1 use crate::check::FnCtxt;
2 use rustc_infer::infer::InferOk;
3 use rustc_trait_selection::infer::InferCtxtExt as _;
4 use rustc_trait_selection::traits::ObligationCause;
6 use rustc_ast::util::parser::PREC_POSTFIX;
7 use rustc_errors::{Applicability, DiagnosticBuilder};
9 use rustc_hir::lang_items::LangItem;
10 use rustc_hir::{is_range_literal, Node};
11 use rustc_middle::ty::adjustment::AllowTwoPhase;
12 use rustc_middle::ty::{self, AssocItem, Ty, TypeAndMut};
13 use rustc_span::symbol::sym;
16 use super::method::probe;
20 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
21 pub fn emit_coerce_suggestions(
23 err: &mut DiagnosticBuilder<'_>,
27 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
29 self.annotate_expected_due_to_let_ty(err, expr);
30 self.suggest_compatible_variants(err, expr, expected, expr_ty);
31 self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr);
32 if self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty) {
35 self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
36 self.suggest_missing_parentheses(err, expr);
37 self.note_need_for_fn_pointer(err, expected, expr_ty);
38 self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
41 // Requires that the two types unify, and prints an error message if
43 pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
44 if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
49 pub fn demand_suptype_diag(
54 ) -> Option<DiagnosticBuilder<'tcx>> {
55 self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
58 pub fn demand_suptype_with_origin(
60 cause: &ObligationCause<'tcx>,
63 ) -> Option<DiagnosticBuilder<'tcx>> {
64 match self.at(cause, self.param_env).sup(expected, actual) {
65 Ok(InferOk { obligations, value: () }) => {
66 self.register_predicates(obligations);
69 Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
73 pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
74 if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
79 pub fn demand_eqtype_diag(
84 ) -> Option<DiagnosticBuilder<'tcx>> {
85 self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
88 pub fn demand_eqtype_with_origin(
90 cause: &ObligationCause<'tcx>,
93 ) -> Option<DiagnosticBuilder<'tcx>> {
94 match self.at(cause, self.param_env).eq(expected, actual) {
95 Ok(InferOk { obligations, value: () }) => {
96 self.register_predicates(obligations);
99 Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
103 pub fn demand_coerce(
105 expr: &hir::Expr<'_>,
106 checked_ty: Ty<'tcx>,
108 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
109 allow_two_phase: AllowTwoPhase,
112 self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
113 if let Some(mut err) = err {
119 /// Checks that the type of `expr` can be coerced to `expected`.
121 /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
122 /// will be permitted if the diverges flag is currently "always".
123 pub fn demand_coerce_diag(
125 expr: &hir::Expr<'_>,
126 checked_ty: Ty<'tcx>,
128 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
129 allow_two_phase: AllowTwoPhase,
130 ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
131 let expected = self.resolve_vars_with_obligations(expected);
133 let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
134 Ok(ty) => return (ty, None),
138 let expr = expr.peel_drop_temps();
139 let cause = self.misc(expr.span);
140 let expr_ty = self.resolve_vars_with_obligations(checked_ty);
141 let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
143 if self.is_assign_to_bool(expr, expected) {
144 // Error reported in `check_assign` so avoid emitting error again.
146 return (expected, None);
149 self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr);
151 (expected, Some(err))
154 fn annotate_expected_due_to_let_ty(
156 err: &mut DiagnosticBuilder<'_>,
157 expr: &hir::Expr<'_>,
159 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
160 if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
161 self.tcx.hir().find(parent)
163 if init.hir_id == expr.hir_id {
164 // Point at `let` assignment type.
165 err.span_label(ty.span, "expected due to this");
170 /// Returns whether the expected type is `bool` and the expression is `x = y`.
171 pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
172 if let hir::ExprKind::Assign(..) = expr.kind {
173 return expected == self.tcx.types.bool;
178 /// If the expected type is an enum (Issue #55250) with any variants whose
179 /// sole field is of the found type, suggest such variants. (Issue #42764)
180 fn suggest_compatible_variants(
182 err: &mut DiagnosticBuilder<'_>,
183 expr: &hir::Expr<'_>,
187 if let ty::Adt(expected_adt, substs) = expected.kind() {
188 if !expected_adt.is_enum() {
192 let mut compatible_variants = expected_adt
195 .filter(|variant| variant.fields.len() == 1)
196 .filter_map(|variant| {
197 let sole_field = &variant.fields[0];
198 let sole_field_ty = sole_field.ty(self.tcx, substs);
199 if self.can_coerce(expr_ty, sole_field_ty) {
200 let variant_path = self.tcx.def_path_str(variant.def_id);
201 // FIXME #56861: DRYer prelude filtering
202 Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
209 if compatible_variants.peek().is_some() {
210 if let Ok(expr_text) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
211 let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
212 let msg = "try using a variant of the expected enum";
213 err.span_suggestions(
217 Applicability::MaybeIncorrect,
224 pub fn get_conversion_methods(
228 checked_ty: Ty<'tcx>,
230 ) -> Vec<AssocItem> {
232 self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
234 self.has_only_self_parameter(m)
239 // This special internal attribute is used to permit
240 // "identity-like" conversion methods to be suggested here.
