1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use check::FnCtxt;
use rustc::infer::InferOk;
use rustc::traits::ObligationCause;

use syntax::ast;
use syntax::util::parser::PREC_POSTFIX;
use syntax_pos::Span;
use rustc::hir;
use rustc::hir::def::Def;
use rustc::hir::Node;
use rustc::hir::{Item, ItemKind, print};
use rustc::ty::{self, Ty, AssociatedItem};
use rustc::ty::adjustment::AllowTwoPhase;
use errors::{Applicability, DiagnosticBuilder, SourceMapper};

use super::method::probe;

impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
    // Requires that the two types unify, and prints an error message if
    // they don't.
    pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
        self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
    }

    pub fn demand_suptype_diag(&self,
                               sp: Span,
                               expected: Ty<'tcx>,
                               actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
        let cause = &self.misc(sp);
        match self.at(cause, self.param_env).sup(expected, actual) {
            Ok(InferOk { obligations, value: () }) => {
                self.register_predicates(obligations);
                None
            },
            Err(e) => {
                Some(self.report_mismatched_types(&cause, expected, actual, e))
            }
        }
    }

    pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
        if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
            err.emit();
        }
    }

    pub fn demand_eqtype_diag(&self,
                             sp: Span,
                             expected: Ty<'tcx>,
                             actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
        self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
    }

    pub fn demand_eqtype_with_origin(&self,
                                     cause: &ObligationCause<'tcx>,
                                     expected: Ty<'tcx>,
                                     actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
        match self.at(cause, self.param_env).eq(expected, actual) {
            Ok(InferOk { obligations, value: () }) => {
                self.register_predicates(obligations);
                None
            }
            Err(e) => {
                Some(self.report_mismatched_types(cause, expected, actual, e))
            }
        }
    }

    pub fn demand_coerce(&self,
                         expr: &hir::Expr,
                         checked_ty: Ty<'tcx>,
                         expected: Ty<'tcx>,
                         allow_two_phase: AllowTwoPhase)
                         -> Ty<'tcx> {
        let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
        if let Some(mut err) = err {
            err.emit();
        }
        ty
    }

    // Checks that the type of `expr` can be coerced to `expected`.
    //
    // NB: This code relies on `self.diverges` to be accurate. In
    // particular, assignments to `!` will be permitted if the
    // diverges flag is currently "always".
    pub fn demand_coerce_diag(&self,
                              expr: &hir::Expr,
                              checked_ty: Ty<'tcx>,
                              expected: Ty<'tcx>,
                              allow_two_phase: AllowTwoPhase)
                              -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
        let expected = self.resolve_type_vars_with_obligations(expected);

        let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
            Ok(ty) => return (ty, None),
            Err(e) => e
        };

        let cause = self.misc(expr.span);
        let expr_ty = self.resolve_type_vars_with_obligations(checked_ty);
        let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);

        // If the expected type is an enum with any variants whose sole
        // field is of the found type, suggest such variants. See Issue
        // #42764.
        if let ty::Adt(expected_adt, substs) = expected.sty {
            let mut compatible_variants = vec![];
            for variant in &expected_adt.variants {
                if variant.fields.len() == 1 {
                    let sole_field = &variant.fields[0];
                    let sole_field_ty = sole_field.ty(self.tcx, substs);
                    if self.can_coerce(expr_ty, sole_field_ty) {
                        let mut variant_path = self.tcx.item_path_str(variant.did);
                        variant_path = variant_path.trim_left_matches("std::prelude::v1::")
                            .to_string();
                        compatible_variants.push(variant_path);
                    }
                }
            }
            if !compatible_variants.is_empty() {
                let expr_text = print::to_string(print::NO_ANN, |s| s.print_expr(expr));
                let suggestions = compatible_variants.iter()
                    .map(|v| format!("{}({})", v, expr_text)).collect::<Vec<_>>();
                err.span_suggestions(expr.span,
                                     "try using a variant of the expected type",
                                     suggestions);
            }
        }

        self.suggest_ref_or_into(&mut err, expr, expected, expr_ty);

