1 use crate::check::FnCtxt;
2 use rustc_infer::infer::InferOk;
3 use rustc_trait_selection::infer::InferCtxtExt as _;
4 use rustc_trait_selection::traits::ObligationCause;
6 use rustc_ast::util::parser::PREC_POSTFIX;
7 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
9 use rustc_hir::lang_items::LangItem;
10 use rustc_hir::{is_range_literal, Node};
11 use rustc_middle::lint::in_external_macro;
12 use rustc_middle::ty::adjustment::AllowTwoPhase;
13 use rustc_middle::ty::error::{ExpectedFound, TypeError};
14 use rustc_middle::ty::print::with_no_trimmed_paths;
15 use rustc_middle::ty::{self, Article, AssocItem, Ty, TypeAndMut};
16 use rustc_span::symbol::{sym, Symbol};
17 use rustc_span::{BytePos, Span};
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);
34 self.suggest_deref_ref_or_into(err, expr, expected, expr_ty, expected_ty_expr);
35 self.suggest_compatible_variants(err, expr, expected, expr_ty);
36 self.suggest_non_zero_new_unwrap(err, expr, expected, expr_ty);
37 if self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty) {
40 self.suggest_no_capture_closure(err, expected, expr_ty);
41 self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
42 self.suggest_missing_parentheses(err, expr);
43 self.suggest_block_to_brackets_peeling_refs(err, expr, expr_ty, expected);
44 self.note_type_is_not_clone(err, expected, expr_ty, expr);
45 self.note_need_for_fn_pointer(err, expected, expr_ty);
46 self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
47 self.report_closure_inferred_return_type(err, expected);
50 // Requires that the two types unify, and prints an error message if
52 pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
53 if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
58 pub fn demand_suptype_diag(
63 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
64 self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
67 #[instrument(skip(self), level = "debug")]
68 pub fn demand_suptype_with_origin(
70 cause: &ObligationCause<'tcx>,
73 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
74 match self.at(cause, self.param_env).sup(expected, actual) {
75 Ok(InferOk { obligations, value: () }) => {
76 self.register_predicates(obligations);
79 Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
83 pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
84 if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
89 pub fn demand_eqtype_diag(
94 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
95 self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
98 pub fn demand_eqtype_with_origin(
100 cause: &ObligationCause<'tcx>,
103 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
104 match self.at(cause, self.param_env).eq(expected, actual) {
105 Ok(InferOk { obligations, value: () }) => {
106 self.register_predicates(obligations);
109 Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
113 pub fn demand_coerce(
115 expr: &hir::Expr<'tcx>,
116 checked_ty: Ty<'tcx>,
118 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
119 allow_two_phase: AllowTwoPhase,
122 self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
123 if let Some(mut err) = err {
129 /// Checks that the type of `expr` can be coerced to `expected`.
131 /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
132 /// will be permitted if the diverges flag is currently "always".
133 #[tracing::instrument(level = "debug", skip(self, expr, expected_ty_expr, allow_two_phase))]
134 pub fn demand_coerce_diag(
136 expr: &hir::Expr<'tcx>,
137 checked_ty: Ty<'tcx>,
139 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
140 allow_two_phase: AllowTwoPhase,
141 ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>) {
142 let expected = self.resolve_vars_with_obligations(expected);
144 let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase, None) {
145 Ok(ty) => return (ty, None),
149 self.set_tainted_by_errors();
150 let expr = expr.peel_drop_temps();
151 let cause = self.misc(expr.span);
152 let expr_ty = self.resolve_vars_with_obligations(checked_ty);
153 let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e.clone());
155 let is_insufficiently_polymorphic =
156 matches!(e, TypeError::RegionsInsufficientlyPolymorphic(..));
158 // FIXME(#73154): For now, we do leak check when coercing function
159 // pointers in typeck, instead of only during borrowck. This can lead
160 // to these `RegionsInsufficientlyPolymorphic` errors that aren't helpful.
161 if !is_insufficiently_polymorphic {
162 self.emit_coerce_suggestions(
172 (expected, Some(err))
175 fn annotate_expected_due_to_let_ty(
177 err: &mut Diagnostic,
178 expr: &hir::Expr<'_>,
179 error: Option<TypeError<'_>>,
181 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
182 match (self.tcx.hir().find(parent), error) {
183 (Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })), _)
184 if init.hir_id == expr.hir_id =>
186 // Point at `let` assignment type.
