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.note_need_for_fn_pointer(err, expected, expr_ty);
  38     }
  39
  40     // Requires that the two types unify, and prints an error message if
  41     // they don't.
  42     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  43         if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
  44             e.emit();
  45         }
  46     }
  47
  48     pub fn demand_suptype_diag(
  49         &self,
  50         sp: Span,
  51         expected: Ty<'tcx>,
  52         actual: Ty<'tcx>,
  53     ) -> Option<DiagnosticBuilder<'tcx>> {
  54         self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
  55     }
  56
  57     pub fn demand_suptype_with_origin(
  58         &self,
  59         cause: &ObligationCause<'tcx>,
  60         expected: Ty<'tcx>,
  61         actual: Ty<'tcx>,
  62     ) -> Option<DiagnosticBuilder<'tcx>> {
  63         match self.at(cause, self.param_env).sup(expected, actual) {
  64             Ok(InferOk { obligations, value: () }) => {
  65                 self.register_predicates(obligations);
  66                 None
  67             }
  68             Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
  69         }
  70     }
  71
  72     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  73         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  74             err.emit();
  75         }
  76     }
  77
  78     pub fn demand_eqtype_diag(
  79         &self,
  80         sp: Span,
  81         expected: Ty<'tcx>,
  82         actual: Ty<'tcx>,
  83     ) -> Option<DiagnosticBuilder<'tcx>> {
  84         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  85     }
  86
  87     pub fn demand_eqtype_with_origin(
  88         &self,
  89         cause: &ObligationCause<'tcx>,
  90         expected: Ty<'tcx>,
  91         actual: Ty<'tcx>,
  92     ) -> Option<DiagnosticBuilder<'tcx>> {
  93         match self.at(cause, self.param_env).eq(expected, actual) {
  94             Ok(InferOk { obligations, value: () }) => {
  95                 self.register_predicates(obligations);
  96                 None
  97             }
  98             Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
  99         }
 100     }
 101
 102     pub fn demand_coerce(
 103         &self,
 104         expr: &hir::Expr<'_>,
 105         checked_ty: Ty<'tcx>,
 106         expected: Ty<'tcx>,
 107         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 108         allow_two_phase: AllowTwoPhase,
 109     ) -> Ty<'tcx> {
 110         let (ty, err) =
 111             self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
 112         if let Some(mut err) = err {
 113             err.emit();
 114         }
 115         ty
 116     }
 117
 118     // Checks that the type of `expr` can be coerced to `expected`.
 119     //
 120     // N.B., this code relies on `self.diverges` to be accurate. In
 121     // particular, assignments to `!` will be permitted if the
 122     // diverges flag is currently "always".
 123     pub fn demand_coerce_diag(
 124         &self,
 125         expr: &hir::Expr<'_>,
 126         checked_ty: Ty<'tcx>,
 127         expected: Ty<'tcx>,
 128         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 129         allow_two_phase: AllowTwoPhase,
 130     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
 131         let expected = self.resolve_vars_with_obligations(expected);
 132
 133         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
 134             Ok(ty) => return (ty, None),
 135             Err(e) => e,
 136         };
 137
 138         let expr = expr.peel_drop_temps();
 139         let cause = self.misc(expr.span);
 140         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 141         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
 142
 143         if self.is_assign_to_bool(expr, expected) {
 144             // Error reported in `check_assign` so avoid emitting error again.
 145             err.delay_as_bug();
 146             return (expected, None);
 147         }
 148
 149         self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr);
 150
 151         (expected, Some(err))
 152     }
 153
 154     fn annotate_expected_due_to_let_ty(
 155         &self,
 156         err: &mut DiagnosticBuilder<'_>,
 157         expr: &hir::Expr<'_>,
 158     ) {
 159         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 160         if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
 161             self.tcx.hir().find(parent)
 162         {
 163             if init.hir_id == expr.hir_id {
 164                 // Point at `let` assignment type.
