src/librustc_typeck/check/demand.rs

   1 use crate::check::FnCtxt;
   2 use rustc::infer::InferOk;
   3 use rustc::traits::{self, ObligationCause, ObligationCauseCode};
   4
   5 use syntax::symbol::sym;
   6 use syntax::util::parser::PREC_POSTFIX;
   7 use syntax_pos::Span;
   8 use rustc::hir;
   9 use rustc::hir::Node;
  10 use rustc::hir::{print, lowering::is_range_literal};
  11 use rustc::ty::{self, Ty, AssocItem};
  12 use rustc::ty::adjustment::AllowTwoPhase;
  13 use errors::{Applicability, DiagnosticBuilder};
  14
  15 use super::method::probe;
  16
  17 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  18     // Requires that the two types unify, and prints an error message if
  19     // they don't.
  20     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  21         self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
  22     }
  23
  24     pub fn demand_suptype_diag(&self,
  25                                sp: Span,
  26                                expected: Ty<'tcx>,
  27                                actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
  28         let cause = &self.misc(sp);
  29         match self.at(cause, self.param_env).sup(expected, actual) {
  30             Ok(InferOk { obligations, value: () }) => {
  31                 self.register_predicates(obligations);
  32                 None
  33             },
  34             Err(e) => {
  35                 Some(self.report_mismatched_types(&cause, expected, actual, e))
  36             }
  37         }
  38     }
  39
  40     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  41         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  42             err.emit();
  43         }
  44     }
  45
  46     pub fn demand_eqtype_diag(&self,
  47                              sp: Span,
  48                              expected: Ty<'tcx>,
  49                              actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
  50         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  51     }
  52
  53     pub fn demand_eqtype_with_origin(&self,
  54                                      cause: &ObligationCause<'tcx>,
  55                                      expected: Ty<'tcx>,
  56                                      actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
  57         match self.at(cause, self.param_env).eq(expected, actual) {
  58             Ok(InferOk { obligations, value: () }) => {
  59                 self.register_predicates(obligations);
  60                 None
  61             }
  62             Err(e) => {
  63                 Some(self.report_mismatched_types(cause, expected, actual, e))
  64             }
  65         }
  66     }
  67
  68     pub fn demand_eqtype_pat_diag(
  69         &self,
  70         cause_span: Span,
  71         expected: Ty<'tcx>,
  72         actual: Ty<'tcx>,
  73         match_expr_span: Option<Span>,
  74     ) -> Option<DiagnosticBuilder<'tcx>> {
  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)
  84     }
  85
  86     pub fn demand_eqtype_pat(
  87         &self,
  88         cause_span: Span,
  89         expected: Ty<'tcx>,
  90         actual: Ty<'tcx>,
  91         match_expr_span: Option<Span>,
  92     ) {
  93         self.demand_eqtype_pat_diag(cause_span, expected, actual, match_expr_span)
  94             .map(|mut err| err.emit());
  95     }
  96
  97     pub fn demand_coerce(&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.annotate_expected_due_to_let_ty(&mut err, expr);
 141         self.suggest_compatible_variants(&mut err, expr, expected, expr_ty);
 142         self.suggest_ref_or_into(&mut err, expr, expected, expr_ty);
 143         self.suggest_boxing_when_appropriate(&mut err, expr, expected, expr_ty);
 144         self.suggest_missing_await(&mut err, expr, expected, expr_ty);
 145
 146         (expected, Some(err))
 147     }
 148
 149     fn annotate_expected_due_to_let_ty(&self, err: &mut DiagnosticBuilder<'_>, expr: &hir::Expr) {
 150         let parent = self.tcx.hir().get_parent_node(expr.hir_id);
 151         if let Some(hir::Node::Local(hir::Local {
 152             ty: Some(ty),
 153             init: Some(init),
 154             ..
 155         })) = self.tcx.hir().find(parent) {
 156             if init.hir_id == expr.hir_id {
 157                 // Point at `let` assignment type.
 158                 err.span_label(ty.span, "expected due to this");
 159             }
 160         }
 161     }
 162
 163     /// Returns whether the expected type is `bool` and the expression is `x = y`.