187 err.span_label(ty.span, "expected due to this");
190 Some(hir::Node::Expr(hir::Expr {
191 kind: hir::ExprKind::Assign(lhs, rhs, _), ..
193 Some(TypeError::Sorts(ExpectedFound { expected, .. })),
194 ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
195 // We ignore closures explicitly because we already point at them elsewhere.
196 // Point at the assigned-to binding.
197 let mut primary_span = lhs.span;
198 let mut secondary_span = lhs.span;
199 let mut post_message = "";
201 hir::ExprKind::Path(hir::QPath::Resolved(
206 hir::def::DefKind::Static(_) | hir::def::DefKind::Const,
212 if let Some(hir::Node::Item(hir::Item {
214 kind: hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..),
216 })) = self.tcx.hir().get_if_local(*def_id)
218 primary_span = ty.span;
219 secondary_span = ident.span;
220 post_message = " type";
223 hir::ExprKind::Path(hir::QPath::Resolved(
225 hir::Path { res: hir::def::Res::Local(hir_id), .. },
227 if let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(*hir_id) {
228 let parent = self.tcx.hir().get_parent_node(pat.hir_id);
229 primary_span = pat.span;
230 secondary_span = pat.span;
231 match self.tcx.hir().find(parent) {
232 Some(hir::Node::Local(hir::Local { ty: Some(ty), .. })) => {
233 primary_span = ty.span;
234 post_message = " type";
236 Some(hir::Node::Local(hir::Local { init: Some(init), .. })) => {
237 primary_span = init.span;
238 post_message = " value";
240 Some(hir::Node::Param(hir::Param { ty_span, .. })) => {
241 primary_span = *ty_span;
242 post_message = " parameter type";
251 if primary_span != secondary_span
256 .is_multiline(secondary_span.shrink_to_hi().until(primary_span))
258 // We are pointing at the binding's type or initializer value, but it's pattern
259 // is in a different line, so we point at both.
260 err.span_label(secondary_span, "expected due to the type of this binding");
261 err.span_label(primary_span, &format!("expected due to this{post_message}"));
262 } else if post_message == "" {
263 // We are pointing at either the assignment lhs or the binding def pattern.
264 err.span_label(primary_span, "expected due to the type of this binding");
266 // We are pointing at the binding's type or initializer value.
267 err.span_label(primary_span, &format!("expected due to this{post_message}"));
270 if !lhs.is_syntactic_place_expr() {
271 // We already emitted E0070 "invalid left-hand side of assignment", so we
273 err.downgrade_to_delayed_bug();
280 /// If the expected type is an enum (Issue #55250) with any variants whose
281 /// sole field is of the found type, suggest such variants. (Issue #42764)
282 fn suggest_compatible_variants(
284 err: &mut Diagnostic,
285 expr: &hir::Expr<'_>,
289 if let ty::Adt(expected_adt, substs) = expected.kind() {
290 // If the expression is of type () and it's the return expression of a block,
291 // we suggest adding a separate return expression instead.
292 // (To avoid things like suggesting `Ok(while .. { .. })`.)
293 if expr_ty.is_unit() {
294 let mut id = expr.hir_id;
297 // Unroll desugaring, to make sure this works for `for` loops etc.
299 parent = self.tcx.hir().get_parent_node(id);
300 if let Some(parent_span) = self.tcx.hir().opt_span(parent) {
301 if parent_span.find_ancestor_inside(expr.span).is_some() {
302 // The parent node is part of the same span, so is the result of the
303 // same expansion/desugaring and not the 'real' parent node.
311 if let Some(hir::Node::Block(&hir::Block {
312 span: block_span, expr: Some(e), ..
313 })) = self.tcx.hir().find(parent)
316 if let Some(span) = expr.span.find_ancestor_inside(block_span) {
317 let return_suggestions = if self
319 .is_diagnostic_item(sym::Result, expected_adt.did())
322 } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did()) {
323 vec!["None", "Some(())"]
327 if let Some(indent) =
328 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
330 // Add a semicolon, except after `}`.
