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.note_type_is_not_clone(err, expected, expr_ty, expr);
46 self.note_need_for_fn_pointer(err, expected, expr_ty);
47 self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
48 self.report_closure_inferred_return_type(err, expected);
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 #[tracing::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.to_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!(),
421 (expr.span.shrink_to_lo(), format!("{prefix}{variant}{open}")),
422 (expr.span.shrink_to_hi(), close.to_owned()),
426 match &compatible_variants[..] {
427 [] => { /* No variants to format */ }
428 [(variant, ctor_kind, field_name, note)] => {
429 // Just a single matching variant.
430 err.multipart_suggestion_verbose(
432 "try wrapping the expression in `{variant}`{note}",
433 note = note.as_deref().unwrap_or("")
435 suggestions_for(&**variant, *ctor_kind, *field_name),
436 Applicability::MaybeIncorrect,
440 // More than one matching variant.
441 err.multipart_suggestions(
443 "try wrapping the expression in a variant of `{}`",
444 self.tcx.def_path_str(expected_adt.did())
446 compatible_variants.into_iter().map(
447 |(variant, ctor_kind, field_name, _)| {
448 suggestions_for(&variant, ctor_kind, field_name)
451 Applicability::MaybeIncorrect,
458 fn suggest_non_zero_new_unwrap(
460 err: &mut Diagnostic,
461 expr: &hir::Expr<'_>,
466 let (adt, unwrap) = match expected.kind() {
467 // In case Option<NonZero*> is wanted, but * is provided, suggest calling new
468 ty::Adt(adt, substs) if tcx.is_diagnostic_item(sym::Option, adt.did()) => {
470 let ty::Adt(adt, _) = substs.type_at(0).kind() else { return };
474 // In case NonZero* is wanted, but * is provided also add `.unwrap()` to satisfy types
475 ty::Adt(adt, _) => (adt, ".unwrap()"),
480 (sym::NonZeroU8, tcx.types.u8),
481 (sym::NonZeroU16, tcx.types.u16),
482 (sym::NonZeroU32, tcx.types.u32),
483 (sym::NonZeroU64, tcx.types.u64),
484 (sym::NonZeroU128, tcx.types.u128),
485 (sym::NonZeroI8, tcx.types.i8),
486 (sym::NonZeroI16, tcx.types.i16),
487 (sym::NonZeroI32, tcx.types.i32),
488 (sym::NonZeroI64, tcx.types.i64),
489 (sym::NonZeroI128, tcx.types.i128),
492 let Some((s, _)) = map
494 .find(|&&(s, t)| self.tcx.is_diagnostic_item(s, adt.did()) && self.can_coerce(expr_ty, t))
497 let path = self.tcx.def_path_str(adt.non_enum_variant().def_id);
499 err.multipart_suggestion(
500 format!("consider calling `{s}::new`"),
502 (expr.span.shrink_to_lo(), format!("{path}::new(")),
503 (expr.span.shrink_to_hi(), format!("){unwrap}")),
505 Applicability::MaybeIncorrect,
509 pub fn get_conversion_methods(
513 checked_ty: Ty<'tcx>,
515 ) -> Vec<AssocItem> {
517 self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
519 self.has_only_self_parameter(m)
522 // This special internal attribute is used to permit
523 // "identity-like" conversion methods to be suggested here.
525 // FIXME (#46459 and #46460): ideally
526 // `std::convert::Into::into` and `std::borrow:ToOwned` would
527 // also be `#[rustc_conversion_suggestion]`, if not for
528 // method-probing false-positives and -negatives (respectively).
530 // FIXME? Other potential candidate methods: `as_ref` and
532 .has_attr(m.def_id, sym::rustc_conversion_suggestion)
538 /// This function checks whether the method is not static and does not accept other parameters than `self`.
