx> {
 111         let (ty, err) =
 112             self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
 113         if let Some(mut err) = err {
 114             err.emit();
 115         }
 116         ty
 117     }
 118
 119     // Checks that the type of `expr` can be coerced to `expected`.
 120     //
 121     // N.B., this code relies on `self.diverges` to be accurate. In
 122     // particular, assignments to `!` will be permitted if the
 123     // diverges flag is currently "always".
 124     pub fn demand_coerce_diag(
 125         &self,
 126         expr: &hir::Expr<'_>,
 127         checked_ty: Ty<'tcx>,
 128         expected: Ty<'tcx>,
 129         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 130         allow_two_phase: AllowTwoPhase,
 131     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
 132         let expected = self.resolve_vars_with_obligations(expected);
 133
 134         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
 135             Ok(ty) => return (ty, None),
 136             Err(e) => e,
 137         };
 138
 139         let expr = expr.peel_drop_temps();
 140         let cause = self.misc(expr.span);
 141         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 142         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
 143
 144         if self.is_assign_to_bool(expr, expected) {
 145             // Error reported in `check_assign` so avoid emitting error again.
 146             err.delay_as_bug();
 147             return (expected, None);
 148         }
 149
 150         self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr);
 151
 152         (expected, Some(err))
 153     }
 154
 155     fn annotate_expected_due_to_let_ty(
 156         &self,
 157         err: &mut DiagnosticBuilder<'_>,
 158         expr: &hir::Expr<'_>,
 159     ) {
 160         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 161         if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
 162             self.tcx.hir().find(parent)
 163         {
 164             if init.hir_id == expr.hir_id {
 165                 // Point at `let` assignment type.
 166                 err.span_label(ty.span, "expected due to this");
 167             }
 168         }
 169     }
 170
 171     /// Returns whether the expected type is `bool` and the expression is `x = y`.
 172     pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
 173         if let hir::ExprKind::Assign(..) = expr.kind {
 174             return expected == self.tcx.types.bool;
 175         }
 176         false
 177     }
 178
 179     /// If the expected type is an enum (Issue #55250) with any variants whose
 180     /// sole field is of the found type, suggest such variants. (Issue #42764)
 181     fn suggest_compatible_variants(
 182         &self,
 183         err: &mut DiagnosticBuilder<'_>,
 184         expr: &hir::Expr<'_>,
 185         expected: Ty<'tcx>,
 186         expr_ty: Ty<'tcx>,
 187     ) {
 188         if let ty::Adt(expected_adt, substs) = expected.kind {
 189             if !expected_adt.is_enum() {
 190                 return;
 191             }
 192
 193             let mut compatible_variants = expected_adt
 194                 .variants
 195                 .iter()
 196                 .filter(|variant| variant.fields.len() == 1)
 197                 .filter_map(|variant| {
 198                     let sole_field = &variant.fields[0];
 199                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 200                     if self.can_coerce(expr_ty, sole_field_ty) {
 201                         let variant_path = self.tcx.def_path_str(variant.def_id);
 202                         // FIXME #56861: DRYer prelude filtering
 203                         Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
 204                     } else {
 205                         None
 206                     }
 207                 })
 208                 .peekable();
 209
 210             if compatible_variants.peek().is_some() {
 211                 if let Ok(expr_text) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 212                     let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
 213                     let msg = "try using a variant of the expected enum";
 214                     err.span_suggestions(
 215                         expr.span,
 216                         msg,
 217                         suggestions,
 218                         Applicability::MaybeIncorrect,
 219                     );
 220                 }
 221             }
 222         }
 223     }
 224
 225     pub fn get_conversion_methods(
 226         &self,
 227         span: Span,
 228         expected: Ty<'tcx>,
 229         checked_ty: Ty<'tcx>,
 230         hir_id: hir::HirId,
 231     ) -> Vec<AssocItem> {
 232         let mut methods =
 233             self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
 234         methods.retain(|m| {
 235             self.has_only_self_parameter(m)
 236                 && self
 237                     .tcx
 238                     .get_attrs(m.def_id)
 239                     .iter()
 240                     // This special internal attribute is used to permit
 241                     // "identity-like" conversion methods to be suggested here.
