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(
  91                 cause_span,
  92                 ObligationCauseCode::MatchExpressionArmPattern { span, ty: expected },
  93             )
  94         } else {
  95             self.misc(cause_span)
  96         };
  97         self.demand_eqtype_with_origin(&cause, expected, actual)
  98     }
  99
 100     pub fn demand_eqtype_pat(
 101         &self,
 102         cause_span: Span,
 103         expected: Ty<'tcx>,
 104         actual: Ty<'tcx>,
 105         match_expr_span: Option<Span>,
 106     ) {
 107         self.demand_eqtype_pat_diag(cause_span, expected, actual, match_expr_span)
 108             .map(|mut err| err.emit());
 109     }
 110
 111     pub fn demand_coerce(
 112         &self,
 113         expr: &hir::Expr<'_>,
 114         checked_ty: Ty<'tcx>,
 115         expected: Ty<'tcx>,
 116         allow_two_phase: AllowTwoPhase,
 117     ) -> Ty<'tcx> {
 118         let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
 119         if let Some(mut err) = err {
 120             err.emit();
 121         }
 122         ty
 123     }
 124
 125     // Checks that the type of `expr` can be coerced to `expected`.
 126     //
 127     // N.B., this code relies on `self.diverges` to be accurate. In
 128     // particular, assignments to `!` will be permitted if the
 129     // diverges flag is currently "always".
 130     pub fn demand_coerce_diag(
 131         &self,
 132         expr: &hir::Expr<'_>,
 133         checked_ty: Ty<'tcx>,
 134         expected: Ty<'tcx>,
 135         allow_two_phase: AllowTwoPhase,
 136     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
 137         let expected = self.resolve_vars_with_obligations(expected);
 138
 139         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
 140             Ok(ty) => return (ty, None),
 141             Err(e) => e,
 142         };
 143
 144         let expr = expr.peel_drop_temps();
 145         let cause = self.misc(expr.span);
 146         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 147         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
 148
 149         if self.is_assign_to_bool(expr, expected) {
 150             // Error reported in `check_assign` so avoid emitting error again.
 151             err.delay_as_bug();
 152             return (expected, None);
 153         }
 154
 155         self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected);
 156
 157         (expected, Some(err))
 158     }
 159
 160     fn annotate_expected_due_to_let_ty(
 161         &self,
 162         err: &mut DiagnosticBuilder<'_>,
 163         expr: &hir::Expr<'_>,
 164     ) {
 165         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 166         if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
 167             self.tcx.hir().find(parent)
 168         {
 169             if init.hir_id == expr.hir_id {
 170                 // Point at `let` assignment type.
 171                 err.span_label(ty.span, "expected due to this");
 172             }
 173         }
 174     }
 175
 176     /// Returns whether the expected type is `bool` and the expression is `x = y`.
 177     pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
 178         if let hir::ExprKind::Assign(..) = expr.kind {
 179             return expected == self.tcx.types.bool;
 180         }
 181         false
 182     }
 183
 184     /// If the expected type is an enum (Issue #55250) with any variants whose
 185     /// sole field is of the found type, suggest such variants. (Issue #42764)
 186     fn suggest_compatible_variants(
 187         &self,
 188         err: &mut DiagnosticBuilder<'_>,
 189         expr: &hir::Expr<'_>,
 190         expected: Ty<'tcx>,
 191         expr_ty: Ty<'tcx>,
 192     ) {
 193         if let ty::Adt(expected_adt, substs) = expected.kind {
 194             if !expected_adt.is_enum() {
 195                 return;
 196             }
 197
 198             let mut compatible_variants = expected_adt
 199                 .variants
 200                 .iter()
 201                 .filter(|variant| variant.fields.len() == 1)
 202                 .filter_map(|variant| {
 203                     let sole_field = &variant.fields[0];
 204                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 205                     if self.can_coerce(expr_ty, sole_field_ty) {
 206                         let variant_path = self.tcx.def_path_str(variant.def_id);
 207                         // FIXME #56861: DRYer prelude filtering
 208                         Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
 209                     } else {
 210                         None
 211                     }
 212                 })
 213                 .peekable();
 214
 215             if compatible_variants.peek().is_some() {
 216                 let expr_text =
 217                     self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or_else(|_| {
 218                         print::to_string(print::NO_ANN, |s| s.print_expr(expr))
 219                     });
 220                 let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
 221                 let msg = "try using a variant of the expected enum";
 222                 err.span_suggestions(expr.span, msg, suggestions, Applicability::MaybeIncorrect);
 223             }
 224         }
 225     }
 226
 227     pub fn get_conversion_methods(
 228         &self,
 229         span: Span,
 230         expected: Ty<'tcx>,
 231         checked_ty: Ty<'tcx>,
 232     ) -> Vec<AssocItem> {
 233         let mut methods = self.probe_for_return_type(
 234             span,
 235             probe::Mode::MethodCall,
 236             expected,
 237             checked_ty,
 238             hir::DUMMY_HIR_ID,
 239         );
 240         methods.retain(|m| {
 241             self.has_no_input_arg(m)
 242                 && self
 243                     .tcx
 244                     .get_attrs(m.def_id)
 245                     .iter()
 246                     // This special internal attribute is used to whitelist
 247                     // "identity-like" conversion methods to be suggested here.