242 // FIXME (#46459 and #46460): ideally
243 // `std::convert::Into::into` and `std::borrow:ToOwned` would
244 // also be `#[rustc_conversion_suggestion]`, if not for
245 // method-probing false-positives and -negatives (respectively).
247 // FIXME? Other potential candidate methods: `as_ref` and
249 .any(|a| self.sess().check_name(a, sym::rustc_conversion_suggestion))
255 /// This function checks whether the method is not static and does not accept other parameters than `self`.
256 fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
258 ty::AssocKind::Fn => {
259 method.fn_has_self_parameter
260 && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
266 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
268 /// Given the following code:
271 /// fn takes_ref(_: &Foo) {}
272 /// let ref opt = Some(Foo);
274 /// opt.map(|param| takes_ref(param));
276 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
278 /// It only checks for `Option` and `Result` and won't work with
280 /// opt.map(|param| { takes_ref(param) });
282 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
283 let path = match expr.kind {
284 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
288 let local_id = match path.res {
289 hir::def::Res::Local(id) => id,
293 let local_parent = self.tcx.hir().get_parent_node(local_id);
294 let param_hir_id = match self.tcx.hir().find(local_parent) {
295 Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
299 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
300 let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
301 Some(Node::Expr(hir::Expr {
303 kind: hir::ExprKind::Closure(_, decl, ..),
305 })) => (hir_id, decl),
309 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
310 let hir = self.tcx.hir().find(expr_parent);
311 let closure_params_len = closure_fn_decl.inputs.len();
312 let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
314 Some(Node::Expr(hir::Expr {
315 kind: hir::ExprKind::MethodCall(path, span, expr, _),
319 ) => (path, span, expr),
323 let self_ty = self.typeck_results.borrow().node_type(method_expr[0].hir_id);
324 let self_ty = format!("{:?}", self_ty);
325 let name = method_path.ident.name;
326 let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
327 || self_ty.starts_with("&std::result::Result")
328 || self_ty.starts_with("std::option::Option")
329 || self_ty.starts_with("std::result::Result"))
330 && (name == sym::map || name == sym::and_then);
331 match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
333 let suggestion = format!("as_ref().{}", src);
334 Some((*method_span, "consider using `as_ref` instead", suggestion))
340 crate fn is_hir_id_from_struct_pattern_shorthand_field(
345 let sm = self.sess().source_map();
346 let parent_id = self.tcx.hir().get_parent_node(hir_id);
347 if let Some(parent) = self.tcx.hir().find(parent_id) {
348 // Account for fields
349 if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
351 if let Ok(src) = sm.span_to_snippet(sp) {
352 for field in *fields {
353 if field.ident.as_str() == src && field.is_shorthand {
363 fn replace_prefix(&self, s: &str, old: &str, new: &str) -> Option<String> {
364 s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
367 /// This function is used to determine potential "simple" improvements or users' errors and
368 /// provide them useful help. For example:
371 /// fn some_fn(s: &str) {}
373 /// let x = "hey!".to_owned();
374 /// some_fn(x); // error
377 /// No need to find every potential function which could make a coercion to transform a
378 /// `String` into a `&str` since a `&` would do the trick!
380 /// In addition of this check, it also checks between references mutability state. If the
381 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
385 expr: &hir::Expr<'_>,
386 checked_ty: Ty<'tcx>,
388 ) -> Option<(Span, &'static str, String, Applicability)> {
389 let sm = self.sess().source_map();
391 if sm.is_imported(sp) {
392 // Ignore if span is from within a macro #41858, #58298. We previously used the macro
393 // call span, but that breaks down when the type error comes from multiple calls down.
397 let is_struct_pat_shorthand_field =
398 self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
400 // If the span is from a macro, then it's hard to extract the text
401 // and make a good suggestion, so don't bother.