 164     pub fn is_assign_to_bool(&self, expr: &hir::Expr, expected: Ty<'tcx>) -> bool {
 165         if let hir::ExprKind::Assign(..) = expr.kind {
 166             return expected == self.tcx.types.bool;
 167         }
 168         false
 169     }
 170
 171     /// If the expected type is an enum (Issue #55250) with any variants whose
 172     /// sole field is of the found type, suggest such variants. (Issue #42764)
 173     fn suggest_compatible_variants(
 174         &self,
 175         err: &mut DiagnosticBuilder<'_>,
 176         expr: &hir::Expr,
 177         expected: Ty<'tcx>,
 178         expr_ty: Ty<'tcx>,
 179     ) {
 180         if let ty::Adt(expected_adt, substs) = expected.kind {
 181             if !expected_adt.is_enum() {
 182                 return;
 183             }
 184
 185             let mut compatible_variants = expected_adt.variants
 186                 .iter()
 187                 .filter(|variant| variant.fields.len() == 1)
 188                 .filter_map(|variant| {
 189                     let sole_field = &variant.fields[0];
 190                     let sole_field_ty = sole_field.ty(self.tcx, substs);
 191                     if self.can_coerce(expr_ty, sole_field_ty) {
 192                         let variant_path = self.tcx.def_path_str(variant.def_id);
 193                         // FIXME #56861: DRYer prelude filtering
 194                         Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
 195                     } else {
 196                         None
 197                     }
 198                 }).peekable();
 199
 200             if compatible_variants.peek().is_some() {
 201                 let expr_text = self.tcx.sess
 202                     .source_map()
 203                     .span_to_snippet(expr.span)
 204                     .unwrap_or_else(|_| {
 205                         print::to_string(print::NO_ANN, |s| s.print_expr(expr))
 206                     });
 207                 let suggestions = compatible_variants
 208                     .map(|v| format!("{}({})", v, expr_text));
 209                 let msg = "try using a variant of the expected enum";
 210                 err.span_suggestions(expr.span, msg, suggestions, Applicability::MaybeIncorrect);
 211             }
 212         }
 213     }
 214
 215     pub fn get_conversion_methods(&self, span: Span, expected: Ty<'tcx>, checked_ty: Ty<'tcx>)
 216                               -> Vec<AssocItem> {
 217         let mut methods = self.probe_for_return_type(span,
 218                                                      probe::Mode::MethodCall,
 219                                                      expected,
 220                                                      checked_ty,
 221                                                      hir::DUMMY_HIR_ID);
 222         methods.retain(|m| {
 223             self.has_no_input_arg(m) &&
 224                 self.tcx.get_attrs(m.def_id).iter()
 225                 // This special internal attribute is used to whitelist
 226                 // "identity-like" conversion methods to be suggested here.
 227                 //
 228                 // FIXME (#46459 and #46460): ideally
 229                 // `std::convert::Into::into` and `std::borrow:ToOwned` would
 230                 // also be `#[rustc_conversion_suggestion]`, if not for
 231                 // method-probing false-positives and -negatives (respectively).
 232                 //
 233                 // FIXME? Other potential candidate methods: `as_ref` and
 234                 // `as_mut`?
 235                 .find(|a| a.check_name(sym::rustc_conversion_suggestion)).is_some()
 236         });
 237
 238         methods
 239     }
 240
 241     // This function checks if the method isn't static and takes other arguments than `self`.
 242     fn has_no_input_arg(&self, method: &AssocItem) -> bool {
 243         match method.kind {
 244             ty::AssocKind::Method => {
 245                 self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
 246             }
 247             _ => false,
 248         }
 249     }
 250
 251     /// Identify some cases where `as_ref()` would be appropriate and suggest it.
