2 use rustc_ast::util::parser::PREC_POSTFIX;
3 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
5 use rustc_hir::lang_items::LangItem;
6 use rustc_hir::{is_range_literal, Node};
7 use rustc_infer::infer::InferOk;
8 use rustc_middle::lint::in_external_macro;
9 use rustc_middle::middle::stability::EvalResult;
10 use rustc_middle::ty::adjustment::AllowTwoPhase;
11 use rustc_middle::ty::error::{ExpectedFound, TypeError};
12 use rustc_middle::ty::print::with_no_trimmed_paths;
13 use rustc_middle::ty::{self, Article, AssocItem, Ty, TypeAndMut};
14 use rustc_span::symbol::{sym, Symbol};
15 use rustc_span::{BytePos, Span};
16 use rustc_trait_selection::infer::InferCtxtExt as _;
17 use rustc_trait_selection::traits::ObligationCause;
19 use super::method::probe;
23 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
24 pub fn emit_coerce_suggestions(
27 expr: &hir::Expr<'tcx>,
30 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
31 error: Option<TypeError<'tcx>>,
33 self.annotate_expected_due_to_let_ty(err, expr, error);
35 // Use `||` to give these suggestions a precedence
36 let _ = self.suggest_missing_parentheses(err, expr)
37 || self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr)
38 || self.suggest_compatible_variants(err, expr, expected, expr_ty)
39 || self.suggest_non_zero_new_unwrap(err, expr, expected, expr_ty)
40 || self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty)
41 || self.suggest_no_capture_closure(err, expected, expr_ty)
42 || self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty)
43 || self.suggest_block_to_brackets_peeling_refs(err, expr, expr_ty, expected)
44 || self.suggest_copied_or_cloned(err, expr, expr_ty, expected)
45 || self.suggest_into(err, expr, expr_ty, expected);
47 self.note_type_is_not_clone(err, expected, expr_ty, expr);
48 self.note_need_for_fn_pointer(err, expected, expr_ty);
49 self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
52 // Requires that the two types unify, and prints an error message if
54 pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
55 if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
60 pub fn demand_suptype_diag(
65 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
66 self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
69 #[instrument(skip(self), level = "debug")]
70 pub fn demand_suptype_with_origin(
72 cause: &ObligationCause<'tcx>,
75 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
76 match self.at(cause, self.param_env).sup(expected, actual) {
77 Ok(InferOk { obligations, value: () }) => {
78 self.register_predicates(obligations);
81 Err(e) => Some(self.err_ctxt().report_mismatched_types(&cause, expected, actual, e)),
85 pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
86 if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
91 pub fn demand_eqtype_diag(
96 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
97 self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
100 pub fn demand_eqtype_with_origin(
102 cause: &ObligationCause<'tcx>,
105 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
106 match self.at(cause, self.param_env).eq(expected, actual) {
107 Ok(InferOk { obligations, value: () }) => {
108 self.register_predicates(obligations);
111 Err(e) => Some(self.err_ctxt().report_mismatched_types(cause, expected, actual, e)),
115 pub fn demand_coerce(
117 expr: &hir::Expr<'tcx>,
118 checked_ty: Ty<'tcx>,
120 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
121 allow_two_phase: AllowTwoPhase,
124 self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
125 if let Some(mut err) = err {
131 /// Checks that the type of `expr` can be coerced to `expected`.
133 /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
134 /// will be permitted if the diverges flag is currently "always".
135 #[instrument(level = "debug", skip(self, expr, expected_ty_expr, allow_two_phase))]
136 pub fn demand_coerce_diag(
138 expr: &hir::Expr<'tcx>,
139 checked_ty: Ty<'tcx>,
141 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
142 allow_two_phase: AllowTwoPhase,
143 ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>) {
144 let expected = self.resolve_vars_with_obligations(expected);
146 let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase, None) {
147 Ok(ty) => return (ty, None),
151 self.set_tainted_by_errors();
152 let expr = expr.peel_drop_temps();
153 let cause = self.misc(expr.span);
154 let expr_ty = self.resolve_vars_with_obligations(checked_ty);
155 let mut err = self.err_ctxt().report_mismatched_types(&cause, expected, expr_ty, e.clone());
157 let is_insufficiently_polymorphic =
158 matches!(e, TypeError::RegionsInsufficientlyPolymorphic(..));
160 // FIXME(#73154): For now, we do leak check when coercing function
161 // pointers in typeck, instead of only during borrowck. This can lead
162 // to these `RegionsInsufficientlyPolymorphic` errors that aren't helpful.
