src/librustc_typeck/check/demand.rs

   1 use crate::check::FnCtxt;
   2 use rustc_infer::infer::InferOk;
   3 use rustc_infer::traits::{self, ObligationCause};
   4
   5 use rustc::ty::adjustment::AllowTwoPhase;
   6 use rustc::ty::{self, AssocItem, Ty};
   7 use rustc_ast::util::parser::PREC_POSTFIX;
   8 use rustc_errors::{Applicability, DiagnosticBuilder};
   9 use rustc_hir as hir;
  10 use rustc_hir::{is_range_literal, print, Node};
  11 use rustc_span::symbol::sym;
  12 use rustc_span::Span;
  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         if self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty) {
  28             return;
  29         }
  30         self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
  31         self.suggest_missing_await(err, expr, expected, expr_ty);
  32     }
  33
  34     // Requires that the two types unify, and prints an error message if
  35     // they don't.
  36     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  37         self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
  38     }
  39
  40     pub fn demand_suptype_diag(
  41         &self,
  42         sp: Span,
  43         expected: Ty<'tcx>,
  44         actual: Ty<'tcx>,
  45     ) -> Option<DiagnosticBuilder<'tcx>> {
  46         self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
  47     }
  48
  49     pub fn demand_suptype_with_origin(
  50         &self,
  51         cause: &ObligationCause<'tcx>,
  52         expected: Ty<'tcx>,
  53         actual: Ty<'tcx>,
  54     ) -> Option<DiagnosticBuilder<'tcx>> {
  55         match self.at(cause, self.param_env).sup(expected, actual) {
  56             Ok(InferOk { obligations, value: () }) => {
  57                 self.register_predicates(obligations);
  58                 None
  59             }
  60             Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
  61         }
  62     }
  63
  64     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  65         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  66             err.emit();
  67         }
  68     }
  69
  70     pub fn demand_eqtype_diag(
  71         &self,
  72         sp: Span,
  73         expected: Ty<'tcx>,
  74         actual: Ty<'tcx>,
  75     ) -> Option<DiagnosticBuilder<'tcx>> {
  76         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  77     }
  78
  79     pub fn demand_eqtype_with_origin(
  80         &self,
  81         cause: &ObligationCause<'tcx>,
  82         expected: Ty<'tcx>,
  83         actual: Ty<'tcx>,
  84     ) -> Option<DiagnosticBuilder<'tcx>> {
  85         match self.at(cause, self.param_env).eq(expected, actual) {
  86             Ok(InferOk { obligations, value: () }) => {
  87                 self.register_predicates(obligations);
  88                 None
  89             }
  90             Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
  91         }
  92     }
  93
  94     pub fn demand_coerce(
  95         &self,
  96         expr: &hir::Expr<'_>,
  97         checked_ty: Ty<'tcx>,
  98         expected: Ty<'tcx>,
  99         allow_two_phase: AllowTwoPhase,
 100     ) -> Ty<'tcx> {
 101         let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
 102         if let Some(mut err) = err {
 103             err.emit();
 104         }
 105         ty
 106     }
 107
 108     // Checks that the type of `expr` can be coerced to `expected`.
 109     //
 110     // N.B., this code relies on `self.diverges` to be accurate. In
 111     // particular, assignments to `!` will be permitted if the
 112     // diverges flag is currently "always".
 113     pub fn demand_coerce_diag(
 114         &self,
 115         expr: &hir::Expr<'_>,
 116         checked_ty: Ty<'tcx>,
 117         expected: Ty<'tcx>,
 118         allow_two_phase: AllowTwoPhase,
 119     ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
 120         let expected = self.resolve_vars_with_obligations(expected);
 121
 122         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
 123             Ok(ty) => return (ty, None),
 124             Err(e) => e,
 125         };
 126
 127         let expr = expr.peel_drop_temps();
 128         let cause = self.misc(expr.span);
 129         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
 130         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
 131
 132         if self.is_assign_to_bool(expr, expected) {
 133             // Error reported in `check_assign` so avoid emitting error again.
