1 use crate::check::FnCtxt;
2 use rustc_infer::infer::InferOk;
3 use rustc_middle::middle::stability::EvalResult;
4 use rustc_trait_selection::infer::InferCtxtExt as _;
5 use rustc_trait_selection::traits::ObligationCause;
7 use rustc_ast::util::parser::PREC_POSTFIX;
8 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
10 use rustc_hir::lang_items::LangItem;
11 use rustc_hir::{is_range_literal, Node};
12 use rustc_middle::lint::in_external_macro;
13 use rustc_middle::ty::adjustment::AllowTwoPhase;
14 use rustc_middle::ty::error::{ExpectedFound, TypeError};
15 use rustc_middle::ty::print::with_no_trimmed_paths;
16 use rustc_middle::ty::{self, Article, AssocItem, Ty, TypeAndMut};
17 use rustc_span::symbol::{sym, Symbol};
18 use rustc_span::{BytePos, Span};
20 use super::method::probe;
24 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
25 pub fn emit_coerce_suggestions(
28 expr: &hir::Expr<'tcx>,
31 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
32 error: Option<TypeError<'tcx>>,
34 self.annotate_expected_due_to_let_ty(err, expr, error);
35 self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr);
36 self.suggest_compatible_variants(err, expr, expected, expr_ty);
37 self.suggest_non_zero_new_unwrap(err, expr, expected, expr_ty);
38 if 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_missing_parentheses(err, expr);
44 self.suggest_block_to_brackets_peeling_refs(err, expr, expr_ty, expected);
45 self.suggest_copied_or_cloned(err, expr, expr_ty, expected);
46 self.note_type_is_not_clone(err, expected, expr_ty, expr);
47 self.note_need_for_fn_pointer(err, expected, expr_ty);
48 self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
51 // Requires that the two types unify, and prints an error message if
53 pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
54 if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
59 pub fn demand_suptype_diag(
64 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
65 self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
68 #[instrument(skip(self), level = "debug")]
69 pub fn demand_suptype_with_origin(
71 cause: &ObligationCause<'tcx>,
74 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
75 match self.at(cause, self.param_env).sup(expected, actual) {
76 Ok(InferOk { obligations, value: () }) => {
77 self.register_predicates(obligations);
80 Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
84 pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
85 if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
90 pub fn demand_eqtype_diag(
95 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
96 self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
99 pub fn demand_eqtype_with_origin(
101 cause: &ObligationCause<'tcx>,
104 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
105 match self.at(cause, self.param_env).eq(expected, actual) {
106 Ok(InferOk { obligations, value: () }) => {
107 self.register_predicates(obligations);
110 Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
114 pub fn demand_coerce(
116 expr: &hir::Expr<'tcx>,
117 checked_ty: Ty<'tcx>,
119 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
120 allow_two_phase: AllowTwoPhase,
123 self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
124 if let Some(mut err) = err {
130 /// Checks that the type of `expr` can be coerced to `expected`.
132 /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
133 /// will be permitted if the diverges flag is currently "always".
134 #[instrument(level = "debug", skip(self, expr, expected_ty_expr, allow_two_phase))]
135 pub fn demand_coerce_diag(
137 expr: &hir::Expr<'tcx>,
138 checked_ty: Ty<'tcx>,
140 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
141 allow_two_phase: AllowTwoPhase,
142 ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>) {
143 let expected = self.resolve_vars_with_obligations(expected);
145 let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase, None) {
146 Ok(ty) => return (ty, None),
150 self.set_tainted_by_errors();
151 let expr = expr.peel_drop_temps();
152 let cause = self.misc(expr.span);
153 let expr_ty = self.resolve_vars_with_obligations(checked_ty);
154 let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e.clone());
156 let is_insufficiently_polymorphic =
157 matches!(e, TypeError::RegionsInsufficientlyPolymorphic(..));
159 // FIXME(#73154): For now, we do leak check when coercing function
160 // pointers in typeck, instead of only during borrowck. This can lead
161 // to these `RegionsInsufficientlyPolymorphic` errors that aren't helpful.
162 if !is_insufficiently_polymorphic {
163 self.emit_coerce_suggestions(
173 (expected, Some(err))
176 fn annotate_expected_due_to_let_ty(
178 err: &mut Diagnostic,
179 expr: &hir::Expr<'_>,
180 error: Option<TypeError<'_>>,
182 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
183 match (self.tcx.hir().find(parent), error) {
184 (Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })), _)
185 if init.hir_id == expr.hir_id =>
187 // Point at `let` assignment type.