332 match self.tcx.sess.source_map().span_to_snippet(span) {
333 Ok(s) if s.ends_with('}') => "",
336 err.span_suggestions(
338 "try adding an expression at the end of the block",
341 .map(|r| format!("{semicolon}\n{indent}{r}")),
342 Applicability::MaybeIncorrect,
351 let compatible_variants: Vec<String> = expected_adt
355 variant.fields.len() == 1 && variant.ctor_kind == hir::def::CtorKind::Fn
357 .filter_map(|variant| {
358 let sole_field = &variant.fields[0];
360 if !sole_field.did.is_local()
361 && !sole_field.vis.is_accessible_from(
362 self.tcx.parent_module(expr.hir_id).to_def_id(),
369 let sole_field_ty = sole_field.ty(self.tcx, substs);
370 if self.can_coerce(expr_ty, sole_field_ty) {
372 with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
373 // FIXME #56861: DRYer prelude filtering
374 if let Some(path) = variant_path.strip_prefix("std::prelude::")
375 && let Some((_, path)) = path.split_once("::")
377 return Some(path.to_string());
386 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
387 Some(ident) => format!("{ident}: "),
388 None => String::new(),
391 match &compatible_variants[..] {
392 [] => { /* No variants to format */ }
394 // Just a single matching variant.
395 err.multipart_suggestion_verbose(
396 &format!("try wrapping the expression in `{variant}`"),
398 (expr.span.shrink_to_lo(), format!("{prefix}{variant}(")),
399 (expr.span.shrink_to_hi(), ")".to_string()),
401 Applicability::MaybeIncorrect,
405 // More than one matching variant.
406 err.multipart_suggestions(
408 "try wrapping the expression in a variant of `{}`",
409 self.tcx.def_path_str(expected_adt.did())
411 compatible_variants.into_iter().map(|variant| {
413 (expr.span.shrink_to_lo(), format!("{prefix}{variant}(")),
414 (expr.span.shrink_to_hi(), ")".to_string()),
417 Applicability::MaybeIncorrect,
424 fn suggest_non_zero_new_unwrap(
426 err: &mut Diagnostic,
427 expr: &hir::Expr<'_>,
432 let (adt, unwrap) = match expected.kind() {
433 // In case Option<NonZero*> is wanted, but * is provided, suggest calling new
434 ty::Adt(adt, substs) if tcx.is_diagnostic_item(sym::Option, adt.did()) => {
436 let Some(fst) = substs.first() else { return };
437 let ty::Adt(adt, _) = fst.expect_ty().kind() else { return };
441 // In case NonZero* is wanted, but * is provided also add `.unwrap()` to satisfy types
442 ty::Adt(adt, _) => (adt, ".unwrap()"),
447 (sym::NonZeroU8, tcx.types.u8),
448 (sym::NonZeroU16, tcx.types.u16),
449 (sym::NonZeroU32, tcx.types.u32),
450 (sym::NonZeroU64, tcx.types.u64),
451 (sym::NonZeroU128, tcx.types.u128),
452 (sym::NonZeroI8, tcx.types.i8),
453 (sym::NonZeroI16, tcx.types.i16),
454 (sym::NonZeroI32, tcx.types.i32),
455 (sym::NonZeroI64, tcx.types.i64),
456 (sym::NonZeroI128, tcx.types.i128),
459 let Some((s, _)) = map
461 .find(|&&(s, _)| self.tcx.is_diagnostic_item(s, adt.did()))
462 .filter(|&&(_, t)| { self.can_coerce(expr_ty, t) })
465 let path = self.tcx.def_path_str(adt.non_enum_variant().def_id);
467 err.multipart_suggestion(
468 format!("consider calling `{s}::new`"),
470 (expr.span.shrink_to_lo(), format!("{path}::new(")),
471 (expr.span.shrink_to_hi(), format!("){unwrap}")),
473 Applicability::MaybeIncorrect,
477 pub fn get_conversion_methods(
481 checked_ty: Ty<'tcx>,
483 ) -> Vec<AssocItem> {
485 self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
487 self.has_only_self_parameter(m)
490 // This special internal attribute is used to permit
491 // "identity-like" conversion methods to be suggested here.