 248                     //
 249                     // FIXME (#46459 and #46460): ideally
 250                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 251                     // also be `#[rustc_conversion_suggestion]`, if not for
 252                     // method-probing false-positives and -negatives (respectively).
 253                     //
 254                     // FIXME? Other potential candidate methods: `as_ref` and
 255                     // `as_mut`?
 256                     .find(|a| a.check_name(sym::rustc_conversion_suggestion))
 257                     .is_some()
 258         });
 259
 260         methods
 261     }
 262
 263     // This function checks if the method isn't static and takes other arguments than `self`.
 264     fn has_no_input_arg(&self, method: &AssocItem) -> bool {
 265         match method.kind {
 266             ty::AssocKind::Method => {
 267                 self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 268             }
 269             _ => false,
 270         }
 271     }
 272
 273     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 274     ///
 275     /// Given the following code:
 276     /// ```
 277     /// struct Foo;
 278     /// fn takes_ref(_: &Foo) {}
 279     /// let ref opt = Some(Foo);
 280     ///
 281     /// opt.map(|param| takes_ref(param));
 282     /// ```
 283     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 284     ///
 285     /// It only checks for `Option` and `Result` and won't work with
 286     /// ```
 287     /// opt.map(|param| { takes_ref(param) });
 288     /// ```
 289     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 290         let path = match expr.kind {
 291             hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
 292             _ => return None,
 293         };
 294
 295         let local_id = match path.res {
 296             hir::def::Res::Local(id) => id,
 297             _ => return None,
 298         };
 299
 300         let local_parent = self.tcx.hir().get_parent_node(local_id);
 301         let param_hir_id = match self.tcx.hir().find(local_parent) {
 302             Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
 303             _ => return None,
 304         };
 305
 306         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 307         let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
 308             Some(Node::Expr(hir::Expr {
 309                 hir_id,
 310                 kind: hir::ExprKind::Closure(_, decl, ..),
 311                 ..
 312             })) => (hir_id, decl),
 313             _ => return None,
 314         };
 315
 316         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 317         let hir = self.tcx.hir().find(expr_parent);
 318         let closure_params_len = closure_fn_decl.inputs.len();
 319         let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
 320             (
 321                 Some(Node::Expr(hir::Expr {
 322                     kind: hir::ExprKind::MethodCall(path, span, expr),
 323                     ..
 324                 })),
 325                 1,
 326             ) => (path, span, expr),
 327             _ => return None,
 328         };
 329
 330         let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
 331         let self_ty = format!("{:?}", self_ty);
 332         let name = method_path.ident.as_str();
 333         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 334             || self_ty.starts_with("&std::result::Result")
 335             || self_ty.starts_with("std::option::Option")
 336             || self_ty.starts_with("std::result::Result"))
 337             && (name == "map" || name == "and_then");
 338         match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
 339             (true, Ok(src)) => {
 340                 let suggestion = format!("as_ref().{}", src);
 341                 Some((*method_span, "consider using `as_ref` instead", suggestion))
 342             }
 343             _ => None,
 344         }
 345     }
 346
 347     crate fn is_hir_id_from_struct_pattern_shorthand_field(
 348         &self,
 349         hir_id: hir::HirId,
 350         sp: Span,
 351     ) -> bool {
 352         let cm = self.sess().source_map();
 353         let parent_id = self.tcx.hir().get_parent_node(hir_id);
 354         if let Some(parent) = self.tcx.hir().find(parent_id) {
 355             // Account for fields
 356             if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
 357             {
 358                 if let Ok(src) = cm.span_to_snippet(sp) {
 359                     for field in *fields {
 360                         if field.ident.as_str() == src && field.is_shorthand {
 361                             return true;
 362                         }
 363                     }
 364                 }
 365             }
 366         }
 367         false
 368     }
 369
 370     /// This function is used to determine potential "simple" improvements or users' errors and
 371     /// provide them useful help. For example:
 372     ///
 373     /// ```
 374     /// fn some_fn(s: &str) {}
 375     ///
 376     /// let x = "hey!".to_owned();
 377     /// some_fn(x); // error
 378     /// ```
 379     ///
 380     /// No need to find every potential function which could make a coercion to transform a
 381     /// `String` into a `&str` since a `&` would do the trick!