188 err.span_label(ty.span, "expected due to this");
191 Some(hir::Node::Expr(hir::Expr {
192 kind: hir::ExprKind::Assign(lhs, rhs, _), ..
194 Some(TypeError::Sorts(ExpectedFound { expected, .. })),
195 ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
196 // We ignore closures explicitly because we already point at them elsewhere.
197 // Point at the assigned-to binding.
198 let mut primary_span = lhs.span;
199 let mut secondary_span = lhs.span;
200 let mut post_message = "";
202 hir::ExprKind::Path(hir::QPath::Resolved(
207 hir::def::DefKind::Static(_) | hir::def::DefKind::Const,
213 if let Some(hir::Node::Item(hir::Item {
215 kind: hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..),
217 })) = self.tcx.hir().get_if_local(*def_id)
219 primary_span = ty.span;
220 secondary_span = ident.span;
221 post_message = " type";
224 hir::ExprKind::Path(hir::QPath::Resolved(
226 hir::Path { res: hir::def::Res::Local(hir_id), .. },
228 if let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(*hir_id) {
229 let parent = self.tcx.hir().get_parent_node(pat.hir_id);
230 primary_span = pat.span;
231 secondary_span = pat.span;
232 match self.tcx.hir().find(parent) {
233 Some(hir::Node::Local(hir::Local { ty: Some(ty), .. })) => {
234 primary_span = ty.span;
235 post_message = " type";
237 Some(hir::Node::Local(hir::Local { init: Some(init), .. })) => {
238 primary_span = init.span;
239 post_message = " value";
241 Some(hir::Node::Param(hir::Param { ty_span, .. })) => {
242 primary_span = *ty_span;
243 post_message = " parameter type";
252 if primary_span != secondary_span
257 .is_multiline(secondary_span.shrink_to_hi().until(primary_span))
259 // We are pointing at the binding's type or initializer value, but it's pattern
260 // is in a different line, so we point at both.
261 err.span_label(secondary_span, "expected due to the type of this binding");
262 err.span_label(primary_span, &format!("expected due to this{post_message}"));
263 } else if post_message == "" {
264 // We are pointing at either the assignment lhs or the binding def pattern.
265 err.span_label(primary_span, "expected due to the type of this binding");
267 // We are pointing at the binding's type or initializer value.
268 err.span_label(primary_span, &format!("expected due to this{post_message}"));
271 if !lhs.is_syntactic_place_expr() {
272 // We already emitted E0070 "invalid left-hand side of assignment", so we
274 err.downgrade_to_delayed_bug();
281 /// If the expected type is an enum (Issue #55250) with any variants whose
282 /// sole field is of the found type, suggest such variants. (Issue #42764)
283 fn suggest_compatible_variants(
285 err: &mut Diagnostic,
286 expr: &hir::Expr<'_>,
290 if let ty::Adt(expected_adt, substs) = expected.kind() {
291 if let hir::ExprKind::Field(base, ident) = expr.kind {
292 let base_ty = self.typeck_results.borrow().expr_ty(base);
293 if self.can_eq(self.param_env, base_ty, expected).is_ok()
294 && let Some(base_span) = base.span.find_ancestor_inside(expr.span)
296 err.span_suggestion_verbose(
297 expr.span.with_lo(base_span.hi()),
298 format!("consider removing the tuple struct field `{ident}`"),
300 Applicability::MaybeIncorrect,
306 // If the expression is of type () and it's the return expression of a block,
307 // we suggest adding a separate return expression instead.
308 // (To avoid things like suggesting `Ok(while .. { .. })`.)
309 if expr_ty.is_unit() {
310 let mut id = expr.hir_id;
313 // Unroll desugaring, to make sure this works for `for` loops etc.
315 parent = self.tcx.hir().get_parent_node(id);
316 if let Some(parent_span) = self.tcx.hir().opt_span(parent) {
317 if parent_span.find_ancestor_inside(expr.span).is_some() {
318 // The parent node is part of the same span, so is the result of the
319 // same expansion/desugaring and not the 'real' parent node.
327 if let Some(hir::Node::Block(&hir::Block {
328 span: block_span, expr: Some(e), ..