 252     ///
 253     /// Given the following code:
 254     /// ```
 255     /// struct Foo;
 256     /// fn takes_ref(_: &Foo) {}
 257     /// let ref opt = Some(Foo);
 258     ///
 259     /// opt.map(|param| takes_ref(param));
 260     /// ```
 261     /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
 262     ///
 263     /// It only checks for `Option` and `Result` and won't work with
 264     /// ```
 265     /// opt.map(|param| { takes_ref(param) });
 266     /// ```
 267     fn can_use_as_ref(
 268         &self,
 269         expr: &hir::Expr,
 270     ) -> 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(
 290                 hir::Expr { hir_id, kind: hir::ExprKind::Closure(_, decl, ..), .. }
 291             )) => (hir_id, decl),
 292             _ => return None
 293         };
 294
 295         let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
 296         let hir = self.tcx.hir().find(expr_parent);
 297         let closure_params_len = closure_fn_decl.inputs.len();
 298         let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
 299             (Some(Node::Expr(
 300                 hir::Expr { kind: hir::ExprKind::MethodCall(path, span, expr), .. }
 301             )), 1) => (path, span, expr),
 302             _ => return None
 303         };
 304
 305         let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
 306         let self_ty = format!("{:?}", self_ty);
 307         let name = method_path.ident.as_str();
 308         let is_as_ref_able = (
 309             self_ty.starts_with("&std::option::Option") ||
 310             self_ty.starts_with("&std::result::Result") ||
 311             self_ty.starts_with("std::option::Option") ||
 312             self_ty.starts_with("std::result::Result")
 313         ) && (name == "map" || name == "and_then");
 314         match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
 315             (true, Ok(src)) => {
 316                 let suggestion = format!("as_ref().{}", src);
 317                 Some((*method_span, "consider using `as_ref` instead", suggestion))
 318             },
 319             _ => None
 320         }
 321     }
 322
 323     crate fn is_hir_id_from_struct_pattern_shorthand_field(
 324         &self,
 325         hir_id: hir::HirId,
 326         sp: Span,
 327     ) -> bool {
 328         let cm = self.sess().source_map();
 329         let parent_id = self.tcx.hir().get_parent_node(hir_id);
 330         if let Some(parent) = self.tcx.hir().find(parent_id) {
 331             // Account for fields
 332             if let Node::Expr(hir::Expr {
 333                 kind: hir::ExprKind::Struct(_, fields, ..), ..
 334             }) = parent {
 335                 if let Ok(src) = cm.span_to_snippet(sp) {
 336                     for field in fields {
 337                         if field.ident.as_str() == src && field.is_shorthand {
 338                             return true;
 339                         }
 340                     }
 341                 }
 342             }
 343         }
 344         false
 345     }
 346
 347     /// This function is used to determine potential "simple" improvements or users' errors and
 348     /// provide them useful help. For example:
 349     ///
 350     /// ```
 351     /// fn some_fn(s: &str) {}
 352     ///
 353     /// let x = "hey!".to_owned();
 354     /// some_fn(x); // error
 355     /// ```
 356     ///
 357     /// No need to find every potential function which could make a coercion to transform a
 358     /// `String` into a `&str` since a `&` would do the trick!
 359     ///
 360     /// In addition of this check, it also checks between references mutability state. If the
 361     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 362     /// `&mut`!".
 363     pub fn check_ref(
 364         &self,
 365         expr: &hir::Expr,
 366         checked_ty: Ty<'tcx>,
 367         expected: Ty<'tcx>,
 368     ) -> Option<(Span, &'static str, String)> {
 369         let cm = self.sess().source_map();
 370         let sp = expr.span;
 371         if !cm.span_to_filename(sp).is_real() {
 372             // Ignore if span is from within a macro #41858, #58298. We previously used the macro
 373             // call span, but that breaks down when the type error comes from multiple calls down.
 374             return None;
 375         }
 376
 377         let is_struct_pat_shorthand_field = self.is_hir_id_from_struct_pattern_shorthand_field(
 378             expr.hir_id,
 379             sp,
 380         );
 381
 382         // If the span is from a macro, then it's hard to extract the text
 383         // and make a good suggestion, so don't bother.
