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                     if let Ok(src) = cm.span_to_snippet(sp) {
 383                         let needs_parens = match expr.node {
 384                             // parenthesize if needed (Issue #46756)
 385                             hir::ExprKind::Cast(_, _) |
 386                             hir::ExprKind::Binary(_, _, _) => true,
 387                             // parenthesize borrows of range literals (Issue #54505)
 388                             _ if is_range_literal(self.tcx.sess, expr) => true,
 389                             _ => false,
 390                         };
 391                         let sugg_expr = if needs_parens {
 392                             format!("({})", src)
 393                         } else {
 394                             src
 395                         };
 396
 397                         if let Some(sugg) = self.can_use_as_ref(expr) {
 398                             return Some(sugg);
 399                         }
 400                         let field_name = if is_struct_pat_shorthand_field {
 401                             format!("{}: ", sugg_expr)
 402                         } else {
 403                             String::new()
 404                         };
 405                         if let Some(hir::Node::Expr(hir::Expr {
 406                             node: hir::ExprKind::Assign(left_expr, _),
 407                             ..
 408                         })) = self.tcx.hir().find_by_hir_id(
 409                             self.tcx.hir().get_parent_node_by_hir_id(expr.hir_id),
 410                         ) {
 411                             if mutability == hir::Mutability::MutMutable {
 412                                 // Found the following case:
 413                                 // fn foo(opt: &mut Option<String>){ opt = None }
 414                                 //                                   ---   ^^^^
 415                                 //                                   |     |
 416                                 //    consider dereferencing here: `*opt`  |
 417                                 // expected mutable reference, found enum `Option`
 418                                 if let Ok(src) = cm.span_to_snippet(left_expr.span) {
 419                                     return Some((
 420                                         left_expr.span,
 421                                         "consider dereferencing here to assign to the mutable \
 422                                          borrowed piece of memory",
 423                                         format!("*{}", src),
 424                                     ));
 425                                 }
 426                             }
 427                         }
 428                         // If this expression had a clone call, when suggesting borrowing, we
 429                         // want to suggest removing it
 430                         let sugg_expr = sugg_expr.trim_end_matches(".clone()");
 431                         return Some(match mutability {
 432                             hir::Mutability::MutMutable => (
 433                                 sp,
 434                                 "consider mutably borrowing here",
 435                                 format!("{}&mut {}", field_name, sugg_expr),
 436                             ),
 437                             hir::Mutability::MutImmutable => (
 438                                 sp,
 439                                 "consider borrowing here",
 440                                 format!("{}&{}", field_name, sugg_expr),
 441                             ),
 442                         });
 443                     }
 444                 }
 445             },
 446             (hir::ExprKind::AddrOf(_, ref expr), _, &ty::Ref(_, checked, _)) if {
 447                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 448             } => {
 449                 // We have `&T`, check if what was expected was `T`. If so,
 450                 // we may want to suggest removing a `&`.
 451                 if !cm.span_to_filename(expr.span).is_real() {
 452                     if let Ok(code) = cm.span_to_snippet(sp) {
 453                         if code.chars().next() == Some('&') {
 454                             return Some((
 455                                 sp,
 456                                 "consider removing the borrow",
 457                                 code[1..].to_string(),
 458                             ));
 459                         }
 460                     }
 461                     return None;
 462                 }
 463                 if let Ok(code) = cm.span_to_snippet(expr.span) {
 464                     return Some((sp, "consider removing the borrow", code));
 465                 }
 466             },
 467             _ if sp == expr.span && !is_macro => {
 468                 // Check for `Deref` implementations by constructing a predicate to
 469                 // prove: `<T as Deref>::Output == U`
 470                 let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
 471                 let item_def_id = self.tcx.associated_items(deref_trait).next().unwrap().def_id;
 472                 let predicate = ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
 473                     // `<T as Deref>::Output`
 474                     projection_ty: ty::ProjectionTy {
 475                         // `T`
 476                         substs: self.tcx.mk_substs_trait(
 477                             checked_ty,
 478                             self.fresh_substs_for_item(sp, item_def_id),
 479                         ),
 480                         // `Deref::Output`
 481                         item_def_id,
 482                     },
 483                     // `U`
 484                     ty: expected,
 485                 }));
 486                 let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
 487                 let impls_deref = self.infcx.predicate_may_hold(&obligation);
 488
 489                 // For a suggestion to make sense, the type would need to be `Copy`.