402 let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
404 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
405 let expr = expr.peel_drop_temps();
407 match (&expr.kind, expected.kind(), checked_ty.kind()) {
408 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
409 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
410 if let hir::ExprKind::Lit(_) = expr.kind {
411 if let Ok(src) = sm.span_to_snippet(sp) {
412 if let Some(src) = self.replace_prefix(&src, "b\"", "\"") {
415 "consider removing the leading `b`",
417 Applicability::MachineApplicable,
423 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
424 if let hir::ExprKind::Lit(_) = expr.kind {
425 if let Ok(src) = sm.span_to_snippet(sp) {
426 if let Some(src) = self.replace_prefix(&src, "\"", "b\"") {
429 "consider adding a leading `b`",
431 Applicability::MachineApplicable,
439 (_, &ty::Ref(_, _, mutability), _) => {
440 // Check if it can work when put into a ref. For example:
443 // fn bar(x: &mut i32) {}
446 // bar(&x); // error, expected &mut
448 let ref_ty = match mutability {
449 hir::Mutability::Mut => {
450 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
452 hir::Mutability::Not => {
453 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
456 if self.can_coerce(ref_ty, expected) {
457 let mut sugg_sp = sp;
458 if let hir::ExprKind::MethodCall(ref segment, sp, ref args, _) = expr.kind {
459 let clone_trait = self.tcx.require_lang_item(LangItem::Clone, Some(sp));
460 if let ([arg], Some(true), sym::clone) = (
462 self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
464 let ai = self.tcx.associated_item(did);
465 ai.container == ty::TraitContainer(clone_trait)
470 // If this expression had a clone call when suggesting borrowing
471 // we want to suggest removing it because it'd now be unnecessary.
475 if let Ok(src) = sm.span_to_snippet(sugg_sp) {
476 let needs_parens = match expr.kind {
477 // parenthesize if needed (Issue #46756)
478 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
479 // parenthesize borrows of range literals (Issue #54505)
480 _ if is_range_literal(expr) => true,
483 let sugg_expr = if needs_parens { format!("({})", src) } else { src };
485 if let Some(sugg) = self.can_use_as_ref(expr) {
490 Applicability::MachineApplicable,
493 let field_name = if is_struct_pat_shorthand_field {
494 format!("{}: ", sugg_expr)
498 if let Some(hir::Node::Expr(hir::Expr {
499 kind: hir::ExprKind::Assign(left_expr, ..),
501 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
503 if mutability == hir::Mutability::Mut {
504 // Found the following case:
505 // fn foo(opt: &mut Option<String>){ opt = None }
508 // consider dereferencing here: `*opt` |
509 // expected mutable reference, found enum `Option`
510 if let Ok(src) = sm.span_to_snippet(left_expr.span) {
513 "consider dereferencing here to assign to the mutable \
514 borrowed piece of memory",
516 Applicability::MachineApplicable,
522 return Some(match mutability {
523 hir::Mutability::Mut => (
525 "consider mutably borrowing here",
526 format!("{}&mut {}", field_name, sugg_expr),
527 Applicability::MachineApplicable,
529 hir::Mutability::Not => (
531 "consider borrowing here",
532 format!("{}&{}", field_name, sugg_expr),
533 Applicability::MachineApplicable,
540 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
542 &ty::Ref(_, checked, _),
544 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
547 // We have `&T`, check if what was expected was `T`. If so,
548 // we may want to suggest removing a `&`.
549 if sm.is_imported(expr.span) {
550 if let Ok(src) = sm.span_to_snippet(sp) {
551 if let Some(src) = src.strip_prefix('&') {
554 "consider removing the borrow",
556 Applicability::MachineApplicable,
562 if let Ok(code) = sm.span_to_snippet(expr.span) {
565 "consider removing the borrow",
567 Applicability::MachineApplicable,
573 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
574 &ty::Ref(_, ty_a, mutbl_a),
576 if let Some(steps) = self.deref_steps(ty_a, ty_b) {
577 // Only suggest valid if dereferencing needed.
579 // The pointer type implements `Copy` trait so the suggestion is always valid.