329 })) = self.tcx.hir().find(parent)
332 if let Some(span) = expr.span.find_ancestor_inside(block_span) {
333 let return_suggestions = if self
335 .is_diagnostic_item(sym::Result, expected_adt.did())
338 } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did()) {
339 vec!["None", "Some(())"]
343 if let Some(indent) =
344 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
346 // Add a semicolon, except after `}`.
348 match self.tcx.sess.source_map().span_to_snippet(span) {
349 Ok(s) if s.ends_with('}') => "",
352 err.span_suggestions(
354 "try adding an expression at the end of the block",
357 .map(|r| format!("{semicolon}\n{indent}{r}")),
358 Applicability::MaybeIncorrect,
367 let compatible_variants: Vec<(String, _, _, Option<String>)> = expected_adt
371 variant.fields.len() == 1
373 .filter_map(|variant| {
374 let sole_field = &variant.fields[0];
376 let field_is_local = sole_field.did.is_local();
377 let field_is_accessible =
378 sole_field.vis.is_accessible_from(expr.hir_id.owner.def_id, self.tcx)
379 // Skip suggestions for unstable public fields (for example `Pin::pointer`)
380 && matches!(self.tcx.eval_stability(sole_field.did, None, expr.span, None), EvalResult::Allow | EvalResult::Unmarked);
382 if !field_is_local && !field_is_accessible {
386 let note_about_variant_field_privacy = (field_is_local && !field_is_accessible)
387 .then(|| format!(" (its field is private, but it's local to this crate and its privacy can be changed)"));
389 let sole_field_ty = sole_field.ty(self.tcx, substs);
390 if self.can_coerce(expr_ty, sole_field_ty) {
392 with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
393 // FIXME #56861: DRYer prelude filtering
394 if let Some(path) = variant_path.strip_prefix("std::prelude::")
395 && let Some((_, path)) = path.split_once("::")
397 return Some((path.to_string(), variant.ctor_kind, sole_field.name, note_about_variant_field_privacy));
399 Some((variant_path, variant.ctor_kind, sole_field.name, note_about_variant_field_privacy))
406 let suggestions_for = |variant: &_, ctor, field_name| {
407 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
408 Some(ident) => format!("{ident}: "),
409 None => String::new(),
412 let (open, close) = match ctor {
413 hir::def::CtorKind::Fn => ("(".to_owned(), ")"),
414 hir::def::CtorKind::Fictive => (format!(" {{ {field_name}: "), " }"),
416 // unit variants don't have fields
417 hir::def::CtorKind::Const => unreachable!(),
420 // Suggest constructor as deep into the block tree as possible.
421 // This fixes https://github.com/rust-lang/rust/issues/101065,
422 // and also just helps make the most minimal suggestions.
424 while let hir::ExprKind::Block(block, _) = &expr.kind
425 && let Some(expr_) = &block.expr
431 (expr.span.shrink_to_lo(), format!("{prefix}{variant}{open}")),
432 (expr.span.shrink_to_hi(), close.to_owned()),
436 match &compatible_variants[..] {
437 [] => { /* No variants to format */ }
438 [(variant, ctor_kind, field_name, note)] => {
439 // Just a single matching variant.
440 err.multipart_suggestion_verbose(
442 "try wrapping the expression in `{variant}`{note}",
443 note = note.as_deref().unwrap_or("")
445 suggestions_for(&**variant, *ctor_kind, *field_name),
446 Applicability::MaybeIncorrect,
450 // More than one matching variant.
