compiler/rustc_typeck/src/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::LangItem;
  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_no_capture_closure(err, expected, expr_ty);
  36         self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
  37         self.suggest_missing_parentheses(err, expr);
  38         self.note_need_for_fn_pointer(err, expected, expr_ty);
  39         self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
  40     }
  41
  42     // Requires that the two types unify, and prints an error message if
  43     // they don't.
  44     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  45         if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
  46             e.emit();
  47         }
  48     }
  49
  50     pub fn demand_suptype_diag(
  51         &self,
  52         sp: Span,
  53         expected: Ty<'tcx>,
  54         actual: Ty<'tcx>,
  55     ) -> Option<DiagnosticBuilder<'tcx>> {
  56         self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
  57     }
  58
  59     pub fn demand_suptype_with_origin(
  60         &self,
  61         cause: &ObligationCause<'tcx>,
  62         expected: Ty<'tcx>,
  63         actual: Ty<'tcx>,
  64     ) -> Option<DiagnosticBuilder<'tcx>> {
  65         match self.at(cause, self.param_env).sup(expected, actual) {
  66             Ok(InferOk { obligations, value: () }) => {
  67                 self.register_predicates(obligations);
  68                 None
  69             }
  70             Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
  71         }
  72     }
  73
  74     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  75         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  76             err.emit();
  77         }
  78     }
  79
  80     pub fn demand_eqtype_diag(
  81         &self,
  82         sp: Span,
  83         expected: Ty<'tcx>,
  84         actual: Ty<'tcx>,
  85     ) -> Option<DiagnosticBuilder<'tcx>> {
  86         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  87     }
  88
  89     pub fn demand_eqtype_with_origin(
  90         &self,
  91         cause: &ObligationCause<'tcx>,
  92         expected: Ty<'tcx>,
  93         actual: Ty<'tcx>,
  94     ) -> Option<DiagnosticBuilder<'tcx>> {
  95         match self.at(cause, self.param_env).eq(expected, actual) {
  96             Ok(InferOk { obligations, value: () }) => {
  97                 self.register_predicates(obligations);
  98                 None
  99             }
 100             Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
 101         }
 102     }
 103
 104     pub fn demand_coerce(
 105         &self,
 106         expr: &hir::Expr<'_>,
 107         checked_ty: Ty<'tcx>,
 108         expected: Ty<'tcx>,
 109         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 110         allow_two_phase: AllowTwoPhase,
 111     ) -> Ty<'tcx> {
 112         let (ty, err) =
 113             self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
 114         if let Some(mut err) = err {
 115             err.emit();
 116         }
 117         ty
 118     }
 119
 120     /// Checks that the type of `expr` can be coerced to `expected`.
 121     ///
 122     /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
 123     /// will be permitted if the 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| self.sess().check_name(a, 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(&self, s: &str, old: &str, new: &str) -> Option<String> {
 365         if let Some(stripped) = s.strip_prefix(old) {
 366             Some(new.to_string() + stripped)
 367         } else {
 368             None
 369         }
 370     }
 371
 372     /// This function is used to determine potential "simple" improvements or users' errors and
 373     /// provide them useful help. For example:
 374     ///
 375     /// ```
 376     /// fn some_fn(s: &str) {}
 377     ///
 378     /// let x = "hey!".to_owned();
 379     /// some_fn(x); // error
 380     /// ```
 381     ///
 382     /// No need to find every potential function which could make a coercion to transform a
 383     /// `String` into a `&str` since a `&` would do the trick!
 384     ///
 385     /// In addition of this check, it also checks between references mutability state. If the
 386     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 387     /// `&mut`!".
 388     pub fn check_ref(
 389         &self,
 390         expr: &hir::Expr<'_>,
 391         checked_ty: Ty<'tcx>,
 392         expected: Ty<'tcx>,
 393     ) -> Option<(Span, &'static str, String, Applicability)> {
 394         let sm = self.sess().source_map();
 395         let sp = expr.span;
 396         if sm.is_imported(sp) {
 397             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 398             // call span, but that breaks down when the type error comes from multiple calls down.
 399             return None;
 400         }
 401
 402         let is_struct_pat_shorthand_field =
 403             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 404
 405         // If the span is from a macro, then it's hard to extract the text
 406         // and make a good suggestion, so don't bother.
