src/librustc_typeck/check/demand.rs

   1 use crate::check::FnCtxt;
   2 use rustc::infer::InferOk;
   3 use rustc::traits::{self, ObligationCause};
   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::util::parser::PREC_POSTFIX;
  10 use syntax_pos::symbol::sym;
  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_coerce(
  83         &self,
  84         expr: &hir::Expr<'_>,
  85         checked_ty: Ty<'tcx>,
  86         expected: Ty<'tcx>,
  87         allow_two_phase: AllowTwoPhase,
  88     ) -> Ty<'tcx> {
  89         let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
  90         if let Some(mut err) = err {
  91             err.emit();
  92         }
  93         ty
  94     }
  95
  96     // Checks that the type of `expr` can be coerced to `expected`.
  97     //
  98     // N.B., this code relies on `self.diverges` to be accurate. In
  99     // particular, assignments to `!` will be permitted if the
 100     // diverges flag is currently "always".
 101     pub fn demand_coerce_diag(
 102         &self,
 103         expr: &hir::Expr<'_>,
 104         checked_ty: Ty<'tcx>,
 105         expected: Ty<'tcx>,
 106         allow_two_phase: AllowTwoPhase,
 107     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
 108         let expected = self.resolve_vars_with_obligations(expected);
 109
 110         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
 111             Ok(ty) => return (ty, None),
 112             Err(e) => e,
 113         };
 114
 115         let expr = expr.peel_drop_temps();
 116         let cause = self.misc(expr.span);
 117         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 118         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
 119
 120         if self.is_assign_to_bool(expr, expected) {
 121             // Error reported in `check_assign` so avoid emitting error again.
 122             err.delay_as_bug();
 123             return (expected, None);
 124         }
 125
 126         self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected);
 127
 128         (expected, Some(err))
 129     }
 130
 131     fn annotate_expected_due_to_let_ty(
 132         &self,
 133         err: &mut DiagnosticBuilder<'_>,
 134         expr: &hir::Expr<'_>,
 135     ) {
 136         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 137         if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
 138             self.tcx.hir().find(parent)
 139         {
 140             if init.hir_id == expr.hir_id {
 141                 // Point at `let` assignment type.
 142                 err.span_label(ty.span, "expected due to this");
 143             }
 144         }
 145     }
 146
 147     /// Returns whether the expected type is `bool` and the expression is `x = y`.
 148     pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
 149         if let hir::ExprKind::Assign(..) = expr.kind {
 150             return expected == self.tcx.types.bool;
 151         }
 152         false
 153     }
 154
 155     /// If the expected type is an enum (Issue #55250) with any variants whose
 156     /// sole field is of the found type, suggest such variants. (Issue #42764)
 157     fn suggest_compatible_variants(
 158         &self,
 159         err: &mut DiagnosticBuilder<'_>,
 160         expr: &hir::Expr<'_>,
 161         expected: Ty<'tcx>,
 162         expr_ty: Ty<'tcx>,
 163     ) {
 164         if let ty::Adt(expected_adt, substs) = expected.kind {
 165             if !expected_adt.is_enum() {
 166                 return;
 167             }
 168
 169             let mut compatible_variants = expected_adt
 170                 .variants
 171                 .iter()
 172                 .filter(|variant| variant.fields.len() == 1)
 173                 .filter_map(|variant| {
 174                     let sole_field = &variant.fields[0];
 175                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 176                     if self.can_coerce(expr_ty, sole_field_ty) {
 177                         let variant_path = self.tcx.def_path_str(variant.def_id);
 178                         // FIXME #56861: DRYer prelude filtering
 179                         Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
 180                     } else {
 181                         None
 182                     }
 183                 })
 184                 .peekable();
 185
 186             if compatible_variants.peek().is_some() {
 187                 let expr_text =
 188                     self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or_else(|_| {
 189                         print::to_string(print::NO_ANN, |s| s.print_expr(expr))
 190                     });
 191                 let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
 192                 let msg = "try using a variant of the expected enum";
 193                 err.span_suggestions(expr.span, msg, suggestions, Applicability::MaybeIncorrect);
 194             }
 195         }
 196     }
 197
 198     pub fn get_conversion_methods(
 199         &self,
 200         span: Span,
 201         expected: Ty<'tcx>,
 202         checked_ty: Ty<'tcx>,
 203     ) -> Vec<AssocItem> {
 204         let mut methods = self.probe_for_return_type(
 205             span,
 206             probe::Mode::MethodCall,
 207             expected,
 208             checked_ty,
 209             hir::DUMMY_HIR_ID,
 210         );
 211         methods.retain(|m| {
 212             self.has_no_input_arg(m)
 213                 && self
 214                     .tcx
 215                     .get_attrs(m.def_id)
 216                     .iter()
 217                     // This special internal attribute is used to whitelist
 218                     // "identity-like" conversion methods to be suggested here.