 242                     //
 243                     // FIXME (#46459 and #46460): ideally
 244                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 245                     // also be `#[rustc_conversion_suggestion]`, if not for
 246                     // method-probing false-positives and -negatives (respectively).
 247                     //
 248                     // FIXME? Other potential candidate methods: `as_ref` and
 249                     // `as_mut`?
 250                     .any(|a| a.check_name(sym::rustc_conversion_suggestion))
 251         });
 252
 253         methods
 254     }
 255
 256     /// This function checks whether the method is not static and does not accept other parameters than `self`.
 257     fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
 258         match method.kind {
 259             ty::AssocKind::Fn => {
 260                 method.fn_has_self_parameter
 261                     && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 262             }
 263             _ => false,
 264         }
 265     }
 266
 267     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 268     ///
 269     /// Given the following code:
 270     /// ```
 271     /// struct Foo;
 272     /// fn takes_ref(_: &Foo) {}
 273     /// let ref opt = Some(Foo);
 274     ///
 275     /// opt.map(|param| takes_ref(param));
 276     /// ```
 277     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 278     ///
 279     /// It only checks for `Option` and `Result` and won't work with
 280     /// ```
 281     /// opt.map(|param| { takes_ref(param) });
 282     /// ```
 283     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 284         let path = match expr.kind {
 285             hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
 286             _ => return None,
 287         };
 288
 289         let local_id = match path.res {
 290             hir::def::Res::Local(id) => id,
 291             _ => return None,
 292         };
 293
 294         let local_parent = self.tcx.hir().get_parent_node(local_id);
 295         let param_hir_id = match self.tcx.hir().find(local_parent) {
 296             Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
 297             _ => return None,
 298         };
 299
 300         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 301         let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
 302             Some(Node::Expr(hir::Expr {
 303                 hir_id,
 304                 kind: hir::ExprKind::Closure(_, decl, ..),
 305                 ..
 306             })) => (hir_id, decl),
 307             _ => return None,
 308         };
 309
 310         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 311         let hir = self.tcx.hir().find(expr_parent);
 312         let closure_params_len = closure_fn_decl.inputs.len();
 313         let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
 314             (
 315                 Some(Node::Expr(hir::Expr {
 316                     kind: hir::ExprKind::MethodCall(path, span, expr, _),
 317                     ..
 318                 })),
 319                 1,
 320             ) => (path, span, expr),
 321             _ => return None,
 322         };
 323
 324         let self_ty = self.typeck_results.borrow().node_type(method_expr[0].hir_id);
 325         let self_ty = format!("{:?}", self_ty);
 326         let name = method_path.ident.name;
 327         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 328             || self_ty.starts_with("&std::result::Result")
 329             || self_ty.starts_with("std::option::Option")
 330             || self_ty.starts_with("std::result::Result"))
 331             && (name == sym::map || name == sym::and_then);
 332         match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
 333             (true, Ok(src)) => {
 334                 let suggestion = format!("as_ref().{}", src);
 335                 Some((*method_span, "consider using `as_ref` instead", suggestion))
 336             }
 337             _ => None,
 338         }
 339     }
 340
 341     crate fn is_hir_id_from_struct_pattern_shorthand_field(
 342         &self,
 343         hir_id: hir::HirId,
 344         sp: Span,
 345     ) -> bool {
 346         let sm = self.sess().source_map();
 347         let parent_id = self.tcx.hir().get_parent_node(hir_id);
 348         if let Some(parent) = self.tcx.hir().find(parent_id) {
 349             // Account for fields
 350             if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
 351             {
 352                 if let Ok(src) = sm.span_to_snippet(sp) {
 353                     for field in *fields {
 354                         if field.ident.as_str() == src && field.is_shorthand {
 355                             return true;
 356                         }
 357                     }
 358                 }
 359             }
 360         }
 361         false
 362     }
 363
 364     fn replace_prefix<A, B, C>(&self, s: A, old: B, new: C) -> Option<String>
 365     where
 366         A: AsRef<str>,
 367         B: AsRef<str>,
 368         C: AsRef<str>,
 369     {
 370         let s = s.as_ref();
 371         let old = old.as_ref();
 372         if s.starts_with(old) { Some(new.as_ref().to_owned() + &s[old.len()..]) } else { None }
 373     }
 374
 375     /// This function is used to determine potential "simple" improvements or users' errors and
 376     /// provide them useful help. For example:
 377     ///
 378     /// ```
 379     /// fn some_fn(s: &str) {}
 380     ///
 381     /// let x = "hey!".to_owned();
 382     /// some_fn(x); // error
 383     /// ```
 384     ///
 385     /// No need to find every potential function which could make a coercion to transform a
 386     /// `String` into a `&str` since a `&` would do the trick!