 407         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 408
 409         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 410         let expr = expr.peel_drop_temps();
 411
 412         match (&expr.kind, expected.kind(), checked_ty.kind()) {
 413             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
 414                 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
 415                     if let hir::ExprKind::Lit(_) = expr.kind {
 416                         if let Ok(src) = sm.span_to_snippet(sp) {
 417                             if let Some(src) = self.replace_prefix(&src, "b\"", "\"") {
 418                                 return Some((
 419                                     sp,
 420                                     "consider removing the leading `b`",
 421                                     src,
 422                                     Applicability::MachineApplicable,
 423                                 ));
 424                             }
 425                         }
 426                     }
 427                 }
 428                 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
 429                     if let hir::ExprKind::Lit(_) = expr.kind {
 430                         if let Ok(src) = sm.span_to_snippet(sp) {
 431                             if let Some(src) = self.replace_prefix(&src, "\"", "b\"") {
 432                                 return Some((
 433                                     sp,
 434                                     "consider adding a leading `b`",
 435                                     src,
 436                                     Applicability::MachineApplicable,
 437                                 ));
 438                             }
 439                         }
 440                     }
 441                 }
 442                 _ => {}
 443             },
 444             (_, &ty::Ref(_, _, mutability), _) => {
 445                 // Check if it can work when put into a ref. For example:
 446                 //
 447                 // ```
 448                 // fn bar(x: &mut i32) {}
 449                 //
 450                 // let x = 0u32;
 451                 // bar(&x); // error, expected &mut
 452                 // ```
 453                 let ref_ty = match mutability {
 454                     hir::Mutability::Mut => {
 455                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 456                     }
 457                     hir::Mutability::Not => {
 458                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 459                     }
 460                 };
 461                 if self.can_coerce(ref_ty, expected) {
 462                     let mut sugg_sp = sp;
 463                     if let hir::ExprKind::MethodCall(ref segment, sp, ref args, _) = expr.kind {
 464                         let clone_trait = self.tcx.require_lang_item(LangItem::Clone, Some(sp));
 465                         if let ([arg], Some(true), sym::clone) = (
 466                             &args[..],
 467                             self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
 468                                 |did| {
 469                                     let ai = self.tcx.associated_item(did);
 470                                     ai.container == ty::TraitContainer(clone_trait)
 471                                 },
 472                             ),
 473                             segment.ident.name,
 474                         ) {
 475                             // If this expression had a clone call when suggesting borrowing
 476                             // we want to suggest removing it because it'd now be unnecessary.
 477                             sugg_sp = arg.span;
 478                         }
 479                     }
 480                     if let Ok(src) = sm.span_to_snippet(sugg_sp) {
 481                         let needs_parens = match expr.kind {
 482                             // parenthesize if needed (Issue #46756)
 483                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 484                             // parenthesize borrows of range literals (Issue #54505)
 485                             _ if is_range_literal(expr) => true,
 486                             _ => false,
 487                         };
 488                         let sugg_expr = if needs_parens { format!("({})", src) } else { src };
 489
 490                         if let Some(sugg) = self.can_use_as_ref(expr) {
 491                             return Some((
 492                                 sugg.0,
 493                                 sugg.1,
 494                                 sugg.2,
 495                                 Applicability::MachineApplicable,
 496                             ));
 497                         }
 498                         let field_name = if is_struct_pat_shorthand_field {
 499                             format!("{}: ", sugg_expr)
 500                         } else {
 501                             String::new()
 502                         };
 503                         if let Some(hir::Node::Expr(hir::Expr {
 504                             kind: hir::ExprKind::Assign(left_expr, ..),
 505                             ..