 134             err.delay_as_bug();
 135             return (expected, None);
 136         }
 137
 138         self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected);
 139
 140         (expected, Some(err))
 141     }
 142
 143     fn annotate_expected_due_to_let_ty(
 144         &self,
 145         err: &mut DiagnosticBuilder<'_>,
 146         expr: &hir::Expr<'_>,
 147     ) {
 148         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 149         if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
 150             self.tcx.hir().find(parent)
 151         {
 152             if init.hir_id == expr.hir_id {
 153                 // Point at `let` assignment type.
 154                 err.span_label(ty.span, "expected due to this");
 155             }
 156         }
 157     }
 158
 159     /// Returns whether the expected type is `bool` and the expression is `x = y`.
 160     pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
 161         if let hir::ExprKind::Assign(..) = expr.kind {
 162             return expected == self.tcx.types.bool;
 163         }
 164         false
 165     }
 166
 167     /// If the expected type is an enum (Issue #55250) with any variants whose
 168     /// sole field is of the found type, suggest such variants. (Issue #42764)
 169     fn suggest_compatible_variants(
 170         &self,
 171         err: &mut DiagnosticBuilder<'_>,
 172         expr: &hir::Expr<'_>,
 173         expected: Ty<'tcx>,
 174         expr_ty: Ty<'tcx>,
 175     ) {
 176         if let ty::Adt(expected_adt, substs) = expected.kind {
 177             if !expected_adt.is_enum() {
 178                 return;
 179             }
 180
 181             let mut compatible_variants = expected_adt
 182                 .variants
 183                 .iter()
 184                 .filter(|variant| variant.fields.len() == 1)
 185                 .filter_map(|variant| {
 186                     let sole_field = &variant.fields[0];
 187                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 188                     if self.can_coerce(expr_ty, sole_field_ty) {
 189                         let variant_path = self.tcx.def_path_str(variant.def_id);
 190                         // FIXME #56861: DRYer prelude filtering
 191                         Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
 192                     } else {
 193                         None
 194                     }
 195                 })
 196                 .peekable();
 197
 198             if compatible_variants.peek().is_some() {
 199                 let expr_text =
 200                     self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or_else(|_| {
 201                         print::to_string(print::NO_ANN, |s| s.print_expr(expr))
 202                     });
 203                 let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
 204                 let msg = "try using a variant of the expected enum";
 205                 err.span_suggestions(expr.span, msg, suggestions, Applicability::MaybeIncorrect);
 206             }
 207         }
 208     }
 209
 210     pub fn get_conversion_methods(
 211         &self,
 212         span: Span,
 213         expected: Ty<'tcx>,
 214         checked_ty: Ty<'tcx>,
 215     ) -> Vec<AssocItem> {
 216         let mut methods = self.probe_for_return_type(
 217             span,
 218             probe::Mode::MethodCall,
 219             expected,
 220             checked_ty,
 221             hir::DUMMY_HIR_ID,
 222         );
 223         methods.retain(|m| {
 224             self.has_no_input_arg(m)
 225                 && self
 226                     .tcx
 227                     .get_attrs(m.def_id)
 228                     .iter()
 229                     // This special internal attribute is used to whitelist
 230                     // "identity-like" conversion methods to be suggested here.
 231                     //
 232                     // FIXME (#46459 and #46460): ideally
 233                     // `std::convert::Into::into` and `std::borrow:ToOwned` would
 234                     // also be `#[rustc_conversion_suggestion]`, if not for
 235                     // method-probing false-positives and -negatives (respectively).
 236                     //
 237                     // FIXME? Other potential candidate methods: `as_ref` and
 238                     // `as_mut`?
 239                     .find(|a| a.check_name(sym::rustc_conversion_suggestion))
 240                     .is_some()
 241         });
 242
 243         methods
 244     }
 245
 246     // This function checks if the method isn't static and takes other arguments than `self`.