539 fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
541 ty::AssocKind::Fn => {
542 method.fn_has_self_parameter
543 && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
549 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
551 /// Given the following code:
552 /// ```compile_fail,E0308
554 /// fn takes_ref(_: &Foo) {}
555 /// let ref opt = Some(Foo);
557 /// opt.map(|param| takes_ref(param));
559 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
561 /// It only checks for `Option` and `Result` and won't work with
562 /// ```ignore (illustrative)
563 /// opt.map(|param| { takes_ref(param) });
565 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
566 let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
570 let hir::def::Res::Local(local_id) = path.res else {
574 let local_parent = self.tcx.hir().get_parent_node(local_id);
575 let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
579 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
580 let Some(Node::Expr(hir::Expr {
582 kind: hir::ExprKind::Closure(hir::Closure { fn_decl: closure_fn_decl, .. }),
584 })) = self.tcx.hir().find(param_parent) else {
588 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
589 let hir = self.tcx.hir().find(expr_parent);
590 let closure_params_len = closure_fn_decl.inputs.len();
592 Some(Node::Expr(hir::Expr {
593 kind: hir::ExprKind::MethodCall(method_path, method_expr, _),
597 ) = (hir, closure_params_len) else {
601 let self_ty = self.typeck_results.borrow().expr_ty(&method_expr[0]);
602 let self_ty = format!("{:?}", self_ty);
603 let name = method_path.ident.name;
604 let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
605 || self_ty.starts_with("&std::result::Result")
606 || self_ty.starts_with("std::option::Option")
607 || self_ty.starts_with("std::result::Result"))
608 && (name == sym::map || name == sym::and_then);
609 match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
611 let suggestion = format!("as_ref().{}", src);
612 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
618 pub(crate) fn maybe_get_struct_pattern_shorthand_field(
620 expr: &hir::Expr<'_>,
621 ) -> Option<Symbol> {
622 let hir = self.tcx.hir();
623 let local = match expr {
626 hir::ExprKind::Path(hir::QPath::Resolved(
629 res: hir::def::Res::Local(_),
630 segments: [hir::PathSegment { ident, .. }],
639 match hir.find(hir.get_parent_node(expr.hir_id))? {
640 Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) => {
641 for field in *fields {
642 if field.ident.name == local.name && field.is_shorthand {
643 return Some(local.name);
653 /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
654 pub(crate) fn maybe_get_block_expr(
656 expr: &hir::Expr<'tcx>,
657 ) -> Option<&'tcx hir::Expr<'tcx>> {
659 hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
664 /// Returns whether the given expression is an `else if`.
665 pub(crate) fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
666 if let hir::ExprKind::If(..) = expr.kind {
667 let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
668 if let Some(Node::Expr(hir::Expr {
669 kind: hir::ExprKind::If(_, _, Some(else_expr)),
671 })) = self.tcx.hir().find(parent_id)
673 return else_expr.hir_id == expr.hir_id;
679 /// This function is used to determine potential "simple" improvements or users' errors and
680 /// provide them useful help. For example:
682 /// ```compile_fail,E0308
683 /// fn some_fn(s: &str) {}
685 /// let x = "hey!".to_owned();
686 /// some_fn(x); // error
689 /// No need to find every potential function which could make a coercion to transform a
690 /// `String` into a `&str` since a `&` would do the trick!
692 /// In addition of this check, it also checks between references mutability state. If the
693 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
697 expr: &hir::Expr<'tcx>,
698 checked_ty: Ty<'tcx>,
700 ) -> Option<(Span, String, String, Applicability, bool /* verbose */)> {
701 let sess = self.sess();
704 // If the span is from an external macro, there's no suggestion we can make.