 506                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 507                         {
 508                             if mutability == hir::Mutability::Mut {
 509                                 // Found the following case:
 510                                 // fn foo(opt: &mut Option<String>){ opt = None }
 511                                 //                                   ---   ^^^^
 512                                 //                                   |     |
 513                                 //    consider dereferencing here: `*opt`  |
 514                                 // expected mutable reference, found enum `Option`
 515                                 if let Ok(src) = sm.span_to_snippet(left_expr.span) {
 516                                     return Some((
 517                                         left_expr.span,
 518                                         "consider dereferencing here to assign to the mutable \
 519                                          borrowed piece of memory",
 520                                         format!("*{}", src),
 521                                         Applicability::MachineApplicable,
 522                                     ));
 523                                 }
 524                             }
 525                         }
 526
 527                         return Some(match mutability {
 528                             hir::Mutability::Mut => (
 529                                 sp,
 530                                 "consider mutably borrowing here",
 531                                 format!("{}&mut {}", field_name, sugg_expr),
 532                                 Applicability::MachineApplicable,
 533                             ),
 534                             hir::Mutability::Not => (
 535                                 sp,
 536                                 "consider borrowing here",
 537                                 format!("{}&{}", field_name, sugg_expr),
 538                                 Applicability::MachineApplicable,
 539                             ),
 540                         });
 541                     }
 542                 }
 543             }
 544             (
 545                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 546                 _,
 547                 &ty::Ref(_, checked, _),
 548             ) if {
 549                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 550             } =>
 551             {
 552                 // We have `&T`, check if what was expected was `T`. If so,
 553                 // we may want to suggest removing a `&`.
 554                 if sm.is_imported(expr.span) {
 555                     if let Ok(src) = sm.span_to_snippet(sp) {
 556                         if let Some(src) = self.replace_prefix(&src, "&", "") {
 557                             return Some((
 558                                 sp,
 559                                 "consider removing the borrow",
 560                                 src,
 561                                 Applicability::MachineApplicable,
 562                             ));
 563                         }
 564                     }
 565                     return None;
 566                 }
 567                 if let Ok(code) = sm.span_to_snippet(expr.span) {
 568                     return Some((
 569                         sp,
 570                         "consider removing the borrow",
 571                         code,
 572                         Applicability::MachineApplicable,
 573                     ));
 574                 }
 575             }
 576             (
 577                 _,
 578                 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
 579                 &ty::Ref(_, ty_a, mutbl_a),
 580             ) => {
 581                 if let Some(steps) = self.deref_steps(ty_a, ty_b) {
 582                     // Only suggest valid if dereferencing needed.
 583                     if steps > 0 {
 584                         // The pointer type implements `Copy` trait so the suggestion is always valid.
 585                         if let Ok(src) = sm.span_to_snippet(sp) {
 586                             let derefs = &"*".repeat(steps);
 587                             if let Some((src, applicability)) = match mutbl_b {
 588                                 hir::Mutability::Mut => {
 589                                     let new_prefix = "&mut ".to_owned() + derefs;
 590                                     match mutbl_a {
 591                                         hir::Mutability::Mut => {
 592                                             if let Some(s) =
 593                                                 self.replace_prefix(&src, "&mut ", &new_prefix)
 594                                             {
 595                                                 Some((s, Applicability::MachineApplicable))
 596                                             } else {
 597                                                 None
 598                                             }
 599                                         }
 600                                         hir::Mutability::Not => {
 601                                             if let Some(s) =
 602                                                 self.replace_prefix(&src, "&", &new_prefix)
 603                                             {
 604                                                 Some((s, Applicability::Unspecified))
 605                                             } else {
 606                                                 None
 607                                             }
 608                                         }
 609                                     }
 610                                 }
 611                                 hir::Mutability::Not => {
 612                                     let new_prefix = "&".to_owned() + derefs;
 613                                     match mutbl_a {
 614                                         hir::Mutability::Mut => {
 615                                             if let Some(s) =
 616                                                 self.replace_prefix(&src, "&mut ", &new_prefix)
 617                                             {
 618                                                 Some((s, Applicability::MachineApplicable))
 619                                             } else {
 620                                                 None
 621                                             }
 622                                         }
 623                                         hir::Mutability::Not => {
 624                                             if let Some(s) =
 625                                                 self.replace_prefix(&src, "&", &new_prefix)
 626                                             {
 627                                                 Some((s, Applicability::MachineApplicable))
 628                                             } else {
 629                                                 None
 630                                             }
 631                                         }
 632                                     }
 633                                 }
 634                             } {
 635                                 return Some((sp, "consider dereferencing", src, applicability));
 636                             }
 637                         }
 638                     }
 639                 }
 640             }
 641             _ if sp == expr.span && !is_macro => {
 642                 if let Some(steps) = self.deref_steps(checked_ty, expected) {
 643                     if steps == 1 {
 644                         // For a suggestion to make sense, the type would need to be `Copy`.
