src/librustc_typeck/check/demand.rs

   1 use crate::check::FnCtxt;
   2 use rustc::infer::InferOk;
   3 use rustc::traits::{self, ObligationCause, ObligationCauseCode};
   4
   5 use errors::{Applicability, DiagnosticBuilder};
   6 use rustc::hir::{self, is_range_literal, print, Node};
   7 use rustc::ty::adjustment::AllowTwoPhase;
   8 use rustc::ty::{self, AssocItem, Ty};
   9 use syntax::symbol::sym;
  10 use syntax::util::parser::PREC_POSTFIX;
  11 use syntax_pos::Span;
  12
  13 use super::method::probe;
  14
  15 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  16     pub fn emit_coerce_suggestions(
  17         &self,
  18         err: &mut DiagnosticBuilder<'_>,
  19         expr: &hir::Expr<'_>,
  20         expr_ty: Ty<'tcx>,
  21         expected: Ty<'tcx>,
  22     ) {
  23         self.annotate_expected_due_to_let_ty(err, expr);
  24         self.suggest_compatible_variants(err, expr, expected, expr_ty);
  25         self.suggest_ref_or_into(err, expr, expected, expr_ty);
  26         self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
  27         self.suggest_missing_await(err, expr, expected, expr_ty);
  28     }
  29
  30     // Requires that the two types unify, and prints an error message if
  31     // they don't.
  32     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  33         self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
  34     }
  35
  36     pub fn demand_suptype_diag(
  37         &self,
  38         sp: Span,
  39         expected: Ty<'tcx>,
  40         actual: Ty<'tcx>,
  41     ) -> Option<DiagnosticBuilder<'tcx>> {
  42         let cause = &self.misc(sp);
  43         match self.at(cause, self.param_env).sup(expected, actual) {
  44             Ok(InferOk { obligations, value: () }) => {
  45                 self.register_predicates(obligations);
  46                 None
  47             }
  48             Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
  49         }
  50     }
  51
  52     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  53         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  54             err.emit();
  55         }
  56     }
  57
  58     pub fn demand_eqtype_diag(
  59         &self,
  60         sp: Span,
  61         expected: Ty<'tcx>,
  62         actual: Ty<'tcx>,
  63     ) -> Option<DiagnosticBuilder<'tcx>> {
  64         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  65     }
  66
  67     pub fn demand_eqtype_with_origin(
  68         &self,
  69         cause: &ObligationCause<'tcx>,
  70         expected: Ty<'tcx>,
  71         actual: Ty<'tcx>,
  72     ) -> Option<DiagnosticBuilder<'tcx>> {
  73         match self.at(cause, self.param_env).eq(expected, actual) {
  74             Ok(InferOk { obligations, value: () }) => {
  75                 self.register_predicates(obligations);
  76                 None
  77             }
  78             Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
  79         }
  80     }
  81
  82     pub fn demand_eqtype_pat_diag(
  83         &self,
  84         cause_span: Span,
  85         expected: Ty<'tcx>,
  86         actual: Ty<'tcx>,
  87         match_expr_span: Option<Span>,
  88     ) -> Option<DiagnosticBuilder<'tcx>> {
  89         let cause = if let Some(span) = match_expr_span {
  90             self.cause(cause_span, ObligationCauseCode::Pattern { span, ty: expected })
  91         } else {
  92             self.misc(cause_span)
  93         };
  94         self.demand_eqtype_with_origin(&cause, expected, actual)
  95     }
  96
  97     pub fn demand_eqtype_pat(
  98         &self,
  99         cause_span: Span,
 100         expected: Ty<'tcx>,
 101         actual: Ty<'tcx>,
 102         match_expr_span: Option<Span>,
 103     ) {
 104         self.demand_eqtype_pat_diag(cause_span, expected, actual, match_expr_span)
 105             .map(|mut err| err.emit());
 106     }
 107
 108     pub fn demand_coerce(
 109         &self,
 110         expr: &hir::Expr<'_>,
 111         checked_ty: Ty<'tcx>,
 112         expected: Ty<'tcx>,
 113         allow_two_phase: AllowTwoPhase,
 114     ) -> Ty<'tcx> {
 115         let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
 116         if let Some(mut err) = err {
 117             err.emit();
 118         }
 119         ty
 120     }
 121
 122     // Checks that the type of `expr` can be coerced to `expected`.
