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 rustc::ty::adjustment::AllowTwoPhase;
   6 use rustc::ty::{self, AssocItem, Ty};
   7 use rustc_errors::{Applicability, DiagnosticBuilder};
   8 use rustc_hir as hir;
   9 use rustc_hir::{is_range_literal, print, Node};
  10 use rustc_span::symbol::sym;
  11 use rustc_span::Span;
  12 use syntax::util::parser::PREC_POSTFIX;
  13
  14 use super::method::probe;
  15
  16 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  17     pub fn emit_coerce_suggestions(
  18         &self,
  19         err: &mut DiagnosticBuilder<'_>,
  20         expr: &hir::Expr<'_>,
  21         expr_ty: Ty<'tcx>,
  22         expected: Ty<'tcx>,
  23     ) {
  24         self.annotate_expected_due_to_let_ty(err, expr);
  25         self.suggest_compatible_variants(err, expr, expected, expr_ty);
  26         self.suggest_ref_or_into(err, expr, expected, expr_ty);
  27         self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
  28         self.suggest_missing_await(err, expr, expected, expr_ty);
  29     }
  30
  31     // Requires that the two types unify, and prints an error message if
  32     // they don't.
  33     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  34         self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
  35     }
  36
  37     pub fn demand_suptype_diag(
  38         &self,
  39         sp: Span,
  40         expected: Ty<'tcx>,
  41         actual: Ty<'tcx>,
  42     ) -> Option<DiagnosticBuilder<'tcx>> {
  43         let cause = &self.misc(sp);
  44         match self.at(cause, self.param_env).sup(expected, actual) {
  45             Ok(InferOk { obligations, value: () }) => {
  46                 self.register_predicates(obligations);
  47                 None
  48             }
  49             Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
  50         }
  51     }
  52
  53     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  54         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  55             err.emit();
  56         }
  57     }
  58
  59     pub fn demand_eqtype_diag(
  60         &self,
  61         sp: Span,
  62         expected: Ty<'tcx>,
  63         actual: Ty<'tcx>,
  64     ) -> Option<DiagnosticBuilder<'tcx>> {
  65         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  66     }
  67
  68     pub fn demand_eqtype_with_origin(
  69         &self,
  70         cause: &ObligationCause<'tcx>,
  71         expected: Ty<'tcx>,
  72         actual: Ty<'tcx>,
  73     ) -> Option<DiagnosticBuilder<'tcx>> {
  74         match self.at(cause, self.param_env).eq(expected, actual) {
  75             Ok(InferOk { obligations, value: () }) => {
  76                 self.register_predicates(obligations);
  77                 None
  78             }
  79             Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
  80         }
  81     }
  82
  83     pub fn demand_coerce(
  84         &self,
  85         expr: &hir::Expr<'_>,
  86         checked_ty: Ty<'tcx>,
  87         expected: Ty<'tcx>,
  88         allow_two_phase: AllowTwoPhase,
  89     ) -> Ty<'tcx> {
  90         let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
  91         if let Some(mut err) = err {
  92             err.emit();
  93         }
  94         ty
  95     }
  96
  97     // Checks that the type of `expr` can be coerced to `expected`.
  98     //
  99     // N.B., this code relies on `self.diverges` to be accurate. In
 100     // particular, assignments to `!` will be permitted if the
 101     // diverges flag is currently "always".
 102     pub fn demand_coerce_diag(
 103         &self,
 104         expr: &hir::Expr<'_>,
 105         checked_ty: Ty<'tcx>,
 106         expected: Ty<'tcx>,
 107         allow_two_phase: AllowTwoPhase,
 108     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
 109         let expected = self.resolve_vars_with_obligations(expected);
 110
 111         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
 112             Ok(ty) => return (ty, None),
 113             Err(e) => e,
 114         };
 115
 116         let expr = expr.peel_drop_temps();
 117         let cause = self.misc(expr.span);
 118         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 119         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
 120
 121         if self.is_assign_to_bool(expr, expected) {
 122             // Error reported in `check_assign` so avoid emitting error again.