 382     ///
 383     /// In addition of this check, it also checks between references mutability state. If the
 384     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 385     /// `&mut`!".
 386     pub fn check_ref(
 387         &self,
 388         expr: &hir::Expr<'_>,
 389         checked_ty: Ty<'tcx>,
 390         expected: Ty<'tcx>,
 391     ) -> Option<(Span, &'static str, String)> {
 392         let cm = self.sess().source_map();
 393         let sp = expr.span;
 394         if !cm.span_to_filename(sp).is_real() {
 395             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 396             // call span, but that breaks down when the type error comes from multiple calls down.
 397             return None;
 398         }
 399
 400         let is_struct_pat_shorthand_field =
 401             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 402
 403         // If the span is from a macro, then it's hard to extract the text
 404         // and make a good suggestion, so don't bother.
 405         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 406
 407         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 408         let expr = expr.peel_drop_temps();
 409
 410         match (&expr.kind, &expected.kind, &checked_ty.kind) {
 411             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
 412                 (&ty::Str, &ty::Array(arr, _)) | (&ty::Str, &ty::Slice(arr))
 413                     if arr == self.tcx.types.u8 =>
 414                 {
 415                     if let hir::ExprKind::Lit(_) = expr.kind {
 416                         if let Ok(src) = cm.span_to_snippet(sp) {
 417                             if src.starts_with("b\"") {
 418                                 return Some((
 419                                     sp,
 420                                     "consider removing the leading `b`",
 421                                     src[1..].to_string(),
 422                                 ));
 423                             }
 424                         }
 425                     }
 426                 }
 427                 (&ty::Array(arr, _), &ty::Str) | (&ty::Slice(arr), &ty::Str)
 428                     if arr == self.tcx.types.u8 =>
 429                 {
 430                     if let hir::ExprKind::Lit(_) = expr.kind {
 431                         if let Ok(src) = cm.span_to_snippet(sp) {
 432                             if src.starts_with("\"") {
 433                                 return Some((
 434                                     sp,
 435                                     "consider adding a leading `b`",
 436                                     format!("b{}", src),
 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(segment, _sp, args) = &expr.kind {
 464                         let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
 465                         if let ([arg], Some(true), sym::clone) = (
 466                             &args[..],
 467                             self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
 468                                 let ai = self.tcx.associated_item(did);
 469                                 ai.container == ty::TraitContainer(clone_trait)
 470                             }),
 471                             segment.ident.name,
 472                         ) {
 473                             // If this expression had a clone call when suggesting borrowing
 474                             // we want to suggest removing it because it'd now be unnecessary.
 475                             sugg_sp = arg.span;
 476                         }
 477                     }
 478                     if let Ok(src) = cm.span_to_snippet(sugg_sp) {
 479                         let needs_parens = match expr.kind {
 480                             // parenthesize if needed (Issue #46756)
 481                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 482                             // parenthesize borrows of range literals (Issue #54505)
 483                             _ if is_range_literal(self.tcx.sess.source_map(), expr) => true,
 484                             _ => false,
 485                         };
 486                         let sugg_expr = if needs_parens { format!("({})", src) } else { src };
 487
 488                         if let Some(sugg) = self.can_use_as_ref(expr) {
 489                             return Some(sugg);
 490                         }
 491                         let field_name = if is_struct_pat_shorthand_field {
 492                             format!("{}: ", sugg_expr)
 493                         } else {
 494                             String::new()
 495                         };
 496                         if let Some(hir::Node::Expr(hir::Expr {
 497                             kind: hir::ExprKind::Assign(left_expr, ..),
 498                             ..
