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_await(err, expr, expected, expr_ty);
37 self.suggest_missing_parentheses(err, expr);
38 self.note_need_for_fn_pointer(err, expected, expr_ty);
39 self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
42 // Requires that the two types unify, and prints an error message if
44 pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
45 if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
50 pub fn demand_suptype_diag(
55 ) -> Option<DiagnosticBuilder<'tcx>> {
56 self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
59 pub fn demand_suptype_with_origin(
61 cause: &ObligationCause<'tcx>,
64 ) -> Option<DiagnosticBuilder<'tcx>> {
65 match self.at(cause, self.param_env).sup(expected, actual) {
66 Ok(InferOk { obligations, value: () }) => {
67 self.register_predicates(obligations);
70 Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
74 pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
75 if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
80 pub fn demand_eqtype_diag(
85 ) -> Option<DiagnosticBuilder<'tcx>> {
86 self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
89 pub fn demand_eqtype_with_origin(
91 cause: &ObligationCause<'tcx>,
94 ) -> Option<DiagnosticBuilder<'tcx>> {
95 match self.at(cause, self.param_env).eq(expected, actual) {
96 Ok(InferOk { obligations, value: () }) => {
97 self.register_predicates(obligations);
100 Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
104 pub fn demand_coerce(
106 expr: &hir::Expr<'_>,
107 checked_ty: Ty<'tcx>,
109 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
110 allow_two_phase: AllowTwoPhase,
113 self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
114 if let Some(mut err) = err {
120 // Checks that the type of `expr` can be coerced to `expected`.
122 // N.B., this code relies on `self.diverges` to be accurate. In
123 // particular, assignments to `!` will be permitted if the
124 // diverges flag is currently "always".
125 pub fn demand_coerce_diag(
127 expr: &hir::Expr<'_>,
128 checked_ty: Ty<'tcx>,
130 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
131 allow_two_phase: AllowTwoPhase,
132 ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
133 let expected = self.resolve_vars_with_obligations(expected);
135 let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
136 Ok(ty) => return (ty, None),
140 let expr = expr.peel_drop_temps();
141 let cause = self.misc(expr.span);
142 let expr_ty = self.resolve_vars_with_obligations(checked_ty);
143 let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
145 if self.is_assign_to_bool(expr, expected) {
146 // Error reported in `check_assign` so avoid emitting error again.
148 return (expected, None);
151 self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr);
153 (expected, Some(err))
156 fn annotate_expected_due_to_let_ty(
158 err: &mut DiagnosticBuilder<'_>,
159 expr: &hir::Expr<'_>,
161 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
162 if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
163 self.tcx.hir().find(parent)
165 if init.hir_id == expr.hir_id {
166 // Point at `let` assignment type.
167 err.span_label(ty.span, "expected due to this");
172 /// Returns whether the expected type is `bool` and the expression is `x = y`.
173 pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
174 if let hir::ExprKind::Assign(..) = expr.kind {
175 return expected == self.tcx.types.bool;
180 /// If the expected type is an enum (Issue #55250) with any variants whose
181 /// sole field is of the found type, suggest such variants. (Issue #42764)
182 fn suggest_compatible_variants(
184 err: &mut DiagnosticBuilder<'_>,
185 expr: &hir::Expr<'_>,
189 if let ty::Adt(expected_adt, substs) = expected.kind() {
190 if !expected_adt.is_enum() {
194 let mut compatible_variants = expected_adt
197 .filter(|variant| variant.fields.len() == 1)
198 .filter_map(|variant| {
199 let sole_field = &variant.fields[0];
200 let sole_field_ty = sole_field.ty(self.tcx, substs);
201 if self.can_coerce(expr_ty, sole_field_ty) {
202 let variant_path = self.tcx.def_path_str(variant.def_id);
203 // FIXME #56861: DRYer prelude filtering
204 Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
211 if compatible_variants.peek().is_some() {
212 if let Ok(expr_text) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
213 let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
214 let msg = "try using a variant of the expected enum";
215 err.span_suggestions(
219 Applicability::MaybeIncorrect,
226 pub fn get_conversion_methods(
230 checked_ty: Ty<'tcx>,
232 ) -> Vec<AssocItem> {
234 self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
236 self.has_only_self_parameter(m)
241 // This special internal attribute is used to permit
242 // "identity-like" conversion methods to be suggested here.