493 // FIXME (#46459 and #46460): ideally
494 // `std::convert::Into::into` and `std::borrow:ToOwned` would
495 // also be `#[rustc_conversion_suggestion]`, if not for
496 // method-probing false-positives and -negatives (respectively).
498 // FIXME? Other potential candidate methods: `as_ref` and
500 .has_attr(m.def_id, sym::rustc_conversion_suggestion)
506 /// This function checks whether the method is not static and does not accept other parameters than `self`.
507 fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
509 ty::AssocKind::Fn => {
510 method.fn_has_self_parameter
511 && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
517 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
519 /// Given the following code:
520 /// ```compile_fail,E0308
522 /// fn takes_ref(_: &Foo) {}
523 /// let ref opt = Some(Foo);
525 /// opt.map(|param| takes_ref(param));
527 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
529 /// It only checks for `Option` and `Result` and won't work with
530 /// ```ignore (illustrative)
531 /// opt.map(|param| { takes_ref(param) });
533 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
534 let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
538 let hir::def::Res::Local(local_id) = path.res else {
542 let local_parent = self.tcx.hir().get_parent_node(local_id);
543 let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
547 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
548 let Some(Node::Expr(hir::Expr {
550 kind: hir::ExprKind::Closure(hir::Closure { fn_decl: closure_fn_decl, .. }),
552 })) = self.tcx.hir().find(param_parent) else {
556 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
557 let hir = self.tcx.hir().find(expr_parent);
558 let closure_params_len = closure_fn_decl.inputs.len();
560 Some(Node::Expr(hir::Expr {
561 kind: hir::ExprKind::MethodCall(method_path, method_expr, _),
565 ) = (hir, closure_params_len) else {
569 let self_ty = self.typeck_results.borrow().expr_ty(&method_expr[0]);
570 let self_ty = format!("{:?}", self_ty);
571 let name = method_path.ident.name;
572 let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
573 || self_ty.starts_with("&std::result::Result")
574 || self_ty.starts_with("std::option::Option")
575 || self_ty.starts_with("std::result::Result"))
576 && (name == sym::map || name == sym::and_then);
577 match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
579 let suggestion = format!("as_ref().{}", src);
580 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
586 pub(crate) fn maybe_get_struct_pattern_shorthand_field(
588 expr: &hir::Expr<'_>,
589 ) -> Option<Symbol> {
590 let hir = self.tcx.hir();
591 let local = match expr {
594 hir::ExprKind::Path(hir::QPath::Resolved(
597 res: hir::def::Res::Local(_),
598 segments: [hir::PathSegment { ident, .. }],
607 match hir.find(hir.get_parent_node(expr.hir_id))? {
608 Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) => {
609 for field in *fields {
610 if field.ident.name == local.name && field.is_shorthand {
611 return Some(local.name);
621 /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
622 pub(crate) fn maybe_get_block_expr(
624 expr: &hir::Expr<'tcx>,
625 ) -> Option<&'tcx hir::Expr<'tcx>> {
627 hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
632 /// Returns whether the given expression is an `else if`.
633 pub(crate) fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
634 if let hir::ExprKind::If(..) = expr.kind {
635 let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
636 if let Some(Node::Expr(hir::Expr {
637 kind: hir::ExprKind::If(_, _, Some(else_expr)),
639 })) = self.tcx.hir().find(parent_id)
641 return else_expr.hir_id == expr.hir_id;
647 /// This function is used to determine potential "simple" improvements or users' errors and
648 /// provide them useful help. For example:
650 /// ```compile_fail,E0308
651 /// fn some_fn(s: &str) {}
653 /// let x = "hey!".to_owned();
654 /// some_fn(x); // error
657 /// No need to find every potential function which could make a coercion to transform a
658 /// `String` into a `&str` since a `&` would do the trick!
660 /// In addition of this check, it also checks between references mutability state. If the
661 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
665 expr: &hir::Expr<'tcx>,
666 checked_ty: Ty<'tcx>,
668 ) -> Option<(Span, String, String, Applicability, bool /* verbose */)> {
669 let sess = self.sess();
672 // If the span is from an external macro, there's no suggestion we can make.