 387     ///
 388     /// In addition of this check, it also checks between references mutability state. If the
 389     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 390     /// `&mut`!".
 391     pub fn check_ref(
 392         &self,
 393         expr: &hir::Expr<'_>,
 394         checked_ty: Ty<'tcx>,
 395         expected: Ty<'tcx>,
 396     ) -> Option<(Span, &'static str, String, Applicability)> {
 397         let sm = self.sess().source_map();
 398         let sp = expr.span;
 399         if sm.is_imported(sp) {
 400             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 401             // call span, but that breaks down when the type error comes from multiple calls down.
 402             return None;
 403         }
 404
 405         let is_struct_pat_shorthand_field =
 406             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 407
 408         // If the span is from a macro, then it's hard to extract the text
 409         // and make a good suggestion, so don't bother.
 410         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 411
 412         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 413         let expr = expr.peel_drop_temps();
 414
 415         match (&expr.kind, &expected.kind, &checked_ty.kind) {
 416             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
 417                 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
 418                     if let hir::ExprKind::Lit(_) = expr.kind {
 419                         if let Ok(src) = sm.span_to_snippet(sp) {
 420                             if let Some(src) = self.replace_prefix(src, "b\"", "\"") {
 421                                 return Some((
 422                                     sp,
 423                                     "consider removing the leading `b`",
 424                                     src,
 425                                     Applicability::MachineApplicable,
 426                                 ));
 427                             }
 428                         }
 429                     }
 430                 }
 431                 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
 432                     if let hir::ExprKind::Lit(_) = expr.kind {
 433                         if let Ok(src) = sm.span_to_snippet(sp) {
 434                             if let Some(src) = self.replace_prefix(src, "\"", "b\"") {
 435                                 return Some((
 436                                     sp,
 437                                     "consider adding a leading `b`",
 438                                     src,
 439                                     Applicability::MachineApplicable,
 440                                 ));
 441                             }
 442                         }
 443                     }
 444                 }
 445                 _ => {}
 446             },
 447             (_, &ty::Ref(_, _, mutability), _) => {
 448                 // Check if it can work when put into a ref. For example:
 449                 //
 450                 // ```
 451                 // fn bar(x: &mut i32) {}
 452                 //
 453                 // let x = 0u32;
 454                 // bar(&x); // error, expected &mut
 455                 // ```
 456                 let ref_ty = match mutability {
 457                     hir::Mutability::Mut => {
 458                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 459                     }
 460                     hir::Mutability::Not => {
 461                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 462                     }
 463                 };
 464                 if self.can_coerce(ref_ty, expected) {
 465                     let mut sugg_sp = sp;
 466                     if let hir::ExprKind::MethodCall(ref segment, sp, ref args, _) = expr.kind {
 467                         let clone_trait = self.tcx.require_lang_item(CloneTraitLangItem, Some(sp));
 468                         if let ([arg], Some(true), sym::clone) = (
 469                             &args[..],
 470                             self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
 471                                 |did| {
 472                                     let ai = self.tcx.associated_item(did);
 473                                     ai.container == ty::TraitContainer(clone_trait)
 474                                 },
 475                             ),
 476                             segment.ident.name,
 477                         ) {
 478                             // If this expression had a clone call when suggesting borrowing
 479                             // we want to suggest removing it because it'd now be unnecessary.