244 // FIXME (#46459 and #46460): ideally
245 // `std::convert::Into::into` and `std::borrow:ToOwned` would
246 // also be `#[rustc_conversion_suggestion]`, if not for
247 // method-probing false-positives and -negatives (respectively).
249 // FIXME? Other potential candidate methods: `as_ref` and
251 .any(|a| self.sess().check_name(a, sym::rustc_conversion_suggestion))
257 /// This function checks whether the method is not static and does not accept other parameters than `self`.
258 fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
260 ty::AssocKind::Fn => {
261 method.fn_has_self_parameter
262 && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
268 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
270 /// Given the following code:
273 /// fn takes_ref(_: &Foo) {}
274 /// let ref opt = Some(Foo);
276 /// opt.map(|param| takes_ref(param));
278 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
280 /// It only checks for `Option` and `Result` and won't work with
282 /// opt.map(|param| { takes_ref(param) });
284 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
285 let path = match expr.kind {
286 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
290 let local_id = match path.res {
291 hir::def::Res::Local(id) => id,
295 let local_parent = self.tcx.hir().get_parent_node(local_id);
296 let param_hir_id = match self.tcx.hir().find(local_parent) {
297 Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
301 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
302 let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
303 Some(Node::Expr(hir::Expr {
305 kind: hir::ExprKind::Closure(_, decl, ..),
307 })) => (hir_id, decl),
311 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
312 let hir = self.tcx.hir().find(expr_parent);
313 let closure_params_len = closure_fn_decl.inputs.len();
314 let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
316 Some(Node::Expr(hir::Expr {
317 kind: hir::ExprKind::MethodCall(path, span, expr, _),
321 ) => (path, span, expr),
325 let self_ty = self.typeck_results.borrow().node_type(method_expr[0].hir_id);
326 let self_ty = format!("{:?}", self_ty);
327 let name = method_path.ident.name;
328 let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
329 || self_ty.starts_with("&std::result::Result")
330 || self_ty.starts_with("std::option::Option")
331 || self_ty.starts_with("std::result::Result"))
332 && (name == sym::map || name == sym::and_then);
333 match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
335 let suggestion = format!("as_ref().{}", src);
336 Some((*method_span, "consider using `as_ref` instead", suggestion))
342 crate fn is_hir_id_from_struct_pattern_shorthand_field(
347 let sm = self.sess().source_map();
348 let parent_id = self.tcx.hir().get_parent_node(hir_id);
349 if let Some(parent) = self.tcx.hir().find(parent_id) {
350 // Account for fields
351 if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
353 if let Ok(src) = sm.span_to_snippet(sp) {
354 for field in *fields {
355 if field.ident.as_str() == src && field.is_shorthand {
365 fn replace_prefix<A, B, C>(&self, s: A, old: B, new: C) -> Option<String>
372 let old = old.as_ref();
373 if let Some(stripped) = s.strip_prefix(old) {
374 Some(new.as_ref().to_owned() + stripped)
380 /// This function is used to determine potential "simple" improvements or users' errors and
381 /// provide them useful help. For example:
384 /// fn some_fn(s: &str) {}
386 /// let x = "hey!".to_owned();
387 /// some_fn(x); // error
390 /// No need to find every potential function which could make a coercion to transform a
391 /// `String` into a `&str` since a `&` would do the trick!
393 /// In addition of this check, it also checks between references mutability state. If the
394 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
398 expr: &hir::Expr<'_>,
399 checked_ty: Ty<'tcx>,
401 ) -> Option<(Span, &'static str, String, Applicability)> {
402 let sm = self.sess().source_map();
404 if sm.is_imported(sp) {
405 // Ignore if span is from within a macro #41858, #58298. We previously used the macro
406 // call span, but that breaks down when the type error comes from multiple calls down.
410 let is_struct_pat_shorthand_field =
411 self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
413 // If the span is from a macro, then it's hard to extract the text
414 // and make a good suggestion, so don't bother.