673 if in_external_macro(sess, sp) {
677 let sm = sess.source_map();
679 let replace_prefix = |s: &str, old: &str, new: &str| {
680 s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
683 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
684 let expr = expr.peel_drop_temps();
686 match (&expr.kind, expected.kind(), checked_ty.kind()) {
687 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
688 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
689 if let hir::ExprKind::Lit(_) = expr.kind
690 && let Ok(src) = sm.span_to_snippet(sp)
691 && replace_prefix(&src, "b\"", "\"").is_some()
693 let pos = sp.lo() + BytePos(1);
696 "consider removing the leading `b`".to_string(),
698 Applicability::MachineApplicable,
703 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
704 if let hir::ExprKind::Lit(_) = expr.kind
705 && let Ok(src) = sm.span_to_snippet(sp)
706 && replace_prefix(&src, "\"", "b\"").is_some()
710 "consider adding a leading `b`".to_string(),
712 Applicability::MachineApplicable,
719 (_, &ty::Ref(_, _, mutability), _) => {
720 // Check if it can work when put into a ref. For example:
723 // fn bar(x: &mut i32) {}
726 // bar(&x); // error, expected &mut
728 let ref_ty = match mutability {
729 hir::Mutability::Mut => {
730 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
732 hir::Mutability::Not => {
733 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
736 if self.can_coerce(ref_ty, expected) {
737 let mut sugg_sp = sp;
738 if let hir::ExprKind::MethodCall(ref segment, ref args, _) = expr.kind {
740 self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
741 if let ([arg], Some(true), sym::clone) = (
743 self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
745 let ai = self.tcx.associated_item(did);
746 ai.container == ty::TraitContainer(clone_trait)
751 // If this expression had a clone call when suggesting borrowing
752 // we want to suggest removing it because it'd now be unnecessary.
756 if let Ok(src) = sm.span_to_snippet(sugg_sp) {
757 let needs_parens = match expr.kind {
758 // parenthesize if needed (Issue #46756)
759 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
760 // parenthesize borrows of range literals (Issue #54505)
761 _ if is_range_literal(expr) => true,
764 let sugg_expr = if needs_parens { format!("({src})") } else { src };
766 if let Some(sugg) = self.can_use_as_ref(expr) {
771 Applicability::MachineApplicable,
776 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
777 Some(ident) => format!("{ident}: "),
778 None => String::new(),
781 if let Some(hir::Node::Expr(hir::Expr {
782 kind: hir::ExprKind::Assign(..),
784 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
786 if mutability == hir::Mutability::Mut {
787 // Suppressing this diagnostic, we'll properly print it in `check_expr_assign`
792 return Some(match mutability {
793 hir::Mutability::Mut => (
795 "consider mutably borrowing here".to_string(),
796 format!("{prefix}&mut {sugg_expr}"),
797 Applicability::MachineApplicable,
800 hir::Mutability::Not => (
802 "consider borrowing here".to_string(),
803 format!("{prefix}&{sugg_expr}"),
804 Applicability::MachineApplicable,
812 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
814 &ty::Ref(_, checked, _),
815 ) if self.infcx.can_sub(self.param_env, checked, expected).is_ok() => {
816 // We have `&T`, check if what was expected was `T`. If so,
817 // we may want to suggest removing a `&`.
818 if sm.is_imported(expr.span) {
819 // Go through the spans from which this span was expanded,
820 // and find the one that's pointing inside `sp`.
822 // E.g. for `&format!("")`, where we want the span to the
823 // `format!()` invocation instead of its expansion.
824 if let Some(call_span) =
825 iter::successors(Some(expr.span), |s| s.parent_callsite())
826 .find(|&s| sp.contains(s))
827 && sm.is_span_accessible(call_span)
830 sp.with_hi(call_span.lo()),
831 "consider removing the borrow".to_string(),
833 Applicability::MachineApplicable,
839 if sp.contains(expr.span)
840 && sm.is_span_accessible(expr.span)
843 sp.with_hi(expr.span.lo()),
844 "consider removing the borrow".to_string(),
846 Applicability::MachineApplicable,
853 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
854 &ty::Ref(_, ty_a, mutbl_a),
856 if let Some(steps) = self.deref_steps(ty_a, ty_b)
857 // Only suggest valid if dereferencing needed.