 499                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 500                         {
 501                             if mutability == hir::Mutability::Mut {
 502                                 // Found the following case:
 503                                 // fn foo(opt: &mut Option<String>){ opt = None }
 504                                 //                                   ---   ^^^^
 505                                 //                                   |     |
 506                                 //    consider dereferencing here: `*opt`  |
 507                                 // expected mutable reference, found enum `Option`
 508                                 if let Ok(src) = cm.span_to_snippet(left_expr.span) {
 509                                     return Some((
 510                                         left_expr.span,
 511                                         "consider dereferencing here to assign to the mutable \
 512                                          borrowed piece of memory",
 513                                         format!("*{}", src),
 514                                     ));
 515                                 }
 516                             }
 517                         }
 518
 519                         return Some(match mutability {
 520                             hir::Mutability::Mut => (
 521                                 sp,
 522                                 "consider mutably borrowing here",
 523                                 format!("{}&mut {}", field_name, sugg_expr),
 524                             ),
 525                             hir::Mutability::Not => (
 526                                 sp,
 527                                 "consider borrowing here",
 528                                 format!("{}&{}", field_name, sugg_expr),
 529                             ),
 530                         });
 531                     }
 532                 }
 533             }
 534             (
 535                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 536                 _,
 537                 &ty::Ref(_, checked, _),
 538             ) if {
 539                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 540             } =>
 541             {
 542                 // We have `&T`, check if what was expected was `T`. If so,
 543                 // we may want to suggest removing a `&`.
 544                 if !cm.span_to_filename(expr.span).is_real() {
 545                     if let Ok(code) = cm.span_to_snippet(sp) {
 546                         if code.chars().next() == Some('&') {
 547                             return Some((
 548                                 sp,
 549                                 "consider removing the borrow",
 550                                 code[1..].to_string(),
 551                             ));
 552                         }
 553                     }
 554                     return None;
 555                 }
 556                 if let Ok(code) = cm.span_to_snippet(expr.span) {
 557                     return Some((sp, "consider removing the borrow", code));
 558                 }
 559             }
 560             _ if sp == expr.span && !is_macro => {
 561                 // Check for `Deref` implementations by constructing a predicate to
 562                 // prove: `<T as Deref>::Output == U`
 563                 let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
 564                 let item_def_id = self
 565                     .tcx
 566                     .associated_items(deref_trait)
 567                     .find(|item| item.kind == ty::AssocKind::Type)
 568                     .unwrap()
 569                     .def_id;
 570                 let predicate =
 571                     ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
 572                         // `<T as Deref>::Output`
 573                         projection_ty: ty::ProjectionTy {
 574                             // `T`
 575                             substs: self.tcx.intern_substs(&[checked_ty.into()]),
 576                             // `Deref::Output`
 577                             item_def_id,
 578                         },
 579                         // `U`
 580                         ty: expected,
 581                     }));
 582                 let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
 583                 let impls_deref = self.infcx.predicate_may_hold(&obligation);
 584
 585                 // For a suggestion to make sense, the type would need to be `Copy`.
 586                 let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
 587
 588                 if is_copy && impls_deref {
 589                     if let Ok(code) = cm.span_to_snippet(sp) {
 590                         let message = if checked_ty.is_region_ptr() {
 591                             "consider dereferencing the borrow"
 592                         } else {
 593                             "consider dereferencing the type"
 594                         };
 595                         let suggestion = if is_struct_pat_shorthand_field {
 596                             format!("{}: *{}", code, code)
 597                         } else {
 598                             format!("*{}", code)
 599                         };
 600                         return Some((sp, message, suggestion));
 601                     }
 602                 }
 603             }
 604             _ => {}
 605         }
 606         None
 607     }
 608
 609     pub fn check_for_cast(
 610         &self,
 611         err: &mut DiagnosticBuilder<'_>,
 612         expr: &hir::Expr<'_>,
 613         checked_ty: Ty<'tcx>,
 614         expected_ty: Ty<'tcx>,
 615     ) -> bool {
 616         if self.tcx.hir().is_const_context(expr.hir_id) {
 617             // Shouldn't suggest `.into()` on `const`s.
 618             // FIXME(estebank): modify once we decide to suggest `as` casts
 619             return false;
 620         }
 621         if !self.tcx.sess.source_map().span_to_filename(expr.span).is_real() {
 622             // Ignore if span is from within a macro.
 623             return false;
 624         }
 625
 626         // If casting this expression to a given numeric type would be appropriate in case of a type
 627         // mismatch.
 628         //
 629         // We want to minimize the amount of casting operations that are suggested, as it can be a
 630         // lossy operation with potentially bad side effects, so we only suggest when encountering
 631         // an expression that indicates that the original type couldn't be directly changed.
 632         //
 633         // For now, don't suggest casting with `as`.