163 if !is_insufficiently_polymorphic {
164 self.emit_coerce_suggestions(
174 (expected, Some(err))
177 fn annotate_expected_due_to_let_ty(
179 err: &mut Diagnostic,
180 expr: &hir::Expr<'_>,
181 error: Option<TypeError<'_>>,
183 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
184 match (self.tcx.hir().find(parent), error) {
185 (Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })), _)
186 if init.hir_id == expr.hir_id =>
188 // Point at `let` assignment type.
189 err.span_label(ty.span, "expected due to this");
192 Some(hir::Node::Expr(hir::Expr {
193 kind: hir::ExprKind::Assign(lhs, rhs, _), ..
195 Some(TypeError::Sorts(ExpectedFound { expected, .. })),
196 ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
197 // We ignore closures explicitly because we already point at them elsewhere.
198 // Point at the assigned-to binding.
199 let mut primary_span = lhs.span;
200 let mut secondary_span = lhs.span;
201 let mut post_message = "";
203 hir::ExprKind::Path(hir::QPath::Resolved(
208 hir::def::DefKind::Static(_) | hir::def::DefKind::Const,
214 if let Some(hir::Node::Item(hir::Item {
216 kind: hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..),
218 })) = self.tcx.hir().get_if_local(*def_id)
220 primary_span = ty.span;
221 secondary_span = ident.span;
222 post_message = " type";
225 hir::ExprKind::Path(hir::QPath::Resolved(
227 hir::Path { res: hir::def::Res::Local(hir_id), .. },
229 if let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(*hir_id) {
230 let parent = self.tcx.hir().get_parent_node(pat.hir_id);
231 primary_span = pat.span;
232 secondary_span = pat.span;
233 match self.tcx.hir().find(parent) {
234 Some(hir::Node::Local(hir::Local { ty: Some(ty), .. })) => {
235 primary_span = ty.span;
236 post_message = " type";
238 Some(hir::Node::Local(hir::Local { init: Some(init), .. })) => {
239 primary_span = init.span;
240 post_message = " value";
242 Some(hir::Node::Param(hir::Param { ty_span, .. })) => {
243 primary_span = *ty_span;
244 post_message = " parameter type";
253 if primary_span != secondary_span
258 .is_multiline(secondary_span.shrink_to_hi().until(primary_span))
260 // We are pointing at the binding's type or initializer value, but it's pattern
261 // is in a different line, so we point at both.
262 err.span_label(secondary_span, "expected due to the type of this binding");
263 err.span_label(primary_span, &format!("expected due to this{post_message}"));
264 } else if post_message == "" {
265 // We are pointing at either the assignment lhs or the binding def pattern.
266 err.span_label(primary_span, "expected due to the type of this binding");
268 // We are pointing at the binding's type or initializer value.
269 err.span_label(primary_span, &format!("expected due to this{post_message}"));
272 if !lhs.is_syntactic_place_expr() {
273 // We already emitted E0070 "invalid left-hand side of assignment", so we
275 err.downgrade_to_delayed_bug();
282 /// If the expected type is an enum (Issue #55250) with any variants whose
283 /// sole field is of the found type, suggest such variants. (Issue #42764)
284 fn suggest_compatible_variants(
286 err: &mut Diagnostic,
287 expr: &hir::Expr<'_>,
291 if let ty::Adt(expected_adt, substs) = expected.kind() {
292 if let hir::ExprKind::Field(base, ident) = expr.kind {
293 let base_ty = self.typeck_results.borrow().expr_ty(base);
294 if self.can_eq(self.param_env, base_ty, expected).is_ok()
295 && let Some(base_span) = base.span.find_ancestor_inside(expr.span)
297 err.span_suggestion_verbose(
298 expr.span.with_lo(base_span.hi()),
299 format!("consider removing the tuple struct field `{ident}`"),
301 Applicability::MaybeIncorrect,
307 // If the expression is of type () and it's the return expression of a block,
308 // we suggest adding a separate return expression instead.
309 // (To avoid things like suggesting `Ok(while .. { .. })`.)
310 if expr_ty.is_unit() {
311 let mut id = expr.hir_id;
314 // Unroll desugaring, to make sure this works for `for` loops etc.