        (expected, Some(err))
    }

    pub fn get_conversion_methods(&self, span: Span, expected: Ty<'tcx>, checked_ty: Ty<'tcx>)
                              -> Vec<AssociatedItem> {
        let mut methods = self.probe_for_return_type(span,
                                                     probe::Mode::MethodCall,
                                                     expected,
                                                     checked_ty,
                                                     ast::DUMMY_NODE_ID);
        methods.retain(|m| {
            self.has_no_input_arg(m) &&
                self.tcx.get_attrs(m.def_id).iter()
                // This special internal attribute is used to whitelist
                // "identity-like" conversion methods to be suggested here.
                //
                // FIXME (#46459 and #46460): ideally
                // `std::convert::Into::into` and `std::borrow:ToOwned` would
                // also be `#[rustc_conversion_suggestion]`, if not for
                // method-probing false-positives and -negatives (respectively).
                //
                // FIXME? Other potential candidate methods: `as_ref` and
                // `as_mut`?
                .find(|a| a.check_name("rustc_conversion_suggestion")).is_some()
        });

        methods
    }

    // This function checks if the method isn't static and takes other arguments than `self`.
    fn has_no_input_arg(&self, method: &AssociatedItem) -> bool {
        match method.def() {
            Def::Method(def_id) => {
                self.tcx.fn_sig(def_id).inputs().skip_binder().len() == 1
            }
            _ => false,
        }
    }

    /// Identify some cases where `as_ref()` would be appropriate and suggest it.
    ///
    /// Given the following code:
    /// ```
    /// struct Foo;
    /// fn takes_ref(_: &Foo) {}
    /// let ref opt = Some(Foo);
    ///
    /// opt.map(|arg| takes_ref(arg));
    /// ```
    /// Suggest using `opt.as_ref().map(|arg| takes_ref(arg));` instead.
    ///
    /// It only checks for `Option` and `Result` and won't work with
    /// ```
    /// opt.map(|arg| { takes_ref(arg) });
    /// ```
    fn can_use_as_ref(&self, expr: &hir::Expr) -> Option<(Span, &'static str, String)> {
        if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.node {
            if let hir::def::Def::Local(id) = path.def {
                let parent = self.tcx.hir.get_parent_node(id);
                if let Some(Node::Expr(hir::Expr {
                    id,
                    node: hir::ExprKind::Closure(_, decl, ..),
                    ..
                })) = self.tcx.hir.find(parent) {
                    let parent = self.tcx.hir.get_parent_node(*id);
                    if let (Some(Node::Expr(hir::Expr {
                        node: hir::ExprKind::MethodCall(path, span, expr),
                        ..
                    })), 1) = (self.tcx.hir.find(parent), decl.inputs.len()) {
                        let self_ty = self.tables.borrow().node_id_to_type(expr[0].hir_id);
                        let self_ty = format!("{:?}", self_ty);
                        let name = path.ident.as_str();
                        let is_as_ref_able = (
                            self_ty.starts_with("&std::option::Option") ||
                            self_ty.starts_with("&std::result::Result") ||
                            self_ty.starts_with("std::option::Option") ||
                            self_ty.starts_with("std::result::Result")
                        ) && (name == "map" || name == "and_then");
                        if is_as_ref_able {
                            return Some((span.shrink_to_lo(),
                                         "consider using `as_ref` instead",
                                         "as_ref().".into()));
                        }
                    }
                }
            }
        }
        None
    }