 634         let can_cast = false;
 635
 636         let mut prefix = String::new();
 637         if let Some(hir::Node::Expr(hir::Expr {
 638             kind: hir::ExprKind::Struct(_, fields, _), ..
 639         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 640         {
 641             // `expr` is a literal field for a struct, only suggest if appropriate
 642             for field in *fields {
 643                 if field.expr.hir_id == expr.hir_id && field.is_shorthand {
 644                     // This is a field literal
 645                     prefix = format!("{}: ", field.ident);
 646                     break;
 647                 }
 648             }
 649             if &prefix == "" {
 650                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 651                 return false;
 652             }
 653         }
 654         if let hir::ExprKind::Call(path, args) = &expr.kind {
 655             if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
 656                 (&path.kind, args.len())
 657             {
 658                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 659                 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
 660                     (&base_ty.kind, path_segment.ident.name)
 661                 {
 662                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
 663                         match ident.name {
 664                             sym::i128
 665                             | sym::i64
 666                             | sym::i32
 667                             | sym::i16
 668                             | sym::i8
 669                             | sym::u128
 670                             | sym::u64
 671                             | sym::u32
 672                             | sym::u16
 673                             | sym::u8
 674                             | sym::isize
 675                             | sym::usize
 676                                 if base_ty_path.segments.len() == 1 =>
 677                             {
 678                                 return false;
 679                             }
 680                             _ => {}
 681                         }
 682                     }
 683                 }
 684             }
 685         }
 686
 687         let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 688         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 689         let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
 690         let lit_msg = format!(
 691             "change the type of the numeric literal from `{}` to `{}`",
 692             checked_ty, expected_ty,
 693         );
 694
 695         let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
 696
 697         if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 698             let cast_suggestion = format!(
 699                 "{}{}{}{} as {}",
 700                 prefix,
 701                 if needs_paren { "(" } else { "" },
 702                 src,
 703                 if needs_paren { ")" } else { "" },
 704                 expected_ty,
 705             );
 706             let try_into_suggestion = format!(
 707                 "{}{}{}{}.try_into().unwrap()",
 708                 prefix,
 709                 if needs_paren { "(" } else { "" },
 710                 src,
 711                 if needs_paren { ")" } else { "" },
 712             );
 713             let into_suggestion = format!(
 714                 "{}{}{}{}.into()",
 715                 prefix,
 716                 if needs_paren { "(" } else { "" },
 717                 src,
 718                 if needs_paren { ")" } else { "" },
 719             );
 720             let suffix_suggestion = format!(
 721                 "{}{}{}{}",
 722                 if needs_paren { "(" } else { "" },
 723                 if let (ty::Int(_), ty::Float(_)) | (ty::Uint(_), ty::Float(_)) =
 724                     (&expected_ty.kind, &checked_ty.kind,)
 725                 {
 726                     // Remove fractional part from literal, for example `42.0f32` into `42`
 727                     let src = src.trim_end_matches(&checked_ty.to_string());
 728                     src.split(".").next().unwrap()
 729                 } else {
 730                     src.trim_end_matches(&checked_ty.to_string())
 731                 },
 732                 expected_ty,
 733                 if needs_paren { ")" } else { "" },
 734             );
 735             let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
 736                 if let hir::ExprKind::Lit(lit) = &expr.kind {
 737                     lit.node.is_suffixed()
 738                 } else {
 739                     false
 740                 }
 741             };
 742
 743             let suggest_to_change_suffix_or_into =
 744                 |err: &mut DiagnosticBuilder<'_>, is_fallible: bool| {
 745                     let into_sugg = into_suggestion.clone();
 746                     err.span_suggestion(
 747                         expr.span,
 748                         if literal_is_ty_suffixed(expr) {
 749                             &lit_msg
 750                         } else if is_fallible {
 751                             &try_msg
 752                         } else {
 753                             &msg
 754                         },
 755                         if literal_is_ty_suffixed(expr) {
 756                             suffix_suggestion.clone()
 757                         } else if is_fallible {
 758                             try_into_suggestion
 759                         } else {
 760                             into_sugg
 761                         },
 762                         Applicability::MachineApplicable,
 763                     );
 764                 };
 765
 766             match (&expected_ty.kind, &checked_ty.kind) {
 767                 (&ty::Int(ref exp), &ty::Int(ref found)) => {
 768                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 769                         (Some(found), Some(exp)) if found > exp => true,
 770                         (None, _) | (_, None) => true,
 771                         _ => false,
 772                     };
 773                     suggest_to_change_suffix_or_into(err, is_fallible);
 774                     true
 775                 }
 776                 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 777                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 778                         (Some(found), Some(exp)) if found > exp => true,
 779                         (None, _) | (_, None) => true,