 480                             sugg_sp = arg.span;
 481                         }
 482                     }
 483                     if let Ok(src) = sm.span_to_snippet(sugg_sp) {
 484                         let needs_parens = match expr.kind {
 485                             // parenthesize if needed (Issue #46756)
 486                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 487                             // parenthesize borrows of range literals (Issue #54505)
 488                             _ if is_range_literal(self.tcx.sess.source_map(), expr) => true,
 489                             _ => false,
 490                         };
 491                         let sugg_expr = if needs_parens { format!("({})", src) } else { src };
 492
 493                         if let Some(sugg) = self.can_use_as_ref(expr) {
 494                             return Some((
 495                                 sugg.0,
 496                                 sugg.1,
 497                                 sugg.2,
 498                                 Applicability::MachineApplicable,
 499                             ));
 500                         }
 501                         let field_name = if is_struct_pat_shorthand_field {
 502                             format!("{}: ", sugg_expr)
 503                         } else {
 504                             String::new()
 505                         };
 506                         if let Some(hir::Node::Expr(hir::Expr {
 507                             kind: hir::ExprKind::Assign(left_expr, ..),
 508                             ..
 509                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 510                         {
 511                             if mutability == hir::Mutability::Mut {
 512                                 // Found the following case:
 513                                 // fn foo(opt: &mut Option<String>){ opt = None }
 514                                 //                                   ---   ^^^^
 515                                 //                                   |     |
 516                                 //    consider dereferencing here: `*opt`  |
 517                                 // expected mutable reference, found enum `Option`
 518                                 if let Ok(src) = sm.span_to_snippet(left_expr.span) {
 519                                     return Some((
 520                                         left_expr.span,
 521                                         "consider dereferencing here to assign to the mutable \
 522                                          borrowed piece of memory",
 523                                         format!("*{}", src),
 524                                         Applicability::MachineApplicable,
 525                                     ));
 526                                 }
 527                             }
 528                         }
 529
 530                         return Some(match mutability {
 531                             hir::Mutability::Mut => (
 532                                 sp,
 533                                 "consider mutably borrowing here",
 534                                 format!("{}&mut {}", field_name, sugg_expr),
 535                                 Applicability::MachineApplicable,
 536                             ),
 537                             hir::Mutability::Not => (
 538                                 sp,
 539                                 "consider borrowing here",
 540                                 format!("{}&{}", field_name, sugg_expr),
 541                                 Applicability::MachineApplicable,
 542                             ),
 543                         });
 544                     }
 545                 }
 546             }
 547             (
 548                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 549                 _,
 550                 &ty::Ref(_, checked, _),
 551             ) if {
 552                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 553             } =>
 554             {
 555                 // We have `&T`, check if what was expected was `T`. If so,
 556                 // we may want to suggest removing a `&`.
 557                 if sm.is_imported(expr.span) {
 558                     if let Ok(src) = sm.span_to_snippet(sp) {
 559                         if let Some(src) = self.replace_prefix(src, "&", "") {
 560                             return Some((
 561                                 sp,
 562                                 "consider removing the borrow",
 563                                 src,
 564                                 Applicability::MachineApplicable,
 565                             ));
 566                         }
 567                     }
 568                     return None;
 569                 }
 570                 if let Ok(code) = sm.span_to_snippet(expr.span) {
 571                     return Some((
 572                         sp,
 573                         "consider removing the borrow",
 574                         code,
 575                         Applicability::MachineApplicable,
 576                     ));
 577                 }
 578             }
 579             (
 580                 _,
 581                 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
 582                 &ty::Ref(_, ty_a, mutbl_a),
 583             ) => {
 584                 if let Some(steps) = self.deref_steps(ty_a, ty_b) {
 585                     // Only suggest valid if dereferencing needed.