 165                 err.span_label(ty.span, "expected due to this");
 166             }
 167         }
 168     }
 169
 170     /// Returns whether the expected type is `bool` and the expression is `x = y`.
 171     pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
 172         if let hir::ExprKind::Assign(..) = expr.kind {
 173             return expected == self.tcx.types.bool;
 174         }
 175         false
 176     }
 177
 178     /// If the expected type is an enum (Issue #55250) with any variants whose
 179     /// sole field is of the found type, suggest such variants. (Issue #42764)
 180     fn suggest_compatible_variants(
 181         &self,
 182         err: &mut DiagnosticBuilder<'_>,
 183         expr: &hir::Expr<'_>,
 184         expected: Ty<'tcx>,
 185         expr_ty: Ty<'tcx>,
 186     ) {
 187         if let ty::Adt(expected_adt, substs) = expected.kind {
 188             if !expected_adt.is_enum() {
 189                 return;
 190             }
 191
 192             let mut compatible_variants = expected_adt
 193                 .variants
 194                 .iter()
 195                 .filter(|variant| variant.fields.len() == 1)
 196                 .filter_map(|variant| {
 197                     let sole_field = &variant.fields[0];
 198                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 199                     if self.can_coerce(expr_ty, sole_field_ty) {
 200                         let variant_path = self.tcx.def_path_str(variant.def_id);
 201                         // FIXME #56861: DRYer prelude filtering
 202                         Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
 203                     } else {
 204                         None
 205                     }
 206                 })
 207                 .peekable();
 208
 209             if compatible_variants.peek().is_some() {
 210                 if let Ok(expr_text) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 211                     let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
 212                     let msg = "try using a variant of the expected enum";
 213                     err.span_suggestions(
 214                         expr.span,
 215                         msg,
 216                         suggestions,
 217                         Applicability::MaybeIncorrect,
 218                     );
 219                 }
 220             }
 221         }
 222     }
 223
 224     pub fn get_conversion_methods(
 225         &self,
 226         span: Span,
 227         expected: Ty<'tcx>,
 228         checked_ty: Ty<'tcx>,
 229         hir_id: hir::HirId,
 230     ) -> Vec<AssocItem> {
 231         let mut methods =
 232             self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
 233         methods.retain(|m| {
 234             self.has_only_self_parameter(m)
 235                 && self
 236                     .tcx
 237                     .get_attrs(m.def_id)
 238                     .iter()
 239                     // This special internal attribute is used to permit
 240                     // "identity-like" conversion methods to be suggested here.
 241                     //
 242                     // FIXME (#46459 and #46460): ideally
 243                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 244                     // also be `#[rustc_conversion_suggestion]`, if not for
 245                     // method-probing false-positives and -negatives (respectively).
 246                     //
 247                     // FIXME? Other potential candidate methods: `as_ref` and
 248                     // `as_mut`?
 249                     .any(|a| a.check_name(sym::rustc_conversion_suggestion))
 250         });
 251
 252         methods
 253     }
 254
 255     /// This function checks whether the method is not static and does not accept other parameters than `self`.
 256     fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
 257         match method.kind {
 258             ty::AssocKind::Fn => {
 259                 method.fn_has_self_parameter
 260                     && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 261             }
 262             _ => false,
 263         }
 264     }
 265
 266     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 267     ///
 268     /// Given the following code:
 269     /// ```
 270     /// struct Foo;
 271     /// fn takes_ref(_: &Foo) {}
 272     /// let ref opt = Some(Foo);
 273     ///
 274     /// opt.map(|param| takes_ref(param));
 275     /// ```
 276     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 277     ///
 278     /// It only checks for `Option` and `Result` and won't work with
 279     /// ```
 280     /// opt.map(|param| { takes_ref(param) });
 281     /// ```
 282     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 283         let path = match expr.kind {
 284             hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
 285             _ => return None,
 286         };
 287
 288         let local_id = match path.res {
 289             hir::def::Res::Local(id) => id,
 290             _ => return None,
 291         };
 292
 293         let local_parent = self.tcx.hir().get_parent_node(local_id);
 294         let param_hir_id = match self.tcx.hir().find(local_parent) {
 295             Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
 296             _ => return None,
 297         };
 298
 299         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 300         let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
 301             Some(Node::Expr(hir::Expr {
 302                 hir_id,
 303                 kind: hir::ExprKind::Closure(_, decl, ..),
 304                 ..