 490                 let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
 491
 492                 if is_copy && impls_deref {
 493                     if let Ok(code) = cm.span_to_snippet(sp) {
 494                         let message = if checked_ty.is_region_ptr() {
 495                             "consider dereferencing the borrow"
 496                         } else {
 497                             "consider dereferencing the type"
 498                         };
 499                         let suggestion = if is_struct_pat_shorthand_field {
 500                             format!("{}: *{}", code, code)
 501                         } else {
 502                             format!("*{}", code)
 503                         };
 504                         return Some((sp, message, suggestion));
 505                     }
 506                 }
 507             }
 508             _ => {}
 509         }
 510         None
 511     }
 512
 513     pub fn check_for_cast(
 514         &self,
 515         err: &mut DiagnosticBuilder<'tcx>,
 516         expr: &hir::Expr,
 517         checked_ty: Ty<'tcx>,
 518         expected_ty: Ty<'tcx>,
 519     ) -> bool {
 520         if self.tcx.hir().is_const_scope(expr.hir_id) {
 521             // Shouldn't suggest `.into()` on `const`s.
 522             // FIXME(estebank): modify once we decide to suggest `as` casts
 523             return false;
 524         }
 525
 526         // If casting this expression to a given numeric type would be appropriate in case of a type
 527         // mismatch.
 528         //
 529         // We want to minimize the amount of casting operations that are suggested, as it can be a
 530         // lossy operation with potentially bad side effects, so we only suggest when encountering
 531         // an expression that indicates that the original type couldn't be directly changed.
 532         //
 533         // For now, don't suggest casting with `as`.
 534         let can_cast = false;
 535
 536         let mut prefix = String::new();
 537         if let Some(hir::Node::Expr(hir::Expr {
 538             node: hir::ExprKind::Struct(_, fields, _),
 539             ..
 540         })) = self.tcx.hir().find_by_hir_id(self.tcx.hir().get_parent_node_by_hir_id(expr.hir_id)) {
 541             // `expr` is a literal field for a struct, only suggest if appropriate
 542             for field in fields {
 543                 if field.expr.hir_id == expr.hir_id && field.is_shorthand {
 544                     // This is a field literal
 545                     prefix = format!("{}: ", field.ident);
 546                     break;
 547                 }
 548             }
 549             if &prefix == "" {
 550                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 551                 return false;
 552             }
 553         }
 554
 555         let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 556         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 557         let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
 558         let lit_msg = format!(
 559             "change the type of the numeric literal from `{}` to `{}`",
 560             checked_ty,
 561             expected_ty,
 562         );
 563
 564         let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
 565
 566         if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 567             let cast_suggestion = format!(
 568                 "{}{}{}{} as {}",
 569                 prefix,
 570                 if needs_paren { "(" } else { "" },
 571                 src,
 572                 if needs_paren { ")" } else { "" },
 573                 expected_ty,
 574             );
 575             let try_into_suggestion = format!(
 576                 "{}{}{}{}.try_into().unwrap()",
 577                 prefix,
 578                 if needs_paren { "(" } else { "" },
 579                 src,
 580                 if needs_paren { ")" } else { "" },
 581             );
 582             let into_suggestion = format!(
 583                 "{}{}{}{}.into()",
 584                 prefix,
 585                 if needs_paren { "(" } else { "" },
 586                 src,
 587                 if needs_paren { ")" } else { "" },
 588             );
 589             let suffix_suggestion = format!(
 590                 "{}{}{}{}",
 591                 if needs_paren { "(" } else { "" },
 592                 if let (ty::Int(_), ty::Float(_)) | (ty::Uint(_), ty::Float(_)) = (
 593                     &expected_ty.sty,
 594                     &checked_ty.sty,
 595                 ) {
 596                     // Remove fractional part from literal, for example `42.0f32` into `42`
 597                     let src = src.trim_end_matches(&checked_ty.to_string());
 598                     src.split(".").next().unwrap()
 599                 } else {
 600                     src.trim_end_matches(&checked_ty.to_string())
 601                 },
 602                 expected_ty,
 603                 if needs_paren { ")" } else { "" },
 604             );
 605             let literal_is_ty_suffixed = |expr: &hir::Expr| {
 606                 if let hir::ExprKind::Lit(lit) = &expr.node {
 607                     lit.node.is_suffixed()
 608                 } else {
 609                     false
 610                 }
 611             };
 612
 613             let suggest_to_change_suffix_or_into = |
 614                 err: &mut DiagnosticBuilder<'_>,
 615                 is_fallible: bool,
 616             | {
 617                 let into_sugg = into_suggestion.clone();
 618                 err.span_suggestion(
 619                     expr.span,
 620                     if literal_is_ty_suffixed(expr) {
 621                         &lit_msg
 622                     } else if is_fallible {
 623                         &try_msg
 624                     } else {
 625                         &msg
 626                     },
 627                     if literal_is_ty_suffixed(expr) {
 628                         suffix_suggestion.clone()
 629                     } else if is_fallible {
 630                         try_into_suggestion
 631                     } else {
 632                         into_sugg
 633                     },
 634                     Applicability::MachineApplicable,
 635                 );
 636             };
 637
 638             match (&expected_ty.sty, &checked_ty.sty) {
 639                 (&ty::Int(ref exp), &ty::Int(ref found)) => {
 640                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 641                         (Some(found), Some(exp)) if found > exp => true,
 642                         (None, _) | (_, None) => true,
 643                         _ => false,
 644                     };
 645                     suggest_to_change_suffix_or_into(err, is_fallible);