316 parent = self.tcx.hir().get_parent_node(id);
317 if let Some(parent_span) = self.tcx.hir().opt_span(parent) {
318 if parent_span.find_ancestor_inside(expr.span).is_some() {
319 // The parent node is part of the same span, so is the result of the
320 // same expansion/desugaring and not the 'real' parent node.
328 if let Some(hir::Node::Block(&hir::Block {
329 span: block_span, expr: Some(e), ..
330 })) = self.tcx.hir().find(parent)
333 if let Some(span) = expr.span.find_ancestor_inside(block_span) {
334 let return_suggestions = if self
336 .is_diagnostic_item(sym::Result, expected_adt.did())
339 } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did()) {
340 vec!["None", "Some(())"]
344 if let Some(indent) =
345 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
347 // Add a semicolon, except after `}`.
349 match self.tcx.sess.source_map().span_to_snippet(span) {
350 Ok(s) if s.ends_with('}') => "",
353 err.span_suggestions(
355 "try adding an expression at the end of the block",
358 .map(|r| format!("{semicolon}\n{indent}{r}")),
359 Applicability::MaybeIncorrect,
368 let compatible_variants: Vec<(String, _, _, Option<String>)> = expected_adt
372 variant.fields.len() == 1
374 .filter_map(|variant| {
375 let sole_field = &variant.fields[0];
377 let field_is_local = sole_field.did.is_local();
378 let field_is_accessible =
379 sole_field.vis.is_accessible_from(expr.hir_id.owner.def_id, self.tcx)
380 // Skip suggestions for unstable public fields (for example `Pin::pointer`)
381 && matches!(self.tcx.eval_stability(sole_field.did, None, expr.span, None), EvalResult::Allow | EvalResult::Unmarked);
383 if !field_is_local && !field_is_accessible {
387 let note_about_variant_field_privacy = (field_is_local && !field_is_accessible)
388 .then(|| format!(" (its field is private, but it's local to this crate and its privacy can be changed)"));
390 let sole_field_ty = sole_field.ty(self.tcx, substs);
391 if self.can_coerce(expr_ty, sole_field_ty) {
393 with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
394 // FIXME #56861: DRYer prelude filtering
395 if let Some(path) = variant_path.strip_prefix("std::prelude::")
396 && let Some((_, path)) = path.split_once("::")
398 return Some((path.to_string(), variant.ctor_kind, sole_field.name, note_about_variant_field_privacy));
400 Some((variant_path, variant.ctor_kind, sole_field.name, note_about_variant_field_privacy))
407 let suggestions_for = |variant: &_, ctor, field_name| {
408 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
409 Some(ident) => format!("{ident}: "),
410 None => String::new(),
413 let (open, close) = match ctor {
414 hir::def::CtorKind::Fn => ("(".to_owned(), ")"),
415 hir::def::CtorKind::Fictive => (format!(" {{ {field_name}: "), " }"),
417 // unit variants don't have fields
418 hir::def::CtorKind::Const => unreachable!(),
421 // Suggest constructor as deep into the block tree as possible.
422 // This fixes https://github.com/rust-lang/rust/issues/101065,
423 // and also just helps make the most minimal suggestions.
425 while let hir::ExprKind::Block(block, _) = &expr.kind
426 && let Some(expr_) = &block.expr
432 (expr.span.shrink_to_lo(), format!("{prefix}{variant}{open}")),
433 (expr.span.shrink_to_hi(), close.to_owned()),
437 match &compatible_variants[..] {
438 [] => { /* No variants to format */ }
439 [(variant, ctor_kind, field_name, note)] => {
440 // Just a single matching variant.
441 err.multipart_suggestion_verbose(
443 "try wrapping the expression in `{variant}`{note}",
444 note = note.as_deref().unwrap_or("")
446 suggestions_for(&**variant, *ctor_kind, *field_name),
447 Applicability::MaybeIncorrect,
452 // More than one matching variant.