 123             err.delay_as_bug();
 124             return (expected, None);
 125         }
 126
 127         self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected);
 128
 129         (expected, Some(err))
 130     }
 131
 132     fn annotate_expected_due_to_let_ty(
 133         &self,
 134         err: &mut DiagnosticBuilder<'_>,
 135         expr: &hir::Expr<'_>,
 136     ) {
 137         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 138         if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
 139             self.tcx.hir().find(parent)
 140         {
 141             if init.hir_id == expr.hir_id {
 142                 // Point at `let` assignment type.
 143                 err.span_label(ty.span, "expected due to this");
 144             }
 145         }
 146     }
 147
 148     /// Returns whether the expected type is `bool` and the expression is `x = y`.
 149     pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
 150         if let hir::ExprKind::Assign(..) = expr.kind {
 151             return expected == self.tcx.types.bool;
 152         }
 153         false
 154     }
 155
 156     /// If the expected type is an enum (Issue #55250) with any variants whose
 157     /// sole field is of the found type, suggest such variants. (Issue #42764)
 158     fn suggest_compatible_variants(
 159         &self,
 160         err: &mut DiagnosticBuilder<'_>,
 161         expr: &hir::Expr<'_>,
 162         expected: Ty<'tcx>,
 163         expr_ty: Ty<'tcx>,
 164     ) {
 165         if let ty::Adt(expected_adt, substs) = expected.kind {
 166             if !expected_adt.is_enum() {
 167                 return;
 168             }
 169
 170             let mut compatible_variants = expected_adt
 171                 .variants
 172                 .iter()
 173                 .filter(|variant| variant.fields.len() == 1)
 174                 .filter_map(|variant| {
 175                     let sole_field = &variant.fields[0];
 176                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 177                     if self.can_coerce(expr_ty, sole_field_ty) {
 178                         let variant_path = self.tcx.def_path_str(variant.def_id);
 179                         // FIXME #56861: DRYer prelude filtering
 180                         Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
 181                     } else {
 182                         None
 183                     }
 184                 })
 185                 .peekable();
 186
 187             if compatible_variants.peek().is_some() {
 188                 let expr_text =
 189                     self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or_else(|_| {
 190                         print::to_string(print::NO_ANN, |s| s.print_expr(expr))
 191                     });
 192                 let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
 193                 let msg = "try using a variant of the expected enum";
 194                 err.span_suggestions(expr.span, msg, suggestions, Applicability::MaybeIncorrect);
 195             }
 196         }
 197     }
 198
 199     pub fn get_conversion_methods(
 200         &self,
 201         span: Span,
 202         expected: Ty<'tcx>,
 203         checked_ty: Ty<'tcx>,
 204     ) -> Vec<AssocItem> {
 205         let mut methods = self.probe_for_return_type(
 206             span,
 207             probe::Mode::MethodCall,
 208             expected,
 209             checked_ty,
 210             hir::DUMMY_HIR_ID,
 211         );
 212         methods.retain(|m| {
 213             self.has_no_input_arg(m)
 214                 && self
 215                     .tcx
 216                     .get_attrs(m.def_id)
 217                     .iter()
 218                     // This special internal attribute is used to whitelist
 219                     // "identity-like" conversion methods to be suggested here.
 220                     //
 221                     // FIXME (#46459 and #46460): ideally
 222                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 223                     // also be `#[rustc_conversion_suggestion]`, if not for
 224                     // method-probing false-positives and -negatives (respectively).
 225                     //
 226                     // FIXME? Other potential candidate methods: `as_ref` and
 227                     // `as_mut`?
 228                     .find(|a| a.check_name(sym::rustc_conversion_suggestion))
 229                     .is_some()
 230         });
 231
 232         methods
 233     }
 234
 235     // This function checks if the method isn't static and takes other arguments than `self`.