 219                     //
 220                     // FIXME (#46459 and #46460): ideally
 221                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 222                     // also be `#[rustc_conversion_suggestion]`, if not for
 223                     // method-probing false-positives and -negatives (respectively).
 224                     //
 225                     // FIXME? Other potential candidate methods: `as_ref` and
 226                     // `as_mut`?
 227                     .find(|a| a.check_name(sym::rustc_conversion_suggestion))
 228                     .is_some()
 229         });
 230
 231         methods
 232     }
 233
 234     // This function checks if the method isn't static and takes other arguments than `self`.
 235     fn has_no_input_arg(&self, method: &AssocItem) -> bool {
 236         match method.kind {
 237             ty::AssocKind::Method => {
 238                 self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 239             }
 240             _ => false,
 241         }
 242     }
 243
 244     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 245     ///
 246     /// Given the following code:
 247     /// ```
 248     /// struct Foo;
 249     /// fn takes_ref(_: &Foo) {}
 250     /// let ref opt = Some(Foo);
 251     ///
 252     /// opt.map(|param| takes_ref(param));
 253     /// ```
 254     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 255     ///
 256     /// It only checks for `Option` and `Result` and won't work with
 257     /// ```
 258     /// opt.map(|param| { takes_ref(param) });
 259     /// ```
 260     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 261         let path = match expr.kind {
 262             hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
 263             _ => return None,
 264         };
 265
 266         let local_id = match path.res {
 267             hir::def::Res::Local(id) => id,
 268             _ => return None,
 269         };
 270
 271         let local_parent = self.tcx.hir().get_parent_node(local_id);
 272         let param_hir_id = match self.tcx.hir().find(local_parent) {
 273             Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
 274             _ => return None,
 275         };
 276
 277         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 278         let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
 279             Some(Node::Expr(hir::Expr {
 280                 hir_id,
 281                 kind: hir::ExprKind::Closure(_, decl, ..),
 282                 ..
 283             })) => (hir_id, decl),
 284             _ => return None,
 285         };
 286
 287         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 288         let hir = self.tcx.hir().find(expr_parent);
 289         let closure_params_len = closure_fn_decl.inputs.len();
 290         let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
 291             (
 292                 Some(Node::Expr(hir::Expr {
 293                     kind: hir::ExprKind::MethodCall(path, span, expr),
 294                     ..