 384         let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
 385
 386         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
 387         let expr = expr.peel_drop_temps();
 388
 389         match (&expr.kind, &expected.kind, &checked_ty.kind) {
 390             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
 391                 (&ty::Str, &ty::Array(arr, _)) |
 392                 (&ty::Str, &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
 393                     if let hir::ExprKind::Lit(_) = expr.kind {
 394                         if let Ok(src) = cm.span_to_snippet(sp) {
 395                             if src.starts_with("b\"") {
 396                                 return Some((sp,
 397                                              "consider removing the leading `b`",
 398                                              src[1..].to_string()));
 399                             }
 400                         }
 401                     }
 402                 },
 403                 (&ty::Array(arr, _), &ty::Str) |
 404                 (&ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
 405                     if let hir::ExprKind::Lit(_) = expr.kind {
 406                         if let Ok(src) = cm.span_to_snippet(sp) {
 407                             if src.starts_with("\"") {
 408                                 return Some((sp,
 409                                              "consider adding a leading `b`",
 410                                              format!("b{}", src)));
 411                             }
 412                         }
 413                     }
 414                 }
 415                 _ => {}
 416             },
 417             (_, &ty::Ref(_, _, mutability), _) => {
 418                 // Check if it can work when put into a ref. For example:
 419                 //
 420                 // ```
 421                 // fn bar(x: &mut i32) {}
 422                 //
 423                 // let x = 0u32;
 424                 // bar(&x); // error, expected &mut
 425                 // ```
 426                 let ref_ty = match mutability {
 427                     hir::Mutability::Mutable => {
 428                         self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 429                     }
 430                     hir::Mutability::Immutable => {
 431                         self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
 432                     }
 433                 };
 434                 if self.can_coerce(ref_ty, expected) {
 435                     let mut sugg_sp = sp;
 436                     if let hir::ExprKind::MethodCall(segment, _sp, args) = &expr.kind {
 437                         let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
 438                         if let ([arg], Some(true), sym::clone) = (
 439                             &args[..],
 440                             self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
 441                                 let ai = self.tcx.associated_item(did);
 442                                 ai.container == ty::TraitContainer(clone_trait)
 443                             }),
 444                             segment.ident.name,
 445                         ) {
 446                             // If this expression had a clone call when suggesting borrowing
 447                             // we want to suggest removing it because it'd now be unnecessary.
 448                             sugg_sp = arg.span;
 449                         }
 450                     }
 451                     if let Ok(src) = cm.span_to_snippet(sugg_sp) {
 452                         let needs_parens = match expr.kind {
 453                             // parenthesize if needed (Issue #46756)
 454                             hir::ExprKind::Cast(_, _) |
 455                             hir::ExprKind::Binary(_, _, _) => true,
 456                             // parenthesize borrows of range literals (Issue #54505)
 457                             _ if is_range_literal(self.tcx.sess, expr) => true,
 458                             _ => false,
 459                         };
 460                         let sugg_expr = if needs_parens {
 461                             format!("({})", src)
 462                         } else {
 463                             src
 464                         };
 465
 466                         if let Some(sugg) = self.can_use_as_ref(expr) {
 467                             return Some(sugg);
 468                         }
 469                         let field_name = if is_struct_pat_shorthand_field {
 470                             format!("{}: ", sugg_expr)
 471                         } else {
 472                             String::new()
 473                         };
 474                         if let Some(hir::Node::Expr(hir::Expr {
 475                             kind: hir::ExprKind::Assign(left_expr, _),
 476                             ..
 477                         })) = self.tcx.hir().find(
 478                             self.tcx.hir().get_parent_node(expr.hir_id),
 479                         ) {
 480                             if mutability == hir::Mutability::Mutable {
 481                                 // Found the following case:
 482                                 // fn foo(opt: &mut Option<String>){ opt = None }
 483                                 //                                   ---   ^^^^
 484                                 //                                   |     |
 485                                 //    consider dereferencing here: `*opt`  |
 486                                 // expected mutable reference, found enum `Option`
 487                                 if let Ok(src) = cm.span_to_snippet(left_expr.span) {
 488                                     return Some((
 489                                         left_expr.span,
 490                                         "consider dereferencing here to assign to the mutable \
 491                                          borrowed piece of memory",
 492                                         format!("*{}", src),
 493                                     ));
 494                                 }
 495                             }
 496                         }
 497
 498                         return Some(match mutability {
 499                             hir::Mutability::Mutable => (
 500                                 sp,
 501                                 "consider mutably borrowing here",
 502                                 format!("{}&mut {}", field_name, sugg_expr),
 503                             ),
 504                             hir::Mutability::Immutable => (
 505                                 sp,
 506                                 "consider borrowing here",
 507                                 format!("{}&{}", field_name, sugg_expr),
 508                             ),
 509                         });
 510                     }
 511                 }
 512             },
 513             (
 514                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
 515                 _,
 516                 &ty::Ref(_, checked, _)
 517             ) if {
 518                 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
 519             } => {
 520                 // We have `&T`, check if what was expected was `T`. If so,
 521                 // we may want to suggest removing a `&`.