 236     fn has_no_input_arg(&self, method: &AssocItem) -> bool {
 237         match method.kind {
 238             ty::AssocKind::Method => {
 239                 self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 240             }
 241             _ => false,
 242         }
 243     }
 244
 245     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 246     ///
 247     /// Given the following code:
 248     /// ```
 249     /// struct Foo;
 250     /// fn takes_ref(_: &Foo) {}
 251     /// let ref opt = Some(Foo);
 252     ///
 253     /// opt.map(|param| takes_ref(param));
 254     /// ```
 255     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 256     ///
 257     /// It only checks for `Option` and `Result` and won't work with
 258     /// ```
 259     /// opt.map(|param| { takes_ref(param) });
 260     /// ```
 261     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 262         let path = match expr.kind {
 263             hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
 264             _ => return None,
 265         };
 266
 267         let local_id = match path.res {
 268             hir::def::Res::Local(id) => id,
 269             _ => return None,
 270         };
 271
 272         let local_parent = self.tcx.hir().get_parent_node(local_id);
 273         let param_hir_id = match self.tcx.hir().find(local_parent) {
 274             Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
 275             _ => return None,
 276         };
 277
 278         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 279         let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
 280             Some(Node::Expr(hir::Expr {
 281                 hir_id,
 282                 kind: hir::ExprKind::Closure(_, decl, ..),
 283                 ..
 284             })) => (hir_id, decl),
 285             _ => return None,
 286         };
 287
 288         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 289         let hir = self.tcx.hir().find(expr_parent);
 290         let closure_params_len = closure_fn_decl.inputs.len();
 291         let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
 292             (
 293                 Some(Node::Expr(hir::Expr {
 294                     kind: hir::ExprKind::MethodCall(path, span, expr),
 295                     ..
 296                 })),
 297                 1,
 298             ) => (path, span, expr),
 299             _ => return None,
 300         };
 301
 302         let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
 303         let self_ty = format!("{:?}", self_ty);
 304         let name = method_path.ident.as_str();
 305         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 306             || self_ty.starts_with("&std::result::Result")
 307             || self_ty.starts_with("std::option::Option")
 308             || self_ty.starts_with("std::result::Result"))
 309             && (name == "map" || name == "and_then");
 310         match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
 311             (true, Ok(src)) => {
 312                 let suggestion = format!("as_ref().{}", src);
 313                 Some((*method_span, "consider using `as_ref` instead", suggestion))
 314             }
 315             _ => None,
 316         }
 317     }
 318
 319     crate fn is_hir_id_from_struct_pattern_shorthand_field(
 320         &self,
 321         hir_id: hir::HirId,
 322         sp: Span,
 323     ) -> bool {
 324         let cm = self.sess().source_map();
 325         let parent_id = self.tcx.hir().get_parent_node(hir_id);
 326         if let Some(parent) = self.tcx.hir().find(parent_id) {
 327             // Account for fields
 328             if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
 329             {
 330                 if let Ok(src) = cm.span_to_snippet(sp) {
 331                     for field in *fields {
 332                         if field.ident.as_str() == src && field.is_shorthand {
 333                             return true;
 334                         }
 335                     }
 336                 }
 337             }
 338         }
 339         false
 340     }
 341
 342     /// This function is used to determine potential "simple" improvements or users' errors and
 343     /// provide them useful help. For example:
 344     ///
 345     /// ```
 346     /// fn some_fn(s: &str) {}
 347     ///
 348     /// let x = "hey!".to_owned();
 349     /// some_fn(x); // error
 350     /// ```
 351     ///
 352     /// No need to find every potential function which could make a coercion to transform a
 353     /// `String` into a `&str` since a `&` would do the trick!
 354     ///
 355     /// In addition of this check, it also checks between references mutability state. If the
 356     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 357     /// `&mut`!".
 358     pub fn check_ref(
 359         &self,
 360         expr: &hir::Expr<'_>,
 361         checked_ty: Ty<'tcx>,
 362         expected: Ty<'tcx>,
 363     ) -> Option<(Span, &'static str, String)> {
 364         let cm = self.sess().source_map();
 365         let sp = expr.span;
 366         if !cm.span_to_filename(sp).is_real() {
 367             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 368             // call span, but that breaks down when the type error comes from multiple calls down.
 369             return None;
 370         }
 371
 372         let is_struct_pat_shorthand_field =
 373             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 374
 375         // If the span is from a macro, then it's hard to extract the text
 376         // and make a good suggestion, so don't bother.