705 if in_external_macro(sess, sp) {
709 let sm = sess.source_map();
711 let replace_prefix = |s: &str, old: &str, new: &str| {
712 s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
715 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
716 let expr = expr.peel_drop_temps();
718 match (&expr.kind, expected.kind(), checked_ty.kind()) {
719 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
720 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
721 if let hir::ExprKind::Lit(_) = expr.kind
722 && let Ok(src) = sm.span_to_snippet(sp)
723 && replace_prefix(&src, "b\"", "\"").is_some()
725 let pos = sp.lo() + BytePos(1);
728 "consider removing the leading `b`".to_string(),
730 Applicability::MachineApplicable,
735 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
736 if let hir::ExprKind::Lit(_) = expr.kind
737 && let Ok(src) = sm.span_to_snippet(sp)
738 && replace_prefix(&src, "\"", "b\"").is_some()
742 "consider adding a leading `b`".to_string(),
744 Applicability::MachineApplicable,
751 (_, &ty::Ref(_, _, mutability), _) => {
752 // Check if it can work when put into a ref. For example:
755 // fn bar(x: &mut i32) {}
758 // bar(&x); // error, expected &mut
760 let ref_ty = match mutability {
761 hir::Mutability::Mut => {
762 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
764 hir::Mutability::Not => {
765 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
768 if self.can_coerce(ref_ty, expected) {
769 let mut sugg_sp = sp;
770 if let hir::ExprKind::MethodCall(ref segment, ref args, _) = expr.kind {
772 self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
773 if let ([arg], Some(true), sym::clone) = (
775 self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
777 let ai = self.tcx.associated_item(did);
778 ai.trait_container(self.tcx) == Some(clone_trait)
783 // If this expression had a clone call when suggesting borrowing
784 // we want to suggest removing it because it'd now be unnecessary.
788 if let Ok(src) = sm.span_to_snippet(sugg_sp) {
789 let needs_parens = match expr.kind {
790 // parenthesize if needed (Issue #46756)
791 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
792 // parenthesize borrows of range literals (Issue #54505)
793 _ if is_range_literal(expr) => true,
796 let sugg_expr = if needs_parens { format!("({src})") } else { src };
798 if let Some(sugg) = self.can_use_as_ref(expr) {
803 Applicability::MachineApplicable,
808 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
809 Some(ident) => format!("{ident}: "),
810 None => String::new(),
813 if let Some(hir::Node::Expr(hir::Expr {
814 kind: hir::ExprKind::Assign(..),
816 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
818 if mutability == hir::Mutability::Mut {
819 // Suppressing this diagnostic, we'll properly print it in `check_expr_assign`
824 return Some(match mutability {
825 hir::Mutability::Mut => (
827 "consider mutably borrowing here".to_string(),
828 format!("{prefix}&mut {sugg_expr}"),
829 Applicability::MachineApplicable,
832 hir::Mutability::Not => (
834 "consider borrowing here".to_string(),
835 format!("{prefix}&{sugg_expr}"),
836 Applicability::MachineApplicable,
844 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
846 &ty::Ref(_, checked, _),
847 ) if self.can_sub(self.param_env, checked, expected).is_ok() => {
848 // We have `&T`, check if what was expected was `T`. If so,
849 // we may want to suggest removing a `&`.
850 if sm.is_imported(expr.span) {
851 // Go through the spans from which this span was expanded,
852 // and find the one that's pointing inside `sp`.
854 // E.g. for `&format!("")`, where we want the span to the
855 // `format!()` invocation instead of its expansion.
856 if let Some(call_span) =
857 iter::successors(Some(expr.span), |s| s.parent_callsite())
858 .find(|&s| sp.contains(s))
859 && sm.is_span_accessible(call_span)
862 sp.with_hi(call_span.lo()),
863 "consider removing the borrow".to_string(),
865 Applicability::MachineApplicable,
871 if sp.contains(expr.span)
872 && sm.is_span_accessible(expr.span)
875 sp.with_hi(expr.span.lo()),
876 "consider removing the borrow".to_string(),
878 Applicability::MachineApplicable,
885 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
886 &ty::Ref(_, ty_a, mutbl_a),
888 if let Some(steps) = self.deref_steps(ty_a, ty_b)
889 // Only suggest valid if dereferencing needed.
891 // The pointer type implements `Copy` trait so the suggestion is always valid.