 295                 })),
 296                 1,
 297             ) => (path, span, expr),
 298             _ => return None,
 299         };
 300
 301         let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
 302         let self_ty = format!("{:?}", self_ty);
 303         let name = method_path.ident.as_str();
 304         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 305             || self_ty.starts_with("&std::result::Result")
 306             || self_ty.starts_with("std::option::Option")
 307             || self_ty.starts_with("std::result::Result"))
 308             && (name == "map" || name == "and_then");
 309         match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
 310             (true, Ok(src)) => {
 311                 let suggestion = format!("as_ref().{}", src);
 312                 Some((*method_span, "consider using `as_ref` instead", suggestion))
 313             }
 314             _ => None,
 315         }
 316     }
 317
 318     crate fn is_hir_id_from_struct_pattern_shorthand_field(
 319         &self,
 320         hir_id: hir::HirId,
 321         sp: Span,
 322     ) -> bool {
 323         let cm = self.sess().source_map();
 324         let parent_id = self.tcx.hir().get_parent_node(hir_id);
 325         if let Some(parent) = self.tcx.hir().find(parent_id) {
 326             // Account for fields
 327             if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
 328             {
 329                 if let Ok(src) = cm.span_to_snippet(sp) {
 330                     for field in *fields {
 331                         if field.ident.as_str() == src && field.is_shorthand {
 332                             return true;
 333                         }
 334                     }
 335                 }
 336             }
 337         }
 338         false
 339     }
 340
 341     /// This function is used to determine potential "simple" improvements or users' errors and
 342     /// provide them useful help. For example:
 343     ///
 344     /// ```
 345     /// fn some_fn(s: &str) {}
 346     ///
 347     /// let x = "hey!".to_owned();
 348     /// some_fn(x); // error
 349     /// ```
 350     ///
 351     /// No need to find every potential function which could make a coercion to transform a
 352     /// `String` into a `&str` since a `&` would do the trick!
 353     ///
 354     /// In addition of this check, it also checks between references mutability state. If the
 355     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 356     /// `&mut`!".
 357     pub fn check_ref(
 358         &self,
 359         expr: &hir::Expr<'_>,
 360         checked_ty: Ty<'tcx>,
 361         expected: Ty<'tcx>,
 362     ) -> Option<(Span, &'static str, String)> {
 363         let cm = self.sess().source_map();
 364         let sp = expr.span;
 365         if !cm.span_to_filename(sp).is_real() {
 366             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 367             // call span, but that breaks down when the type error comes from multiple calls down.
 368             return None;
 369         }
 370
 371         let is_struct_pat_shorthand_field =
 372             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 373
 374         // If the span is from a macro, then it's hard to extract the text
 375         // and make a good suggestion, so don't bother.
 376         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 377
 378         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 379         let expr = expr.peel_drop_temps();
 380
 381         match (&expr.kind, &expected.kind, &checked_ty.kind) {
 382             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
 383                 (&ty::Str, &ty::Array(arr, _)) | (&ty::Str, &ty::Slice(arr))
 384                     if arr == self.tcx.types.u8 =>
 385                 {
 386                     if let hir::ExprKind::Lit(_) = expr.kind {
 387                         if let Ok(src) = cm.span_to_snippet(sp) {
 388                             if src.starts_with("b\"") {
 389                                 return Some((
 390                                     sp,
 391                                     "consider removing the leading `b`",
 392                                     src[1..].to_string(),
 393                                 ));
 394                             }
 395                         }
 396                     }
 397                 }
 398                 (&ty::Array(arr, _), &ty::Str) | (&ty::Slice(arr), &ty::Str)
 399                     if arr == self.tcx.types.u8 =>
 400                 {
 401                     if let hir::ExprKind::Lit(_) = expr.kind {
 402                         if let Ok(src) = cm.span_to_snippet(sp) {
 403                             if src.starts_with("\"") {
 404                                 return Some((
 405                                     sp,
 406                                     "consider adding a leading `b`",
 407                                     format!("b{}", src),
 408                                 ));
 409                             }
 410                         }
 411                     }
 412                 }
 413                 _ => {}
 414             },
 415             (_, &ty::Ref(_, _, mutability), _) => {
 416                 // Check if it can work when put into a ref. For example:
 417                 //
 418                 // ```
 419                 // fn bar(x: &mut i32) {}
 420                 //
 421                 // let x = 0u32;
 422                 // bar(&x); // error, expected &mut
 423                 // ```
 424                 let ref_ty = match mutability {
 425                     hir::Mutability::Mut => {
 426                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 427                     }
 428                     hir::Mutability::Not => {
 429                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 430                     }
 431                 };
 432                 if self.can_coerce(ref_ty, expected) {
 433                     let mut sugg_sp = sp;
 434                     if let hir::ExprKind::MethodCall(segment, _sp, args) = &expr.kind {
 435                         let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
 436                         if let ([arg], Some(true), sym::clone) = (
 437                             &args[..],
 438                             self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
 439                                 let ai = self.tcx.associated_item(did);
 440                                 ai.container == ty::TraitContainer(clone_trait)
 441                             }),
 442                             segment.ident.name,
 443                         ) {
 444                             // If this expression had a clone call when suggesting borrowing
 445                             // we want to suggest removing it because it'd now be unnecessary.