 780                         _ => false,
 781                     };
 782                     suggest_to_change_suffix_or_into(err, is_fallible);
 783                     true
 784                 }
 785                 (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
 786                     suggest_to_change_suffix_or_into(err, true);
 787                     true
 788                 }
 789                 (&ty::Float(ref exp), &ty::Float(ref found)) => {
 790                     if found.bit_width() < exp.bit_width() {
 791                         suggest_to_change_suffix_or_into(err, false);
 792                     } else if literal_is_ty_suffixed(expr) {
 793                         err.span_suggestion(
 794                             expr.span,
 795                             &lit_msg,
 796                             suffix_suggestion,
 797                             Applicability::MachineApplicable,
 798                         );
 799                     } else if can_cast {
 800                         // Missing try_into implementation for `f64` to `f32`
 801                         err.span_suggestion(
 802                             expr.span,
 803                             &format!("{}, producing the closest possible value", cast_msg),
 804                             cast_suggestion,
 805                             Applicability::MaybeIncorrect, // lossy conversion
 806                         );
 807                     }
 808                     true
 809                 }
 810                 (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
 811                     if literal_is_ty_suffixed(expr) {
 812                         err.span_suggestion(
 813                             expr.span,
 814                             &lit_msg,
 815                             suffix_suggestion,
 816                             Applicability::MachineApplicable,
 817                         );
 818                     } else if can_cast {
 819                         // Missing try_into implementation for `{float}` to `{integer}`
 820                         err.span_suggestion(
 821                             expr.span,
 822                             &format!("{}, rounding the float towards zero", msg),
 823                             cast_suggestion,
 824                             Applicability::MaybeIncorrect, // lossy conversion
 825                         );
 826                         err.warn(
 827                             "if the rounded value cannot be represented by the target \
 828                                   integer type, including `Inf` and `NaN`, casting will cause \
 829                                   undefined behavior \
 830                                   (https://github.com/rust-lang/rust/issues/10184)",
 831                         );
 832                     }
 833                     true
 834                 }
 835                 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 836                     // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 837                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 838                         err.span_suggestion(
 839                             expr.span,
 840                             &format!(
 841                                 "{}, producing the floating point representation of the integer",
 842                                 msg,
 843                             ),
 844                             into_suggestion,
 845                             Applicability::MachineApplicable,
 846                         );
 847                     } else if literal_is_ty_suffixed(expr) {
 848                         err.span_suggestion(
 849                             expr.span,
 850                             &lit_msg,
 851                             suffix_suggestion,
 852                             Applicability::MachineApplicable,
 853                         );
 854                     } else {
 855                         // Missing try_into implementation for `{integer}` to `{float}`
 856                         err.span_suggestion(
 857                             expr.span,
 858                             &format!(
 859                                 "{}, producing the floating point representation of the integer,
 860                                  rounded if necessary",
 861                                 cast_msg,
 862                             ),
 863                             cast_suggestion,
 864                             Applicability::MaybeIncorrect, // lossy conversion
 865                         );
 866                     }
 867                     true
 868                 }
 869                 (&ty::Float(ref exp), &ty::Int(ref found)) => {
 870                     // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 871                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 872                         err.span_suggestion(
 873                             expr.span,
 874                             &format!(
 875                                 "{}, producing the floating point representation of the integer",
 876                                 &msg,
 877                             ),
 878                             into_suggestion,
 879                             Applicability::MachineApplicable,
 880                         );
 881                     } else if literal_is_ty_suffixed(expr) {
 882                         err.span_suggestion(
 883                             expr.span,
 884                             &lit_msg,
 885                             suffix_suggestion,
 886                             Applicability::MachineApplicable,
 887                         );
 888                     } else {
 889                         // Missing try_into implementation for `{integer}` to `{float}`
 890                         err.span_suggestion(
 891                             expr.span,
 892                             &format!(
 893                                 "{}, producing the floating point representation of the integer, \
 894                                  rounded if necessary",
 895                                 &msg,
 896                             ),
 897                             cast_suggestion,
 898                             Applicability::MaybeIncorrect, // lossy conversion
 899                         );
 900                     }
 901                     true
 902                 }
 903                 _ => false,
 904             }
 905         } else {
 906             false
 907         }
 908     }
 909 }