415 let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
417 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
418 let expr = expr.peel_drop_temps();
420 match (&expr.kind, expected.kind(), checked_ty.kind()) {
421 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
422 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
423 if let hir::ExprKind::Lit(_) = expr.kind {
424 if let Ok(src) = sm.span_to_snippet(sp) {
425 if let Some(src) = self.replace_prefix(src, "b\"", "\"") {
428 "consider removing the leading `b`",
430 Applicability::MachineApplicable,
436 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
437 if let hir::ExprKind::Lit(_) = expr.kind {
438 if let Ok(src) = sm.span_to_snippet(sp) {
439 if let Some(src) = self.replace_prefix(src, "\"", "b\"") {
442 "consider adding a leading `b`",
444 Applicability::MachineApplicable,
452 (_, &ty::Ref(_, _, mutability), _) => {
453 // Check if it can work when put into a ref. For example:
456 // fn bar(x: &mut i32) {}
459 // bar(&x); // error, expected &mut
461 let ref_ty = match mutability {
462 hir::Mutability::Mut => {
463 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
465 hir::Mutability::Not => {
466 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
469 if self.can_coerce(ref_ty, expected) {
470 let mut sugg_sp = sp;
471 if let hir::ExprKind::MethodCall(ref segment, sp, ref args, _) = expr.kind {
472 let clone_trait = self.tcx.require_lang_item(LangItem::Clone, Some(sp));
473 if let ([arg], Some(true), sym::clone) = (
475 self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
477 let ai = self.tcx.associated_item(did);
478 ai.container == ty::TraitContainer(clone_trait)
483 // If this expression had a clone call when suggesting borrowing
484 // we want to suggest removing it because it'd now be unnecessary.
488 if let Ok(src) = sm.span_to_snippet(sugg_sp) {
489 let needs_parens = match expr.kind {
490 // parenthesize if needed (Issue #46756)
491 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
492 // parenthesize borrows of range literals (Issue #54505)
493 _ if is_range_literal(expr) => true,
496 let sugg_expr = if needs_parens { format!("({})", src) } else { src };
498 if let Some(sugg) = self.can_use_as_ref(expr) {
503 Applicability::MachineApplicable,
506 let field_name = if is_struct_pat_shorthand_field {
507 format!("{}: ", sugg_expr)
511 if let Some(hir::Node::Expr(hir::Expr {
512 kind: hir::ExprKind::Assign(left_expr, ..),
514 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
516 if mutability == hir::Mutability::Mut {
517 // Found the following case:
518 // fn foo(opt: &mut Option<String>){ opt = None }
521 // consider dereferencing here: `*opt` |
522 // expected mutable reference, found enum `Option`
523 if let Ok(src) = sm.span_to_snippet(left_expr.span) {
526 "consider dereferencing here to assign to the mutable \
527 borrowed piece of memory",
529 Applicability::MachineApplicable,
535 return Some(match mutability {
536 hir::Mutability::Mut => (
538 "consider mutably borrowing here",
539 format!("{}&mut {}", field_name, sugg_expr),
540 Applicability::MachineApplicable,
542 hir::Mutability::Not => (
544 "consider borrowing here",
545 format!("{}&{}", field_name, sugg_expr),
546 Applicability::MachineApplicable,
553 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
555 &ty::Ref(_, checked, _),
557 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
560 // We have `&T`, check if what was expected was `T`. If so,
561 // we may want to suggest removing a `&`.
562 if sm.is_imported(expr.span) {
563 if let Ok(src) = sm.span_to_snippet(sp) {
564 if let Some(src) = self.replace_prefix(src, "&", "") {
567 "consider removing the borrow",
569 Applicability::MachineApplicable,
575 if let Ok(code) = sm.span_to_snippet(expr.span) {
578 "consider removing the borrow",
580 Applicability::MachineApplicable,
586 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
587 &ty::Ref(_, ty_a, mutbl_a),
589 if let Some(steps) = self.deref_steps(ty_a, ty_b) {
590 // Only suggest valid if dereferencing needed.
592 // The pointer type implements `Copy` trait so the suggestion is always valid.
593 if let Ok(src) = sm.span_to_snippet(sp) {
594 let derefs = &"*".repeat(steps);
595 if let Some((src, applicability)) = match mutbl_b {
596 hir::Mutability::Mut => {
597 let new_prefix = "&mut ".to_owned() + derefs;
599 hir::Mutability::Mut => {
601 self.replace_prefix(src, "&mut ", new_prefix)
603 Some((s, Applicability::MachineApplicable))
608 hir::Mutability::Not => {
610 self.replace_prefix(src, "&", new_prefix)
612 Some((s, Applicability::Unspecified))
619 hir::Mutability::Not => {
620 let new_prefix = "&".to_owned() + derefs;
622 hir::Mutability::Mut => {
624 self.replace_prefix(src, "&mut ", new_prefix)
626 Some((s, Applicability::MachineApplicable))
631 hir::Mutability::Not => {
633 self.replace_prefix(src, "&", new_prefix)
635 Some((s, Applicability::MachineApplicable))
643 return Some((sp, "consider dereferencing", src, applicability));
649 _ if sp == expr.span && !is_macro => {
650 if let Some(steps) = self.deref_steps(checked_ty, expected) {
652 // For a suggestion to make sense, the type would need to be `Copy`.