451 err.multipart_suggestions(
453 "try wrapping the expression in a variant of `{}`",
454 self.tcx.def_path_str(expected_adt.did())
456 compatible_variants.into_iter().map(
457 |(variant, ctor_kind, field_name, _)| {
458 suggestions_for(&variant, ctor_kind, field_name)
461 Applicability::MaybeIncorrect,
468 fn suggest_non_zero_new_unwrap(
470 err: &mut Diagnostic,
471 expr: &hir::Expr<'_>,
476 let (adt, unwrap) = match expected.kind() {
477 // In case Option<NonZero*> is wanted, but * is provided, suggest calling new
478 ty::Adt(adt, substs) if tcx.is_diagnostic_item(sym::Option, adt.did()) => {
480 let ty::Adt(adt, _) = substs.type_at(0).kind() else { return };
484 // In case NonZero* is wanted, but * is provided also add `.unwrap()` to satisfy types
485 ty::Adt(adt, _) => (adt, ".unwrap()"),
490 (sym::NonZeroU8, tcx.types.u8),
491 (sym::NonZeroU16, tcx.types.u16),
492 (sym::NonZeroU32, tcx.types.u32),
493 (sym::NonZeroU64, tcx.types.u64),
494 (sym::NonZeroU128, tcx.types.u128),
495 (sym::NonZeroI8, tcx.types.i8),
496 (sym::NonZeroI16, tcx.types.i16),
497 (sym::NonZeroI32, tcx.types.i32),
498 (sym::NonZeroI64, tcx.types.i64),
499 (sym::NonZeroI128, tcx.types.i128),
502 let Some((s, _)) = map
504 .find(|&&(s, t)| self.tcx.is_diagnostic_item(s, adt.did()) && self.can_coerce(expr_ty, t))
507 let path = self.tcx.def_path_str(adt.non_enum_variant().def_id);
509 err.multipart_suggestion(
510 format!("consider calling `{s}::new`"),
512 (expr.span.shrink_to_lo(), format!("{path}::new(")),
513 (expr.span.shrink_to_hi(), format!("){unwrap}")),
515 Applicability::MaybeIncorrect,
519 pub fn get_conversion_methods(
523 checked_ty: Ty<'tcx>,
525 ) -> Vec<AssocItem> {
527 self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
529 self.has_only_self_parameter(m)
532 // This special internal attribute is used to permit
533 // "identity-like" conversion methods to be suggested here.
535 // FIXME (#46459 and #46460): ideally
536 // `std::convert::Into::into` and `std::borrow:ToOwned` would
537 // also be `#[rustc_conversion_suggestion]`, if not for
538 // method-probing false-positives and -negatives (respectively).
540 // FIXME? Other potential candidate methods: `as_ref` and
542 .has_attr(m.def_id, sym::rustc_conversion_suggestion)
548 /// This function checks whether the method is not static and does not accept other parameters than `self`.
549 fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
551 ty::AssocKind::Fn => {
552 method.fn_has_self_parameter
553 && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
559 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
561 /// Given the following code:
562 /// ```compile_fail,E0308
564 /// fn takes_ref(_: &Foo) {}
565 /// let ref opt = Some(Foo);
567 /// opt.map(|param| takes_ref(param));
569 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
571 /// It only checks for `Option` and `Result` and won't work with
572 /// ```ignore (illustrative)
573 /// opt.map(|param| { takes_ref(param) });
575 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
576 let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
580 let hir::def::Res::Local(local_id) = path.res else {
584 let local_parent = self.tcx.hir().get_parent_node(local_id);
585 let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
589 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
590 let Some(Node::Expr(hir::Expr {
592 kind: hir::ExprKind::Closure(hir::Closure { fn_decl: closure_fn_decl, .. }),
594 })) = self.tcx.hir().find(param_parent) else {
598 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
599 let hir = self.tcx.hir().find(expr_parent);
600 let closure_params_len = closure_fn_decl.inputs.len();
602 Some(Node::Expr(hir::Expr {
603 kind: hir::ExprKind::MethodCall(method_path, receiver, ..),
607 ) = (hir, closure_params_len) else {
611 let self_ty = self.typeck_results.borrow().expr_ty(receiver);
612 let name = method_path.ident.name;
613 let is_as_ref_able = match self_ty.peel_refs().kind() {
615 (self.tcx.is_diagnostic_item(sym::Option, def.did())
616 || self.tcx.is_diagnostic_item(sym::Result, def.did()))
617 && (name == sym::map || name == sym::and_then)
621 match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
623 let suggestion = format!("as_ref().{}", src);
624 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
630 pub(crate) fn maybe_get_struct_pattern_shorthand_field(
632 expr: &hir::Expr<'_>,
633 ) -> Option<Symbol> {
634 let hir = self.tcx.hir();
635 let local = match expr {
638 hir::ExprKind::Path(hir::QPath::Resolved(
641 res: hir::def::Res::Local(_),
642 segments: [hir::PathSegment { ident, .. }],
651 match hir.find(hir.get_parent_node(expr.hir_id))? {
652 Node::ExprField(field) => {
653 if field.ident.name == local.name && field.is_shorthand {
654 return Some(local.name);
663 /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
664 pub(crate) fn maybe_get_block_expr(
666 expr: &hir::Expr<'tcx>,
667 ) -> Option<&'tcx hir::Expr<'tcx>> {
669 hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
674 /// Returns whether the given expression is an `else if`.