 123     //
 124     // N.B., this code relies on `self.diverges` to be accurate. In
 125     // particular, assignments to `!` will be permitted if the
 126     // diverges flag is currently "always".
 127     pub fn demand_coerce_diag(
 128         &self,
 129         expr: &hir::Expr<'_>,
 130         checked_ty: Ty<'tcx>,
 131         expected: Ty<'tcx>,
 132         allow_two_phase: AllowTwoPhase,
 133     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
 134         let expected = self.resolve_vars_with_obligations(expected);
 135
 136         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
 137             Ok(ty) => return (ty, None),
 138             Err(e) => e,
 139         };
 140
 141         let expr = expr.peel_drop_temps();
 142         let cause = self.misc(expr.span);
 143         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 144         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
 145
 146         if self.is_assign_to_bool(expr, expected) {
 147             // Error reported in `check_assign` so avoid emitting error again.
 148             err.delay_as_bug();
 149             return (expected, None);
 150         }
 151
 152         self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected);
 153
 154         (expected, Some(err))
 155     }
 156
 157     fn annotate_expected_due_to_let_ty(
 158         &self,
 159         err: &mut DiagnosticBuilder<'_>,
 160         expr: &hir::Expr<'_>,
 161     ) {
 162         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 163         if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
 164             self.tcx.hir().find(parent)
 165         {
 166             if init.hir_id == expr.hir_id {
 167                 // Point at `let` assignment type.
 168                 err.span_label(ty.span, "expected due to this");
 169             }
 170         }
 171     }
 172
 173     /// Returns whether the expected type is `bool` and the expression is `x = y`.
 174     pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
 175         if let hir::ExprKind::Assign(..) = expr.kind {
 176             return expected == self.tcx.types.bool;
 177         }
 178         false
 179     }
 180
 181     /// If the expected type is an enum (Issue #55250) with any variants whose
 182     /// sole field is of the found type, suggest such variants. (Issue #42764)
 183     fn suggest_compatible_variants(
 184         &self,
 185         err: &mut DiagnosticBuilder<'_>,
 186         expr: &hir::Expr<'_>,
 187         expected: Ty<'tcx>,
 188         expr_ty: Ty<'tcx>,
 189     ) {
 190         if let ty::Adt(expected_adt, substs) = expected.kind {
 191             if !expected_adt.is_enum() {
 192                 return;
 193             }
 194
 195             let mut compatible_variants = expected_adt
 196                 .variants
 197                 .iter()
 198                 .filter(|variant| variant.fields.len() == 1)
 199                 .filter_map(|variant| {
 200                     let sole_field = &variant.fields[0];
 201                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 202                     if self.can_coerce(expr_ty, sole_field_ty) {
 203                         let variant_path = self.tcx.def_path_str(variant.def_id);
 204                         // FIXME #56861: DRYer prelude filtering
 205                         Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
 206                     } else {
 207                         None
 208                     }
 209                 })
 210                 .peekable();
 211
 212             if compatible_variants.peek().is_some() {
 213                 let expr_text =
 214                     self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or_else(|_| {
 215                         print::to_string(print::NO_ANN, |s| s.print_expr(expr))
 216                     });
 217                 let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
 218                 let msg = "try using a variant of the expected enum";
 219                 err.span_suggestions(expr.span, msg, suggestions, Applicability::MaybeIncorrect);
 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     ) -> Vec<AssocItem> {
 230         let mut methods = self.probe_for_return_type(
 231             span,
 232             probe::Mode::MethodCall,
 233             expected,
 234             checked_ty,
 235             hir::DUMMY_HIR_ID,
 236         );
 237         methods.retain(|m| {
 238             self.has_no_input_arg(m)
 239                 && self
 240                     .tcx
 241                     .get_attrs(m.def_id)
 242                     .iter()
 243                     // This special internal attribute is used to whitelist
 244                     // "identity-like" conversion methods to be suggested here.
 245                     //
 246                     // FIXME (#46459 and #46460): ideally
 247                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 248                     // also be `#[rustc_conversion_suggestion]`, if not for
 249                     // method-probing false-positives and -negatives (respectively).
 250                     //
 251                     // FIXME? Other potential candidate methods: `as_ref` and
 252                     // `as_mut`?
 253                     .find(|a| a.check_name(sym::rustc_conversion_suggestion))
 254                     .is_some()
 255         });
 256
 257         methods
 258     }
 259
 260     // This function checks if the method isn't static and takes other arguments than `self`.