859 // The pointer type implements `Copy` trait so the suggestion is always valid.
860 && let Ok(src) = sm.span_to_snippet(sp)
862 let derefs = "*".repeat(steps);
863 if let Some((span, src, applicability)) = match mutbl_b {
864 hir::Mutability::Mut => {
865 let new_prefix = "&mut ".to_owned() + &derefs;
867 hir::Mutability::Mut => {
868 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
869 let pos = sp.lo() + BytePos(5);
870 let sp = sp.with_lo(pos).with_hi(pos);
871 (sp, derefs, Applicability::MachineApplicable)
874 hir::Mutability::Not => {
875 replace_prefix(&src, "&", &new_prefix).map(|_| {
876 let pos = sp.lo() + BytePos(1);
877 let sp = sp.with_lo(pos).with_hi(pos);
880 format!("mut {derefs}"),
881 Applicability::Unspecified,
887 hir::Mutability::Not => {
888 let new_prefix = "&".to_owned() + &derefs;
890 hir::Mutability::Mut => {
891 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
892 let lo = sp.lo() + BytePos(1);
893 let hi = sp.lo() + BytePos(5);
894 let sp = sp.with_lo(lo).with_hi(hi);
895 (sp, derefs, Applicability::MachineApplicable)
898 hir::Mutability::Not => {
899 replace_prefix(&src, "&", &new_prefix).map(|_| {
900 let pos = sp.lo() + BytePos(1);
901 let sp = sp.with_lo(pos).with_hi(pos);
902 (sp, derefs, Applicability::MachineApplicable)
910 "consider dereferencing".to_string(),
918 _ if sp == expr.span => {
919 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
920 let mut expr = expr.peel_blocks();
921 let mut prefix_span = expr.span.shrink_to_lo();
922 let mut remove = String::new();
924 // Try peeling off any existing `&` and `&mut` to reach our target type
926 if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
927 // If the expression has `&`, removing it would fix the error
928 prefix_span = prefix_span.with_hi(inner.span.lo());
930 remove += match mutbl {
931 hir::Mutability::Not => "&",
932 hir::Mutability::Mut => "&mut ",
939 // If we've reached our target type with just removing `&`, then just print now.
943 format!("consider removing the `{}`", remove.trim()),
945 // Do not remove `&&` to get to bool, because it might be something like
946 // { a } && b, which we have a separate fixup suggestion that is more
948 if remove.trim() == "&&" && expected == self.tcx.types.bool {
949 Applicability::MaybeIncorrect
951 Applicability::MachineApplicable
957 // For this suggestion to make sense, the type would need to be `Copy`,
958 // or we have to be moving out of a `Box<T>`
959 if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp)
960 // FIXME(compiler-errors): We can actually do this if the checked_ty is
961 // `steps` layers of boxes, not just one, but this is easier and most likely.
962 || (checked_ty.is_box() && steps == 1)
964 let deref_kind = if checked_ty.is_box() {
966 } else if checked_ty.is_region_ptr() {
967 "dereferencing the borrow"
969 "dereferencing the type"
972 // Suggest removing `&` if we have removed any, otherwise suggest just
973 // dereferencing the remaining number of steps.
974 let message = if remove.is_empty() {
975 format!("consider {deref_kind}")
978 "consider removing the `{}` and {} instead",
984 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
985 Some(ident) => format!("{ident}: "),
986 None => String::new(),
989 let (span, suggestion) = if self.is_else_if_block(expr) {
990 // Don't suggest nonsense like `else *if`
992 } else if let Some(expr) = self.maybe_get_block_expr(expr) {
993 // prefix should be empty here..
994 (expr.span.shrink_to_lo(), "*".to_string())
996 (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
1003 Applicability::MachineApplicable,
1014 pub fn check_for_cast(
1016 err: &mut Diagnostic,
1017 expr: &hir::Expr<'_>,
1018 checked_ty: Ty<'tcx>,
1019 expected_ty: Ty<'tcx>,
1020 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
1022 if self.tcx.sess.source_map().is_imported(expr.span) {
1023 // Ignore if span is from within a macro.