 586                     if steps > 0 {
 587                         // The pointer type implements `Copy` trait so the suggestion is always valid.
 588                         if let Ok(src) = sm.span_to_snippet(sp) {
 589                             let derefs = &"*".repeat(steps);
 590                             if let Some((src, applicability)) = match mutbl_b {
 591                                 hir::Mutability::Mut => {
 592                                     let new_prefix = "&mut ".to_owned() + derefs;
 593                                     match mutbl_a {
 594                                         hir::Mutability::Mut => {
 595                                             if let Some(s) =
 596                                                 self.replace_prefix(src, "&mut ", new_prefix)
 597                                             {
 598                                                 Some((s, Applicability::MachineApplicable))
 599                                             } else {
 600                                                 None
 601                                             }
 602                                         }
 603                                         hir::Mutability::Not => {
 604                                             if let Some(s) =
 605                                                 self.replace_prefix(src, "&", new_prefix)
 606                                             {
 607                                                 Some((s, Applicability::Unspecified))
 608                                             } else {
 609                                                 None
 610                                             }
 611                                         }
 612                                     }
 613                                 }
 614                                 hir::Mutability::Not => {
 615                                     let new_prefix = "&".to_owned() + derefs;
 616                                     match mutbl_a {
 617                                         hir::Mutability::Mut => {
 618                                             if let Some(s) =
 619                                                 self.replace_prefix(src, "&mut ", new_prefix)
 620                                             {
 621                                                 Some((s, Applicability::MachineApplicable))
 622                                             } else {
 623                                                 None
 624                                             }
 625                                         }
 626                                         hir::Mutability::Not => {
 627                                             if let Some(s) =
 628                                                 self.replace_prefix(src, "&", new_prefix)
 629                                             {
 630                                                 Some((s, Applicability::MachineApplicable))
 631                                             } else {
 632                                                 None
 633                                             }
 634                                         }
 635                                     }
 636                                 }
 637                             } {
 638                                 return Some((sp, "consider dereferencing", src, applicability));
 639                             }
 640                         }
 641                     }
 642                 }
 643             }
 644             _ if sp == expr.span && !is_macro => {
 645                 if let Some(steps) = self.deref_steps(checked_ty, expected) {
 646                     if steps == 1 {
 647                         // For a suggestion to make sense, the type would need to be `Copy`.
 648                         if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp) {
 649                             if let Ok(code) = sm.span_to_snippet(sp) {
 650                                 let message = if checked_ty.is_region_ptr() {
 651                                     "consider dereferencing the borrow"
 652                                 } else {
 653                                     "consider dereferencing the type"
 654                                 };
 655                                 let suggestion = if is_struct_pat_shorthand_field {
 656                                     format!("{}: *{}", code, code)
 657                                 } else {
 658                                     format!("*{}", code)
 659                                 };
 660                                 return Some((
 661                                     sp,
 662                                     message,
 663                                     suggestion,
 664                                     Applicability::MachineApplicable,
 665                                 ));
 666                             }
 667                         }
 668                     }
 669                 }
 670             }
 671             _ => {}
 672         }
 673         None
 674     }
 675
 676     pub fn check_for_cast(
 677         &self,
 678         err: &mut DiagnosticBuilder<'_>,
 679         expr: &hir::Expr<'_>,
 680         checked_ty: Ty<'tcx>,
 681         expected_ty: Ty<'tcx>,
 682         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 683     ) -> bool {
 684         if self.tcx.sess.source_map().is_imported(expr.span) {
 685             // Ignore if span is from within a macro.