 261     fn has_no_input_arg(&self, method: &AssocItem) -> bool {
 262         match method.kind {
 263             ty::AssocKind::Method => {
 264                 self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 265             }
 266             _ => false,
 267         }
 268     }
 269
 270     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 271     ///
 272     /// Given the following code:
 273     /// ```
 274     /// struct Foo;
 275     /// fn takes_ref(_: &Foo) {}
 276     /// let ref opt = Some(Foo);
 277     ///
 278     /// opt.map(|param| takes_ref(param));
 279     /// ```
 280     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 281     ///
 282     /// It only checks for `Option` and `Result` and won't work with
 283     /// ```
 284     /// opt.map(|param| { takes_ref(param) });
 285     /// ```
 286     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 287         let path = match expr.kind {
 288             hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
 289             _ => return None,
 290         };
 291
 292         let local_id = match path.res {
 293             hir::def::Res::Local(id) => id,
 294             _ => return None,
 295         };
 296
 297         let local_parent = self.tcx.hir().get_parent_node(local_id);
 298         let param_hir_id = match self.tcx.hir().find(local_parent) {
 299             Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
 300             _ => return None,
 301         };
 302
 303         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 304         let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
 305             Some(Node::Expr(hir::Expr {
 306                 hir_id,
 307                 kind: hir::ExprKind::Closure(_, decl, ..),
 308                 ..
 309             })) => (hir_id, decl),
 310             _ => return None,
 311         };
 312
 313         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 314         let hir = self.tcx.hir().find(expr_parent);
 315         let closure_params_len = closure_fn_decl.inputs.len();
 316         let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
 317             (
 318                 Some(Node::Expr(hir::Expr {
 319                     kind: hir::ExprKind::MethodCall(path, span, expr),
 320                     ..
 321                 })),
 322                 1,
 323             ) => (path, span, expr),
 324             _ => return None,
 325         };
 326
 327         let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
 328         let self_ty = format!("{:?}", self_ty);
 329         let name = method_path.ident.as_str();
 330         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 331             || self_ty.starts_with("&std::result::Result")
 332             || self_ty.starts_with("std::option::Option")
 333             || self_ty.starts_with("std::result::Result"))
 334             && (name == "map" || name == "and_then");
 335         match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
 336             (true, Ok(src)) => {
 337                 let suggestion = format!("as_ref().{}", src);
 338                 Some((*method_span, "consider using `as_ref` instead", suggestion))
 339             }
 340             _ => None,
 341         }
 342     }
 343
 344     crate fn is_hir_id_from_struct_pattern_shorthand_field(
 345         &self,
 346         hir_id: hir::HirId,
 347         sp: Span,
 348     ) -> bool {
 349         let cm = self.sess().source_map();
 350         let parent_id = self.tcx.hir().get_parent_node(hir_id);
 351         if let Some(parent) = self.tcx.hir().find(parent_id) {
 352             // Account for fields
 353             if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
 354             {
 355                 if let Ok(src) = cm.span_to_snippet(sp) {
 356                     for field in *fields {
 357                         if field.ident.as_str() == src && field.is_shorthand {
 358                             return true;
 359                         }
 360                     }
 361                 }
 362             }
 363         }
 364         false
 365     }
 366
 367     /// This function is used to determine potential "simple" improvements or users' errors and
 368     /// provide them useful help. For example:
 369     ///
 370     /// ```
 371     /// fn some_fn(s: &str) {}
 372     ///
 373     /// let x = "hey!".to_owned();
 374     /// some_fn(x); // error
 375     /// ```
 376     ///
 377     /// No need to find every potential function which could make a coercion to transform a
 378     /// `String` into a `&str` since a `&` would do the trick!
 379     ///
 380     /// In addition of this check, it also checks between references mutability state. If the
 381     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 382     /// `&mut`!".
 383     pub fn check_ref(
 384         &self,
 385         expr: &hir::Expr<'_>,
 386         checked_ty: Ty<'tcx>,
 387         expected: Ty<'tcx>,
 388     ) -> Option<(Span, &'static str, String)> {
 389         let cm = self.sess().source_map();
 390         let sp = expr.span;
 391         if !cm.span_to_filename(sp).is_real() {
 392             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 393             // call span, but that breaks down when the type error comes from multiple calls down.