 646                     true
 647                 }
 648                 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 649                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 650                         (Some(found), Some(exp)) if found > exp => true,
 651                         (None, _) | (_, None) => true,
 652                         _ => false,
 653                     };
 654                     suggest_to_change_suffix_or_into(err, is_fallible);
 655                     true
 656                 }
 657                 (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
 658                     suggest_to_change_suffix_or_into(err, true);
 659                     true
 660                 }
 661                 (&ty::Float(ref exp), &ty::Float(ref found)) => {
 662                     if found.bit_width() < exp.bit_width() {
 663                         suggest_to_change_suffix_or_into(err, false);
 664                     } else if literal_is_ty_suffixed(expr) {
 665                         err.span_suggestion(
 666                             expr.span,
 667                             &lit_msg,
 668                             suffix_suggestion,
 669                             Applicability::MachineApplicable,
 670                         );
 671                     } else if can_cast { // Missing try_into implementation for `f64` to `f32`
 672                         err.span_suggestion(
 673                             expr.span,
 674                             &format!("{}, producing the closest possible value", cast_msg),
 675                             cast_suggestion,
 676                             Applicability::MaybeIncorrect,  // lossy conversion
 677                         );
 678                     }
 679                     true
 680                 }
 681                 (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
 682                     if literal_is_ty_suffixed(expr) {
 683                         err.span_suggestion(
 684                             expr.span,
 685                             &lit_msg,
 686                             suffix_suggestion,
 687                             Applicability::MachineApplicable,
 688                         );
 689                     } else if can_cast {
 690                         // Missing try_into implementation for `{float}` to `{integer}`
 691                         err.span_suggestion(
 692                             expr.span,
 693                             &format!("{}, rounding the float towards zero", msg),
 694                             cast_suggestion,
 695                             Applicability::MaybeIncorrect  // lossy conversion
 696                         );
 697                         err.warn("if the rounded value cannot be represented by the target \
 698                                   integer type, including `Inf` and `NaN`, casting will cause \
 699                                   undefined behavior \
 700                                   (https://github.com/rust-lang/rust/issues/10184)");
 701                     }
 702                     true
 703                 }
 704                 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 705                     // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 706                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 707                         err.span_suggestion(
 708                             expr.span,
 709                             &format!(
 710                                 "{}, producing the floating point representation of the integer",
 711                                 msg,
 712                             ),
 713                             into_suggestion,
 714                             Applicability::MachineApplicable
 715                         );
 716                     } else if literal_is_ty_suffixed(expr) {
 717                         err.span_suggestion(
 718                             expr.span,
 719                             &lit_msg,
 720                             suffix_suggestion,
 721                             Applicability::MachineApplicable,
 722                         );
 723                     } else {
 724                         // Missing try_into implementation for `{integer}` to `{float}`
 725                         err.span_suggestion(
 726                             expr.span,
 727                             &format!(
 728                                 "{}, producing the floating point representation of the integer,
 729                                  rounded if necessary",
 730                                 cast_msg,
 731                             ),
 732                             cast_suggestion,
 733                             Applicability::MaybeIncorrect  // lossy conversion
 734                         );
 735                     }
 736                     true
 737                 }
 738                 (&ty::Float(ref exp), &ty::Int(ref found)) => {
 739                     // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 740                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 741                         err.span_suggestion(
 742                             expr.span,
 743                             &format!(
 744                                 "{}, producing the floating point representation of the integer",
 745                                 &msg,
 746                             ),
 747                             into_suggestion,
 748                             Applicability::MachineApplicable
 749                         );
 750                     } else if literal_is_ty_suffixed(expr) {
 751                         err.span_suggestion(
 752                             expr.span,
 753                             &lit_msg,
 754                             suffix_suggestion,
 755                             Applicability::MachineApplicable,
 756                         );
 757                     } else {
 758                         // Missing try_into implementation for `{integer}` to `{float}`
 759                         err.span_suggestion(
 760                             expr.span,
 761                             &format!(
 762                                 "{}, producing the floating point representation of the integer, \
 763                                  rounded if necessary",
 764                                 &msg,
 765                             ),
 766                             cast_suggestion,
 767                             Applicability::MaybeIncorrect  // lossy conversion
 768                         );
 769                     }
 770                     true
 771                 }
 772                 _ => false,
 773             }
 774         } else {
 775             false
 776         }
 777     }
 778 }