 522                 if !cm.span_to_filename(expr.span).is_real() {
 523                     if let Ok(code) = cm.span_to_snippet(sp) {
 524                         if code.chars().next() == Some('&') {
 525                             return Some((
 526                                 sp,
 527                                 "consider removing the borrow",
 528                                 code[1..].to_string(),
 529                             ));
 530                         }
 531                     }
 532                     return None;
 533                 }
 534                 if let Ok(code) = cm.span_to_snippet(expr.span) {
 535                     return Some((sp, "consider removing the borrow", code));
 536                 }
 537             },
 538             _ if sp == expr.span && !is_macro => {
 539                 // Check for `Deref` implementations by constructing a predicate to
 540                 // prove: `<T as Deref>::Output == U`
 541                 let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
 542                 let item_def_id = self.tcx.associated_items(deref_trait).next().unwrap().def_id;
 543                 let predicate = ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
 544                     // `<T as Deref>::Output`
 545                     projection_ty: ty::ProjectionTy {
 546                         // `T`
 547                         substs: self.tcx.mk_substs_trait(
 548                             checked_ty,
 549                             self.fresh_substs_for_item(sp, item_def_id),
 550                         ),
 551                         // `Deref::Output`
 552                         item_def_id,
 553                     },
 554                     // `U`
 555                     ty: expected,
 556                 }));
 557                 let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
 558                 let impls_deref = self.infcx.predicate_may_hold(&obligation);
 559
 560                 // For a suggestion to make sense, the type would need to be `Copy`.
 561                 let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
 562
 563                 if is_copy && impls_deref {
 564                     if let Ok(code) = cm.span_to_snippet(sp) {
 565                         let message = if checked_ty.is_region_ptr() {
 566                             "consider dereferencing the borrow"
 567                         } else {
 568                             "consider dereferencing the type"
 569                         };
 570                         let suggestion = if is_struct_pat_shorthand_field {
 571                             format!("{}: *{}", code, code)
 572                         } else {
 573                             format!("*{}", code)
 574                         };
 575                         return Some((sp, message, suggestion));
 576                     }
 577                 }
 578             }
 579             _ => {}
 580         }
 581         None
 582     }
 583
 584     pub fn check_for_cast(
 585         &self,
 586         err: &mut DiagnosticBuilder<'_>,
 587         expr: &hir::Expr,
 588         checked_ty: Ty<'tcx>,
 589         expected_ty: Ty<'tcx>,
 590     ) -> bool {
 591         if self.tcx.hir().is_const_context(expr.hir_id) {
 592             // Shouldn't suggest `.into()` on `const`s.
 593             // FIXME(estebank): modify once we decide to suggest `as` casts
 594             return false;
 595         }
 596         if !self.tcx.sess.source_map().span_to_filename(expr.span).is_real() {
 597             // Ignore if span is from within a macro.
 598             return false;
 599         }
 600
 601         // If casting this expression to a given numeric type would be appropriate in case of a type
 602         // mismatch.
 603         //
 604         // We want to minimize the amount of casting operations that are suggested, as it can be a
 605         // lossy operation with potentially bad side effects, so we only suggest when encountering
 606         // an expression that indicates that the original type couldn't be directly changed.
 607         //
 608         // For now, don't suggest casting with `as`.
 609         let can_cast = false;
 610
 611         let mut prefix = String::new();
 612         if let Some(hir::Node::Expr(hir::Expr {
 613             kind: hir::ExprKind::Struct(_, fields, _),
 614             ..