580 if let Ok(src) = sm.span_to_snippet(sp) {
581 let derefs = &"*".repeat(steps);
582 if let Some((src, applicability)) = match mutbl_b {
583 hir::Mutability::Mut => {
584 let new_prefix = "&mut ".to_owned() + derefs;
586 hir::Mutability::Mut => self
587 .replace_prefix(&src, "&mut ", &new_prefix)
588 .map(|s| (s, Applicability::MachineApplicable)),
589 hir::Mutability::Not => self
590 .replace_prefix(&src, "&", &new_prefix)
591 .map(|s| (s, Applicability::Unspecified)),
594 hir::Mutability::Not => {
595 let new_prefix = "&".to_owned() + derefs;
597 hir::Mutability::Mut => self
598 .replace_prefix(&src, "&mut ", &new_prefix)
599 .map(|s| (s, Applicability::MachineApplicable)),
600 hir::Mutability::Not => self
601 .replace_prefix(&src, "&", &new_prefix)
602 .map(|s| (s, Applicability::MachineApplicable)),
606 return Some((sp, "consider dereferencing", src, applicability));
612 _ if sp == expr.span && !is_macro => {
613 if let Some(steps) = self.deref_steps(checked_ty, expected) {
615 // For a suggestion to make sense, the type would need to be `Copy`.
616 if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp) {
617 if let Ok(code) = sm.span_to_snippet(sp) {
618 let message = if checked_ty.is_region_ptr() {
619 "consider dereferencing the borrow"
621 "consider dereferencing the type"
623 let suggestion = if is_struct_pat_shorthand_field {
624 format!("{}: *{}", code, code)
632 Applicability::MachineApplicable,
644 pub fn check_for_cast(
646 err: &mut DiagnosticBuilder<'_>,
647 expr: &hir::Expr<'_>,
648 checked_ty: Ty<'tcx>,
649 expected_ty: Ty<'tcx>,
650 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
652 if self.tcx.sess.source_map().is_imported(expr.span) {
653 // Ignore if span is from within a macro.
657 let src = if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
663 // If casting this expression to a given numeric type would be appropriate in case of a type
666 // We want to minimize the amount of casting operations that are suggested, as it can be a
667 // lossy operation with potentially bad side effects, so we only suggest when encountering
668 // an expression that indicates that the original type couldn't be directly changed.
670 // For now, don't suggest casting with `as`.
671 let can_cast = false;
673 let prefix = if let Some(hir::Node::Expr(hir::Expr {
674 kind: hir::ExprKind::Struct(_, fields, _),
676 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
678 // `expr` is a literal field for a struct, only suggest if appropriate
681 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
683 // This is a field literal
684 Some(field) => format!("{}: ", field.ident),
685 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
686 None => return false,
692 if let hir::ExprKind::Call(path, args) = &expr.kind {
693 if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
694 (&path.kind, args.len())
696 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
697 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
698 (&base_ty.kind, path_segment.ident.name)
700 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
714 if base_ty_path.segments.len() == 1 =>
726 "you can convert {} `{}` to {} `{}`",
727 checked_ty.kind().article(),
729 expected_ty.kind().article(),
732 let cast_msg = format!(
733 "you can cast {} `{}` to {} `{}`",
734 checked_ty.kind().article(),
736 expected_ty.kind().article(),
739 let lit_msg = format!(
740 "change the type of the numeric literal from `{}` to `{}`",
741 checked_ty, expected_ty,
744 let with_opt_paren: fn(&dyn fmt::Display) -> String =
745 if expr.precedence().order() < PREC_POSTFIX {
746 |s| format!("({})", s)
751 let cast_suggestion = format!("{}{} as {}", prefix, with_opt_paren(&src), expected_ty);
752 let into_suggestion = format!("{}{}.into()", prefix, with_opt_paren(&src));
753 let suffix_suggestion = with_opt_paren(&format_args!(
756 (&expected_ty.kind(), &checked_ty.kind()),
757 (ty::Int(_) | ty::Uint(_), ty::Float(_))
759 // Remove fractional part from literal, for example `42.0f32` into `42`
760 let src = src.trim_end_matches(&checked_ty.to_string());
761 src.split('.').next().unwrap()
763 src.trim_end_matches(&checked_ty.to_string())
767 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
768 if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
770 let is_negative_int =
771 |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::UnNeg, ..));
772 let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
774 let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
776 let suggest_fallible_into_or_lhs_from =
777 |err: &mut DiagnosticBuilder<'_>, exp_to_found_is_fallible: bool| {
778 // If we know the expression the expected type is derived from, we might be able
779 // to suggest a widening conversion rather than a narrowing one (which may
780 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
782 // can be given the suggestion "u32::from(x) > y" rather than
783 // "x > y.try_into().unwrap()".