 377         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 378
 379         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 380         let expr = expr.peel_drop_temps();
 381
 382         match (&expr.kind, &expected.kind, &checked_ty.kind) {
 383             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
 384                 (&ty::Str, &ty::Array(arr, _)) | (&ty::Str, &ty::Slice(arr))
 385                     if arr == self.tcx.types.u8 =>
 386                 {
 387                     if let hir::ExprKind::Lit(_) = expr.kind {
 388                         if let Ok(src) = cm.span_to_snippet(sp) {
 389                             if src.starts_with("b\"") {
 390                                 return Some((
 391                                     sp,
 392                                     "consider removing the leading `b`",
 393                                     src[1..].to_string(),
 394                                 ));
 395                             }
 396                         }
 397                     }
 398                 }
 399                 (&ty::Array(arr, _), &ty::Str) | (&ty::Slice(arr), &ty::Str)
 400                     if arr == self.tcx.types.u8 =>
 401                 {
 402                     if let hir::ExprKind::Lit(_) = expr.kind {
 403                         if let Ok(src) = cm.span_to_snippet(sp) {
 404                             if src.starts_with("\"") {
 405                                 return Some((
 406                                     sp,
 407                                     "consider adding a leading `b`",
 408                                     format!("b{}", src),
 409                                 ));
 410                             }
 411                         }
 412                     }
 413                 }
 414                 _ => {}
 415             },
 416             (_, &ty::Ref(_, _, mutability), _) => {
 417                 // Check if it can work when put into a ref. For example:
 418                 //
 419                 // ```
 420                 // fn bar(x: &mut i32) {}
 421                 //
 422                 // let x = 0u32;
 423                 // bar(&x); // error, expected &mut
 424                 // ```
 425                 let ref_ty = match mutability {
 426                     hir::Mutability::Mut => {
 427                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 428                     }
 429                     hir::Mutability::Not => {
 430                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 431                     }
 432                 };
 433                 if self.can_coerce(ref_ty, expected) {
 434                     let mut sugg_sp = sp;
 435                     if let hir::ExprKind::MethodCall(segment, _sp, args) = &expr.kind {
 436                         let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
 437                         if let ([arg], Some(true), sym::clone) = (
 438                             &args[..],
 439                             self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
 440                                 let ai = self.tcx.associated_item(did);
 441                                 ai.container == ty::TraitContainer(clone_trait)
 442                             }),
 443                             segment.ident.name,
 444                         ) {
 445                             // If this expression had a clone call when suggesting borrowing
 446                             // we want to suggest removing it because it'd now be unnecessary.
 447                             sugg_sp = arg.span;
 448                         }
 449                     }
 450                     if let Ok(src) = cm.span_to_snippet(sugg_sp) {
 451                         let needs_parens = match expr.kind {
 452                             // parenthesize if needed (Issue #46756)
 453                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 454                             // parenthesize borrows of range literals (Issue #54505)
 455                             _ if is_range_literal(self.tcx.sess.source_map(), expr) => true,
 456                             _ => false,
 457                         };
 458                         let sugg_expr = if needs_parens { format!("({})", src) } else { src };
 459
 460                         if let Some(sugg) = self.can_use_as_ref(expr) {
 461                             return Some(sugg);
 462                         }
 463                         let field_name = if is_struct_pat_shorthand_field {
 464                             format!("{}: ", sugg_expr)
 465                         } else {
 466                             String::new()
 467                         };
 468                         if let Some(hir::Node::Expr(hir::Expr {
 469                             kind: hir::ExprKind::Assign(left_expr, ..),
 470                             ..
 471                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 472                         {
 473                             if mutability == hir::Mutability::Mut {
 474                                 // Found the following case:
 475                                 // fn foo(opt: &mut Option<String>){ opt = None }
 476                                 //                                   ---   ^^^^
 477                                 //                                   |     |
 478                                 //    consider dereferencing here: `*opt`  |
 479                                 // expected mutable reference, found enum `Option`
 480                                 if let Ok(src) = cm.span_to_snippet(left_expr.span) {
 481                                     return Some((
 482                                         left_expr.span,
 483                                         "consider dereferencing here to assign to the mutable \
 484                                          borrowed piece of memory",
 485                                         format!("*{}", src),
 486                                     ));
 487                                 }
 488                             }
 489                         }
 490
 491                         return Some(match mutability {
 492                             hir::Mutability::Mut => (
 493                                 sp,
 494                                 "consider mutably borrowing here",
 495                                 format!("{}&mut {}", field_name, sugg_expr),
 496                             ),
 497                             hir::Mutability::Not => (
 498                                 sp,
 499                                 "consider borrowing here",
 500                                 format!("{}&{}", field_name, sugg_expr),
 501                             ),
 502                         });
 503                     }
 504                 }
 505             }
 506             (
 507                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 508                 _,
 509                 &ty::Ref(_, checked, _),
 510             ) if {
 511                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 512             } =>
 513             {
 514                 // We have `&T`, check if what was expected was `T`. If so,
 515                 // we may want to suggest removing a `&`.