 394             return None;
 395         }
 396
 397         let is_struct_pat_shorthand_field =
 398             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 399
 400         // If the span is from a macro, then it's hard to extract the text
 401         // and make a good suggestion, so don't bother.
 402         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 403
 404         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 405         let expr = expr.peel_drop_temps();
 406
 407         match (&expr.kind, &expected.kind, &checked_ty.kind) {
 408             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
 409                 (&ty::Str, &ty::Array(arr, _)) | (&ty::Str, &ty::Slice(arr))
 410                     if arr == self.tcx.types.u8 =>
 411                 {
 412                     if let hir::ExprKind::Lit(_) = expr.kind {
 413                         if let Ok(src) = cm.span_to_snippet(sp) {
 414                             if src.starts_with("b\"") {
 415                                 return Some((
 416                                     sp,
 417                                     "consider removing the leading `b`",
 418                                     src[1..].to_string(),
 419                                 ));
 420                             }
 421                         }
 422                     }
 423                 }
 424                 (&ty::Array(arr, _), &ty::Str) | (&ty::Slice(arr), &ty::Str)
 425                     if arr == self.tcx.types.u8 =>
 426                 {
 427                     if let hir::ExprKind::Lit(_) = expr.kind {
 428                         if let Ok(src) = cm.span_to_snippet(sp) {
 429                             if src.starts_with("\"") {
 430                                 return Some((
 431                                     sp,
 432                                     "consider adding a leading `b`",
 433                                     format!("b{}", src),
 434                                 ));
 435                             }
 436                         }
 437                     }
 438                 }
 439                 _ => {}
 440             },
 441             (_, &ty::Ref(_, _, mutability), _) => {
 442                 // Check if it can work when put into a ref. For example:
 443                 //
 444                 // ```
 445                 // fn bar(x: &mut i32) {}
 446                 //
 447                 // let x = 0u32;
 448                 // bar(&x); // error, expected &mut
 449                 // ```
 450                 let ref_ty = match mutability {
 451                     hir::Mutability::Mut => {
 452                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 453                     }
 454                     hir::Mutability::Not => {
 455                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 456                     }
 457                 };
 458                 if self.can_coerce(ref_ty, expected) {
 459                     let mut sugg_sp = sp;
 460                     if let hir::ExprKind::MethodCall(segment, _sp, args) = &expr.kind {
 461                         let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
 462                         if let ([arg], Some(true), sym::clone) = (
 463                             &args[..],
 464                             self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
 465                                 let ai = self.tcx.associated_item(did);
 466                                 ai.container == ty::TraitContainer(clone_trait)
 467                             }),
 468                             segment.ident.name,
 469                         ) {
 470                             // If this expression had a clone call when suggesting borrowing
 471                             // we want to suggest removing it because it'd now be unnecessary.
 472                             sugg_sp = arg.span;
 473                         }
 474                     }
 475                     if let Ok(src) = cm.span_to_snippet(sugg_sp) {
 476                         let needs_parens = match expr.kind {
 477                             // parenthesize if needed (Issue #46756)
 478                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 479                             // parenthesize borrows of range literals (Issue #54505)
 480                             _ if is_range_literal(self.tcx.sess.source_map(), expr) => true,
 481                             _ => false,
 482                         };
 483                         let sugg_expr = if needs_parens { format!("({})", src) } else { src };
 484
 485                         if let Some(sugg) = self.can_use_as_ref(expr) {
 486                             return Some(sugg);
 487                         }
 488                         let field_name = if is_struct_pat_shorthand_field {
 489                             format!("{}: ", sugg_expr)
 490                         } else {
 491                             String::new()
 492                         };
 493                         if let Some(hir::Node::Expr(hir::Expr {
 494                             kind: hir::ExprKind::Assign(left_expr, ..),
 495                             ..