    /// This function is used to determine potential "simple" improvements or users' errors and
    /// provide them useful help. For example:
    ///
    /// ```
    /// fn some_fn(s: &str) {}
    ///
    /// let x = "hey!".to_owned();
    /// some_fn(x); // error
    /// ```
    ///
    /// No need to find every potential function which could make a coercion to transform a
    /// `String` into a `&str` since a `&` would do the trick!
    ///
    /// In addition of this check, it also checks between references mutability state. If the
    /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
    /// `&mut`!".
    pub fn check_ref(&self,
                 expr: &hir::Expr,
                 checked_ty: Ty<'tcx>,
                 expected: Ty<'tcx>)
                 -> Option<(Span, &'static str, String)> {
        let cm = self.sess().source_map();
        // Use the callsite's span if this is a macro call. #41858
        let sp = cm.call_span_if_macro(expr.span);
        if !cm.span_to_filename(sp).is_real() {
            return None;
        }

        match (&expected.sty, &checked_ty.sty) {
            (&ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.sty, &check.sty) {
                (&ty::Str, &ty::Array(arr, _)) |
                (&ty::Str, &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
                    if let hir::ExprKind::Lit(_) = expr.node {
                        if let Ok(src) = cm.span_to_snippet(sp) {
                            if src.starts_with("b\"") {
                                return Some((sp,
                                             "consider removing the leading `b`",
                                             src[1..].to_string()));
                            }
                        }
                    }
                },
                (&ty::Array(arr, _), &ty::Str) |
                (&ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
                    if let hir::ExprKind::Lit(_) = expr.node {
                        if let Ok(src) = cm.span_to_snippet(sp) {
                            if src.starts_with("\"") {
                                return Some((sp,
                                             "consider adding a leading `b`",
                                             format!("b{}", src)));
                            }
                        }
                    }
                }
                _ => {}
            },
            (&ty::Ref(_, _, mutability), _) => {
                // Check if it can work when put into a ref. For example:
                //
                // ```
                // fn bar(x: &mut i32) {}
                //
                // let x = 0u32;
                // bar(&x); // error, expected &mut
                // ```
                let ref_ty = match mutability {
                    hir::Mutability::MutMutable => self.tcx.mk_mut_ref(
                                                       self.tcx.mk_region(ty::ReStatic),
                                                       checked_ty),
                    hir::Mutability::MutImmutable => self.tcx.mk_imm_ref(
                                                       self.tcx.mk_region(ty::ReStatic),
                                                       checked_ty),
                };
                if self.can_coerce(ref_ty, expected) {
                    if let Ok(src) = cm.span_to_snippet(sp) {
                        let sugg_expr = match expr.node { // parenthesize if needed (Issue #46756)
                            hir::ExprKind::Cast(_, _) |
                            hir::ExprKind::Binary(_, _, _) => format!("({})", src),
                            _ => src,
                        };
                        if let Some(sugg) = self.can_use_as_ref(expr) {
                            return Some(sugg);
                        }
                        return Some(match mutability {
                            hir::Mutability::MutMutable => {
                                (sp, "consider mutably borrowing here", format!("&mut {}",
                                                                                sugg_expr))
                            }
                            hir::Mutability::MutImmutable => {
                                (sp, "consider borrowing here", format!("&{}", sugg_expr))
                            }
                        });
                    }
                }
            }
            (_, &ty::Ref(_, checked, _)) => {
                // We have `&T`, check if what was expected was `T`. If so,
                // we may want to suggest adding a `*`, or removing
                // a `&`.
                //
                // (But, also check check the `expn_info()` to see if this is
                // a macro; if so, it's hard to extract the text and make a good
                // suggestion, so don't bother.)
                if self.infcx.can_sub(self.param_env, checked, &expected).is_ok() &&
                   sp.ctxt().outer().expn_info().is_none() {
                    match expr.node {
                        // Maybe remove `&`?
                        hir::ExprKind::AddrOf(_, ref expr) => {
                            if !cm.span_to_filename(expr.span).is_real() {
                                return None;
                            }
                            if let Ok(code) = cm.span_to_snippet(expr.span) {
                                return Some((sp, "consider removing the borrow", code));
                            }
                        }

