src/librustc_typeck/check/demand.rs

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