675 pub(crate) fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
676 if let hir::ExprKind::If(..) = expr.kind {
677 let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
678 if let Some(Node::Expr(hir::Expr {
679 kind: hir::ExprKind::If(_, _, Some(else_expr)),
681 })) = self.tcx.hir().find(parent_id)
683 return else_expr.hir_id == expr.hir_id;
689 /// This function is used to determine potential "simple" improvements or users' errors and
690 /// provide them useful help. For example:
692 /// ```compile_fail,E0308
693 /// fn some_fn(s: &str) {}
695 /// let x = "hey!".to_owned();
696 /// some_fn(x); // error
699 /// No need to find every potential function which could make a coercion to transform a
700 /// `String` into a `&str` since a `&` would do the trick!
702 /// In addition of this check, it also checks between references mutability state. If the
703 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
707 expr: &hir::Expr<'tcx>,
708 checked_ty: Ty<'tcx>,
710 ) -> Option<(Span, String, String, Applicability, bool /* verbose */)> {
711 let sess = self.sess();
714 // If the span is from an external macro, there's no suggestion we can make.
715 if in_external_macro(sess, sp) {
719 let sm = sess.source_map();
721 let replace_prefix = |s: &str, old: &str, new: &str| {
722 s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
725 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
726 let expr = expr.peel_drop_temps();
728 match (&expr.kind, expected.kind(), checked_ty.kind()) {
729 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
730 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
731 if let hir::ExprKind::Lit(_) = expr.kind
732 && let Ok(src) = sm.span_to_snippet(sp)
733 && replace_prefix(&src, "b\"", "\"").is_some()
735 let pos = sp.lo() + BytePos(1);
738 "consider removing the leading `b`".to_string(),
740 Applicability::MachineApplicable,
745 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
746 if let hir::ExprKind::Lit(_) = expr.kind
747 && let Ok(src) = sm.span_to_snippet(sp)
748 && replace_prefix(&src, "\"", "b\"").is_some()
752 "consider adding a leading `b`".to_string(),
754 Applicability::MachineApplicable,
761 (_, &ty::Ref(_, _, mutability), _) => {
762 // Check if it can work when put into a ref. For example:
765 // fn bar(x: &mut i32) {}
768 // bar(&x); // error, expected &mut
770 let ref_ty = match mutability {
771 hir::Mutability::Mut => {
772 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
774 hir::Mutability::Not => {
775 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
778 if self.can_coerce(ref_ty, expected) {
779 let mut sugg_sp = sp;
780 if let hir::ExprKind::MethodCall(ref segment, receiver, args, _) = expr.kind {
782 self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
784 && self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
786 let ai = self.tcx.associated_item(did);
787 ai.trait_container(self.tcx) == Some(clone_trait)
790 && segment.ident.name == sym::clone
792 // If this expression had a clone call when suggesting borrowing
793 // we want to suggest removing it because it'd now be unnecessary.
794 sugg_sp = receiver.span;
797 if let Ok(src) = sm.span_to_snippet(sugg_sp) {
798 let needs_parens = match expr.kind {
799 // parenthesize if needed (Issue #46756)
800 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
801 // parenthesize borrows of range literals (Issue #54505)
802 _ if is_range_literal(expr) => true,
806 if let Some(sugg) = self.can_use_as_ref(expr) {
811 Applicability::MachineApplicable,
816 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
817 Some(ident) => format!("{ident}: "),
818 None => String::new(),
821 if let Some(hir::Node::Expr(hir::Expr {
822 kind: hir::ExprKind::Assign(..),
824 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
826 if mutability == hir::Mutability::Mut {
827 // Suppressing this diagnostic, we'll properly print it in `check_expr_assign`
832 let sugg_expr = if needs_parens { format!("({src})") } else { src };
833 return Some(match mutability {
834 hir::Mutability::Mut => (
836 "consider mutably borrowing here".to_string(),
837 format!("{prefix}&mut {sugg_expr}"),
838 Applicability::MachineApplicable,
841 hir::Mutability::Not => (
843 "consider borrowing here".to_string(),
844 format!("{prefix}&{sugg_expr}"),
845 Applicability::MachineApplicable,
853 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
855 &ty::Ref(_, checked, _),
856 ) if self.can_sub(self.param_env, checked, expected).is_ok() => {
857 // We have `&T`, check if what was expected was `T`. If so,
858 // we may want to suggest removing a `&`.