453 err.multipart_suggestions(
455 "try wrapping the expression in a variant of `{}`",
456 self.tcx.def_path_str(expected_adt.did())
458 compatible_variants.into_iter().map(
459 |(variant, ctor_kind, field_name, _)| {
460 suggestions_for(&variant, ctor_kind, field_name)
463 Applicability::MaybeIncorrect,
473 fn suggest_non_zero_new_unwrap(
475 err: &mut Diagnostic,
476 expr: &hir::Expr<'_>,
481 let (adt, unwrap) = match expected.kind() {
482 // In case Option<NonZero*> is wanted, but * is provided, suggest calling new
483 ty::Adt(adt, substs) if tcx.is_diagnostic_item(sym::Option, adt.did()) => {
485 let ty::Adt(adt, _) = substs.type_at(0).kind() else { return false; };
489 // In case NonZero* is wanted, but * is provided also add `.unwrap()` to satisfy types
490 ty::Adt(adt, _) => (adt, ".unwrap()"),
495 (sym::NonZeroU8, tcx.types.u8),
496 (sym::NonZeroU16, tcx.types.u16),
497 (sym::NonZeroU32, tcx.types.u32),
498 (sym::NonZeroU64, tcx.types.u64),
499 (sym::NonZeroU128, tcx.types.u128),
500 (sym::NonZeroI8, tcx.types.i8),
501 (sym::NonZeroI16, tcx.types.i16),
502 (sym::NonZeroI32, tcx.types.i32),
503 (sym::NonZeroI64, tcx.types.i64),
504 (sym::NonZeroI128, tcx.types.i128),
507 let Some((s, _)) = map
509 .find(|&&(s, t)| self.tcx.is_diagnostic_item(s, adt.did()) && self.can_coerce(expr_ty, t))
510 else { return false; };
512 let path = self.tcx.def_path_str(adt.non_enum_variant().def_id);
514 err.multipart_suggestion(
515 format!("consider calling `{s}::new`"),
517 (expr.span.shrink_to_lo(), format!("{path}::new(")),
518 (expr.span.shrink_to_hi(), format!("){unwrap}")),
520 Applicability::MaybeIncorrect,
526 pub fn get_conversion_methods(
530 checked_ty: Ty<'tcx>,
532 ) -> Vec<AssocItem> {
534 self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
536 self.has_only_self_parameter(m)
539 // This special internal attribute is used to permit
540 // "identity-like" conversion methods to be suggested here.
542 // FIXME (#46459 and #46460): ideally
543 // `std::convert::Into::into` and `std::borrow:ToOwned` would
544 // also be `#[rustc_conversion_suggestion]`, if not for
545 // method-probing false-positives and -negatives (respectively).
547 // FIXME? Other potential candidate methods: `as_ref` and
549 .has_attr(m.def_id, sym::rustc_conversion_suggestion)
555 /// This function checks whether the method is not static and does not accept other parameters than `self`.
556 fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
558 ty::AssocKind::Fn => {
559 method.fn_has_self_parameter
560 && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
566 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
568 /// Given the following code:
569 /// ```compile_fail,E0308
571 /// fn takes_ref(_: &Foo) {}
572 /// let ref opt = Some(Foo);
574 /// opt.map(|param| takes_ref(param));
576 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
578 /// It only checks for `Option` and `Result` and won't work with
579 /// ```ignore (illustrative)
580 /// opt.map(|param| { takes_ref(param) });
582 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
583 let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
587 let hir::def::Res::Local(local_id) = path.res else {
591 let local_parent = self.tcx.hir().get_parent_node(local_id);
592 let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
596 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
597 let Some(Node::Expr(hir::Expr {
599 kind: hir::ExprKind::Closure(hir::Closure { fn_decl: closure_fn_decl, .. }),
601 })) = self.tcx.hir().find(param_parent) else {
605 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
606 let hir = self.tcx.hir().find(expr_parent);
607 let closure_params_len = closure_fn_decl.inputs.len();
609 Some(Node::Expr(hir::Expr {
610 kind: hir::ExprKind::MethodCall(method_path, receiver, ..),
614 ) = (hir, closure_params_len) else {
618 let self_ty = self.typeck_results.borrow().expr_ty(receiver);
619 let name = method_path.ident.name;
620 let is_as_ref_able = match self_ty.peel_refs().kind() {
622 (self.tcx.is_diagnostic_item(sym::Option, def.did())
623 || self.tcx.is_diagnostic_item(sym::Result, def.did()))
624 && (name == sym::map || name == sym::and_then)
628 match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
630 let suggestion = format!("as_ref().{}", src);
631 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
637 pub(crate) fn maybe_get_struct_pattern_shorthand_field(
639 expr: &hir::Expr<'_>,
640 ) -> Option<Symbol> {
641 let hir = self.tcx.hir();
642 let local = match expr {
645 hir::ExprKind::Path(hir::QPath::Resolved(
648 res: hir::def::Res::Local(_),
649 segments: [hir::PathSegment { ident, .. }],
658 match hir.find(hir.get_parent_node(expr.hir_id))? {
659 Node::ExprField(field) => {
660 if field.ident.name == local.name && field.is_shorthand {
661 return Some(local.name);
670 /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
671 pub(crate) fn maybe_get_block_expr(
673 expr: &hir::Expr<'tcx>,
674 ) -> Option<&'tcx hir::Expr<'tcx>> {
676 hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
681 /// Returns whether the given expression is an `else if`.