 247     fn has_no_input_arg(&self, method: &AssocItem) -> bool {
 248         match method.kind {
 249             ty::AssocKind::Method => {
 250                 self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 251             }
 252             _ => false,
 253         }
 254     }
 255
 256     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 257     ///
 258     /// Given the following code:
 259     /// ```
 260     /// struct Foo;
 261     /// fn takes_ref(_: &Foo) {}
 262     /// let ref opt = Some(Foo);
 263     ///
 264     /// opt.map(|param| takes_ref(param));
 265     /// ```
 266     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 267     ///
 268     /// It only checks for `Option` and `Result` and won't work with
 269     /// ```
 270     /// opt.map(|param| { takes_ref(param) });
 271     /// ```
 272     fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
 273         let path = match expr.kind {
 274             hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
 275             _ => return None,
 276         };
 277
 278         let local_id = match path.res {
 279             hir::def::Res::Local(id) => id,
 280             _ => return None,
 281         };
 282
 283         let local_parent = self.tcx.hir().get_parent_node(local_id);
 284         let param_hir_id = match self.tcx.hir().find(local_parent) {
 285             Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
 286             _ => return None,
 287         };
 288
 289         let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
 290         let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
 291             Some(Node::Expr(hir::Expr {
 292                 hir_id,
 293                 kind: hir::ExprKind::Closure(_, decl, ..),
 294                 ..
 295             })) => (hir_id, decl),
 296             _ => return None,
 297         };
 298
 299         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 300         let hir = self.tcx.hir().find(expr_parent);
 301         let closure_params_len = closure_fn_decl.inputs.len();
 302         let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
 303             (
 304                 Some(Node::Expr(hir::Expr {
 305                     kind: hir::ExprKind::MethodCall(path, span, expr),
 306                     ..
 307                 })),
 308                 1,
 309             ) => (path, span, expr),
 310             _ => return None,
 311         };
 312
 313         let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
 314         let self_ty = format!("{:?}", self_ty);
 315         let name = method_path.ident.as_str();
 316         let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
 317             || self_ty.starts_with("&std::result::Result")
 318             || self_ty.starts_with("std::option::Option")
 319             || self_ty.starts_with("std::result::Result"))
 320             && (name == "map" || name == "and_then");
 321         match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
 322             (true, Ok(src)) => {
 323                 let suggestion = format!("as_ref().{}", src);
 324                 Some((*method_span, "consider using `as_ref` instead", suggestion))
 325             }
 326             _ => None,
 327         }
 328     }
 329
 330     crate fn is_hir_id_from_struct_pattern_shorthand_field(
 331         &self,
 332         hir_id: hir::HirId,
 333         sp: Span,
 334     ) -> bool {
 335         let sm = self.sess().source_map();
 336         let parent_id = self.tcx.hir().get_parent_node(hir_id);
 337         if let Some(parent) = self.tcx.hir().find(parent_id) {
 338             // Account for fields
 339             if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
 340             {
 341                 if let Ok(src) = sm.span_to_snippet(sp) {
 342                     for field in *fields {
 343                         if field.ident.as_str() == src && field.is_shorthand {
 344                             return true;
 345                         }
 346                     }
 347                 }
 348             }
 349         }
 350         false
 351     }
 352
 353     /// This function is used to determine potential "simple" improvements or users' errors and
 354     /// provide them useful help. For example:
 355     ///
 356     /// ```
 357     /// fn some_fn(s: &str) {}
 358     ///
 359     /// let x = "hey!".to_owned();
 360     /// some_fn(x); // error
 361     /// ```
 362     ///
 363     /// No need to find every potential function which could make a coercion to transform a
 364     /// `String` into a `&str` since a `&` would do the trick!
 365     ///
 366     /// In addition of this check, it also checks between references mutability state. If the
 367     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 368     /// `&mut`!".
 369     pub fn check_ref(
 370         &self,
 371         expr: &hir::Expr<'_>,
 372         checked_ty: Ty<'tcx>,
 373         expected: Ty<'tcx>,
 374     ) -> Option<(Span, &'static str, String)> {
 375         let sm = self.sess().source_map();
 376         let sp = expr.span;
 377         if !sm.span_to_filename(sp).is_real() {
 378             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 379             // call span, but that breaks down when the type error comes from multiple calls down.
 380             return None;
 381         }
 382
 383         let is_struct_pat_shorthand_field =
 384             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 385
 386         // If the span is from a macro, then it's hard to extract the text
 387         // and make a good suggestion, so don't bother.