892 && let Ok(src) = sm.span_to_snippet(sp)
894 let derefs = "*".repeat(steps);
895 if let Some((span, src, applicability)) = match mutbl_b {
896 hir::Mutability::Mut => {
897 let new_prefix = "&mut ".to_owned() + &derefs;
899 hir::Mutability::Mut => {
900 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
901 let pos = sp.lo() + BytePos(5);
902 let sp = sp.with_lo(pos).with_hi(pos);
903 (sp, derefs, Applicability::MachineApplicable)
906 hir::Mutability::Not => {
907 replace_prefix(&src, "&", &new_prefix).map(|_| {
908 let pos = sp.lo() + BytePos(1);
909 let sp = sp.with_lo(pos).with_hi(pos);
912 format!("mut {derefs}"),
913 Applicability::Unspecified,
919 hir::Mutability::Not => {
920 let new_prefix = "&".to_owned() + &derefs;
922 hir::Mutability::Mut => {
923 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
924 let lo = sp.lo() + BytePos(1);
925 let hi = sp.lo() + BytePos(5);
926 let sp = sp.with_lo(lo).with_hi(hi);
927 (sp, derefs, Applicability::MachineApplicable)
930 hir::Mutability::Not => {
931 replace_prefix(&src, "&", &new_prefix).map(|_| {
932 let pos = sp.lo() + BytePos(1);
933 let sp = sp.with_lo(pos).with_hi(pos);
934 (sp, derefs, Applicability::MachineApplicable)
942 "consider dereferencing".to_string(),
950 _ if sp == expr.span => {
951 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
952 let mut expr = expr.peel_blocks();
953 let mut prefix_span = expr.span.shrink_to_lo();
954 let mut remove = String::new();
956 // Try peeling off any existing `&` and `&mut` to reach our target type
958 if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
959 // If the expression has `&`, removing it would fix the error
960 prefix_span = prefix_span.with_hi(inner.span.lo());
962 remove += match mutbl {
963 hir::Mutability::Not => "&",
964 hir::Mutability::Mut => "&mut ",
971 // If we've reached our target type with just removing `&`, then just print now.
975 format!("consider removing the `{}`", remove.trim()),
977 // Do not remove `&&` to get to bool, because it might be something like
978 // { a } && b, which we have a separate fixup suggestion that is more
980 if remove.trim() == "&&" && expected == self.tcx.types.bool {
981 Applicability::MaybeIncorrect
983 Applicability::MachineApplicable
989 // For this suggestion to make sense, the type would need to be `Copy`,
990 // or we have to be moving out of a `Box<T>`
991 if self.type_is_copy_modulo_regions(self.param_env, expected, sp)
992 // FIXME(compiler-errors): We can actually do this if the checked_ty is
993 // `steps` layers of boxes, not just one, but this is easier and most likely.
994 || (checked_ty.is_box() && steps == 1)
996 let deref_kind = if checked_ty.is_box() {
998 } else if checked_ty.is_region_ptr() {
999 "dereferencing the borrow"
1001 "dereferencing the type"
1004 // Suggest removing `&` if we have removed any, otherwise suggest just
1005 // dereferencing the remaining number of steps.
1006 let message = if remove.is_empty() {
1007 format!("consider {deref_kind}")
1010 "consider removing the `{}` and {} instead",
1016 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
1017 Some(ident) => format!("{ident}: "),
1018 None => String::new(),
1021 let (span, suggestion) = if self.is_else_if_block(expr) {
1022 // Don't suggest nonsense like `else *if`
1024 } else if let Some(expr) = self.maybe_get_block_expr(expr) {
1025 // prefix should be empty here..
1026 (expr.span.shrink_to_lo(), "*".to_string())
1028 (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
1035 Applicability::MachineApplicable,
1046 pub fn check_for_cast(
1048 err: &mut Diagnostic,
1049 expr: &hir::Expr<'_>,
1050 checked_ty: Ty<'tcx>,
1051 expected_ty: Ty<'tcx>,
1052 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
1054 if self.tcx.sess.source_map().is_imported(expr.span) {
1055 // Ignore if span is from within a macro.
1059 let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
1063 // If casting this expression to a given numeric type would be appropriate in case of a type
1066 // We want to minimize the amount of casting operations that are suggested, as it can be a
1067 // lossy operation with potentially bad side effects, so we only suggest when encountering
1068 // an expression that indicates that the original type couldn't be directly changed.