 496                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 497                         {
 498                             if mutability == hir::Mutability::Mut {
 499                                 // Found the following case:
 500                                 // fn foo(opt: &mut Option<String>){ opt = None }
 501                                 //                                   ---   ^^^^
 502                                 //                                   |     |
 503                                 //    consider dereferencing here: `*opt`  |
 504                                 // expected mutable reference, found enum `Option`
 505                                 if let Ok(src) = cm.span_to_snippet(left_expr.span) {
 506                                     return Some((
 507                                         left_expr.span,
 508                                         "consider dereferencing here to assign to the mutable \
 509                                          borrowed piece of memory",
 510                                         format!("*{}", src),
 511                                     ));
 512                                 }
 513                             }
 514                         }
 515
 516                         return Some(match mutability {
 517                             hir::Mutability::Mut => (
 518                                 sp,
 519                                 "consider mutably borrowing here",
 520                                 format!("{}&mut {}", field_name, sugg_expr),
 521                             ),
 522                             hir::Mutability::Not => (
 523                                 sp,
 524                                 "consider borrowing here",
 525                                 format!("{}&{}", field_name, sugg_expr),
 526                             ),
 527                         });
 528                     }
 529                 }
 530             }
 531             (
 532                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 533                 _,
 534                 &ty::Ref(_, checked, _),
 535             ) if {
 536                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 537             } =>
 538             {
 539                 // We have `&T`, check if what was expected was `T`. If so,
 540                 // we may want to suggest removing a `&`.
 541                 if !cm.span_to_filename(expr.span).is_real() {
 542                     if let Ok(code) = cm.span_to_snippet(sp) {
 543                         if code.chars().next() == Some('&') {
 544                             return Some((
 545                                 sp,
 546                                 "consider removing the borrow",
 547                                 code[1..].to_string(),
 548                             ));
 549                         }
 550                     }
 551                     return None;
 552                 }
 553                 if let Ok(code) = cm.span_to_snippet(expr.span) {
 554                     return Some((sp, "consider removing the borrow", code));
 555                 }
 556             }
 557             _ if sp == expr.span && !is_macro => {
 558                 // Check for `Deref` implementations by constructing a predicate to
 559                 // prove: `<T as Deref>::Output == U`
 560                 let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
 561                 let item_def_id = self
 562                     .tcx
 563                     .associated_items(deref_trait)
 564                     .find(|item| item.kind == ty::AssocKind::Type)
 565                     .unwrap()
 566                     .def_id;
 567                 let predicate =
 568                     ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
 569                         // `<T as Deref>::Output`
 570                         projection_ty: ty::ProjectionTy {
 571                             // `T`
 572                             substs: self.tcx.intern_substs(&[checked_ty.into()]),
 573                             // `Deref::Output`
 574                             item_def_id,
 575                         },
 576                         // `U`
 577                         ty: expected,
 578                     }));
 579                 let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
 580                 let impls_deref = self.infcx.predicate_may_hold(&obligation);
 581
 582                 // For a suggestion to make sense, the type would need to be `Copy`.
 583                 let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
 584
 585                 if is_copy && impls_deref {
 586                     if let Ok(code) = cm.span_to_snippet(sp) {
 587                         let message = if checked_ty.is_region_ptr() {
 588                             "consider dereferencing the borrow"
 589                         } else {
 590                             "consider dereferencing the type"
 591                         };
 592                         let suggestion = if is_struct_pat_shorthand_field {
 593                             format!("{}: *{}", code, code)
 594                         } else {
 595                             format!("*{}", code)
 596                         };
 597                         return Some((sp, message, suggestion));
 598                     }
 599                 }
 600             }
 601             _ => {}
 602         }
 603         None
 604     }
 605
 606     pub fn check_for_cast(
 607         &self,
 608         err: &mut DiagnosticBuilder<'_>,
 609         expr: &hir::Expr<'_>,
 610         checked_ty: Ty<'tcx>,
 611         expected_ty: Ty<'tcx>,
 612     ) -> bool {
 613         if self.tcx.hir().is_const_context(expr.hir_id) {
 614             // Shouldn't suggest `.into()` on `const`s.
 615             // FIXME(estebank): modify once we decide to suggest `as` casts
 616             return false;
 617         }
 618         if !self.tcx.sess.source_map().span_to_filename(expr.span).is_real() {
 619             // Ignore if span is from within a macro.
 620             return false;
 621         }
 622
 623         // If casting this expression to a given numeric type would be appropriate in case of a type
 624         // mismatch.
 625         //
 626         // We want to minimize the amount of casting operations that are suggested, as it can be a
 627         // lossy operation with potentially bad side effects, so we only suggest when encountering
 628         // an expression that indicates that the original type couldn't be directly changed.
 629         //
 630         // For now, don't suggest casting with `as`.
 631         let can_cast = false;
 632
 633         let mut prefix = String::new();
 634         if let Some(hir::Node::Expr(hir::Expr {
 635             kind: hir::ExprKind::Struct(_, fields, _), ..