 446                             sugg_sp = arg.span;
 447                         }
 448                     }
 449                     if let Ok(src) = cm.span_to_snippet(sugg_sp) {
 450                         let needs_parens = match expr.kind {
 451                             // parenthesize if needed (Issue #46756)
 452                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 453                             // parenthesize borrows of range literals (Issue #54505)
 454                             _ if is_range_literal(self.tcx.sess.source_map(), expr) => true,
 455                             _ => false,
 456                         };
 457                         let sugg_expr = if needs_parens { format!("({})", src) } else { src };
 458
 459                         if let Some(sugg) = self.can_use_as_ref(expr) {
 460                             return Some(sugg);
 461                         }
 462                         let field_name = if is_struct_pat_shorthand_field {
 463                             format!("{}: ", sugg_expr)
 464                         } else {
 465                             String::new()
 466                         };
 467                         if let Some(hir::Node::Expr(hir::Expr {
 468                             kind: hir::ExprKind::Assign(left_expr, ..),
 469                             ..
 470                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 471                         {
 472                             if mutability == hir::Mutability::Mut {
 473                                 // Found the following case:
 474                                 // fn foo(opt: &mut Option<String>){ opt = None }
 475                                 //                                   ---   ^^^^
 476                                 //                                   |     |
 477                                 //    consider dereferencing here: `*opt`  |
 478                                 // expected mutable reference, found enum `Option`
 479                                 if let Ok(src) = cm.span_to_snippet(left_expr.span) {
 480                                     return Some((
 481                                         left_expr.span,
 482                                         "consider dereferencing here to assign to the mutable \
 483                                          borrowed piece of memory",
 484                                         format!("*{}", src),
 485                                     ));
 486                                 }
 487                             }
 488                         }
 489
 490                         return Some(match mutability {
 491                             hir::Mutability::Mut => (
 492                                 sp,
 493                                 "consider mutably borrowing here",
 494                                 format!("{}&mut {}", field_name, sugg_expr),
 495                             ),
 496                             hir::Mutability::Not => (
 497                                 sp,
 498                                 "consider borrowing here",
 499                                 format!("{}&{}", field_name, sugg_expr),
 500                             ),
 501                         });
 502                     }
 503                 }
 504             }
 505             (
 506                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 507                 _,
 508                 &ty::Ref(_, checked, _),
 509             ) if {
 510                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 511             } =>
 512             {
 513                 // We have `&T`, check if what was expected was `T`. If so,
 514                 // we may want to suggest removing a `&`.