653 if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp) {
654 if let Ok(code) = sm.span_to_snippet(sp) {
655 let message = if checked_ty.is_region_ptr() {
656 "consider dereferencing the borrow"
658 "consider dereferencing the type"
660 let suggestion = if is_struct_pat_shorthand_field {
661 format!("{}: *{}", code, code)
669 Applicability::MachineApplicable,
681 pub fn check_for_cast(
683 err: &mut DiagnosticBuilder<'_>,
684 expr: &hir::Expr<'_>,
685 checked_ty: Ty<'tcx>,
686 expected_ty: Ty<'tcx>,
687 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
689 if self.tcx.sess.source_map().is_imported(expr.span) {
690 // Ignore if span is from within a macro.
694 let src = if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
700 // If casting this expression to a given numeric type would be appropriate in case of a type
703 // We want to minimize the amount of casting operations that are suggested, as it can be a
704 // lossy operation with potentially bad side effects, so we only suggest when encountering
705 // an expression that indicates that the original type couldn't be directly changed.
707 // For now, don't suggest casting with `as`.
708 let can_cast = false;
710 let prefix = if let Some(hir::Node::Expr(hir::Expr {
711 kind: hir::ExprKind::Struct(_, fields, _),
713 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
715 // `expr` is a literal field for a struct, only suggest if appropriate
718 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
720 // This is a field literal
721 Some(field) => format!("{}: ", field.ident),
722 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
723 None => return false,
729 if let hir::ExprKind::Call(path, args) = &expr.kind {
730 if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
731 (&path.kind, args.len())
733 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
734 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
735 (&base_ty.kind, path_segment.ident.name)
737 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
751 if base_ty_path.segments.len() == 1 =>
762 let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
763 let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
764 let lit_msg = format!(
765 "change the type of the numeric literal from `{}` to `{}`",
766 checked_ty, expected_ty,
769 let with_opt_paren: fn(&dyn fmt::Display) -> String =
770 if expr.precedence().order() < PREC_POSTFIX {
771 |s| format!("({})", s)
776 let cast_suggestion = format!("{}{} as {}", prefix, with_opt_paren(&src), expected_ty);
777 let into_suggestion = format!("{}{}.into()", prefix, with_opt_paren(&src));
778 let suffix_suggestion = with_opt_paren(&format_args!(
781 (&expected_ty.kind(), &checked_ty.kind()),
782 (ty::Int(_) | ty::Uint(_), ty::Float(_))
784 // Remove fractional part from literal, for example `42.0f32` into `42`
785 let src = src.trim_end_matches(&checked_ty.to_string());
786 src.split('.').next().unwrap()
788 src.trim_end_matches(&checked_ty.to_string())
792 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
793 if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
795 let is_negative_int =
796 |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::UnNeg, ..));
797 let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
799 let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
801 let suggest_fallible_into_or_lhs_from =
802 |err: &mut DiagnosticBuilder<'_>, exp_to_found_is_fallible: bool| {
803 // If we know the expression the expected type is derived from, we might be able
804 // to suggest a widening conversion rather than a narrowing one (which may
805 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
807 // can be given the suggestion "u32::from(x) > y" rather than
808 // "x > y.try_into().unwrap()".