682 pub(crate) fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
683 if let hir::ExprKind::If(..) = expr.kind {
684 let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
685 if let Some(Node::Expr(hir::Expr {
686 kind: hir::ExprKind::If(_, _, Some(else_expr)),
688 })) = self.tcx.hir().find(parent_id)
690 return else_expr.hir_id == expr.hir_id;
696 /// This function is used to determine potential "simple" improvements or users' errors and
697 /// provide them useful help. For example:
699 /// ```compile_fail,E0308
700 /// fn some_fn(s: &str) {}
702 /// let x = "hey!".to_owned();
703 /// some_fn(x); // error
706 /// No need to find every potential function which could make a coercion to transform a
707 /// `String` into a `&str` since a `&` would do the trick!
709 /// In addition of this check, it also checks between references mutability state. If the
710 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
714 expr: &hir::Expr<'tcx>,
715 checked_ty: Ty<'tcx>,
717 ) -> Option<(Span, String, String, Applicability, bool /* verbose */)> {
718 let sess = self.sess();
721 // If the span is from an external macro, there's no suggestion we can make.
722 if in_external_macro(sess, sp) {
726 let sm = sess.source_map();
728 let replace_prefix = |s: &str, old: &str, new: &str| {
729 s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
732 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
733 let expr = expr.peel_drop_temps();
735 match (&expr.kind, expected.kind(), checked_ty.kind()) {
736 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
737 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
738 if let hir::ExprKind::Lit(_) = expr.kind
739 && let Ok(src) = sm.span_to_snippet(sp)
740 && replace_prefix(&src, "b\"", "\"").is_some()
742 let pos = sp.lo() + BytePos(1);
745 "consider removing the leading `b`".to_string(),
747 Applicability::MachineApplicable,
752 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
753 if let hir::ExprKind::Lit(_) = expr.kind
754 && let Ok(src) = sm.span_to_snippet(sp)
755 && replace_prefix(&src, "\"", "b\"").is_some()
759 "consider adding a leading `b`".to_string(),
761 Applicability::MachineApplicable,
768 (_, &ty::Ref(_, _, mutability), _) => {
769 // Check if it can work when put into a ref. For example:
772 // fn bar(x: &mut i32) {}
775 // bar(&x); // error, expected &mut
777 let ref_ty = match mutability {
778 hir::Mutability::Mut => {
779 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
781 hir::Mutability::Not => {
782 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
785 if self.can_coerce(ref_ty, expected) {
786 let mut sugg_sp = sp;
787 if let hir::ExprKind::MethodCall(ref segment, receiver, args, _) = expr.kind {
789 self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
791 && self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
793 let ai = self.tcx.associated_item(did);
794 ai.trait_container(self.tcx) == Some(clone_trait)
797 && segment.ident.name == sym::clone
799 // If this expression had a clone call when suggesting borrowing
800 // we want to suggest removing it because it'd now be unnecessary.
801 sugg_sp = receiver.span;
804 if let Ok(src) = sm.span_to_snippet(sugg_sp) {
805 let needs_parens = match expr.kind {
806 // parenthesize if needed (Issue #46756)
807 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
808 // parenthesize borrows of range literals (Issue #54505)
809 _ if is_range_literal(expr) => true,
813 if let Some(sugg) = self.can_use_as_ref(expr) {
818 Applicability::MachineApplicable,
823 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
824 Some(ident) => format!("{ident}: "),
825 None => String::new(),
828 if let Some(hir::Node::Expr(hir::Expr {
829 kind: hir::ExprKind::Assign(..),
831 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
833 if mutability == hir::Mutability::Mut {
834 // Suppressing this diagnostic, we'll properly print it in `check_expr_assign`
839 let sugg_expr = if needs_parens { format!("({src})") } else { src };
840 return Some(match mutability {
841 hir::Mutability::Mut => (
843 "consider mutably borrowing here".to_string(),
844 format!("{prefix}&mut {sugg_expr}"),
845 Applicability::MachineApplicable,
848 hir::Mutability::Not => (
850 "consider borrowing here".to_string(),
851 format!("{prefix}&{sugg_expr}"),
852 Applicability::MachineApplicable,
860 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
862 &ty::Ref(_, checked, _),
863 ) if self.can_sub(self.param_env, checked, expected).is_ok() => {
864 // We have `&T`, check if what was expected was `T`. If so,
865 // we may want to suggest removing a `&`.