 515                 if !cm.span_to_filename(expr.span).is_real() {
 516                     if let Ok(code) = cm.span_to_snippet(sp) {
 517                         if code.chars().next() == Some('&') {
 518                             return Some((
 519                                 sp,
 520                                 "consider removing the borrow",
 521                                 code[1..].to_string(),
 522                             ));
 523                         }
 524                     }
 525                     return None;
 526                 }
 527                 if let Ok(code) = cm.span_to_snippet(expr.span) {
 528                     return Some((sp, "consider removing the borrow", code));
 529                 }
 530             }
 531             _ if sp == expr.span && !is_macro => {
 532                 // Check for `Deref` implementations by constructing a predicate to
 533                 // prove: `<T as Deref>::Output == U`
 534                 let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
 535                 let item_def_id = self
 536                     .tcx
 537                     .associated_items(deref_trait)
 538                     .find(|item| item.kind == ty::AssocKind::Type)
 539                     .unwrap()
 540                     .def_id;
 541                 let predicate =
 542                     ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
 543                         // `<T as Deref>::Output`
 544                         projection_ty: ty::ProjectionTy {
 545                             // `T`
 546                             substs: self.tcx.intern_substs(&[checked_ty.into()]),
 547                             // `Deref::Output`
 548                             item_def_id,
 549                         },
 550                         // `U`
 551                         ty: expected,
 552                     }));
 553                 let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
 554                 let impls_deref = self.infcx.predicate_may_hold(&obligation);
 555
 556                 // For a suggestion to make sense, the type would need to be `Copy`.
 557                 let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
 558
 559                 if is_copy && impls_deref {
 560                     if let Ok(code) = cm.span_to_snippet(sp) {
 561                         let message = if checked_ty.is_region_ptr() {
 562                             "consider dereferencing the borrow"
 563                         } else {
 564                             "consider dereferencing the type"
 565                         };
 566                         let suggestion = if is_struct_pat_shorthand_field {
 567                             format!("{}: *{}", code, code)
 568                         } else {
 569                             format!("*{}", code)
 570                         };
 571                         return Some((sp, message, suggestion));
 572                     }
 573                 }
 574             }
 575             _ => {}
 576         }
 577         None
 578     }
 579
 580     pub fn check_for_cast(
 581         &self,
 582         err: &mut DiagnosticBuilder<'_>,
 583         expr: &hir::Expr<'_>,
 584         checked_ty: Ty<'tcx>,
 585         expected_ty: Ty<'tcx>,
 586     ) -> bool {
 587         if self.tcx.hir().is_const_context(expr.hir_id) {
 588             // Shouldn't suggest `.into()` on `const`s.
 589             // FIXME(estebank): modify once we decide to suggest `as` casts
 590             return false;
 591         }
 592         if !self.tcx.sess.source_map().span_to_filename(expr.span).is_real() {
 593             // Ignore if span is from within a macro.
 594             return false;
 595         }
 596
 597         // If casting this expression to a given numeric type would be appropriate in case of a type
 598         // mismatch.
 599         //
 600         // We want to minimize the amount of casting operations that are suggested, as it can be a
 601         // lossy operation with potentially bad side effects, so we only suggest when encountering
 602         // an expression that indicates that the original type couldn't be directly changed.
 603         //
 604         // For now, don't suggest casting with `as`.
 605         let can_cast = false;
 606
 607         let mut prefix = String::new();
 608         if let Some(hir::Node::Expr(hir::Expr {
 609             kind: hir::ExprKind::Struct(_, fields, _), ..