809 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
810 match self.tcx.sess.source_map().span_to_snippet(expr.span).ok() {
811 Some(src) => Some((expr, src)),
815 let (span, msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
816 (lhs_expr_and_src, exp_to_found_is_fallible)
819 "you can convert `{}` from `{}` to `{}`, matching the type of `{}`",
820 lhs_src, expected_ty, checked_ty, src
822 let suggestion = format!("{}::from({})", checked_ty, lhs_src);
823 (lhs_expr.span, msg, suggestion)
825 let msg = format!("{} and panic if the converted value wouldn't fit", msg);
827 format!("{}{}.try_into().unwrap()", prefix, with_opt_paren(&src));
828 (expr.span, msg, suggestion)
830 err.span_suggestion(span, &msg, suggestion, Applicability::MachineApplicable);
833 let suggest_to_change_suffix_or_into =
834 |err: &mut DiagnosticBuilder<'_>,
835 found_to_exp_is_fallible: bool,
836 exp_to_found_is_fallible: bool| {
837 let always_fallible = found_to_exp_is_fallible
838 && (exp_to_found_is_fallible || expected_ty_expr.is_none());
839 let msg = if literal_is_ty_suffixed(expr) {
841 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
842 // We now know that converting either the lhs or rhs is fallible. Before we
843 // suggest a fallible conversion, check if the value can never fit in the
845 let msg = format!("`{}` cannot fit into type `{}`", src, expected_ty);
848 } else if in_const_context {
849 // Do not recommend `into` or `try_into` in const contexts.
851 } else if found_to_exp_is_fallible {
852 return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
856 let suggestion = if literal_is_ty_suffixed(expr) {
857 suffix_suggestion.clone()
859 into_suggestion.clone()
861 err.span_suggestion(expr.span, msg, suggestion, Applicability::MachineApplicable);
864 match (&expected_ty.kind(), &checked_ty.kind()) {
865 (&ty::Int(ref exp), &ty::Int(ref found)) => {
866 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
868 (Some(exp), Some(found)) if exp < found => (true, false),
869 (Some(exp), Some(found)) if exp > found => (false, true),
870 (None, Some(8 | 16)) => (false, true),
871 (Some(8 | 16), None) => (true, false),
872 (None, _) | (_, None) => (true, true),
875 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
878 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
879 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
881 (Some(exp), Some(found)) if exp < found => (true, false),
882 (Some(exp), Some(found)) if exp > found => (false, true),
883 (None, Some(8 | 16)) => (false, true),
884 (Some(8 | 16), None) => (true, false),
885 (None, _) | (_, None) => (true, true),
888 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
891 (&ty::Int(exp), &ty::Uint(found)) => {
892 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
894 (Some(exp), Some(found)) if found < exp => (false, true),
895 (None, Some(8)) => (false, true),
898 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
901 (&ty::Uint(exp), &ty::Int(found)) => {
902 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
904 (Some(exp), Some(found)) if found > exp => (true, false),
905 (Some(8), None) => (true, false),
908 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
911 (&ty::Float(ref exp), &ty::Float(ref found)) => {
912 if found.bit_width() < exp.bit_width() {
913 suggest_to_change_suffix_or_into(err, false, true);
914 } else if literal_is_ty_suffixed(expr) {
919 Applicability::MachineApplicable,
922 // Missing try_into implementation for `f64` to `f32`
925 &format!("{}, producing the closest possible value", cast_msg),
927 Applicability::MaybeIncorrect, // lossy conversion
932 (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
933 if literal_is_ty_suffixed(expr) {
938 Applicability::MachineApplicable,
941 // Missing try_into implementation for `{float}` to `{integer}`
944 &format!("{}, rounding the float towards zero", msg),
946 Applicability::MaybeIncorrect, // lossy conversion
951 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
952 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
953 if exp.bit_width() > found.bit_width().unwrap_or(256) {
957 "{}, producing the floating point representation of the integer",
961 Applicability::MachineApplicable,
963 } else if literal_is_ty_suffixed(expr) {
968 Applicability::MachineApplicable,
971 // Missing try_into implementation for `{integer}` to `{float}`
975 "{}, producing the floating point representation of the integer,
976 rounded if necessary",
980 Applicability::MaybeIncorrect, // lossy conversion
985 (&ty::Float(ref exp), &ty::Int(ref found)) => {
986 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
987 if exp.bit_width() > found.bit_width().unwrap_or(256) {
991 "{}, producing the floating point representation of the integer",
995 Applicability::MachineApplicable,
997 } else if literal_is_ty_suffixed(expr) {
1002 Applicability::MachineApplicable,
1005 // Missing try_into implementation for `{integer}` to `{float}`
1006 err.span_suggestion(
1009 "{}, producing the floating point representation of the integer, \
1010 rounded if necessary",
1014 Applicability::MaybeIncorrect, // lossy conversion