 516                 if !cm.span_to_filename(expr.span).is_real() {
 517                     if let Ok(code) = cm.span_to_snippet(sp) {
 518                         if code.chars().next() == Some('&') {
 519                             return Some((
 520                                 sp,
 521                                 "consider removing the borrow",
 522                                 code[1..].to_string(),
 523                             ));
 524                         }
 525                     }
 526                     return None;
 527                 }
 528                 if let Ok(code) = cm.span_to_snippet(expr.span) {
 529                     return Some((sp, "consider removing the borrow", code));
 530                 }
 531             }
 532             _ if sp == expr.span && !is_macro => {
 533                 // Check for `Deref` implementations by constructing a predicate to
 534                 // prove: `<T as Deref>::Output == U`
 535                 let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
 536                 let item_def_id = self
 537                     .tcx
 538                     .associated_items(deref_trait)
 539                     .find(|item| item.kind == ty::AssocKind::Type)
 540                     .unwrap()
 541                     .def_id;
 542                 let predicate =
 543                     ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
 544                         // `<T as Deref>::Output`
 545                         projection_ty: ty::ProjectionTy {
 546                             // `T`
 547                             substs: self.tcx.intern_substs(&[checked_ty.into()]),
 548                             // `Deref::Output`
 549                             item_def_id,
 550                         },
 551                         // `U`
 552                         ty: expected,
 553                     }));
 554                 let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
 555                 let impls_deref = self.infcx.predicate_may_hold(&obligation);
 556
 557                 // For a suggestion to make sense, the type would need to be `Copy`.
 558                 let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
 559
 560                 if is_copy && impls_deref {
 561                     if let Ok(code) = cm.span_to_snippet(sp) {
 562                         let message = if checked_ty.is_region_ptr() {
 563                             "consider dereferencing the borrow"
 564                         } else {
 565                             "consider dereferencing the type"
 566                         };
 567                         let suggestion = if is_struct_pat_shorthand_field {
 568                             format!("{}: *{}", code, code)
 569                         } else {
 570                             format!("*{}", code)
 571                         };
 572                         return Some((sp, message, suggestion));
 573                     }
 574                 }
 575             }
 576             _ => {}
 577         }
 578         None
 579     }
 580
 581     pub fn check_for_cast(
 582         &self,
 583         err: &mut DiagnosticBuilder<'_>,
 584         expr: &hir::Expr<'_>,
 585         checked_ty: Ty<'tcx>,
 586         expected_ty: Ty<'tcx>,
 587     ) -> bool {
 588         if self.tcx.hir().is_const_context(expr.hir_id) {
 589             // Shouldn't suggest `.into()` on `const`s.
 590             // FIXME(estebank): modify once we decide to suggest `as` casts
 591             return false;
 592         }
 593         if !self.tcx.sess.source_map().span_to_filename(expr.span).is_real() {
 594             // Ignore if span is from within a macro.
 595             return false;
 596         }
 597
 598         // If casting this expression to a given numeric type would be appropriate in case of a type
 599         // mismatch.
 600         //
 601         // We want to minimize the amount of casting operations that are suggested, as it can be a
 602         // lossy operation with potentially bad side effects, so we only suggest when encountering
 603         // an expression that indicates that the original type couldn't be directly changed.
 604         //
 605         // For now, don't suggest casting with `as`.
 606         let can_cast = false;
 607
 608         let mut prefix = String::new();
 609         if let Some(hir::Node::Expr(hir::Expr {
 610             kind: hir::ExprKind::Struct(_, fields, _), ..