1070 // For now, don't suggest casting with `as`.
1071 let can_cast = false;
1073 let mut sugg = vec![];
1075 if let Some(hir::Node::Expr(hir::Expr {
1076 kind: hir::ExprKind::Struct(_, fields, _), ..
1077 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
1079 // `expr` is a literal field for a struct, only suggest if appropriate
1082 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
1084 // This is a field literal
1086 sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
1088 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
1089 None => return false,
1093 if let hir::ExprKind::Call(path, args) = &expr.kind
1094 && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
1095 (&path.kind, args.len())
1096 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1097 && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1098 (&base_ty.kind, path_segment.ident.name)
1100 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1114 if base_ty_path.segments.len() == 1 =>
1124 "you can convert {} `{}` to {} `{}`",
1125 checked_ty.kind().article(),
1127 expected_ty.kind().article(),
1130 let cast_msg = format!(
1131 "you can cast {} `{}` to {} `{}`",
1132 checked_ty.kind().article(),
1134 expected_ty.kind().article(),
1137 let lit_msg = format!(
1138 "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1141 let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1142 sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1148 let mut cast_suggestion = sugg.clone();
1149 cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1150 let mut into_suggestion = sugg.clone();
1151 into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1152 let mut suffix_suggestion = sugg.clone();
1153 suffix_suggestion.push((
1155 (&expected_ty.kind(), &checked_ty.kind()),
1156 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1158 // Remove fractional part from literal, for example `42.0f32` into `42`
1159 let src = src.trim_end_matches(&checked_ty.to_string());
1160 let len = src.split('.').next().unwrap().len();
1161 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1163 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1164 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1166 if expr.precedence().order() < PREC_POSTFIX {
1168 format!("{expected_ty})")
1170 expected_ty.to_string()
1173 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1174 if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1176 let is_negative_int =
1177 |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1178 let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1180 let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1182 let suggest_fallible_into_or_lhs_from =
1183 |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1184 // If we know the expression the expected type is derived from, we might be able
1185 // to suggest a widening conversion rather than a narrowing one (which may
1186 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1188 // can be given the suggestion "u32::from(x) > y" rather than
1189 // "x > y.try_into().unwrap()".
1190 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1194 .span_to_snippet(expr.span)
1196 .map(|src| (expr, src))
1198 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1199 (lhs_expr_and_src, exp_to_found_is_fallible)
1202 "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1204 let suggestion = vec![
1205 (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1206 (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1210 let msg = format!("{msg} and panic if the converted value doesn't fit");
1211 let mut suggestion = sugg.clone();
1213 expr.span.shrink_to_hi(),
1214 format!("{close_paren}.try_into().unwrap()"),
1218 err.multipart_suggestion_verbose(
1221 Applicability::MachineApplicable,
1225 let suggest_to_change_suffix_or_into =
1226 |err: &mut Diagnostic,
1227 found_to_exp_is_fallible: bool,
1228 exp_to_found_is_fallible: bool| {
1230 expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1236 let always_fallible = found_to_exp_is_fallible
1237 && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1238 let msg = if literal_is_ty_suffixed(expr) {
1240 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1241 // We now know that converting either the lhs or rhs is fallible. Before we
1242 // suggest a fallible conversion, check if the value can never fit in the
1244 let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1247 } else if in_const_context {
1248 // Do not recommend `into` or `try_into` in const contexts.
