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