 388         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 389
 390         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 391         let expr = expr.peel_drop_temps();
 392
 393         match (&expr.kind, &expected.kind, &checked_ty.kind) {
 394             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
 395                 (&ty::Str, &ty::Array(arr, _)) | (&ty::Str, &ty::Slice(arr))
 396                     if arr == self.tcx.types.u8 =>
 397                 {
 398                     if let hir::ExprKind::Lit(_) = expr.kind {
 399                         if let Ok(src) = sm.span_to_snippet(sp) {
 400                             if src.starts_with("b\"") {
 401                                 return Some((
 402                                     sp,
 403                                     "consider removing the leading `b`",
 404                                     src[1..].to_string(),
 405                                 ));
 406                             }
 407                         }
 408                     }
 409                 }
 410                 (&ty::Array(arr, _), &ty::Str) | (&ty::Slice(arr), &ty::Str)
 411                     if arr == self.tcx.types.u8 =>
 412                 {
 413                     if let hir::ExprKind::Lit(_) = expr.kind {
 414                         if let Ok(src) = sm.span_to_snippet(sp) {
 415                             if src.starts_with('"') {
 416                                 return Some((
 417                                     sp,
 418                                     "consider adding a leading `b`",
 419                                     format!("b{}", src),
 420                                 ));
 421                             }
 422                         }
 423                     }
 424                 }
 425                 _ => {}
 426             },
 427             (_, &ty::Ref(_, _, mutability), _) => {
 428                 // Check if it can work when put into a ref. For example:
 429                 //
 430                 // ```
 431                 // fn bar(x: &mut i32) {}
 432                 //
 433                 // let x = 0u32;
 434                 // bar(&x); // error, expected &mut
 435                 // ```
 436                 let ref_ty = match mutability {
 437                     hir::Mutability::Mut => {
 438                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 439                     }
 440                     hir::Mutability::Not => {
 441                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 442                     }
 443                 };
 444                 if self.can_coerce(ref_ty, expected) {
 445                     let mut sugg_sp = sp;
 446                     if let hir::ExprKind::MethodCall(segment, _sp, args) = &expr.kind {
 447                         let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
 448                         if let ([arg], Some(true), sym::clone) = (
 449                             &args[..],
 450                             self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
 451                                 let ai = self.tcx.associated_item(did);
 452                                 ai.container == ty::TraitContainer(clone_trait)
 453                             }),
 454                             segment.ident.name,
 455                         ) {
 456                             // If this expression had a clone call when suggesting borrowing
 457                             // we want to suggest removing it because it'd now be unnecessary.
 458                             sugg_sp = arg.span;
 459                         }
 460                     }
 461                     if let Ok(src) = sm.span_to_snippet(sugg_sp) {
 462                         let needs_parens = match expr.kind {
 463                             // parenthesize if needed (Issue #46756)
 464                             hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
 465                             // parenthesize borrows of range literals (Issue #54505)
 466                             _ if is_range_literal(self.tcx.sess.source_map(), expr) => true,
 467                             _ => false,
 468                         };
 469                         let sugg_expr = if needs_parens { format!("({})", src) } else { src };
 470
 471                         if let Some(sugg) = self.can_use_as_ref(expr) {
 472                             return Some(sugg);
 473                         }
 474                         let field_name = if is_struct_pat_shorthand_field {
 475                             format!("{}: ", sugg_expr)
 476                         } else {
 477                             String::new()
 478                         };
 479                         if let Some(hir::Node::Expr(hir::Expr {
 480                             kind: hir::ExprKind::Assign(left_expr, ..),
 481                             ..
 482                         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 483                         {
 484                             if mutability == hir::Mutability::Mut {
 485                                 // Found the following case:
 486                                 // fn foo(opt: &mut Option<String>){ opt = None }
 487                                 //                                   ---   ^^^^
 488                                 //                                   |     |
 489                                 //    consider dereferencing here: `*opt`  |
 490                                 // expected mutable reference, found enum `Option`
 491                                 if let Ok(src) = sm.span_to_snippet(left_expr.span) {
 492                                     return Some((
 493                                         left_expr.span,
 494                                         "consider dereferencing here to assign to the mutable \
 495                                          borrowed piece of memory",
 496                                         format!("*{}", src),
 497                                     ));
 498                                 }
 499                             }
 500                         }
 501
 502                         return Some(match mutability {
 503                             hir::Mutability::Mut => (
 504                                 sp,
 505                                 "consider mutably borrowing here",
 506                                 format!("{}&mut {}", field_name, sugg_expr),
 507                             ),
 508                             hir::Mutability::Not => (
 509                                 sp,
 510                                 "consider borrowing here",
 511                                 format!("{}&{}", field_name, sugg_expr),
 512                             ),
 513                         });
 514                     }
 515                 }
 516             }
 517             (
 518                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 519                 _,
 520                 &ty::Ref(_, checked, _),
 521             ) if {
 522                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 523             } =>
 524             {
 525                 // We have `&T`, check if what was expected was `T`. If so,
 526                 // we may want to suggest removing a `&`.