 645                         if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp) {
 646                             if let Ok(code) = sm.span_to_snippet(sp) {
 647                                 let message = if checked_ty.is_region_ptr() {
 648                                     "consider dereferencing the borrow"
 649                                 } else {
 650                                     "consider dereferencing the type"
 651                                 };
 652                                 let suggestion = if is_struct_pat_shorthand_field {
 653                                     format!("{}: *{}", code, code)
 654                                 } else {
 655                                     format!("*{}", code)
 656                                 };
 657                                 return Some((
 658                                     sp,
 659                                     message,
 660                                     suggestion,
 661                                     Applicability::MachineApplicable,
 662                                 ));
 663                             }
 664                         }
 665                     }
 666                 }
 667             }
 668             _ => {}
 669         }
 670         None
 671     }
 672
 673     pub fn check_for_cast(
 674         &self,
 675         err: &mut DiagnosticBuilder<'_>,
 676         expr: &hir::Expr<'_>,
 677         checked_ty: Ty<'tcx>,
 678         expected_ty: Ty<'tcx>,
 679         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 680     ) -> bool {
 681         if self.tcx.sess.source_map().is_imported(expr.span) {
 682             // Ignore if span is from within a macro.
 683             return false;
 684         }
 685
 686         let src = if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 687             src
 688         } else {
 689             return false;
 690         };
 691
 692         // If casting this expression to a given numeric type would be appropriate in case of a type
 693         // mismatch.
 694         //
 695         // We want to minimize the amount of casting operations that are suggested, as it can be a
 696         // lossy operation with potentially bad side effects, so we only suggest when encountering
 697         // an expression that indicates that the original type couldn't be directly changed.
 698         //
 699         // For now, don't suggest casting with `as`.
 700         let can_cast = false;
 701
 702         let prefix = if let Some(hir::Node::Expr(hir::Expr {
 703             kind: hir::ExprKind::Struct(_, fields, _),
 704             ..
 705         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 706         {
 707             // `expr` is a literal field for a struct, only suggest if appropriate
 708             match (*fields)
 709                 .iter()
 710                 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
 711             {
 712                 // This is a field literal
 713                 Some(field) => format!("{}: ", field.ident),
 714                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 715                 None => return false,
 716             }
 717         } else {
 718             String::new()
 719         };
 720
 721         if let hir::ExprKind::Call(path, args) = &expr.kind {
 722             if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
 723                 (&path.kind, args.len())
 724             {
 725                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 726                 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
 727                     (&base_ty.kind, path_segment.ident.name)
 728                 {
 729                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
 730                         match ident.name {
 731                             sym::i128
 732                             | sym::i64
 733                             | sym::i32
 734                             | sym::i16
 735                             | sym::i8
 736                             | sym::u128
 737                             | sym::u64
 738                             | sym::u32
 739                             | sym::u16
 740                             | sym::u8
 741                             | sym::isize
 742                             | sym::usize
 743                                 if base_ty_path.segments.len() == 1 =>
 744                             {
 745                                 return false;
 746                             }
 747                             _ => {}
 748                         }
 749                     }
 750                 }
 751             }
 752         }
 753
 754         let msg = format!(
 755             "you can convert {} `{}` to {} `{}`",
 756             checked_ty.kind().article(),
 757             checked_ty,
 758             expected_ty.kind().article(),
 759             expected_ty,
 760         );
 761         let cast_msg = format!(
 762             "you can cast {} `{}` to {} `{}`",
 763             checked_ty.kind().article(),
 764             checked_ty,
 765             expected_ty.kind().article(),
 766             expected_ty,
 767         );
 768         let lit_msg = format!(
 769             "change the type of the numeric literal from `{}` to `{}`",
 770             checked_ty, expected_ty,
 771         );
 772
 773         let with_opt_paren: fn(&dyn fmt::Display) -> String =
 774             if expr.precedence().order() < PREC_POSTFIX {
 775                 |s| format!("({})", s)
 776             } else {
 777                 |s| s.to_string()
 778             };
 779
 780         let cast_suggestion = format!("{}{} as {}", prefix, with_opt_paren(&src), expected_ty);
 781         let into_suggestion = format!("{}{}.into()", prefix, with_opt_paren(&src));
 782         let suffix_suggestion = with_opt_paren(&format_args!(
 783             "{}{}",
 784             if matches!(
 785                 (&expected_ty.kind(), &checked_ty.kind()),
 786                 (ty::Int(_) | ty::Uint(_), ty::Float(_))
 787             ) {
 788                 // Remove fractional part from literal, for example `42.0f32` into `42`
 789                 let src = src.trim_end_matches(&checked_ty.to_string());
 790                 src.split('.').next().unwrap()
 791             } else {
 792                 src.trim_end_matches(&checked_ty.to_string())
 793             },
 794             expected_ty,
 795         ));
 796         let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
 797             if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
 798         };
 799         let is_negative_int =
 800             |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::UnNeg, ..));
 801         let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
 802
 803         let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
 804
 805         let suggest_fallible_into_or_lhs_from =
 806             |err: &mut DiagnosticBuilder<'_>, exp_to_found_is_fallible: bool| {
 807                 // If we know the expression the expected type is derived from, we might be able
 808                 // to suggest a widening conversion rather than a narrowing one (which may
 809                 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
 810                 //   x > y
 811                 // can be given the suggestion "u32::from(x) > y" rather than
 812                 // "x > y.try_into().unwrap()".