 305             })) => (hir_id, decl),
 306             _ => return None,
 307         };
 308
 309         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 310         let hir = self.tcx.hir().find(expr_parent);
 311         let closure_params_len = closure_fn_decl.inputs.len();
 312         let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
 313             (
 314                 Some(Node::Expr(hir::Expr {
 315                     kind: hir::ExprKind::MethodCall(path, span, expr, _),
 316                     ..
 317                 })),
 318                 1,
 319             ) => (path, span, expr),
 320             _ => return None,
 321         };
 322
 323         let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
 324         let self_ty = format!("{:?}", self_ty);
 325         let name = method_path.ident.as_str();
 326         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 327             || self_ty.starts_with("&std::result::Result")
 328             || self_ty.starts_with("std::option::Option")
 329             || self_ty.starts_with("std::result::Result"))
 330             && (name == "map" || name == "and_then");
 331         match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
 332             (true, Ok(src)) => {
 333                 let suggestion = format!("as_ref().{}", src);
 334                 Some((*method_span, "consider using `as_ref` instead", suggestion))
 335             }
 336             _ => None,
 337         }
 338     }
 339
 340     crate fn is_hir_id_from_struct_pattern_shorthand_field(
 341         &self,
 342         hir_id: hir::HirId,
 343         sp: Span,
 344     ) -> bool {
 345         let sm = self.sess().source_map();
 346         let parent_id = self.tcx.hir().get_parent_node(hir_id);
 347         if let Some(parent) = self.tcx.hir().find(parent_id) {
 348             // Account for fields
 349             if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
 350             {
 351                 if let Ok(src) = sm.span_to_snippet(sp) {
 352                     for field in *fields {
 353                         if field.ident.as_str() == src && field.is_shorthand {
 354                             return true;
 355                         }
 356                     }
 357                 }
 358             }
 359         }
 360         false
 361     }
 362
 363     fn replace_prefix<A, B, C>(&self, s: A, old: B, new: C) -> Option<String>
 364     where
 365         A: AsRef<str>,
 366         B: AsRef<str>,
 367         C: AsRef<str>,
 368     {
 369         let s = s.as_ref();
 370         let old = old.as_ref();
 371         if s.starts_with(old) { Some(new.as_ref().to_owned() + &s[old.len()..]) } else { None }
 372     }
 373
 374     /// This function is used to determine potential "simple" improvements or users' errors and
 375     /// provide them useful help. For example:
 376     ///
 377     /// ```
 378     /// fn some_fn(s: &str) {}
 379     ///
 380     /// let x = "hey!".to_owned();
 381     /// some_fn(x); // error
 382     /// ```
 383     ///
 384     /// No need to find every potential function which could make a coercion to transform a
 385     /// `String` into a `&str` since a `&` would do the trick!
 386     ///
 387     /// In addition of this check, it also checks between references mutability state. If the
 388     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 389     /// `&mut`!".
 390     pub fn check_ref(
 391         &self,
 392         expr: &hir::Expr<'_>,
 393         checked_ty: Ty<'tcx>,
 394         expected: Ty<'tcx>,
 395     ) -> Option<(Span, &'static str, String, Applicability)> {
 396         let sm = self.sess().source_map();
 397         let sp = expr.span;
 398         if sm.is_imported(sp) {
 399             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 400             // call span, but that breaks down when the type error comes from multiple calls down.
 401             return None;
 402         }
 403
 404         let is_struct_pat_shorthand_field =
 405             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 406
 407         // If the span is from a macro, then it's hard to extract the text
 408         // and make a good suggestion, so don't bother.