 527                 if !sm.span_to_filename(expr.span).is_real() {
 528                     if let Ok(code) = sm.span_to_snippet(sp) {
 529                         if code.chars().next() == Some('&') {
 530                             return Some((
 531                                 sp,
 532                                 "consider removing the borrow",
 533                                 code[1..].to_string(),
 534                             ));
 535                         }
 536                     }
 537                     return None;
 538                 }
 539                 if let Ok(code) = sm.span_to_snippet(expr.span) {
 540                     return Some((sp, "consider removing the borrow", code));
 541                 }
 542             }
 543             _ if sp == expr.span && !is_macro => {
 544                 // Check for `Deref` implementations by constructing a predicate to
 545                 // prove: `<T as Deref>::Output == U`
 546                 let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
 547                 let item_def_id = self
 548                     .tcx
 549                     .associated_items(deref_trait)
 550                     .in_definition_order()
 551                     .find(|item| item.kind == ty::AssocKind::Type)
 552                     .unwrap()
 553                     .def_id;
 554                 let predicate =
 555                     ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
 556                         // `<T as Deref>::Output`
 557                         projection_ty: ty::ProjectionTy {
 558                             // `T`
 559                             substs: self.tcx.intern_substs(&[checked_ty.into()]),
 560                             // `Deref::Output`
 561                             item_def_id,
 562                         },
 563                         // `U`
 564                         ty: expected,
 565                     }));
 566                 let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
 567                 let impls_deref = self.infcx.predicate_may_hold(&obligation);
 568
 569                 // For a suggestion to make sense, the type would need to be `Copy`.
 570                 let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
 571
 572                 if is_copy && impls_deref {
 573                     if let Ok(code) = sm.span_to_snippet(sp) {
 574                         let message = if checked_ty.is_region_ptr() {
 575                             "consider dereferencing the borrow"
 576                         } else {
 577                             "consider dereferencing the type"
 578                         };
 579                         let suggestion = if is_struct_pat_shorthand_field {
 580                             format!("{}: *{}", code, code)
 581                         } else {
 582                             format!("*{}", code)
 583                         };
 584                         return Some((sp, message, suggestion));
 585                     }
 586                 }
 587             }
 588             _ => {}
 589         }
 590         None
 591     }
 592
 593     pub fn check_for_cast(
 594         &self,
 595         err: &mut DiagnosticBuilder<'_>,
 596         expr: &hir::Expr<'_>,
 597         checked_ty: Ty<'tcx>,
 598         expected_ty: Ty<'tcx>,
 599     ) -> bool {
 600         if self.tcx.hir().is_const_context(expr.hir_id) {
 601             // Shouldn't suggest `.into()` on `const`s.
 602             // FIXME(estebank): modify once we decide to suggest `as` casts
 603             return false;
 604         }
 605         if !self.tcx.sess.source_map().span_to_filename(expr.span).is_real() {
 606             // Ignore if span is from within a macro.
 607             return false;
 608         }
 609
 610         // If casting this expression to a given numeric type would be appropriate in case of a type
 611         // mismatch.
 612         //
 613         // We want to minimize the amount of casting operations that are suggested, as it can be a
 614         // lossy operation with potentially bad side effects, so we only suggest when encountering
 615         // an expression that indicates that the original type couldn't be directly changed.
 616         //
 617         // For now, don't suggest casting with `as`.
 618         let can_cast = false;
 619
 620         let mut prefix = String::new();
 621         if let Some(hir::Node::Expr(hir::Expr {
 622             kind: hir::ExprKind::Struct(_, fields, _), ..