 686             return false;
 687         }
 688
 689         let src = if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 690             src
 691         } else {
 692             return false;
 693         };
 694
 695         // If casting this expression to a given numeric type would be appropriate in case of a type
 696         // mismatch.
 697         //
 698         // We want to minimize the amount of casting operations that are suggested, as it can be a
 699         // lossy operation with potentially bad side effects, so we only suggest when encountering
 700         // an expression that indicates that the original type couldn't be directly changed.
 701         //
 702         // For now, don't suggest casting with `as`.
 703         let can_cast = false;
 704
 705         let prefix = if let Some(hir::Node::Expr(hir::Expr {
 706             kind: hir::ExprKind::Struct(_, fields, _),
 707             ..
 708         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 709         {
 710             // `expr` is a literal field for a struct, only suggest if appropriate
 711             match (*fields)
 712                 .iter()
 713                 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
 714             {
 715                 // This is a field literal
 716                 Some(field) => format!("{}: ", field.ident),
 717                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 718                 None => return false,
 719             }
 720         } else {
 721             String::new()
 722         };
 723
 724         if let hir::ExprKind::Call(path, args) = &expr.kind {
 725             if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
 726                 (&path.kind, args.len())
 727             {
 728                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 729                 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
 730                     (&base_ty.kind, path_segment.ident.name)
 731                 {
 732                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
 733                         match ident.name {
 734                             sym::i128
 735                             | sym::i64
 736                             | sym::i32
 737                             | sym::i16
 738                             | sym::i8
 739                             | sym::u128
 740                             | sym::u64
 741                             | sym::u32
 742                             | sym::u16
 743                             | sym::u8
 744                             | sym::isize
 745                             | sym::usize
 746                                 if base_ty_path.segments.len() == 1 =>
 747                             {
 748                                 return false;
 749                             }
 750                             _ => {}
 751                         }
 752                     }
 753                 }
 754             }
 755         }
 756
 757         let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 758         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 759         let lit_msg = format!(
 760             "change the type of the numeric literal from `{}` to `{}`",
 761             checked_ty, expected_ty,
 762         );
 763
 764         let with_opt_paren: fn(&dyn fmt::Display) -> String =
 765             if expr.precedence().order() < PREC_POSTFIX {
 766                 |s| format!("({})", s)
 767             } else {
 768                 |s| s.to_string()
 769             };
 770
 771         let cast_suggestion = format!("{}{} as {}", prefix, with_opt_paren(&src), expected_ty);
 772         let into_suggestion = format!("{}{}.into()", prefix, with_opt_paren(&src));
 773         let suffix_suggestion = with_opt_paren(&format_args!(
 774             "{}{}",
 775             if matches!(
 776                 (&expected_ty.kind, &checked_ty.kind),
 777                 (ty::Int(_) | ty::Uint(_), ty::Float(_))
 778             ) {
 779                 // Remove fractional part from literal, for example `42.0f32` into `42`
 780                 let src = src.trim_end_matches(&checked_ty.to_string());
 781                 src.split('.').next().unwrap()
 782             } else {
 783                 src.trim_end_matches(&checked_ty.to_string())
 784             },
 785             expected_ty,
 786         ));
 787         let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
 788             if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
 789         };
 790         let is_negative_int =
 791             |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::UnNeg, ..));
 792         let is_uint = |ty: Ty<'_>| matches!(ty.kind, ty::Uint(..));
 793
 794         let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
 795
 796         let suggest_fallible_into_or_lhs_from =
 797             |err: &mut DiagnosticBuilder<'_>, exp_to_found_is_fallible: bool| {
 798                 // If we know the expression the expected type is derived from, we might be able
 799                 // to suggest a widening conversion rather than a narrowing one (which may
 800                 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
 801                 //   x > y
 802                 // can be given the suggestion "u32::from(x) > y" rather than
 803                 // "x > y.try_into().unwrap()".