1027 let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
1031 // If casting this expression to a given numeric type would be appropriate in case of a type
1034 // We want to minimize the amount of casting operations that are suggested, as it can be a
1035 // lossy operation with potentially bad side effects, so we only suggest when encountering
1036 // an expression that indicates that the original type couldn't be directly changed.
1038 // For now, don't suggest casting with `as`.
1039 let can_cast = false;
1041 let mut sugg = vec![];
1043 if let Some(hir::Node::Expr(hir::Expr {
1044 kind: hir::ExprKind::Struct(_, fields, _), ..
1045 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
1047 // `expr` is a literal field for a struct, only suggest if appropriate
1050 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
1052 // This is a field literal
1054 sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
1056 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
1057 None => return false,
1061 if let hir::ExprKind::Call(path, args) = &expr.kind
1062 && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
1063 (&path.kind, args.len())
1064 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1065 && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1066 (&base_ty.kind, path_segment.ident.name)
1068 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1082 if base_ty_path.segments.len() == 1 =>
1092 "you can convert {} `{}` to {} `{}`",
1093 checked_ty.kind().article(),
1095 expected_ty.kind().article(),
1098 let cast_msg = format!(
1099 "you can cast {} `{}` to {} `{}`",
1100 checked_ty.kind().article(),
1102 expected_ty.kind().article(),
1105 let lit_msg = format!(
1106 "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1109 let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1110 sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1116 let mut cast_suggestion = sugg.clone();
1117 cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1118 let mut into_suggestion = sugg.clone();
1119 into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1120 let mut suffix_suggestion = sugg.clone();
1121 suffix_suggestion.push((
1123 (&expected_ty.kind(), &checked_ty.kind()),
1124 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1126 // Remove fractional part from literal, for example `42.0f32` into `42`
1127 let src = src.trim_end_matches(&checked_ty.to_string());
1128 let len = src.split('.').next().unwrap().len();
1129 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1131 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1132 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1134 if expr.precedence().order() < PREC_POSTFIX {
1136 format!("{expected_ty})")
1138 expected_ty.to_string()
1141 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1142 if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1144 let is_negative_int =
1145 |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1146 let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1148 let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1150 let suggest_fallible_into_or_lhs_from =
1151 |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1152 // If we know the expression the expected type is derived from, we might be able
1153 // to suggest a widening conversion rather than a narrowing one (which may
1154 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1156 // can be given the suggestion "u32::from(x) > y" rather than
1157 // "x > y.try_into().unwrap()".
1158 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1162 .span_to_snippet(expr.span)
1164 .map(|src| (expr, src))
1166 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1167 (lhs_expr_and_src, exp_to_found_is_fallible)
1170 "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1172 let suggestion = vec![
1173 (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1174 (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1178 let msg = format!("{msg} and panic if the converted value doesn't fit");
1179 let mut suggestion = sugg.clone();
1181 expr.span.shrink_to_hi(),
1182 format!("{close_paren}.try_into().unwrap()"),
1186 err.multipart_suggestion_verbose(
1189 Applicability::MachineApplicable,
1193 let suggest_to_change_suffix_or_into =
1194 |err: &mut Diagnostic,
1195 found_to_exp_is_fallible: bool,
1196 exp_to_found_is_fallible: bool| {
1198 expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1204 let always_fallible = found_to_exp_is_fallible
1205 && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1206 let msg = if literal_is_ty_suffixed(expr) {
1208 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1209 // We now know that converting either the lhs or rhs is fallible. Before we
1210 // suggest a fallible conversion, check if the value can never fit in the
1212 let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1215 } else if in_const_context {
1216 // Do not recommend `into` or `try_into` in const contexts.