                        // Maybe add `*`? Only if `T: Copy`.
                        _ => {
                            if !self.infcx.type_moves_by_default(self.param_env,
                                                                checked,
                                                                sp) {
                                // do not suggest if the span comes from a macro (#52783)
                                if let (Ok(code),
                                        true) = (cm.span_to_snippet(sp), sp == expr.span) {
                                    return Some((
                                        sp,
                                        "consider dereferencing the borrow",
                                        format!("*{}", code),
                                    ));
                                }
                            }
                        }
                    }
                }
            }
            _ => {}
        }
        None
    }

    pub fn check_for_cast(&self,
                      err: &mut DiagnosticBuilder<'tcx>,
                      expr: &hir::Expr,
                      checked_ty: Ty<'tcx>,
                      expected_ty: Ty<'tcx>)
                      -> bool {
        let parent_id = self.tcx.hir.get_parent_node(expr.id);
        match self.tcx.hir.find(parent_id) {
            Some(parent) => {
                // Shouldn't suggest `.into()` on `const`s.
                if let Node::Item(Item { node: ItemKind::Const(_, _), .. }) = parent {
                    // FIXME(estebank): modify once we decide to suggest `as` casts
                    return false;
                }
            }
            None => {}
        };

        let will_truncate = "will truncate the source value";
        let depending_on_isize = "will truncate or zero-extend depending on the bit width of \
                                  `isize`";
        let depending_on_usize = "will truncate or zero-extend depending on the bit width of \
                                  `usize`";
        let will_sign_extend = "will sign-extend the source value";
        let will_zero_extend = "will zero-extend the source value";

        // If casting this expression to a given numeric type would be appropriate in case of a type
        // mismatch.
        //
        // We want to minimize the amount of casting operations that are suggested, as it can be a
        // lossy operation with potentially bad side effects, so we only suggest when encountering
        // an expression that indicates that the original type couldn't be directly changed.
        //
        // For now, don't suggest casting with `as`.
        let can_cast = false;

        let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);

        if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
            let msg = format!("you can cast an `{}` to `{}`", checked_ty, expected_ty);
            let cast_suggestion = format!("{}{}{} as {}",
                                          if needs_paren { "(" } else { "" },
                                          src,
                                          if needs_paren { ")" } else { "" },
                                          expected_ty);
            let into_suggestion = format!("{}{}{}.into()",
                                          if needs_paren { "(" } else { "" },
                                          src,
                                          if needs_paren { ")" } else { "" });