784 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
788 .span_to_snippet(expr.span)
790 .map(|src| (expr, src))
792 let (span, msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
793 (lhs_expr_and_src, exp_to_found_is_fallible)
796 "you can convert `{}` from `{}` to `{}`, matching the type of `{}`",
797 lhs_src, expected_ty, checked_ty, src
799 let suggestion = format!("{}::from({})", checked_ty, lhs_src);
800 (lhs_expr.span, msg, suggestion)
802 let msg = format!("{} and panic if the converted value doesn't fit", msg);
804 format!("{}{}.try_into().unwrap()", prefix, with_opt_paren(&src));
805 (expr.span, msg, suggestion)
807 err.span_suggestion(span, &msg, suggestion, Applicability::MachineApplicable);
810 let suggest_to_change_suffix_or_into =
811 |err: &mut DiagnosticBuilder<'_>,
812 found_to_exp_is_fallible: bool,
813 exp_to_found_is_fallible: bool| {
814 let always_fallible = found_to_exp_is_fallible
815 && (exp_to_found_is_fallible || expected_ty_expr.is_none());
816 let msg = if literal_is_ty_suffixed(expr) {
818 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
819 // We now know that converting either the lhs or rhs is fallible. Before we
820 // suggest a fallible conversion, check if the value can never fit in the
822 let msg = format!("`{}` cannot fit into type `{}`", src, expected_ty);
825 } else if in_const_context {
826 // Do not recommend `into` or `try_into` in const contexts.
828 } else if found_to_exp_is_fallible {
829 return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
833 let suggestion = if literal_is_ty_suffixed(expr) {
834 suffix_suggestion.clone()
836 into_suggestion.clone()
838 err.span_suggestion(expr.span, msg, suggestion, Applicability::MachineApplicable);
841 match (&expected_ty.kind(), &checked_ty.kind()) {
842 (&ty::Int(ref exp), &ty::Int(ref found)) => {
843 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
845 (Some(exp), Some(found)) if exp < found => (true, false),
846 (Some(exp), Some(found)) if exp > found => (false, true),
847 (None, Some(8 | 16)) => (false, true),
848 (Some(8 | 16), None) => (true, false),
849 (None, _) | (_, None) => (true, true),
852 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
855 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
856 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
858 (Some(exp), Some(found)) if exp < found => (true, false),
859 (Some(exp), Some(found)) if exp > found => (false, true),
860 (None, Some(8 | 16)) => (false, true),
861 (Some(8 | 16), None) => (true, false),
862 (None, _) | (_, None) => (true, true),
865 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
868 (&ty::Int(exp), &ty::Uint(found)) => {
869 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
871 (Some(exp), Some(found)) if found < exp => (false, true),
872 (None, Some(8)) => (false, true),
875 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
878 (&ty::Uint(exp), &ty::Int(found)) => {
879 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
881 (Some(exp), Some(found)) if found > exp => (true, false),
882 (Some(8), None) => (true, false),
885 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
888 (&ty::Float(ref exp), &ty::Float(ref found)) => {
889 if found.bit_width() < exp.bit_width() {
890 suggest_to_change_suffix_or_into(err, false, true);
891 } else if literal_is_ty_suffixed(expr) {
896 Applicability::MachineApplicable,
899 // Missing try_into implementation for `f64` to `f32`
902 &format!("{}, producing the closest possible value", cast_msg),
904 Applicability::MaybeIncorrect, // lossy conversion
909 (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
910 if literal_is_ty_suffixed(expr) {
915 Applicability::MachineApplicable,
918 // Missing try_into implementation for `{float}` to `{integer}`
921 &format!("{}, rounding the float towards zero", msg),
923 Applicability::MaybeIncorrect, // lossy conversion
928 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
929 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
930 if exp.bit_width() > found.bit_width().unwrap_or(256) {
934 "{}, producing the floating point representation of the integer",
938 Applicability::MachineApplicable,
940 } else if literal_is_ty_suffixed(expr) {
945 Applicability::MachineApplicable,
948 // Missing try_into implementation for `{integer}` to `{float}`
952 "{}, producing the floating point representation of the integer,
953 rounded if necessary",
957 Applicability::MaybeIncorrect, // lossy conversion
962 (&ty::Float(ref exp), &ty::Int(ref found)) => {
963 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
964 if exp.bit_width() > found.bit_width().unwrap_or(256) {
968 "{}, producing the floating point representation of the integer",
972 Applicability::MachineApplicable,
974 } else if literal_is_ty_suffixed(expr) {
979 Applicability::MachineApplicable,
982 // Missing try_into implementation for `{integer}` to `{float}`
986 "{}, producing the floating point representation of the integer, \
987 rounded if necessary",
991 Applicability::MaybeIncorrect, // lossy conversion