 409         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 410
 411         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 412         let expr = expr.peel_drop_temps();
 413
 414         match (&expr.kind, &expected.kind, &checked_ty.kind) {
 415             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
 416                 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
 417                     if let hir::ExprKind::Lit(_) = expr.kind {
 418                         if let Ok(src) = sm.span_to_snippet(sp) {
 419                             if let Some(src) = self.replace_prefix(src, "b\"", "\"") {
 420                                 return Some((
 421                                     sp,
 422                                     "consider removing the leading `b`",
 423                                     src,
 424                                     Applicability::MachineApplicable,
 425                                 ));
 426                             }
 427                         }
 428                     }
 429                 }
 430                 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
 431                     if let hir::ExprKind::Lit(_) = expr.kind {
 432                         if let Ok(src) = sm.span_to_snippet(sp) {
 433                             if let Some(src) = self.replace_prefix(src, "\"", "b\"") {
 434                                 return Some((
 435                                     sp,
 436                                     "consider adding a leading `b`",
 437                                     src,
 438                                     Applicability::MachineApplicable,
 439                                 ));
 440                             }
 441                         }
 442                     }
 443                 }
 444                 _ => {}
 445             },
 446             (_, &ty::Ref(_, _, mutability), _) => {
 447                 // Check if it can work when put into a ref. For example:
 448                 //
 449                 // ```
 450                 // fn bar(x: &mut i32) {}
 451                 //
 452                 // let x = 0u32;
 453                 // bar(&x); // error, expected &mut
 454                 // ```
 455                 let ref_ty = match mutability {
 456                     hir::Mutability::Mut => {
 457                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 458                     }
 459                     hir::Mutability::Not => {
 460                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 461                     }
 462                 };
 463                 if self.can_coerce(ref_ty, expected) {
 464                     let mut sugg_sp = sp;
 465                     if let hir::ExprKind::MethodCall(ref segment, sp, ref args, _) = expr.kind {
 466                         let clone_trait = self.tcx.require_lang_item(CloneTraitLangItem, Some(sp));
 467                         if let ([arg], Some(true), sym::clone) = (
 468                             &args[..],
 469                             self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
 470                                 let ai = self.tcx.associated_item(did);
 471                                 ai.container == ty::TraitContainer(clone_trait)
 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(self.tcx.sess.source_map(), 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!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 755         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 756         let lit_msg = format!(
 757             "change the type of the numeric literal from `{}` to `{}`",
 758             checked_ty, expected_ty,
 759         );
 760
 761         let with_opt_paren: fn(&dyn fmt::Display) -> String =
 762             if expr.precedence().order() < PREC_POSTFIX {
 763                 |s| format!("({})", s)
 764             } else {
 765                 |s| s.to_string()
 766             };
 767
 768         let cast_suggestion = format!("{}{} as {}", prefix, with_opt_paren(&src), expected_ty);
 769         let into_suggestion = format!("{}{}.into()", prefix, with_opt_paren(&src));
 770         let suffix_suggestion = with_opt_paren(&format_args!(
 771             "{}{}",
 772             if matches!(
 773                 (&expected_ty.kind, &checked_ty.kind),
 774                 (ty::Int(_) | ty::Uint(_), ty::Float(_))
 775             ) {
 776                 // Remove fractional part from literal, for example `42.0f32` into `42`
 777                 let src = src.trim_end_matches(&checked_ty.to_string());
 778                 src.split('.').next().unwrap()
 779             } else {
 780                 src.trim_end_matches(&checked_ty.to_string())
 781             },
 782             expected_ty,
 783         ));
 784         let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
 785             if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
 786         };
 787         let is_negative_int =
 788             |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::UnNeg, ..));
 789         let is_uint = |ty: Ty<'_>| matches!(ty.kind, ty::Uint(..));
 790
 791         let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
 792
 793         let suggest_fallible_into_or_lhs_from =
 794             |err: &mut DiagnosticBuilder<'_>, exp_to_found_is_fallible: bool| {
 795                 // If we know the expression the expected type is derived from, we might be able
 796                 // to suggest a widening conversion rather than a narrowing one (which may
 797                 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
 798                 //   x > y
 799                 // can be given the suggestion "u32::from(x) > y" rather than
 800                 // "x > y.try_into().unwrap()".