 615         })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id)) {
 616             // `expr` is a literal field for a struct, only suggest if appropriate
 617             for field in fields {
 618                 if field.expr.hir_id == expr.hir_id && field.is_shorthand {
 619                     // This is a field literal
 620                     prefix = format!("{}: ", field.ident);
 621                     break;
 622                 }
 623             }
 624             if &prefix == "" {
 625                 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
 626                 return false;
 627             }
 628         }
 629         if let hir::ExprKind::Call(path, args) = &expr.kind {
 630             if let (
 631                 hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)),
 632                 1,
 633             ) = (&path.kind, args.len()) {
 634                 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
 635                 if let (
 636                     hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)),
 637                     sym::from,
 638                 ) = (&base_ty.kind, path_segment.ident.name) {
 639                     if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
 640                         match ident.name {
 641                             sym::i128 | sym::i64 | sym::i32 | sym::i16 | sym::i8 |
 642                             sym::u128 | sym::u64 | sym::u32 | sym::u16 | sym::u8 |
 643                             sym::isize | sym::usize
 644                             if base_ty_path.segments.len() == 1 => {
 645                                 return false;
 646                             }
 647                             _ => {}
 648                         }
 649                     }
 650                 }
 651             }
 652         }
 653
 654         let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
 655         let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
 656         let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
 657         let lit_msg = format!(
 658             "change the type of the numeric literal from `{}` to `{}`",
 659             checked_ty,
 660             expected_ty,
 661         );
 662
 663         let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
 664
 665         if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 666             let cast_suggestion = format!(
 667                 "{}{}{}{} as {}",
 668                 prefix,
 669                 if needs_paren { "(" } else { "" },
 670                 src,
 671                 if needs_paren { ")" } else { "" },
 672                 expected_ty,
 673             );
 674             let try_into_suggestion = format!(
 675                 "{}{}{}{}.try_into().unwrap()",
 676                 prefix,
 677                 if needs_paren { "(" } else { "" },
 678                 src,
 679                 if needs_paren { ")" } else { "" },
 680             );
 681             let into_suggestion = format!(
 682                 "{}{}{}{}.into()",
 683                 prefix,
 684                 if needs_paren { "(" } else { "" },
 685                 src,
 686                 if needs_paren { ")" } else { "" },
 687             );
 688             let suffix_suggestion = format!(
 689                 "{}{}{}{}",
 690                 if needs_paren { "(" } else { "" },
 691                 if let (ty::Int(_), ty::Float(_)) | (ty::Uint(_), ty::Float(_)) = (
 692                     &expected_ty.kind,
 693                     &checked_ty.kind,
 694                 ) {
 695                     // Remove fractional part from literal, for example `42.0f32` into `42`
 696                     let src = src.trim_end_matches(&checked_ty.to_string());
 697                     src.split(".").next().unwrap()
 698                 } else {
 699                     src.trim_end_matches(&checked_ty.to_string())
 700                 },
 701                 expected_ty,
 702                 if needs_paren { ")" } else { "" },
 703             );
 704             let literal_is_ty_suffixed = |expr: &hir::Expr| {
 705                 if let hir::ExprKind::Lit(lit) = &expr.kind {
 706                     lit.node.is_suffixed()
 707                 } else {
 708                     false
 709                 }
 710             };
 711
 712             let suggest_to_change_suffix_or_into = |
 713                 err: &mut DiagnosticBuilder<'_>,
 714                 is_fallible: bool,
 715             | {
 716                 let into_sugg = into_suggestion.clone();
 717                 err.span_suggestion(
 718                     expr.span,
 719                     if literal_is_ty_suffixed(expr) {
 720                         &lit_msg
 721                     } else if is_fallible {
 722                         &try_msg
 723                     } else {
 724                         &msg
 725                     },
 726                     if literal_is_ty_suffixed(expr) {
 727                         suffix_suggestion.clone()
 728                     } else if is_fallible {
 729                         try_into_suggestion
 730                     } else {
 731                         into_sugg
 732                     },
 733                     Applicability::MachineApplicable,
 734                 );
 735             };
 736
 737             match (&expected_ty.kind, &checked_ty.kind) {
 738                 (&ty::Int(ref exp), &ty::Int(ref found)) => {
 739                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 740                         (Some(found), Some(exp)) if found > exp => true,
 741                         (None, _) | (_, None) => true,
 742                         _ => false,
 743                     };
 744                     suggest_to_change_suffix_or_into(err, is_fallible);
 745                     true
 746                 }
 747                 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
 748                     let is_fallible = match (found.bit_width(), exp.bit_width()) {
 749                         (Some(found), Some(exp)) if found > exp => true,
 750                         (None, _) | (_, None) => true,
 751                         _ => false,
 752                     };
 753                     suggest_to_change_suffix_or_into(err, is_fallible);
 754                     true