 623         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
 624         {
 625             // `expr` is a literal field for a struct, only suggest if appropriate
 626             for field in *fields {
 627                 if field.expr.hir_id == expr.hir_id && field.is_shorthand {
 628                     // This is a field literal
 629                     prefix = format!("{}: ", field.ident);
 630                     break;
 631                 }
 632             }
 633             if &prefix == "" {
 634                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 635                 return false;
 636             }
 637         }
 638         if let hir::ExprKind::Call(path, args) = &expr.kind {
 639             if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
 640                 (&path.kind, args.len())
 641             {
 642                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 643                 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
 644                     (&base_ty.kind, path_segment.ident.name)
 645                 {
 646                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
 647                         match ident.name {
 648                             sym::i128
 649                             | sym::i64
 650                             | sym::i32
 651                             | sym::i16
 652                             | sym::i8
 653                             | sym::u128
 654                             | sym::u64
 655                             | sym::u32
 656                             | sym::u16
 657                             | sym::u8
 658                             | sym::isize
 659                             | sym::usize
 660                                 if base_ty_path.segments.len() == 1 =>
 661                             {
 662                                 return false;
 663                             }
 664                             _ => {}
 665                         }
 666                     }
 667                 }
 668             }
 669         }
 670
 671         let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 672         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 673         let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
 674         let lit_msg = format!(
 675             "change the type of the numeric literal from `{}` to `{}`",
 676             checked_ty, expected_ty,
 677         );
 678
 679         let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
 680
 681         if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 682             let cast_suggestion = format!(
 683                 "{}{}{}{} as {}",
 684                 prefix,
 685                 if needs_paren { "(" } else { "" },
 686                 src,
 687                 if needs_paren { ")" } else { "" },
 688                 expected_ty,
 689             );
 690             let try_into_suggestion = format!(
 691                 "{}{}{}{}.try_into().unwrap()",
 692                 prefix,
 693                 if needs_paren { "(" } else { "" },
 694                 src,
 695                 if needs_paren { ")" } else { "" },
 696             );
 697             let into_suggestion = format!(
 698                 "{}{}{}{}.into()",
 699                 prefix,
 700                 if needs_paren { "(" } else { "" },
 701                 src,
 702                 if needs_paren { ")" } else { "" },
 703             );
 704             let suffix_suggestion = format!(
 705                 "{}{}{}{}",
 706                 if needs_paren { "(" } else { "" },
 707                 if let (ty::Int(_), ty::Float(_)) | (ty::Uint(_), ty::Float(_)) =
 708                     (&expected_ty.kind, &checked_ty.kind,)
 709                 {
 710                     // Remove fractional part from literal, for example `42.0f32` into `42`
 711                     let src = src.trim_end_matches(&checked_ty.to_string());
 712                     src.split('.').next().unwrap()
 713                 } else {
 714                     src.trim_end_matches(&checked_ty.to_string())
 715                 },
 716                 expected_ty,
 717                 if needs_paren { ")" } else { "" },
 718             );
 719             let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
 720                 if let hir::ExprKind::Lit(lit) = &expr.kind {
 721                     lit.node.is_suffixed()
 722                 } else {
 723                     false
 724                 }
 725             };
 726
 727             let suggest_to_change_suffix_or_into =
 728                 |err: &mut DiagnosticBuilder<'_>, is_fallible: bool| {
 729                     let into_sugg = into_suggestion.clone();
 730                     err.span_suggestion(
 731                         expr.span,
 732                         if literal_is_ty_suffixed(expr) {
 733                             &lit_msg
 734                         } else if is_fallible {
 735                             &try_msg
 736                         } else {
 737                             &msg
 738                         },
 739                         if literal_is_ty_suffixed(expr) {
 740                             suffix_suggestion.clone()
 741                         } else if is_fallible {
 742                             try_into_suggestion
 743                         } else {
 744                             into_sugg
 745                         },
 746                         Applicability::MachineApplicable,
 747                     );
 748                 };
 749
 750             match (&expected_ty.kind, &checked_ty.kind) {
 751                 (&ty::Int(ref exp), &ty::Int(ref found)) => {
 752                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 753                         (Some(found), Some(exp)) if found > exp => true,
 754                         (None, _) | (_, None) => true,
 755                         _ => false,
 756                     };
 757                     suggest_to_change_suffix_or_into(err, is_fallible);
 758                     true
 759                 }
 760                 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 761                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 762                         (Some(found), Some(exp)) if found > exp => true,
 763                         (None, _) | (_, None) => true,
 764                         _ => false,
 765                     };
 766                     suggest_to_change_suffix_or_into(err, is_fallible);