 801                 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
 802                     match self.tcx.sess.source_map().span_to_snippet(expr.span).ok() {
 803                         Some(src) => Some((expr, src)),
 804                         None => None,
 805                     }
 806                 });
 807                 let (span, msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
 808                     (lhs_expr_and_src, exp_to_found_is_fallible)
 809                 {
 810                     let msg = format!(
 811                         "you can convert `{}` from `{}` to `{}`, matching the type of `{}`",
 812                         lhs_src, expected_ty, checked_ty, src
 813                     );
 814                     let suggestion = format!("{}::from({})", checked_ty, lhs_src);
 815                     (lhs_expr.span, msg, suggestion)
 816                 } else {
 817                     let msg = format!("{} and panic if the converted value wouldn't fit", msg);
 818                     let suggestion =
 819                         format!("{}{}.try_into().unwrap()", prefix, with_opt_paren(&src));
 820                     (expr.span, msg, suggestion)
 821                 };
 822                 err.span_suggestion(span, &msg, suggestion, Applicability::MachineApplicable);
 823             };
 824
 825         let suggest_to_change_suffix_or_into =
 826             |err: &mut DiagnosticBuilder<'_>,
 827              found_to_exp_is_fallible: bool,
 828              exp_to_found_is_fallible: bool| {
 829                 let always_fallible = found_to_exp_is_fallible
 830                     && (exp_to_found_is_fallible || expected_ty_expr.is_none());
 831                 let msg = if literal_is_ty_suffixed(expr) {
 832                     &lit_msg
 833                 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
 834                     // We now know that converting either the lhs or rhs is fallible. Before we
 835                     // suggest a fallible conversion, check if the value can never fit in the
 836                     // expected type.
 837                     let msg = format!("`{}` cannot fit into type `{}`", src, expected_ty);
 838                     err.note(&msg);
 839                     return;
 840                 } else if in_const_context {
 841                     // Do not recommend `into` or `try_into` in const contexts.
 842                     return;
 843                 } else if found_to_exp_is_fallible {
 844                     return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
 845                 } else {
 846                     &msg
 847                 };
 848                 let suggestion = if literal_is_ty_suffixed(expr) {
 849                     suffix_suggestion.clone()
 850                 } else {
 851                     into_suggestion.clone()
 852                 };
 853                 err.span_suggestion(expr.span, msg, suggestion, Applicability::MachineApplicable);
 854             };
 855
 856         match (&expected_ty.kind, &checked_ty.kind) {
 857             (&ty::Int(ref exp), &ty::Int(ref found)) => {
 858                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 859                 {
 860                     (Some(exp), Some(found)) if exp < found => (true, false),
 861                     (Some(exp), Some(found)) if exp > found => (false, true),
 862                     (None, Some(8 | 16)) => (false, true),
 863                     (Some(8 | 16), None) => (true, false),
 864                     (None, _) | (_, None) => (true, true),
 865                     _ => (false, false),
 866                 };
 867                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 868                 true
 869             }
 870             (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 871                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 872                 {
 873                     (Some(exp), Some(found)) if exp < found => (true, false),
 874                     (Some(exp), Some(found)) if exp > found => (false, true),
 875                     (None, Some(8 | 16)) => (false, true),
 876                     (Some(8 | 16), None) => (true, false),
 877                     (None, _) | (_, None) => (true, true),
 878                     _ => (false, false),
 879                 };
 880                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 881                 true
 882             }
 883             (&ty::Int(exp), &ty::Uint(found)) => {
 884                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 885                 {
 886                     (Some(exp), Some(found)) if found < exp => (false, true),
 887                     (None, Some(8)) => (false, true),
 888                     _ => (true, true),
 889                 };
 890                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 891                 true
 892             }
 893             (&ty::Uint(exp), &ty::Int(found)) => {
 894                 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
 895                 {
 896                     (Some(exp), Some(found)) if found > exp => (true, false),
 897                     (Some(8), None) => (true, false),
 898                     _ => (true, true),
 899                 };
 900                 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