1250 } else if found_to_exp_is_fallible {
1251 return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1255 let suggestion = if literal_is_ty_suffixed(expr) {
1256 suffix_suggestion.clone()
1258 into_suggestion.clone()
1260 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1263 match (&expected_ty.kind(), &checked_ty.kind()) {
1264 (&ty::Int(ref exp), &ty::Int(ref found)) => {
1265 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1267 (Some(exp), Some(found)) if exp < found => (true, false),
1268 (Some(exp), Some(found)) if exp > found => (false, true),
1269 (None, Some(8 | 16)) => (false, true),
1270 (Some(8 | 16), None) => (true, false),
1271 (None, _) | (_, None) => (true, true),
1272 _ => (false, false),
1274 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1277 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1278 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1280 (Some(exp), Some(found)) if exp < found => (true, false),
1281 (Some(exp), Some(found)) if exp > found => (false, true),
1282 (None, Some(8 | 16)) => (false, true),
1283 (Some(8 | 16), None) => (true, false),
1284 (None, _) | (_, None) => (true, true),
1285 _ => (false, false),
1287 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1290 (&ty::Int(exp), &ty::Uint(found)) => {
1291 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1293 (Some(exp), Some(found)) if found < exp => (false, true),
1294 (None, Some(8)) => (false, true),
1297 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1300 (&ty::Uint(exp), &ty::Int(found)) => {
1301 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1303 (Some(exp), Some(found)) if found > exp => (true, false),
1304 (Some(8), None) => (true, false),
1307 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1310 (&ty::Float(ref exp), &ty::Float(ref found)) => {
1311 if found.bit_width() < exp.bit_width() {
1312 suggest_to_change_suffix_or_into(err, false, true);
1313 } else if literal_is_ty_suffixed(expr) {
1314 err.multipart_suggestion_verbose(
1317 Applicability::MachineApplicable,
1319 } else if can_cast {
1320 // Missing try_into implementation for `f64` to `f32`
1321 err.multipart_suggestion_verbose(
1322 &format!("{cast_msg}, producing the closest possible value"),
1324 Applicability::MaybeIncorrect, // lossy conversion
1329 (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1330 if literal_is_ty_suffixed(expr) {
1331 err.multipart_suggestion_verbose(
1334 Applicability::MachineApplicable,
1336 } else if can_cast {
1337 // Missing try_into implementation for `{float}` to `{integer}`
1338 err.multipart_suggestion_verbose(
1339 &format!("{msg}, rounding the float towards zero"),
1341 Applicability::MaybeIncorrect, // lossy conversion
1346 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1347 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1348 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1349 err.multipart_suggestion_verbose(
1351 "{msg}, producing the floating point representation of the integer",
1354 Applicability::MachineApplicable,
1356 } else if literal_is_ty_suffixed(expr) {
1357 err.multipart_suggestion_verbose(
1360 Applicability::MachineApplicable,
1363 // Missing try_into implementation for `{integer}` to `{float}`
1364 err.multipart_suggestion_verbose(
1366 "{cast_msg}, producing the floating point representation of the integer, \
1367 rounded if necessary",
1370 Applicability::MaybeIncorrect, // lossy conversion
1375 (&ty::Float(ref exp), &ty::Int(ref found)) => {
1376 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1377 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1378 err.multipart_suggestion_verbose(
1380 "{}, producing the floating point representation of the integer",
1384 Applicability::MachineApplicable,
1386 } else if literal_is_ty_suffixed(expr) {
1387 err.multipart_suggestion_verbose(
1390 Applicability::MachineApplicable,
1393 // Missing try_into implementation for `{integer}` to `{float}`
1394 err.multipart_suggestion_verbose(
1396 "{}, producing the floating point representation of the integer, \
1397 rounded if necessary",
1401 Applicability::MaybeIncorrect, // lossy conversion
1407 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1408 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1411 err.multipart_suggestion_verbose(
1412 &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1414 Applicability::MachineApplicable,
1422 // Report the type inferred by the return statement.
1423 fn report_closure_inferred_return_type(&self, err: &mut Diagnostic, expected: Ty<'tcx>) {
1424 if let Some(sp) = self.ret_coercion_span.get()
1425 // If the closure has an explicit return type annotation, or if
1426 // the closure's return type has been inferred from outside
1427 // requirements (such as an Fn* trait bound), then a type error
1428 // may occur at the first return expression we see in the closure
1429 // (if it conflicts with the declared return type). Skip adding a
1430 // note in this case, since it would be incorrect.
1431 && !self.return_type_pre_known
1436 "return type inferred to be `{}` here",
1437 self.resolve_vars_if_possible(expected)