866 if sm.is_imported(expr.span) {
867 // Go through the spans from which this span was expanded,
868 // and find the one that's pointing inside `sp`.
870 // E.g. for `&format!("")`, where we want the span to the
871 // `format!()` invocation instead of its expansion.
872 if let Some(call_span) =
873 iter::successors(Some(expr.span), |s| s.parent_callsite())
874 .find(|&s| sp.contains(s))
875 && sm.is_span_accessible(call_span)
878 sp.with_hi(call_span.lo()),
879 "consider removing the borrow".to_string(),
881 Applicability::MachineApplicable,
887 if sp.contains(expr.span)
888 && sm.is_span_accessible(expr.span)
891 sp.with_hi(expr.span.lo()),
892 "consider removing the borrow".to_string(),
894 Applicability::MachineApplicable,
901 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
902 &ty::Ref(_, ty_a, mutbl_a),
904 if let Some(steps) = self.deref_steps(ty_a, ty_b)
905 // Only suggest valid if dereferencing needed.
907 // The pointer type implements `Copy` trait so the suggestion is always valid.
908 && let Ok(src) = sm.span_to_snippet(sp)
910 let derefs = "*".repeat(steps);
911 if let Some((span, src, applicability)) = match mutbl_b {
912 hir::Mutability::Mut => {
913 let new_prefix = "&mut ".to_owned() + &derefs;
915 hir::Mutability::Mut => {
916 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
917 let pos = sp.lo() + BytePos(5);
918 let sp = sp.with_lo(pos).with_hi(pos);
919 (sp, derefs, Applicability::MachineApplicable)
922 hir::Mutability::Not => {
923 replace_prefix(&src, "&", &new_prefix).map(|_| {
924 let pos = sp.lo() + BytePos(1);
925 let sp = sp.with_lo(pos).with_hi(pos);
928 format!("mut {derefs}"),
929 Applicability::Unspecified,
935 hir::Mutability::Not => {
936 let new_prefix = "&".to_owned() + &derefs;
938 hir::Mutability::Mut => {
939 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
940 let lo = sp.lo() + BytePos(1);
941 let hi = sp.lo() + BytePos(5);
942 let sp = sp.with_lo(lo).with_hi(hi);
943 (sp, derefs, Applicability::MachineApplicable)
946 hir::Mutability::Not => {
947 replace_prefix(&src, "&", &new_prefix).map(|_| {
948 let pos = sp.lo() + BytePos(1);
949 let sp = sp.with_lo(pos).with_hi(pos);
950 (sp, derefs, Applicability::MachineApplicable)
958 "consider dereferencing".to_string(),
966 _ if sp == expr.span => {
967 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
968 let mut expr = expr.peel_blocks();
969 let mut prefix_span = expr.span.shrink_to_lo();
970 let mut remove = String::new();
972 // Try peeling off any existing `&` and `&mut` to reach our target type
974 if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
975 // If the expression has `&`, removing it would fix the error
976 prefix_span = prefix_span.with_hi(inner.span.lo());
978 remove += match mutbl {
979 hir::Mutability::Not => "&",
980 hir::Mutability::Mut => "&mut ",
987 // If we've reached our target type with just removing `&`, then just print now.
991 format!("consider removing the `{}`", remove.trim()),
993 // Do not remove `&&` to get to bool, because it might be something like
994 // { a } && b, which we have a separate fixup suggestion that is more
996 if remove.trim() == "&&" && expected == self.tcx.types.bool {
997 Applicability::MaybeIncorrect
999 Applicability::MachineApplicable
1005 // For this suggestion to make sense, the type would need to be `Copy`,
1006 // or we have to be moving out of a `Box<T>`
1007 if self.type_is_copy_modulo_regions(self.param_env, expected, sp)
1008 // FIXME(compiler-errors): We can actually do this if the checked_ty is
1009 // `steps` layers of boxes, not just one, but this is easier and most likely.