 813                 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
 814                     self.tcx
 815                         .sess
 816                         .source_map()
 817                         .span_to_snippet(expr.span)
 818                         .ok()
 819                         .map(|src| (expr, src))
 820                 });
 821                 let (span, msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
 822                     (lhs_expr_and_src, exp_to_found_is_fallible)
 823                 {
 824                     let msg = format!(
 825                         "you can convert `{}` from `{}` to `{}`, matching the type of `{}`",
 826                         lhs_src, expected_ty, checked_ty, src
 827                     );
 828                     let suggestion = format!("{}::from({})", checked_ty, lhs_src);
 829                     (lhs_expr.span, msg, suggestion)
 830                 } else {
 831                     let msg = format!("{} and panic if the converted value doesn't fit", msg);
 832                     let suggestion =
 833                         format!("{}{}.try_into().unwrap()", prefix, with_opt_paren(&src));
 834                     (expr.span, msg, suggestion)
 835                 };
 836                 err.span_suggestion(span, &msg, suggestion, Applicability::MachineApplicable);
 837             };
 838
 839         let suggest_to_change_suffix_or_into =
 840             |err: &mut DiagnosticBuilder<'_>,
 841              found_to_exp_is_fallible: bool,
 842              exp_to_found_is_fallible: bool| {
 843                 let always_fallible = found_to_exp_is_fallible
 844                     && (exp_to_found_is_fallible || expected_ty_expr.is_none());
 845                 let msg = if literal_is_ty_suffixed(expr) {
 846                     &lit_msg
 847                 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
 848                     // We now know that converting either the lhs or rhs is fallible. Before we
 849                     // suggest a fallible conversion, check if the value can never fit in the
 850                     // expected type.
 851                     let msg = format!("`{}` cannot fit into type `{}`", src, expected_ty);
 852                     err.note(&msg);
 853                     return;
 854                 } else if in_const_context {
 855                     // Do not recommend `into` or `try_into` in const contexts.
 856                     return;
 857                 } else if found_to_exp_is_fallible {
 858                     return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
 859                 } else {
 860                     &msg
 861                 };
 862                 let suggestion = if literal_is_ty_suffixed(expr) {
 863                     suffix_suggestion.clone()
 864                 } else {
 865                     into_suggestion.clone()
 866                 };
 867                 err.span_suggestion(expr.span, msg, suggestion, Applicability::MachineApplicable);
 868             };
 869
 870         match (&expected_ty.kind(), &checked_ty.kind()) {
 871             (&ty::Int(ref exp), &ty::Int(ref found)) => {
 872                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 873                 {
 874                     (Some(exp), Some(found)) if exp < found => (true, false),
 875                     (Some(exp), Some(found)) if exp > found => (false, true),
 876                     (None, Some(8 | 16)) => (false, true),
 877                     (Some(8 | 16), None) => (true, false),
 878                     (None, _) | (_, None) => (true, true),
 879                     _ => (false, false),
 880                 };
 881                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 882                 true
 883             }
 884             (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 885                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 886                 {
 887                     (Some(exp), Some(found)) if exp < found => (true, false),
 888                     (Some(exp), Some(found)) if exp > found => (false, true),
 889                     (None, Some(8 | 16)) => (false, true),
 890                     (Some(8 | 16), None) => (true, false),
 891                     (None, _) | (_, None) => (true, true),
 892                     _ => (false, false),
 893                 };
 894                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 895                 true
 896             }
 897             (&ty::Int(exp), &ty::Uint(found)) => {
 898                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 899                 {
 900                     (Some(exp), Some(found)) if found < exp => (false, true),
 901                     (None, Some(8)) => (false, true),
 902                     _ => (true, true),
 903                 };
 904                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 905                 true
 906             }
 907             (&ty::Uint(exp), &ty::Int(found)) => {
 908                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 909                 {
 910                     (Some(exp), Some(found)) if found > exp => (true, false),
 911                     (Some(8), None) => (true, false),
 912                     _ => (true, true),
 913                 };