 610         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 611         {
 612             // `expr` is a literal field for a struct, only suggest if appropriate
 613             for field in *fields {
 614                 if field.expr.hir_id == expr.hir_id && field.is_shorthand {
 615                     // This is a field literal
 616                     prefix = format!("{}: ", field.ident);
 617                     break;
 618                 }
 619             }
 620             if &prefix == "" {
 621                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 622                 return false;
 623             }
 624         }
 625         if let hir::ExprKind::Call(path, args) = &expr.kind {
 626             if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
 627                 (&path.kind, args.len())
 628             {
 629                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 630                 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
 631                     (&base_ty.kind, path_segment.ident.name)
 632                 {
 633                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
 634                         match ident.name {
 635                             sym::i128
 636                             | sym::i64
 637                             | sym::i32
 638                             | sym::i16
 639                             | sym::i8
 640                             | sym::u128
 641                             | sym::u64
 642                             | sym::u32
 643                             | sym::u16
 644                             | sym::u8
 645                             | sym::isize
 646                             | sym::usize
 647                                 if base_ty_path.segments.len() == 1 =>
 648                             {
 649                                 return false;
 650                             }
 651                             _ => {}
 652                         }
 653                     }
 654                 }
 655             }
 656         }
 657
 658         let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 659         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 660         let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
 661         let lit_msg = format!(
 662             "change the type of the numeric literal from `{}` to `{}`",
 663             checked_ty, expected_ty,
 664         );
 665
 666         let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
 667
 668         if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 669             let cast_suggestion = format!(
 670                 "{}{}{}{} as {}",
 671                 prefix,
 672                 if needs_paren { "(" } else { "" },
 673                 src,
 674                 if needs_paren { ")" } else { "" },
 675                 expected_ty,
 676             );
 677             let try_into_suggestion = format!(
 678                 "{}{}{}{}.try_into().unwrap()",
 679                 prefix,
 680                 if needs_paren { "(" } else { "" },
 681                 src,
 682                 if needs_paren { ")" } else { "" },
 683             );
 684             let into_suggestion = format!(
 685                 "{}{}{}{}.into()",
 686                 prefix,
 687                 if needs_paren { "(" } else { "" },
 688                 src,
 689                 if needs_paren { ")" } else { "" },
 690             );
 691             let suffix_suggestion = format!(
 692                 "{}{}{}{}",
 693                 if needs_paren { "(" } else { "" },
 694                 if let (ty::Int(_), ty::Float(_)) | (ty::Uint(_), ty::Float(_)) =
 695                     (&expected_ty.kind, &checked_ty.kind,)
 696                 {
 697                     // Remove fractional part from literal, for example `42.0f32` into `42`
 698                     let src = src.trim_end_matches(&checked_ty.to_string());
 699                     src.split(".").next().unwrap()
 700                 } else {
 701                     src.trim_end_matches(&checked_ty.to_string())
 702                 },
 703                 expected_ty,
 704                 if needs_paren { ")" } else { "" },
 705             );
 706             let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
 707                 if let hir::ExprKind::Lit(lit) = &expr.kind {
 708                     lit.node.is_suffixed()
 709                 } else {
 710                     false
 711                 }
 712             };
 713
 714             let suggest_to_change_suffix_or_into =
 715                 |err: &mut DiagnosticBuilder<'_>, is_fallible: bool| {
 716                     let into_sugg = into_suggestion.clone();
 717                     err.span_suggestion(
 718                         expr.span,
 719                         if literal_is_ty_suffixed(expr) {
 720                             &lit_msg
 721                         } else if is_fallible {
 722                             &try_msg
 723                         } else {
 724                             &msg
 725                         },
 726                         if literal_is_ty_suffixed(expr) {
 727                             suffix_suggestion.clone()
 728                         } else if is_fallible {
 729                             try_into_suggestion
 730                         } else {
 731                             into_sugg
 732                         },
 733                         Applicability::MachineApplicable,
 734                     );
 735                 };
 736
 737             match (&expected_ty.kind, &checked_ty.kind) {
 738                 (&ty::Int(ref exp), &ty::Int(ref found)) => {
 739                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 740                         (Some(found), Some(exp)) if found > exp => true,
 741                         (None, _) | (_, None) => true,
 742                         _ => false,
 743                     };
 744                     suggest_to_change_suffix_or_into(err, is_fallible);
 745                     true
 746                 }
 747                 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 748                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 749                         (Some(found), Some(exp)) if found > exp => true,
 750                         (None, _) | (_, None) => true,
 751                         _ => false,
 752                     };