 804                 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
 805                     match self.tcx.sess.source_map().span_to_snippet(expr.span).ok() {
 806                         Some(src) => Some((expr, src)),
 807                         None => None,
 808                     }
 809                 });
 810                 let (span, msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
 811                     (lhs_expr_and_src, exp_to_found_is_fallible)
 812                 {
 813                     let msg = format!(
 814                         "you can convert `{}` from `{}` to `{}`, matching the type of `{}`",
 815                         lhs_src, expected_ty, checked_ty, src
 816                     );
 817                     let suggestion = format!("{}::from({})", checked_ty, lhs_src);
 818                     (lhs_expr.span, msg, suggestion)
 819                 } else {
 820                     let msg = format!("{} and panic if the converted value wouldn't fit", msg);
 821                     let suggestion =
 822                         format!("{}{}.try_into().unwrap()", prefix, with_opt_paren(&src));
 823                     (expr.span, msg, suggestion)
 824                 };
 825                 err.span_suggestion(span, &msg, suggestion, Applicability::MachineApplicable);
 826             };
 827
 828         let suggest_to_change_suffix_or_into =
 829             |err: &mut DiagnosticBuilder<'_>,
 830              found_to_exp_is_fallible: bool,
 831              exp_to_found_is_fallible: bool| {
 832                 let always_fallible = found_to_exp_is_fallible
 833                     && (exp_to_found_is_fallible || expected_ty_expr.is_none());
 834                 let msg = if literal_is_ty_suffixed(expr) {
 835                     &lit_msg
 836                 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
 837                     // We now know that converting either the lhs or rhs is fallible. Before we
 838                     // suggest a fallible conversion, check if the value can never fit in the
 839                     // expected type.
 840                     let msg = format!("`{}` cannot fit into type `{}`", src, expected_ty);
 841                     err.note(&msg);
 842                     return;
 843                 } else if in_const_context {
 844                     // Do not recommend `into` or `try_into` in const contexts.
 845                     return;
 846                 } else if found_to_exp_is_fallible {
 847                     return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
 848                 } else {
 849                     &msg
 850                 };
 851                 let suggestion = if literal_is_ty_suffixed(expr) {
 852                     suffix_suggestion.clone()
 853                 } else {
 854                     into_suggestion.clone()
 855                 };
 856                 err.span_suggestion(expr.span, msg, suggestion, Applicability::MachineApplicable);
 857             };
 858
 859         match (&expected_ty.kind, &checked_ty.kind) {
 860             (&ty::Int(ref exp), &ty::Int(ref found)) => {
 861                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 862                 {
 863                     (Some(exp), Some(found)) if exp < found => (true, false),
 864                     (Some(exp), Some(found)) if exp > found => (false, true),
 865                     (None, Some(8 | 16)) => (false, true),
 866                     (Some(8 | 16), None) => (true, false),
 867                     (None, _) | (_, None) => (true, true),
 868                     _ => (false, false),
 869                 };
 870                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 871                 true
 872             }
 873             (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 874                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 875                 {
 876                     (Some(exp), Some(found)) if exp < found => (true, false),
 877                     (Some(exp), Some(found)) if exp > found => (false, true),
 878                     (None, Some(8 | 16)) => (false, true),
 879                     (Some(8 | 16), None) => (true, false),
 880                     (None, _) | (_, None) => (true, true),
 881                     _ => (false, false),
 882                 };
 883                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 884                 true
 885             }
 886             (&ty::Int(exp), &ty::Uint(found)) => {
 887                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 888                 {
 889                     (Some(exp), Some(found)) if found < exp => (false, true),
 890                     (None, Some(8)) => (false, true),
 891                     _ => (true, true),
 892                 };
 893                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 894                 true
 895             }
 896             (&ty::Uint(exp), &ty::Int(found)) => {
 897                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 898                 {
 899                     (Some(exp), Some(found)) if found > exp => (true, false),
 900                     (Some(8), None) => (true, false),
 901                     _ => (true, true),
 902                 };
 903                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 904                 true