1010 || (checked_ty.is_box() && steps == 1)
1012 let deref_kind = if checked_ty.is_box() {
1013 "unboxing the value"
1014 } else if checked_ty.is_region_ptr() {
1015 "dereferencing the borrow"
1017 "dereferencing the type"
1020 // Suggest removing `&` if we have removed any, otherwise suggest just
1021 // dereferencing the remaining number of steps.
1022 let message = if remove.is_empty() {
1023 format!("consider {deref_kind}")
1026 "consider removing the `{}` and {} instead",
1032 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
1033 Some(ident) => format!("{ident}: "),
1034 None => String::new(),
1037 let (span, suggestion) = if self.is_else_if_block(expr) {
1038 // Don't suggest nonsense like `else *if`
1040 } else if let Some(expr) = self.maybe_get_block_expr(expr) {
1041 // prefix should be empty here..
1042 (expr.span.shrink_to_lo(), "*".to_string())
1044 (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
1051 Applicability::MachineApplicable,
1062 pub fn check_for_cast(
1064 err: &mut Diagnostic,
1065 expr: &hir::Expr<'_>,
1066 checked_ty: Ty<'tcx>,
1067 expected_ty: Ty<'tcx>,
1068 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
1070 if self.tcx.sess.source_map().is_imported(expr.span) {
1071 // Ignore if span is from within a macro.
1075 let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
1079 // If casting this expression to a given numeric type would be appropriate in case of a type
1082 // We want to minimize the amount of casting operations that are suggested, as it can be a
1083 // lossy operation with potentially bad side effects, so we only suggest when encountering
1084 // an expression that indicates that the original type couldn't be directly changed.
1086 // For now, don't suggest casting with `as`.
1087 let can_cast = false;
1089 let mut sugg = vec![];
1091 if let Some(hir::Node::ExprField(field)) =
1092 self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
1094 // `expr` is a literal field for a struct, only suggest if appropriate
1095 if field.is_shorthand {
1096 // This is a field literal
1097 sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
1099 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
1104 if let hir::ExprKind::Call(path, args) = &expr.kind
1105 && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
1106 (&path.kind, args.len())
1107 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1108 && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1109 (&base_ty.kind, path_segment.ident.name)
1111 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1125 if base_ty_path.segments.len() == 1 =>
1135 "you can convert {} `{}` to {} `{}`",
1136 checked_ty.kind().article(),
1138 expected_ty.kind().article(),
1141 let cast_msg = format!(
1142 "you can cast {} `{}` to {} `{}`",
1143 checked_ty.kind().article(),
1145 expected_ty.kind().article(),
1148 let lit_msg = format!(
1149 "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1152 let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1153 sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1159 let mut cast_suggestion = sugg.clone();
1160 cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1161 let mut into_suggestion = sugg.clone();
1162 into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1163 let mut suffix_suggestion = sugg.clone();
1164 suffix_suggestion.push((
1166 (&expected_ty.kind(), &checked_ty.kind()),
1167 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1169 // Remove fractional part from literal, for example `42.0f32` into `42`
1170 let src = src.trim_end_matches(&checked_ty.to_string());
1171 let len = src.split('.').next().unwrap().len();
1172 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1174 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1175 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1177 if expr.precedence().order() < PREC_POSTFIX {
1179 format!("{expected_ty})")
1181 expected_ty.to_string()
1184 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1185 if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1187 let is_negative_int =
1188 |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1189 let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1191 let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1193 let suggest_fallible_into_or_lhs_from =
1194 |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1195 // If we know the expression the expected type is derived from, we might be able
1196 // to suggest a widening conversion rather than a narrowing one (which may
1197 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1199 // can be given the suggestion "u32::from(x) > y" rather than
1200 // "x > y.try_into().unwrap()".
1201 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1205 .span_to_snippet(expr.span)
1207 .map(|src| (expr, src))
1209 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1210 (lhs_expr_and_src, exp_to_found_is_fallible)
1213 "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1215 let suggestion = vec![
1216 (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1217 (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1221 let msg = format!("{msg} and panic if the converted value doesn't fit");
1222 let mut suggestion = sugg.clone();
1224 expr.span.shrink_to_hi(),
1225 format!("{close_paren}.try_into().unwrap()"),
1229 err.multipart_suggestion_verbose(
1232 Applicability::MachineApplicable,
1236 let suggest_to_change_suffix_or_into =
1237 |err: &mut Diagnostic,
1238 found_to_exp_is_fallible: bool,
1239 exp_to_found_is_fallible: bool| {
1241 expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1247 let always_fallible = found_to_exp_is_fallible
1248 && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1249 let msg = if literal_is_ty_suffixed(expr) {
1251 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1252 // We now know that converting either the lhs or rhs is fallible. Before we
1253 // suggest a fallible conversion, check if the value can never fit in the
1255 let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1258 } else if in_const_context {
1259 // Do not recommend `into` or `try_into` in const contexts.