 636         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 637         {
 638             // `expr` is a literal field for a struct, only suggest if appropriate
 639             for field in *fields {
 640                 if field.expr.hir_id == expr.hir_id && field.is_shorthand {
 641                     // This is a field literal
 642                     prefix = format!("{}: ", field.ident);
 643                     break;
 644                 }
 645             }
 646             if &prefix == "" {
 647                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 648                 return false;
 649             }
 650         }
 651         if let hir::ExprKind::Call(path, args) = &expr.kind {
 652             if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
 653                 (&path.kind, args.len())
 654             {
 655                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 656                 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
 657                     (&base_ty.kind, path_segment.ident.name)
 658                 {
 659                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
 660                         match ident.name {
 661                             sym::i128
 662                             | sym::i64
 663                             | sym::i32
 664                             | sym::i16
 665                             | sym::i8
 666                             | sym::u128
 667                             | sym::u64
 668                             | sym::u32
 669                             | sym::u16
 670                             | sym::u8
 671                             | sym::isize
 672                             | sym::usize
 673                                 if base_ty_path.segments.len() == 1 =>
 674                             {
 675                                 return false;
 676                             }
 677                             _ => {}
 678                         }
 679                     }
 680                 }
 681             }
 682         }
 683
 684         let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 685         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 686         let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
 687         let lit_msg = format!(
 688             "change the type of the numeric literal from `{}` to `{}`",
 689             checked_ty, expected_ty,
 690         );
 691
 692         let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
 693
 694         if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 695             let cast_suggestion = format!(
 696                 "{}{}{}{} as {}",
 697                 prefix,
 698                 if needs_paren { "(" } else { "" },
 699                 src,
 700                 if needs_paren { ")" } else { "" },
 701                 expected_ty,
 702             );
 703             let try_into_suggestion = format!(
 704                 "{}{}{}{}.try_into().unwrap()",
 705                 prefix,
 706                 if needs_paren { "(" } else { "" },
 707                 src,
 708                 if needs_paren { ")" } else { "" },
 709             );
 710             let into_suggestion = format!(
 711                 "{}{}{}{}.into()",
 712                 prefix,
 713                 if needs_paren { "(" } else { "" },
 714                 src,
 715                 if needs_paren { ")" } else { "" },
 716             );
 717             let suffix_suggestion = format!(
 718                 "{}{}{}{}",
 719                 if needs_paren { "(" } else { "" },
 720                 if let (ty::Int(_), ty::Float(_)) | (ty::Uint(_), ty::Float(_)) =
 721                     (&expected_ty.kind, &checked_ty.kind,)
 722                 {
 723                     // Remove fractional part from literal, for example `42.0f32` into `42`
 724                     let src = src.trim_end_matches(&checked_ty.to_string());
 725                     src.split(".").next().unwrap()
 726                 } else {
 727                     src.trim_end_matches(&checked_ty.to_string())
 728                 },
 729                 expected_ty,
 730                 if needs_paren { ")" } else { "" },
 731             );
 732             let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
 733                 if let hir::ExprKind::Lit(lit) = &expr.kind {
 734                     lit.node.is_suffixed()
 735                 } else {
 736                     false
 737                 }
 738             };
 739
 740             let suggest_to_change_suffix_or_into =
 741                 |err: &mut DiagnosticBuilder<'_>, is_fallible: bool| {
 742                     let into_sugg = into_suggestion.clone();
 743                     err.span_suggestion(
 744                         expr.span,
 745                         if literal_is_ty_suffixed(expr) {
 746                             &lit_msg
 747                         } else if is_fallible {
 748                             &try_msg
 749                         } else {
 750                             &msg
 751                         },
 752                         if literal_is_ty_suffixed(expr) {
 753                             suffix_suggestion.clone()
 754                         } else if is_fallible {
 755                             try_into_suggestion
 756                         } else {
 757                             into_sugg
 758                         },
 759                         Applicability::MachineApplicable,
 760                     );
 761                 };
 762
 763             match (&expected_ty.kind, &checked_ty.kind) {
 764                 (&ty::Int(ref exp), &ty::Int(ref found)) => {
 765                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 766                         (Some(found), Some(exp)) if found > exp => true,
 767                         (None, _) | (_, None) => true,
 768                         _ => false,
 769                     };
 770                     suggest_to_change_suffix_or_into(err, is_fallible);
 771                     true
 772                 }
 773                 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 774                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 775                         (Some(found), Some(exp)) if found > exp => true,
 776                         (None, _) | (_, None) => true,
 777                         _ => false,
 778                     };