 611         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 612         {
 613             // `expr` is a literal field for a struct, only suggest if appropriate
 614             for field in *fields {
 615                 if field.expr.hir_id == expr.hir_id && field.is_shorthand {
 616                     // This is a field literal
 617                     prefix = format!("{}: ", field.ident);
 618                     break;
 619                 }
 620             }
 621             if &prefix == "" {
 622                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 623                 return false;
 624             }
 625         }
 626         if let hir::ExprKind::Call(path, args) = &expr.kind {
 627             if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
 628                 (&path.kind, args.len())
 629             {
 630                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 631                 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
 632                     (&base_ty.kind, path_segment.ident.name)
 633                 {
 634                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
 635                         match ident.name {
 636                             sym::i128
 637                             | sym::i64
 638                             | sym::i32
 639                             | sym::i16
 640                             | sym::i8
 641                             | sym::u128
 642                             | sym::u64
 643                             | sym::u32
 644                             | sym::u16
 645                             | sym::u8
 646                             | sym::isize
 647                             | sym::usize
 648                                 if base_ty_path.segments.len() == 1 =>
 649                             {
 650                                 return false;
 651                             }
 652                             _ => {}
 653                         }
 654                     }
 655                 }
 656             }
 657         }
 658
 659         let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 660         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 661         let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
 662         let lit_msg = format!(
 663             "change the type of the numeric literal from `{}` to `{}`",
 664             checked_ty, expected_ty,
 665         );
 666
 667         let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
 668
 669         if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 670             let cast_suggestion = format!(
 671                 "{}{}{}{} as {}",
 672                 prefix,
 673                 if needs_paren { "(" } else { "" },
 674                 src,
 675                 if needs_paren { ")" } else { "" },
 676                 expected_ty,
 677             );
 678             let try_into_suggestion = format!(
 679                 "{}{}{}{}.try_into().unwrap()",
 680                 prefix,
 681                 if needs_paren { "(" } else { "" },
 682                 src,
 683                 if needs_paren { ")" } else { "" },
 684             );
 685             let into_suggestion = format!(
 686                 "{}{}{}{}.into()",
 687                 prefix,
 688                 if needs_paren { "(" } else { "" },
 689                 src,
 690                 if needs_paren { ")" } else { "" },
 691             );
 692             let suffix_suggestion = format!(
 693                 "{}{}{}{}",
 694                 if needs_paren { "(" } else { "" },
 695                 if let (ty::Int(_), ty::Float(_)) | (ty::Uint(_), ty::Float(_)) =
 696                     (&expected_ty.kind, &checked_ty.kind,)
 697                 {
 698                     // Remove fractional part from literal, for example `42.0f32` into `42`
 699                     let src = src.trim_end_matches(&checked_ty.to_string());
 700                     src.split(".").next().unwrap()
 701                 } else {
 702                     src.trim_end_matches(&checked_ty.to_string())
 703                 },
 704                 expected_ty,
 705                 if needs_paren { ")" } else { "" },
 706             );
 707             let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
 708                 if let hir::ExprKind::Lit(lit) = &expr.kind {
 709                     lit.node.is_suffixed()
 710                 } else {
 711                     false
 712                 }
 713             };
 714
 715             let suggest_to_change_suffix_or_into =
 716                 |err: &mut DiagnosticBuilder<'_>, is_fallible: bool| {
 717                     let into_sugg = into_suggestion.clone();
 718                     err.span_suggestion(
 719                         expr.span,
 720                         if literal_is_ty_suffixed(expr) {
 721                             &lit_msg
 722                         } else if is_fallible {
 723                             &try_msg
 724                         } else {
 725                             &msg
 726                         },
 727                         if literal_is_ty_suffixed(expr) {
 728                             suffix_suggestion.clone()
 729                         } else if is_fallible {
 730                             try_into_suggestion
 731                         } else {
 732                             into_sugg
 733                         },
 734                         Applicability::MachineApplicable,
 735                     );
 736                 };
 737
 738             match (&expected_ty.kind, &checked_ty.kind) {
 739                 (&ty::Int(ref exp), &ty::Int(ref found)) => {
 740                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 741                         (Some(found), Some(exp)) if found > exp => true,
 742                         (None, _) | (_, None) => true,
 743                         _ => false,
 744                     };
 745                     suggest_to_change_suffix_or_into(err, is_fallible);
 746                     true
 747                 }
 748                 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 749                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 750                         (Some(found), Some(exp)) if found > exp => true,
 751                         (None, _) | (_, None) => true,
 752                         _ => false,
 753                     };