859 if sm.is_imported(expr.span) {
860 // Go through the spans from which this span was expanded,
861 // and find the one that's pointing inside `sp`.
863 // E.g. for `&format!("")`, where we want the span to the
864 // `format!()` invocation instead of its expansion.
865 if let Some(call_span) =
866 iter::successors(Some(expr.span), |s| s.parent_callsite())
867 .find(|&s| sp.contains(s))
868 && sm.is_span_accessible(call_span)
871 sp.with_hi(call_span.lo()),
872 "consider removing the borrow".to_string(),
874 Applicability::MachineApplicable,
880 if sp.contains(expr.span)
881 && sm.is_span_accessible(expr.span)
884 sp.with_hi(expr.span.lo()),
885 "consider removing the borrow".to_string(),
887 Applicability::MachineApplicable,
894 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
895 &ty::Ref(_, ty_a, mutbl_a),
897 if let Some(steps) = self.deref_steps(ty_a, ty_b)
898 // Only suggest valid if dereferencing needed.
900 // The pointer type implements `Copy` trait so the suggestion is always valid.
901 && let Ok(src) = sm.span_to_snippet(sp)
903 let derefs = "*".repeat(steps);
904 if let Some((span, src, applicability)) = match mutbl_b {
905 hir::Mutability::Mut => {
906 let new_prefix = "&mut ".to_owned() + &derefs;
908 hir::Mutability::Mut => {
909 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
910 let pos = sp.lo() + BytePos(5);
911 let sp = sp.with_lo(pos).with_hi(pos);
912 (sp, derefs, Applicability::MachineApplicable)
915 hir::Mutability::Not => {
916 replace_prefix(&src, "&", &new_prefix).map(|_| {
917 let pos = sp.lo() + BytePos(1);
918 let sp = sp.with_lo(pos).with_hi(pos);
921 format!("mut {derefs}"),
922 Applicability::Unspecified,
928 hir::Mutability::Not => {
929 let new_prefix = "&".to_owned() + &derefs;
931 hir::Mutability::Mut => {
932 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
933 let lo = sp.lo() + BytePos(1);
934 let hi = sp.lo() + BytePos(5);
935 let sp = sp.with_lo(lo).with_hi(hi);
936 (sp, derefs, Applicability::MachineApplicable)
939 hir::Mutability::Not => {
940 replace_prefix(&src, "&", &new_prefix).map(|_| {
941 let pos = sp.lo() + BytePos(1);
942 let sp = sp.with_lo(pos).with_hi(pos);
943 (sp, derefs, Applicability::MachineApplicable)
951 "consider dereferencing".to_string(),
959 _ if sp == expr.span => {
960 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
961 let mut expr = expr.peel_blocks();
962 let mut prefix_span = expr.span.shrink_to_lo();
963 let mut remove = String::new();
965 // Try peeling off any existing `&` and `&mut` to reach our target type
967 if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
968 // If the expression has `&`, removing it would fix the error
969 prefix_span = prefix_span.with_hi(inner.span.lo());
971 remove += match mutbl {
972 hir::Mutability::Not => "&",
973 hir::Mutability::Mut => "&mut ",
980 // If we've reached our target type with just removing `&`, then just print now.
984 format!("consider removing the `{}`", remove.trim()),
986 // Do not remove `&&` to get to bool, because it might be something like
987 // { a } && b, which we have a separate fixup suggestion that is more
989 if remove.trim() == "&&" && expected == self.tcx.types.bool {
990 Applicability::MaybeIncorrect
992 Applicability::MachineApplicable
998 // For this suggestion to make sense, the type would need to be `Copy`,
999 // or we have to be moving out of a `Box<T>`
1000 if self.type_is_copy_modulo_regions(self.param_env, expected, sp)
1001 // FIXME(compiler-errors): We can actually do this if the checked_ty is
1002 // `steps` layers of boxes, not just one, but this is easier and most likely.