 901                 true
 902             }
 903             (&ty::Float(ref exp), &ty::Float(ref found)) => {
 904                 if found.bit_width() < exp.bit_width() {
 905                     suggest_to_change_suffix_or_into(err, false, true);
 906                 } else if literal_is_ty_suffixed(expr) {
 907                     err.span_suggestion(
 908                         expr.span,
 909                         &lit_msg,
 910                         suffix_suggestion,
 911                         Applicability::MachineApplicable,
 912                     );
 913                 } else if can_cast {
 914                     // Missing try_into implementation for `f64` to `f32`
 915                     err.span_suggestion(
 916                         expr.span,
 917                         &format!("{}, producing the closest possible value", cast_msg),
 918                         cast_suggestion,
 919                         Applicability::MaybeIncorrect, // lossy conversion
 920                     );
 921                 }
 922                 true
 923             }
 924             (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
 925                 if literal_is_ty_suffixed(expr) {
 926                     err.span_suggestion(
 927                         expr.span,
 928                         &lit_msg,
 929                         suffix_suggestion,
 930                         Applicability::MachineApplicable,
 931                     );
 932                 } else if can_cast {
 933                     // Missing try_into implementation for `{float}` to `{integer}`
 934                     err.span_suggestion(
 935                         expr.span,
 936                         &format!("{}, rounding the float towards zero", msg),
 937                         cast_suggestion,
 938                         Applicability::MaybeIncorrect, // lossy conversion
 939                     );
 940                 }
 941                 true
 942             }
 943             (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 944                 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 945                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
 946                     err.span_suggestion(
 947                         expr.span,
 948                         &format!(
 949                             "{}, producing the floating point representation of the integer",
 950                             msg,
 951                         ),
 952                         into_suggestion,
 953                         Applicability::MachineApplicable,
 954                     );
 955                 } else if literal_is_ty_suffixed(expr) {
 956                     err.span_suggestion(
 957                         expr.span,
 958                         &lit_msg,
 959                         suffix_suggestion,
 960                         Applicability::MachineApplicable,
 961                     );
 962                 } else {
 963                     // Missing try_into implementation for `{integer}` to `{float}`
 964                     err.span_suggestion(
 965                         expr.span,
 966                         &format!(
 967                             "{}, producing the floating point representation of the integer,
 968                                  rounded if necessary",
 969                             cast_msg,
 970                         ),
 971                         cast_suggestion,
 972                         Applicability::MaybeIncorrect, // lossy conversion
 973                     );
 974                 }
 975                 true
 976             }
 977             (&ty::Float(ref exp), &ty::Int(ref found)) => {
 978                 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 979                 if exp.bit_width() > found.bit_width().unwrap_or(256) {
 980                     err.span_suggestion(
 981                         expr.span,
 982                         &format!(
 983                             "{}, producing the floating point representation of the integer",
 984                             &msg,
 985                         ),
 986                         into_suggestion,
 987                         Applicability::MachineApplicable,
 988                     );
 989                 } else if literal_is_ty_suffixed(expr) {
 990                     err.span_suggestion(
 991                         expr.span,
 992                         &lit_msg,
 993                         suffix_suggestion,
 994                         Applicability::MachineApplicable,
 995                     );
 996                 } else {
 997                     // Missing try_into implementation for `{integer}` to `{float}`
 998                     err.span_suggestion(
 999                         expr.span,
1000                         &format!(
1001                             "{}, producing the floating point representation of the integer, \
1002                                 rounded if necessary",
1003                             &msg,
1004                         ),
1005                         cast_suggestion,
1006                         Applicability::MaybeIncorrect, // lossy conversion
1007                     );
1008                 }
1009                 true
1010             }
1011             _ => false,
1012         }
1013     }
1014 }