 754                     suggest_to_change_suffix_or_into(err, is_fallible);
 755                     true
 756                 }
 757                 (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
 758                     suggest_to_change_suffix_or_into(err, true);
 759                     true
 760                 }
 761                 (&ty::Float(ref exp), &ty::Float(ref found)) => {
 762                     if found.bit_width() < exp.bit_width() {
 763                         suggest_to_change_suffix_or_into(err, false);
 764                     } else if literal_is_ty_suffixed(expr) {
 765                         err.span_suggestion(
 766                             expr.span,
 767                             &lit_msg,
 768                             suffix_suggestion,
 769                             Applicability::MachineApplicable,
 770                         );
 771                     } else if can_cast {
 772                         // Missing try_into implementation for `f64` to `f32`
 773                         err.span_suggestion(
 774                             expr.span,
 775                             &format!("{}, producing the closest possible value", cast_msg),
 776                             cast_suggestion,
 777                             Applicability::MaybeIncorrect, // lossy conversion
 778                         );
 779                     }
 780                     true
 781                 }
 782                 (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
 783                     if literal_is_ty_suffixed(expr) {
 784                         err.span_suggestion(
 785                             expr.span,
 786                             &lit_msg,
 787                             suffix_suggestion,
 788                             Applicability::MachineApplicable,
 789                         );
 790                     } else if can_cast {
 791                         // Missing try_into implementation for `{float}` to `{integer}`
 792                         err.span_suggestion(
 793                             expr.span,
 794                             &format!("{}, rounding the float towards zero", msg),
 795                             cast_suggestion,
 796                             Applicability::MaybeIncorrect, // lossy conversion
 797                         );
 798                         err.warn(
 799                             "if the rounded value cannot be represented by the target \
 800                                   integer type, including `Inf` and `NaN`, casting will cause \
 801                                   undefined behavior \
 802                                   (https://github.com/rust-lang/rust/issues/10184)",
 803                         );
 804                     }
 805                     true
 806                 }
 807                 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 808                     // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 809                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 810                         err.span_suggestion(
 811                             expr.span,
 812                             &format!(
 813                                 "{}, producing the floating point representation of the integer",
 814                                 msg,
 815                             ),
 816                             into_suggestion,
 817                             Applicability::MachineApplicable,
 818                         );
 819                     } else if literal_is_ty_suffixed(expr) {
 820                         err.span_suggestion(
 821                             expr.span,
 822                             &lit_msg,
 823                             suffix_suggestion,
 824                             Applicability::MachineApplicable,
 825                         );
 826                     } else {
 827                         // Missing try_into implementation for `{integer}` to `{float}`
 828                         err.span_suggestion(
 829                             expr.span,
 830                             &format!(
 831                                 "{}, producing the floating point representation of the integer,
 832                                  rounded if necessary",
 833                                 cast_msg,
 834                             ),
 835                             cast_suggestion,
 836                             Applicability::MaybeIncorrect, // lossy conversion
 837                         );
 838                     }
 839                     true
 840                 }
 841                 (&ty::Float(ref exp), &ty::Int(ref found)) => {
 842                     // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 843                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 844                         err.span_suggestion(
 845                             expr.span,
 846                             &format!(
 847                                 "{}, producing the floating point representation of the integer",
 848                                 &msg,
 849                             ),
 850                             into_suggestion,
 851                             Applicability::MachineApplicable,
 852                         );
 853                     } else if literal_is_ty_suffixed(expr) {
 854                         err.span_suggestion(
 855                             expr.span,
 856                             &lit_msg,
 857                             suffix_suggestion,
 858                             Applicability::MachineApplicable,
 859                         );
 860                     } else {
 861                         // Missing try_into implementation for `{integer}` to `{float}`
 862                         err.span_suggestion(
 863                             expr.span,
 864                             &format!(
 865                                 "{}, producing the floating point representation of the integer, \
 866                                  rounded if necessary",
 867                                 &msg,
 868                             ),
 869                             cast_suggestion,
 870                             Applicability::MaybeIncorrect, // lossy conversion
 871                         );
 872                     }
 873                     true
 874                 }
 875                 _ => false,
 876             }
 877         } else {
 878             false
 879         }
 880     }
 881 }