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