 753                     suggest_to_change_suffix_or_into(err, is_fallible);
 754                     true
 755                 }
 756                 (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
 757                     suggest_to_change_suffix_or_into(err, true);
 758                     true
 759                 }
 760                 (&ty::Float(ref exp), &ty::Float(ref found)) => {
 761                     if found.bit_width() < exp.bit_width() {
 762                         suggest_to_change_suffix_or_into(err, false);
 763                     } else if literal_is_ty_suffixed(expr) {
 764                         err.span_suggestion(
 765                             expr.span,
 766                             &lit_msg,
 767                             suffix_suggestion,
 768                             Applicability::MachineApplicable,
 769                         );
 770                     } else if can_cast {
 771                         // Missing try_into implementation for `f64` to `f32`
 772                         err.span_suggestion(
 773                             expr.span,
 774                             &format!("{}, producing the closest possible value", cast_msg),
 775                             cast_suggestion,
 776                             Applicability::MaybeIncorrect, // lossy conversion
 777                         );
 778                     }
 779                     true
 780                 }
 781                 (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
 782                     if literal_is_ty_suffixed(expr) {
 783                         err.span_suggestion(
 784                             expr.span,
 785                             &lit_msg,
 786                             suffix_suggestion,
 787                             Applicability::MachineApplicable,
 788                         );
 789                     } else if can_cast {
 790                         // Missing try_into implementation for `{float}` to `{integer}`
 791                         err.span_suggestion(
 792                             expr.span,
 793                             &format!("{}, rounding the float towards zero", msg),
 794                             cast_suggestion,
 795                             Applicability::MaybeIncorrect, // lossy conversion
 796                         );
 797                         err.warn(
 798                             "if the rounded value cannot be represented by the target \
 799                                   integer type, including `Inf` and `NaN`, casting will cause \
 800                                   undefined behavior \
 801                                   (https://github.com/rust-lang/rust/issues/10184)",
 802                         );
 803                     }
 804                     true
 805                 }
 806                 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 807                     // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 808                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 809                         err.span_suggestion(
 810                             expr.span,
 811                             &format!(
 812                                 "{}, producing the floating point representation of the integer",
 813                                 msg,
 814                             ),
 815                             into_suggestion,
 816                             Applicability::MachineApplicable,
 817                         );
 818                     } else if literal_is_ty_suffixed(expr) {
 819                         err.span_suggestion(
 820                             expr.span,
 821                             &lit_msg,
 822                             suffix_suggestion,
 823                             Applicability::MachineApplicable,
 824                         );
 825                     } else {
 826                         // Missing try_into implementation for `{integer}` to `{float}`
 827                         err.span_suggestion(
 828                             expr.span,
 829                             &format!(
 830                                 "{}, producing the floating point representation of the integer,
 831                                  rounded if necessary",
 832                                 cast_msg,
 833                             ),
 834                             cast_suggestion,
 835                             Applicability::MaybeIncorrect, // lossy conversion
 836                         );
 837                     }
 838                     true
 839                 }
 840                 (&ty::Float(ref exp), &ty::Int(ref found)) => {
 841                     // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 842                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 843                         err.span_suggestion(
 844                             expr.span,
 845                             &format!(
 846                                 "{}, producing the floating point representation of the integer",
 847                                 &msg,
 848                             ),
 849                             into_suggestion,
 850                             Applicability::MachineApplicable,
 851                         );
 852                     } else if literal_is_ty_suffixed(expr) {
 853                         err.span_suggestion(
 854                             expr.span,
 855                             &lit_msg,
 856                             suffix_suggestion,
 857                             Applicability::MachineApplicable,
 858                         );
 859                     } else {
 860                         // Missing try_into implementation for `{integer}` to `{float}`
 861                         err.span_suggestion(
 862                             expr.span,
 863                             &format!(
 864                                 "{}, producing the floating point representation of the integer, \
 865                                  rounded if necessary",
 866                                 &msg,
 867                             ),
 868                             cast_suggestion,
 869                             Applicability::MaybeIncorrect, // lossy conversion
 870                         );
 871                     }
 872                     true
 873                 }
 874                 _ => false,
 875             }
 876         } else {
 877             false
 878         }
 879     }
 880 }