1003 || (checked_ty.is_box() && steps == 1)
1005 let deref_kind = if checked_ty.is_box() {
1006 "unboxing the value"
1007 } else if checked_ty.is_region_ptr() {
1008 "dereferencing the borrow"
1010 "dereferencing the type"
1013 // Suggest removing `&` if we have removed any, otherwise suggest just
1014 // dereferencing the remaining number of steps.
1015 let message = if remove.is_empty() {
1016 format!("consider {deref_kind}")
1019 "consider removing the `{}` and {} instead",
1025 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
1026 Some(ident) => format!("{ident}: "),
1027 None => String::new(),
1030 let (span, suggestion) = if self.is_else_if_block(expr) {
1031 // Don't suggest nonsense like `else *if`
1033 } else if let Some(expr) = self.maybe_get_block_expr(expr) {
1034 // prefix should be empty here..
1035 (expr.span.shrink_to_lo(), "*".to_string())
1037 (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
1044 Applicability::MachineApplicable,
1055 pub fn check_for_cast(
1057 err: &mut Diagnostic,
1058 expr: &hir::Expr<'_>,
1059 checked_ty: Ty<'tcx>,
1060 expected_ty: Ty<'tcx>,
1061 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
1063 if self.tcx.sess.source_map().is_imported(expr.span) {
1064 // Ignore if span is from within a macro.
1068 let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
1072 // If casting this expression to a given numeric type would be appropriate in case of a type
1075 // We want to minimize the amount of casting operations that are suggested, as it can be a
1076 // lossy operation with potentially bad side effects, so we only suggest when encountering
1077 // an expression that indicates that the original type couldn't be directly changed.
1079 // For now, don't suggest casting with `as`.
1080 let can_cast = false;
1082 let mut sugg = vec![];
1084 if let Some(hir::Node::ExprField(field)) =
1085 self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
1087 // `expr` is a literal field for a struct, only suggest if appropriate
1088 if field.is_shorthand {
1089 // This is a field literal
1090 sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
1092 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
1097 if let hir::ExprKind::Call(path, args) = &expr.kind
1098 && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
1099 (&path.kind, args.len())
1100 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1101 && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1102 (&base_ty.kind, path_segment.ident.name)
1104 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1118 if base_ty_path.segments.len() == 1 =>
1128 "you can convert {} `{}` to {} `{}`",
1129 checked_ty.kind().article(),
1131 expected_ty.kind().article(),
1134 let cast_msg = format!(
1135 "you can cast {} `{}` to {} `{}`",
1136 checked_ty.kind().article(),
1138 expected_ty.kind().article(),
1141 let lit_msg = format!(
1142 "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1145 let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1146 sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1152 let mut cast_suggestion = sugg.clone();
1153 cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1154 let mut into_suggestion = sugg.clone();
1155 into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1156 let mut suffix_suggestion = sugg.clone();
1157 suffix_suggestion.push((
1159 (&expected_ty.kind(), &checked_ty.kind()),
1160 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1162 // Remove fractional part from literal, for example `42.0f32` into `42`
1163 let src = src.trim_end_matches(&checked_ty.to_string());
1164 let len = src.split('.').next().unwrap().len();
1165 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1167 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1168 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1170 if expr.precedence().order() < PREC_POSTFIX {
1172 format!("{expected_ty})")
1174 expected_ty.to_string()
1177 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1178 if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1180 let is_negative_int =
1181 |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1182 let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1184 let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1186 let suggest_fallible_into_or_lhs_from =
1187 |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1188 // If we know the expression the expected type is derived from, we might be able
1189 // to suggest a widening conversion rather than a narrowing one (which may
1190 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1192 // can be given the suggestion "u32::from(x) > y" rather than
1193 // "x > y.try_into().unwrap()".
1194 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1198 .span_to_snippet(expr.span)
1200 .map(|src| (expr, src))
1202 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1203 (lhs_expr_and_src, exp_to_found_is_fallible)
1206 "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1208 let suggestion = vec![
1209 (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1210 (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1214 let msg = format!("{msg} and panic if the converted value doesn't fit");
1215 let mut suggestion = sugg.clone();
1217 expr.span.shrink_to_hi(),
1218 format!("{close_paren}.try_into().unwrap()"),
1222 err.multipart_suggestion_verbose(
1225 Applicability::MachineApplicable,
1229 let suggest_to_change_suffix_or_into =
1230 |err: &mut Diagnostic,
1231 found_to_exp_is_fallible: bool,
1232 exp_to_found_is_fallible: bool| {
1234 expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1240 let always_fallible = found_to_exp_is_fallible
1241 && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1242 let msg = if literal_is_ty_suffixed(expr) {
1244 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1245 // We now know that converting either the lhs or rhs is fallible. Before we
1246 // suggest a fallible conversion, check if the value can never fit in the
1248 let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1251 } else if in_const_context {
1252 // Do not recommend `into` or `try_into` in const contexts.