 779                     suggest_to_change_suffix_or_into(err, is_fallible);
 780                     true
 781                 }
 782                 (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
 783                     suggest_to_change_suffix_or_into(err, true);
 784                     true
 785                 }
 786                 (&ty::Float(ref exp), &ty::Float(ref found)) => {
 787                     if found.bit_width() < exp.bit_width() {
 788                         suggest_to_change_suffix_or_into(err, false);
 789                     } else if literal_is_ty_suffixed(expr) {
 790                         err.span_suggestion(
 791                             expr.span,
 792                             &lit_msg,
 793                             suffix_suggestion,
 794                             Applicability::MachineApplicable,
 795                         );
 796                     } else if can_cast {
 797                         // Missing try_into implementation for `f64` to `f32`
 798                         err.span_suggestion(
 799                             expr.span,
 800                             &format!("{}, producing the closest possible value", cast_msg),
 801                             cast_suggestion,
 802                             Applicability::MaybeIncorrect, // lossy conversion
 803                         );
 804                     }
 805                     true
 806                 }
 807                 (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
 808                     if literal_is_ty_suffixed(expr) {
 809                         err.span_suggestion(
 810                             expr.span,
 811                             &lit_msg,
 812                             suffix_suggestion,
 813                             Applicability::MachineApplicable,
 814                         );
 815                     } else if can_cast {
 816                         // Missing try_into implementation for `{float}` to `{integer}`
 817                         err.span_suggestion(
 818                             expr.span,
 819                             &format!("{}, rounding the float towards zero", msg),
 820                             cast_suggestion,
 821                             Applicability::MaybeIncorrect, // lossy conversion
 822                         );
 823                         err.warn(
 824                             "if the rounded value cannot be represented by the target \
 825                                   integer type, including `Inf` and `NaN`, casting will cause \
 826                                   undefined behavior \
 827                                   (https://github.com/rust-lang/rust/issues/10184)",
 828                         );
 829                     }
 830                     true
 831                 }
 832                 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 833                     // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 834                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 835                         err.span_suggestion(
 836                             expr.span,
 837                             &format!(
 838                                 "{}, producing the floating point representation of the integer",
 839                                 msg,
 840                             ),
 841                             into_suggestion,
 842                             Applicability::MachineApplicable,
 843                         );
 844                     } else if literal_is_ty_suffixed(expr) {
 845                         err.span_suggestion(
 846                             expr.span,
 847                             &lit_msg,
 848                             suffix_suggestion,
 849                             Applicability::MachineApplicable,
 850                         );
 851                     } else {
 852                         // Missing try_into implementation for `{integer}` to `{float}`
 853                         err.span_suggestion(
 854                             expr.span,
 855                             &format!(
 856                                 "{}, producing the floating point representation of the integer,
 857                                  rounded if necessary",
 858                                 cast_msg,
 859                             ),
 860                             cast_suggestion,
 861                             Applicability::MaybeIncorrect, // lossy conversion
 862                         );
 863                     }
 864                     true
 865                 }
 866                 (&ty::Float(ref exp), &ty::Int(ref found)) => {
 867                     // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 868                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 869                         err.span_suggestion(
 870                             expr.span,
 871                             &format!(
 872                                 "{}, producing the floating point representation of the integer",
 873                                 &msg,
 874                             ),
 875                             into_suggestion,
 876                             Applicability::MachineApplicable,
 877                         );
 878                     } else if literal_is_ty_suffixed(expr) {
 879                         err.span_suggestion(
 880                             expr.span,
 881                             &lit_msg,
 882                             suffix_suggestion,
 883                             Applicability::MachineApplicable,
 884                         );
 885                     } else {
 886                         // Missing try_into implementation for `{integer}` to `{float}`
 887                         err.span_suggestion(
 888                             expr.span,
 889                             &format!(
 890                                 "{}, producing the floating point representation of the integer, \
 891                                  rounded if necessary",
 892                                 &msg,
 893                             ),
 894                             cast_suggestion,
 895                             Applicability::MaybeIncorrect, // lossy conversion
 896                         );
 897                     }
 898                     true
 899                 }
 900                 _ => false,
 901             }
 902         } else {
 903             false
 904         }
 905     }
 906 }