 767                     true
 768                 }
 769                 (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
 770                     suggest_to_change_suffix_or_into(err, true);
 771                     true
 772                 }
 773                 (&ty::Float(ref exp), &ty::Float(ref found)) => {
 774                     if found.bit_width() < exp.bit_width() {
 775                         suggest_to_change_suffix_or_into(err, false);
 776                     } else if literal_is_ty_suffixed(expr) {
 777                         err.span_suggestion(
 778                             expr.span,
 779                             &lit_msg,
 780                             suffix_suggestion,
 781                             Applicability::MachineApplicable,
 782                         );
 783                     } else if can_cast {
 784                         // Missing try_into implementation for `f64` to `f32`
 785                         err.span_suggestion(
 786                             expr.span,
 787                             &format!("{}, producing the closest possible value", cast_msg),
 788                             cast_suggestion,
 789                             Applicability::MaybeIncorrect, // lossy conversion
 790                         );
 791                     }
 792                     true
 793                 }
 794                 (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
 795                     if literal_is_ty_suffixed(expr) {
 796                         err.span_suggestion(
 797                             expr.span,
 798                             &lit_msg,
 799                             suffix_suggestion,
 800                             Applicability::MachineApplicable,
 801                         );
 802                     } else if can_cast {
 803                         // Missing try_into implementation for `{float}` to `{integer}`
 804                         err.span_suggestion(
 805                             expr.span,
 806                             &format!("{}, rounding the float towards zero", msg),
 807                             cast_suggestion,
 808                             Applicability::MaybeIncorrect, // lossy conversion
 809                         );
 810                         err.warn(
 811                             "if the rounded value cannot be represented by the target \
 812                                 integer type, including `Inf` and `NaN`, casting will cause \
 813                                 undefined behavior \
 814                                 (see issue #10184 <https://github.com/rust-lang/rust/issues/10184> \
 815                                 for more information)",
 816                         );
 817                     }
 818                     true
 819                 }
 820                 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 821                     // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 822                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 823                         err.span_suggestion(
 824                             expr.span,
 825                             &format!(
 826                                 "{}, producing the floating point representation of the integer",
 827                                 msg,
 828                             ),
 829                             into_suggestion,
 830                             Applicability::MachineApplicable,
 831                         );
 832                     } else if literal_is_ty_suffixed(expr) {
 833                         err.span_suggestion(
 834                             expr.span,
 835                             &lit_msg,
 836                             suffix_suggestion,
 837                             Applicability::MachineApplicable,
 838                         );
 839                     } else {
 840                         // Missing try_into implementation for `{integer}` to `{float}`
 841                         err.span_suggestion(
 842                             expr.span,
 843                             &format!(
 844                                 "{}, producing the floating point representation of the integer,
 845                                  rounded if necessary",
 846                                 cast_msg,
 847                             ),
 848                             cast_suggestion,
 849                             Applicability::MaybeIncorrect, // lossy conversion
 850                         );
 851                     }
 852                     true
 853                 }
 854                 (&ty::Float(ref exp), &ty::Int(ref found)) => {
 855                     // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 856                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 857                         err.span_suggestion(
 858                             expr.span,
 859                             &format!(
 860                                 "{}, producing the floating point representation of the integer",
 861                                 &msg,
 862                             ),
 863                             into_suggestion,
 864                             Applicability::MachineApplicable,
 865                         );
 866                     } else if literal_is_ty_suffixed(expr) {
 867                         err.span_suggestion(
 868                             expr.span,
 869                             &lit_msg,
 870                             suffix_suggestion,
 871                             Applicability::MachineApplicable,
 872                         );
 873                     } else {
 874                         // Missing try_into implementation for `{integer}` to `{float}`
 875                         err.span_suggestion(
 876                             expr.span,
 877                             &format!(
 878                                 "{}, producing the floating point representation of the integer, \
 879                                  rounded if necessary",
 880                                 &msg,
 881                             ),
 882                             cast_suggestion,
 883                             Applicability::MaybeIncorrect, // lossy conversion
 884                         );
 885                     }
 886                     true
 887                 }
 888                 _ => false,
 889             }
 890         } else {
 891             false
 892         }
 893     }
 894 }