1254 } else if found_to_exp_is_fallible {
1255 return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1259 let suggestion = if literal_is_ty_suffixed(expr) {
1260 suffix_suggestion.clone()
1262 into_suggestion.clone()
1264 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1267 match (&expected_ty.kind(), &checked_ty.kind()) {
1268 (&ty::Int(ref exp), &ty::Int(ref found)) => {
1269 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1271 (Some(exp), Some(found)) if exp < found => (true, false),
1272 (Some(exp), Some(found)) if exp > found => (false, true),
1273 (None, Some(8 | 16)) => (false, true),
1274 (Some(8 | 16), None) => (true, false),
1275 (None, _) | (_, None) => (true, true),
1276 _ => (false, false),
1278 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1281 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1282 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1284 (Some(exp), Some(found)) if exp < found => (true, false),
1285 (Some(exp), Some(found)) if exp > found => (false, true),
1286 (None, Some(8 | 16)) => (false, true),
1287 (Some(8 | 16), None) => (true, false),
1288 (None, _) | (_, None) => (true, true),
1289 _ => (false, false),
1291 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1294 (&ty::Int(exp), &ty::Uint(found)) => {
1295 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1297 (Some(exp), Some(found)) if found < exp => (false, true),
1298 (None, Some(8)) => (false, true),
1301 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1304 (&ty::Uint(exp), &ty::Int(found)) => {
1305 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1307 (Some(exp), Some(found)) if found > exp => (true, false),
1308 (Some(8), None) => (true, false),
1311 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1314 (&ty::Float(ref exp), &ty::Float(ref found)) => {
1315 if found.bit_width() < exp.bit_width() {
1316 suggest_to_change_suffix_or_into(err, false, true);
1317 } else if literal_is_ty_suffixed(expr) {
1318 err.multipart_suggestion_verbose(
1321 Applicability::MachineApplicable,
1323 } else if can_cast {
1324 // Missing try_into implementation for `f64` to `f32`
1325 err.multipart_suggestion_verbose(
1326 &format!("{cast_msg}, producing the closest possible value"),
1328 Applicability::MaybeIncorrect, // lossy conversion
1333 (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1334 if literal_is_ty_suffixed(expr) {
1335 err.multipart_suggestion_verbose(
1338 Applicability::MachineApplicable,
1340 } else if can_cast {
1341 // Missing try_into implementation for `{float}` to `{integer}`
1342 err.multipart_suggestion_verbose(
1343 &format!("{msg}, rounding the float towards zero"),
1345 Applicability::MaybeIncorrect, // lossy conversion
1350 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1351 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1352 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1353 err.multipart_suggestion_verbose(
1355 "{msg}, producing the floating point representation of the integer",
1358 Applicability::MachineApplicable,
1360 } else if literal_is_ty_suffixed(expr) {
1361 err.multipart_suggestion_verbose(
1364 Applicability::MachineApplicable,
1367 // Missing try_into implementation for `{integer}` to `{float}`
1368 err.multipart_suggestion_verbose(
1370 "{cast_msg}, producing the floating point representation of the integer, \
1371 rounded if necessary",
1374 Applicability::MaybeIncorrect, // lossy conversion
1379 (&ty::Float(ref exp), &ty::Int(ref found)) => {
1380 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1381 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1382 err.multipart_suggestion_verbose(
1384 "{}, producing the floating point representation of the integer",
1388 Applicability::MachineApplicable,
1390 } else if literal_is_ty_suffixed(expr) {
1391 err.multipart_suggestion_verbose(
1394 Applicability::MachineApplicable,
1397 // Missing try_into implementation for `{integer}` to `{float}`
1398 err.multipart_suggestion_verbose(
1400 "{}, producing the floating point representation of the integer, \
1401 rounded if necessary",
1405 Applicability::MaybeIncorrect, // lossy conversion
1411 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1412 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1415 err.multipart_suggestion_verbose(
1416 &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1418 Applicability::MachineApplicable,