 755                 }
 756                 (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
 757                     suggest_to_change_suffix_or_into(err, true);
 758                     true
 759                 }
 760                 (&ty::Float(ref exp), &ty::Float(ref found)) => {
 761                     if found.bit_width() < exp.bit_width() {
 762                         suggest_to_change_suffix_or_into(err, false);
 763                     } else if literal_is_ty_suffixed(expr) {
 764                         err.span_suggestion(
 765                             expr.span,
 766                             &lit_msg,
 767                             suffix_suggestion,
 768                             Applicability::MachineApplicable,
 769                         );
 770                     } else if can_cast { // Missing try_into implementation for `f64` to `f32`
 771                         err.span_suggestion(
 772                             expr.span,
 773                             &format!("{}, producing the closest possible value", cast_msg),
 774                             cast_suggestion,
 775                             Applicability::MaybeIncorrect,  // lossy conversion
 776                         );
 777                     }
 778                     true
 779                 }
 780                 (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
 781                     if literal_is_ty_suffixed(expr) {
 782                         err.span_suggestion(
 783                             expr.span,
 784                             &lit_msg,
 785                             suffix_suggestion,
 786                             Applicability::MachineApplicable,
 787                         );
 788                     } else if can_cast {
 789                         // Missing try_into implementation for `{float}` to `{integer}`
 790                         err.span_suggestion(
 791                             expr.span,
 792                             &format!("{}, rounding the float towards zero", msg),
 793                             cast_suggestion,
 794                             Applicability::MaybeIncorrect  // lossy conversion
 795                         );
 796                         err.warn("if the rounded value cannot be represented by the target \
 797                                   integer type, including `Inf` and `NaN`, casting will cause \
 798                                   undefined behavior \
 799                                   (https://github.com/rust-lang/rust/issues/10184)");
 800                     }
 801                     true
 802                 }
 803                 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
 804                     // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
 805                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 806                         err.span_suggestion(
 807                             expr.span,
 808                             &format!(
 809                                 "{}, producing the floating point representation of the integer",
 810                                 msg,
 811                             ),
 812                             into_suggestion,
 813                             Applicability::MachineApplicable
 814                         );
 815                     } else if literal_is_ty_suffixed(expr) {
 816                         err.span_suggestion(
 817                             expr.span,
 818                             &lit_msg,
 819                             suffix_suggestion,
 820                             Applicability::MachineApplicable,
 821                         );
 822                     } else {
 823                         // Missing try_into implementation for `{integer}` to `{float}`
 824                         err.span_suggestion(
 825                             expr.span,
 826                             &format!(
 827                                 "{}, producing the floating point representation of the integer,
 828                                  rounded if necessary",
 829                                 cast_msg,
 830                             ),
 831                             cast_suggestion,
 832                             Applicability::MaybeIncorrect  // lossy conversion
 833                         );
 834                     }
 835                     true
 836                 }
 837                 (&ty::Float(ref exp), &ty::Int(ref found)) => {
 838                     // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
 839                     if exp.bit_width() > found.bit_width().unwrap_or(256) {
 840                         err.span_suggestion(
 841                             expr.span,
 842                             &format!(
 843                                 "{}, producing the floating point representation of the integer",
 844                                 &msg,
 845                             ),
 846                             into_suggestion,
 847                             Applicability::MachineApplicable
 848                         );
 849                     } else if literal_is_ty_suffixed(expr) {
 850                         err.span_suggestion(
 851                             expr.span,
 852                             &lit_msg,
 853                             suffix_suggestion,
 854                             Applicability::MachineApplicable,
 855                         );
 856                     } else {
 857                         // Missing try_into implementation for `{integer}` to `{float}`
 858                         err.span_suggestion(
 859                             expr.span,
 860                             &format!(
 861                                 "{}, producing the floating point representation of the integer, \
 862                                  rounded if necessary",
 863                                 &msg,
 864                             ),
 865                             cast_suggestion,
 866                             Applicability::MaybeIncorrect  // lossy conversion
 867                         );
 868                     }
 869                     true
 870                 }
 871                 _ => false,
 872             }
 873         } else {
 874             false
 875         }
 876     }
 877 }