 914                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 915                 true
 916             }
 917             (&ty::Float(ref exp), &ty::Float(ref found)) => {
 918                 if found.bit_width() < exp.bit_width() {
 919                     suggest_to_change_suffix_or_into(err, false, true);
 920                 } else if literal_is_ty_suffixed(expr) {
 921                     err.span_suggestion(
 922                         expr.span,
 923                         &lit_msg,
 924                         suffix_suggestion,
 925                         Applicability::MachineApplicable,
 926                     );
 927                 } else if can_cast {
 928                     // Missing try_into implementation for `f64` to `f32`
 929                     err.span_suggestion(
 930                         expr.span,
 931                         &format!("{}, producing the closest possible value", cast_msg),
 932                         cast_suggestion,
 933                         Applicability::MaybeIncorrect, // lossy conversion
 934                     );
 935                 }
 936                 true
 937             }
 938             (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
 939                 if literal_is_ty_suffixed(expr) {
 940                     err.span_suggestion(
 941                         expr.span,
 942                         &lit_msg,
 943                         suffix_suggestion,
 944                         Applicability::MachineApplicable,
 945                     );
 946                 } else if can_cast {
 947                     // Missing try_into implementation for `{float}` to `{integer}`
 948                     err.span_suggestion(
 949                         expr.span,
 950                         &format!("{}, rounding the float towards zero", msg),
 951                         cast_suggestion,
 952                         Applicability::MaybeIncorrect, // lossy conversion
 953                     );
 954                 }
 955                 true
 956             }
 957             (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 958                 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 959                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
 960                     err.span_suggestion(
 961                         expr.span,
 962                         &format!(
 963                             "{}, producing the floating point representation of the integer",
 964                             msg,
 965                         ),
 966                         into_suggestion,
 967                         Applicability::MachineApplicable,
 968                     );
 969                 } else if literal_is_ty_suffixed(expr) {
 970                     err.span_suggestion(
 971                         expr.span,
 972                         &lit_msg,
 973                         suffix_suggestion,
 974                         Applicability::MachineApplicable,
 975                     );
 976                 } else {
 977                     // Missing try_into implementation for `{integer}` to `{float}`
 978                     err.span_suggestion(
 979                         expr.span,
 980                         &format!(
 981                             "{}, producing the floating point representation of the integer,
 982                                  rounded if necessary",
 983                             cast_msg,
 984                         ),
 985                         cast_suggestion,
 986                         Applicability::MaybeIncorrect, // lossy conversion
 987                     );
 988                 }
 989                 true
 990             }
 991             (&ty::Float(ref exp), &ty::Int(ref found)) => {
 992                 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 993                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
 994                     err.span_suggestion(
 995                         expr.span,
 996                         &format!(
 997                             "{}, producing the floating point representation of the integer",
 998                             &msg,
 999                         ),
1000                         into_suggestion,
1001                         Applicability::MachineApplicable,
1002                     );
1003                 } else if literal_is_ty_suffixed(expr) {
1004                     err.span_suggestion(
1005                         expr.span,
1006                         &lit_msg,
1007                         suffix_suggestion,
1008                         Applicability::MachineApplicable,
1009                     );
1010                 } else {
1011                     // Missing try_into implementation for `{integer}` to `{float}`
1012                     err.span_suggestion(
1013                         expr.span,
1014                         &format!(
1015                             "{}, producing the floating point representation of the integer, \
1016                                 rounded if necessary",
1017                             &msg,
1018                         ),
1019                         cast_suggestion,
1020                         Applicability::MaybeIncorrect, // lossy conversion
1021                     );
1022                 }
1023                 true
1024             }
1025             _ => false,
1026         }
1027     }
1028 }