1218 } else if found_to_exp_is_fallible {
1219 return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1223 let suggestion = if literal_is_ty_suffixed(expr) {
1224 suffix_suggestion.clone()
1226 into_suggestion.clone()
1228 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1231 match (&expected_ty.kind(), &checked_ty.kind()) {
1232 (&ty::Int(ref exp), &ty::Int(ref found)) => {
1233 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1235 (Some(exp), Some(found)) if exp < found => (true, false),
1236 (Some(exp), Some(found)) if exp > found => (false, true),
1237 (None, Some(8 | 16)) => (false, true),
1238 (Some(8 | 16), None) => (true, false),
1239 (None, _) | (_, None) => (true, true),
1240 _ => (false, false),
1242 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1245 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1246 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1248 (Some(exp), Some(found)) if exp < found => (true, false),
1249 (Some(exp), Some(found)) if exp > found => (false, true),
1250 (None, Some(8 | 16)) => (false, true),
1251 (Some(8 | 16), None) => (true, false),
1252 (None, _) | (_, None) => (true, true),
1253 _ => (false, false),
1255 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1258 (&ty::Int(exp), &ty::Uint(found)) => {
1259 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1261 (Some(exp), Some(found)) if found < exp => (false, true),
1262 (None, Some(8)) => (false, true),
1265 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1268 (&ty::Uint(exp), &ty::Int(found)) => {
1269 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1271 (Some(exp), Some(found)) if found > exp => (true, false),
1272 (Some(8), None) => (true, false),
1275 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1278 (&ty::Float(ref exp), &ty::Float(ref found)) => {
1279 if found.bit_width() < exp.bit_width() {
1280 suggest_to_change_suffix_or_into(err, false, true);
1281 } else if literal_is_ty_suffixed(expr) {
1282 err.multipart_suggestion_verbose(
1285 Applicability::MachineApplicable,
1287 } else if can_cast {
1288 // Missing try_into implementation for `f64` to `f32`
1289 err.multipart_suggestion_verbose(
1290 &format!("{cast_msg}, producing the closest possible value"),
1292 Applicability::MaybeIncorrect, // lossy conversion
1297 (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1298 if literal_is_ty_suffixed(expr) {
1299 err.multipart_suggestion_verbose(
1302 Applicability::MachineApplicable,
1304 } else if can_cast {
1305 // Missing try_into implementation for `{float}` to `{integer}`
1306 err.multipart_suggestion_verbose(
1307 &format!("{msg}, rounding the float towards zero"),
1309 Applicability::MaybeIncorrect, // lossy conversion
1314 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1315 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1316 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1317 err.multipart_suggestion_verbose(
1319 "{msg}, producing the floating point representation of the integer",
1322 Applicability::MachineApplicable,
1324 } else if literal_is_ty_suffixed(expr) {
1325 err.multipart_suggestion_verbose(
1328 Applicability::MachineApplicable,
1331 // Missing try_into implementation for `{integer}` to `{float}`
1332 err.multipart_suggestion_verbose(
1334 "{cast_msg}, producing the floating point representation of the integer, \
1335 rounded if necessary",
1338 Applicability::MaybeIncorrect, // lossy conversion
1343 (&ty::Float(ref exp), &ty::Int(ref found)) => {
1344 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1345 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1346 err.multipart_suggestion_verbose(
1348 "{}, producing the floating point representation of the integer",
1352 Applicability::MachineApplicable,
1354 } else if literal_is_ty_suffixed(expr) {
1355 err.multipart_suggestion_verbose(
1358 Applicability::MachineApplicable,
1361 // Missing try_into implementation for `{integer}` to `{float}`
1362 err.multipart_suggestion_verbose(
1364 "{}, producing the floating point representation of the integer, \
1365 rounded if necessary",
1369 Applicability::MaybeIncorrect, // lossy conversion
1375 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1376 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1379 err.multipart_suggestion_verbose(
1380 &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1382 Applicability::MachineApplicable,
1390 // Report the type inferred by the return statement.
1391 fn report_closure_inferred_return_type(&self, err: &mut Diagnostic, expected: Ty<'tcx>) {
1392 if let Some(sp) = self.ret_coercion_span.get()
1393 // If the closure has an explicit return type annotation, or if
1394 // the closure's return type has been inferred from outside
1395 // requirements (such as an Fn* trait bound), then a type error
1396 // may occur at the first return expression we see in the closure
1397 // (if it conflicts with the declared return type). Skip adding a
1398 // note in this case, since it would be incorrect.
1399 && !self.return_type_pre_known
1404 "return type inferred to be `{}` here",
1405 self.resolve_vars_if_possible(expected)