 905             }
 906             (&ty::Float(ref exp), &ty::Float(ref found)) => {
 907                 if found.bit_width() < exp.bit_width() {
 908                     suggest_to_change_suffix_or_into(err, false, true);
 909                 } else if literal_is_ty_suffixed(expr) {
 910                     err.span_suggestion(
 911                         expr.span,
 912                         &lit_msg,
 913                         suffix_suggestion,
 914                         Applicability::MachineApplicable,
 915                     );
 916                 } else if can_cast {
 917                     // Missing try_into implementation for `f64` to `f32`
 918                     err.span_suggestion(
 919                         expr.span,
 920                         &format!("{}, producing the closest possible value", cast_msg),
 921                         cast_suggestion,
 922                         Applicability::MaybeIncorrect, // lossy conversion
 923                     );
 924                 }
 925                 true
 926             }
 927             (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
 928                 if literal_is_ty_suffixed(expr) {
 929                     err.span_suggestion(
 930                         expr.span,
 931                         &lit_msg,
 932                         suffix_suggestion,
 933                         Applicability::MachineApplicable,
 934                     );
 935                 } else if can_cast {
 936                     // Missing try_into implementation for `{float}` to `{integer}`
 937                     err.span_suggestion(
 938                         expr.span,
 939                         &format!("{}, rounding the float towards zero", msg),
 940                         cast_suggestion,
 941                         Applicability::MaybeIncorrect, // lossy conversion
 942                     );
 943                 }
 944                 true
 945             }
 946             (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 947                 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 948                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
 949                     err.span_suggestion(
 950                         expr.span,
 951                         &format!(
 952                             "{}, producing the floating point representation of the integer",
 953                             msg,
 954                         ),
 955                         into_suggestion,
 956                         Applicability::MachineApplicable,
 957                     );
 958                 } else if literal_is_ty_suffixed(expr) {
 959                     err.span_suggestion(
 960                         expr.span,
 961                         &lit_msg,
 962                         suffix_suggestion,
 963                         Applicability::MachineApplicable,
 964                     );
 965                 } else {
 966                     // Missing try_into implementation for `{integer}` to `{float}`
 967                     err.span_suggestion(
 968                         expr.span,
 969                         &format!(
 970                             "{}, producing the floating point representation of the integer,
 971                                  rounded if necessary",
 972                             cast_msg,
 973                         ),
 974                         cast_suggestion,
 975                         Applicability::MaybeIncorrect, // lossy conversion
 976                     );
 977                 }
 978                 true
 979             }
 980             (&ty::Float(ref exp), &ty::Int(ref found)) => {
 981                 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 982                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
 983                     err.span_suggestion(
 984                         expr.span,
 985                         &format!(
 986                             "{}, producing the floating point representation of the integer",
 987                             &msg,
 988                         ),
 989                         into_suggestion,
 990                         Applicability::MachineApplicable,
 991                     );
 992                 } else if literal_is_ty_suffixed(expr) {
 993                     err.span_suggestion(
 994                         expr.span,
 995                         &lit_msg,
 996                         suffix_suggestion,
 997                         Applicability::MachineApplicable,
 998                     );
 999                 } else {
1000                     // Missing try_into implementation for `{integer}` to `{float}`
1001                     err.span_suggestion(
1002                         expr.span,
1003                         &format!(
1004                             "{}, producing the floating point representation of the integer, \
1005                                 rounded if necessary",
1006                             &msg,
1007                         ),
1008                         cast_suggestion,
1009                         Applicability::MaybeIncorrect, // lossy conversion
1010                     );
1011                 }
1012                 true
1013             }
1014             _ => false,
1015         }
1016     }
1017 }