            match (&expected_ty.sty, &checked_ty.sty) {
                (&ty::Int(ref exp), &ty::Int(ref found)) => {
                    match (found.bit_width(), exp.bit_width()) {
                        (Some(found), Some(exp)) if found > exp => {
                            if can_cast {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, will_truncate),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect // lossy conversion
                                );
                            }
                        }
                        (None, _) | (_, None) => {
                            if can_cast {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, depending_on_isize),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect // lossy conversion
                                );
                            }
                        }
                        _ => {
                            err.span_suggestion_with_applicability(
                                expr.span,
                                &format!("{}, which {}", msg, will_sign_extend),
                                into_suggestion,
                                Applicability::MachineApplicable
                            );
                        }
                    }
                    true
                }
                (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
                    match (found.bit_width(), exp.bit_width()) {
                        (Some(found), Some(exp)) if found > exp => {
                            if can_cast {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, will_truncate),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                        }
                        (None, _) | (_, None) => {
                            if can_cast {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, depending_on_usize),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                        }
                        _ => {
                            err.span_suggestion_with_applicability(
                                expr.span,
                                &format!("{}, which {}", msg, will_zero_extend),
                                into_suggestion,
                                Applicability::MachineApplicable
                            );
                        }
                    }
                    true
                }
                (&ty::Int(ref exp), &ty::Uint(ref found)) => {
                    if can_cast {
                        match (found.bit_width(), exp.bit_width()) {
                            (Some(found), Some(exp)) if found > exp - 1 => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, will_truncate),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                            (None, None) => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, will_truncate),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                            (None, _) => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, depending_on_isize),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                            (_, None) => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, depending_on_usize),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                            _ => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, will_zero_extend),
                                    cast_suggestion,
                                    Applicability::MachineApplicable
                                );
                            }
                        }
                    }
                    true
                }
                (&ty::Uint(ref exp), &ty::Int(ref found)) => {
                    if can_cast {
                        match (found.bit_width(), exp.bit_width()) {
                            (Some(found), Some(exp)) if found - 1 > exp => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, will_truncate),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                            (None, None) => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, will_sign_extend),
                                    cast_suggestion,
                                    Applicability::MachineApplicable  // lossy conversion
                                );
                            }
                            (None, _) => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, depending_on_usize),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                            (_, None) => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, depending_on_isize),
                                    cast_suggestion,
                                    Applicability::MaybeIncorrect  // lossy conversion
                                );
                            }
                            _ => {
                                err.span_suggestion_with_applicability(
                                    expr.span,
                                    &format!("{}, which {}", msg, will_sign_extend),
                                    cast_suggestion,
                                    Applicability::MachineApplicable
                                );
                            }
                        }
                    }
                    true
                }
                (&ty::Float(ref exp), &ty::Float(ref found)) => {
                    if found.bit_width() < exp.bit_width() {
                        err.span_suggestion_with_applicability(
                            expr.span,
                            &format!("{} in a lossless way", msg),
                            into_suggestion,
                            Applicability::MachineApplicable
                        );
                    } else if can_cast {
                        err.span_suggestion_with_applicability(
                            expr.span,
                            &format!("{}, producing the closest possible value", msg),
                            cast_suggestion,
                            Applicability::MaybeIncorrect  // lossy conversion
                        );
                    }
                    true
                }
                (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
                    if can_cast {
                        err.span_suggestion_with_applicability(
                            expr.span,
                            &format!("{}, rounding the float towards zero", msg),
                            cast_suggestion,
                            Applicability::MaybeIncorrect  // lossy conversion
                        );
                        err.warn("casting here will cause undefined behavior if the rounded value \
                                  cannot be represented by the target integer type, including \
                                  `Inf` and `NaN` (this is a bug and will be fixed)");
                    }
                    true
                }
                (&ty::Float(ref exp), &ty::Uint(ref found)) => {
                    // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
                    if exp.bit_width() > found.bit_width().unwrap_or(256) {
                        err.span_suggestion_with_applicability(
                            expr.span,
                            &format!("{}, producing the floating point representation of the \
                                      integer",
                                      msg),
                            into_suggestion,
                            Applicability::MachineApplicable
                        );
                    } else if can_cast {
                        err.span_suggestion_with_applicability(expr.span,
                            &format!("{}, producing the floating point representation of the \
                                      integer, rounded if necessary",
                                      msg),
                            cast_suggestion,
                            Applicability::MaybeIncorrect  // lossy conversion
                        );
                    }
                    true
                }
                (&ty::Float(ref exp), &ty::Int(ref found)) => {
                    // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
                    if exp.bit_width() > found.bit_width().unwrap_or(256) {
                        err.span_suggestion_with_applicability(
                            expr.span,
                            &format!("{}, producing the floating point representation of the \
                                      integer",
                                      msg),
                            into_suggestion,
                            Applicability::MachineApplicable
                        );
                    } else if can_cast {
                        err.span_suggestion_with_applicability(
                            expr.span,
                            &format!("{}, producing the floating point representation of the \
                                      integer, rounded if necessary",
                                      msg),
                            cast_suggestion,
                            Applicability::MaybeIncorrect  // lossy conversion
                        );
                    }
                    true
                }
                _ => false,
            }
        } else {
            false
        }
    }
}