1261 } else if found_to_exp_is_fallible {
1262 return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1266 let suggestion = if literal_is_ty_suffixed(expr) {
1267 suffix_suggestion.clone()
1269 into_suggestion.clone()
1271 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1274 match (&expected_ty.kind(), &checked_ty.kind()) {
1275 (&ty::Int(ref exp), &ty::Int(ref found)) => {
1276 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1278 (Some(exp), Some(found)) if exp < found => (true, false),
1279 (Some(exp), Some(found)) if exp > found => (false, true),
1280 (None, Some(8 | 16)) => (false, true),
1281 (Some(8 | 16), None) => (true, false),
1282 (None, _) | (_, None) => (true, true),
1283 _ => (false, false),
1285 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1288 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1289 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1291 (Some(exp), Some(found)) if exp < found => (true, false),
1292 (Some(exp), Some(found)) if exp > found => (false, true),
1293 (None, Some(8 | 16)) => (false, true),
1294 (Some(8 | 16), None) => (true, false),
1295 (None, _) | (_, None) => (true, true),
1296 _ => (false, false),
1298 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1301 (&ty::Int(exp), &ty::Uint(found)) => {
1302 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1304 (Some(exp), Some(found)) if found < exp => (false, true),
1305 (None, Some(8)) => (false, true),
1308 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1311 (&ty::Uint(exp), &ty::Int(found)) => {
1312 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1314 (Some(exp), Some(found)) if found > exp => (true, false),
1315 (Some(8), None) => (true, false),
1318 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1321 (&ty::Float(ref exp), &ty::Float(ref found)) => {
1322 if found.bit_width() < exp.bit_width() {
1323 suggest_to_change_suffix_or_into(err, false, true);
1324 } else if literal_is_ty_suffixed(expr) {
1325 err.multipart_suggestion_verbose(
1328 Applicability::MachineApplicable,
1330 } else if can_cast {
1331 // Missing try_into implementation for `f64` to `f32`
1332 err.multipart_suggestion_verbose(
1333 &format!("{cast_msg}, producing the closest possible value"),
1335 Applicability::MaybeIncorrect, // lossy conversion
1340 (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1341 if literal_is_ty_suffixed(expr) {
1342 err.multipart_suggestion_verbose(
1345 Applicability::MachineApplicable,
1347 } else if can_cast {
1348 // Missing try_into implementation for `{float}` to `{integer}`
1349 err.multipart_suggestion_verbose(
1350 &format!("{msg}, rounding the float towards zero"),
1352 Applicability::MaybeIncorrect, // lossy conversion
1357 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1358 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1359 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1360 err.multipart_suggestion_verbose(
1362 "{msg}, producing the floating point representation of the integer",
1365 Applicability::MachineApplicable,
1367 } else if literal_is_ty_suffixed(expr) {
1368 err.multipart_suggestion_verbose(
1371 Applicability::MachineApplicable,
1374 // Missing try_into implementation for `{integer}` to `{float}`
1375 err.multipart_suggestion_verbose(
1377 "{cast_msg}, producing the floating point representation of the integer, \
1378 rounded if necessary",
1381 Applicability::MaybeIncorrect, // lossy conversion
1386 (&ty::Float(ref exp), &ty::Int(ref found)) => {
1387 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1388 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1389 err.multipart_suggestion_verbose(
1391 "{}, producing the floating point representation of the integer",
1395 Applicability::MachineApplicable,
1397 } else if literal_is_ty_suffixed(expr) {
1398 err.multipart_suggestion_verbose(
1401 Applicability::MachineApplicable,
1404 // Missing try_into implementation for `{integer}` to `{float}`
1405 err.multipart_suggestion_verbose(
1407 "{}, producing the floating point representation of the integer, \
1408 rounded if necessary",
1412 Applicability::MaybeIncorrect, // lossy conversion
1418 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1419 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1422 err.multipart_suggestion_verbose(
1423 &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1425 Applicability::MachineApplicable,