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, ErrorReported};
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, 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: 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 if self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty) {
39 self.suggest_no_capture_closure(err, expected, expr_ty);
40 self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
41 self.suggest_missing_parentheses(err, expr);
42 self.note_need_for_fn_pointer(err, expected, expr_ty);
43 self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
44 self.report_closure_inferred_return_type(err, expected);
47 // Requires that the two types unify, and prints an error message if
49 pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
50 if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
55 pub fn demand_suptype_diag(
60 ) -> Option<DiagnosticBuilder<'tcx, ErrorReported>> {
61 self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
64 #[instrument(skip(self), level = "debug")]
65 pub fn demand_suptype_with_origin(
67 cause: &ObligationCause<'tcx>,
70 ) -> Option<DiagnosticBuilder<'tcx, ErrorReported>> {
71 match self.at(cause, self.param_env).sup(expected, actual) {
72 Ok(InferOk { obligations, value: () }) => {
73 self.register_predicates(obligations);
76 Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
80 pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
81 if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
86 pub fn demand_eqtype_diag(
91 ) -> Option<DiagnosticBuilder<'tcx, ErrorReported>> {
92 self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
95 pub fn demand_eqtype_with_origin(
97 cause: &ObligationCause<'tcx>,
100 ) -> Option<DiagnosticBuilder<'tcx, ErrorReported>> {
101 match self.at(cause, self.param_env).eq(expected, actual) {
102 Ok(InferOk { obligations, value: () }) => {
103 self.register_predicates(obligations);
106 Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
110 pub fn demand_coerce(
112 expr: &hir::Expr<'tcx>,
113 checked_ty: Ty<'tcx>,
115 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
116 allow_two_phase: AllowTwoPhase,
119 self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
120 if let Some(mut err) = err {
126 /// Checks that the type of `expr` can be coerced to `expected`.
128 /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
129 /// will be permitted if the diverges flag is currently "always".
130 pub fn demand_coerce_diag(
132 expr: &hir::Expr<'tcx>,
133 checked_ty: Ty<'tcx>,
135 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
136 allow_two_phase: AllowTwoPhase,
137 ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx, ErrorReported>>) {
138 let expected = self.resolve_vars_with_obligations(expected);
140 let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase, None) {
141 Ok(ty) => return (ty, None),
145 self.set_tainted_by_errors();
146 let expr = expr.peel_drop_temps();
147 let cause = self.misc(expr.span);
148 let expr_ty = self.resolve_vars_with_obligations(checked_ty);
149 let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e.clone());
151 self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr, e);
153 (expected, Some(err))
156 fn annotate_expected_due_to_let_ty(
158 err: &mut Diagnostic,
159 expr: &hir::Expr<'_>,
160 error: TypeError<'_>,
162 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
163 match (self.tcx.hir().find(parent), error) {
164 (Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })), _)
165 if init.hir_id == expr.hir_id =>
167 // Point at `let` assignment type.
168 err.span_label(ty.span, "expected due to this");
171 Some(hir::Node::Expr(hir::Expr {
172 kind: hir::ExprKind::Assign(lhs, rhs, _), ..
174 TypeError::Sorts(ExpectedFound { expected, .. }),
175 ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
176 // We ignore closures explicitly because we already point at them elsewhere.
177 // Point at the assigned-to binding.
178 let mut primary_span = lhs.span;
179 let mut secondary_span = lhs.span;
180 let mut post_message = "";
182 hir::ExprKind::Path(hir::QPath::Resolved(
187 hir::def::DefKind::Static | hir::def::DefKind::Const,
193 if let Some(hir::Node::Item(hir::Item {
195 kind: hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..),
197 })) = self.tcx.hir().get_if_local(*def_id)
199 primary_span = ty.span;
200 secondary_span = ident.span;
201 post_message = " type";
204 hir::ExprKind::Path(hir::QPath::Resolved(
206 hir::Path { res: hir::def::Res::Local(hir_id), .. },
208 if let Some(hir::Node::Binding(pat)) = self.tcx.hir().find(*hir_id) {
209 let parent = self.tcx.hir().get_parent_node(pat.hir_id);
210 primary_span = pat.span;
211 secondary_span = pat.span;
212 match self.tcx.hir().find(parent) {
213 Some(hir::Node::Local(hir::Local { ty: Some(ty), .. })) => {
214 primary_span = ty.span;
215 post_message = " type";
217 Some(hir::Node::Local(hir::Local { init: Some(init), .. })) => {
218 primary_span = init.span;
219 post_message = " value";
221 Some(hir::Node::Param(hir::Param { ty_span, .. })) => {
222 primary_span = *ty_span;
223 post_message = " parameter type";
232 if primary_span != secondary_span
237 .is_multiline(secondary_span.shrink_to_hi().until(primary_span))
239 // We are pointing at the binding's type or initializer value, but it's pattern
240 // is in a different line, so we point at both.
241 err.span_label(secondary_span, "expected due to the type of this binding");
242 err.span_label(primary_span, &format!("expected due to this{}", post_message));
243 } else if post_message == "" {
244 // We are pointing at either the assignment lhs or the binding def pattern.
245 err.span_label(primary_span, "expected due to the type of this binding");
247 // We are pointing at the binding's type or initializer value.
248 err.span_label(primary_span, &format!("expected due to this{}", post_message));
251 if !lhs.is_syntactic_place_expr() {
252 // We already emitted E0070 "invalid left-hand side of assignment", so we
254 err.downgrade_to_delayed_bug();
261 /// If the expected type is an enum (Issue #55250) with any variants whose
262 /// sole field is of the found type, suggest such variants. (Issue #42764)
263 fn suggest_compatible_variants(
265 err: &mut Diagnostic,
266 expr: &hir::Expr<'_>,
270 if let ty::Adt(expected_adt, substs) = expected.kind() {
271 if !expected_adt.is_enum() {
275 // If the expression is of type () and it's the return expression of a block,
276 // we suggest adding a separate return expression instead.
277 // (To avoid things like suggesting `Ok(while .. { .. })`.)
278 if expr_ty.is_unit() {
279 if let Some(hir::Node::Block(&hir::Block {
280 span: block_span, expr: Some(e), ..
281 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
283 if e.hir_id == expr.hir_id {
284 if let Some(span) = expr.span.find_ancestor_inside(block_span) {
285 let return_suggestions =
286 if self.tcx.is_diagnostic_item(sym::Result, expected_adt.did) {
287 vec!["Ok(())".to_string()]
288 } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did)
290 vec!["None".to_string(), "Some(())".to_string()]
294 if let Some(indent) =
295 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
297 // Add a semicolon, except after `}`.
299 match self.tcx.sess.source_map().span_to_snippet(span) {
300 Ok(s) if s.ends_with('}') => "",
303 err.span_suggestions(
305 "try adding an expression at the end of the block",
308 .map(|r| format!("{}\n{}{}", semicolon, indent, r)),
309 Applicability::MaybeIncorrect,
318 let compatible_variants: Vec<String> = expected_adt
321 .filter(|variant| variant.fields.len() == 1)
322 .filter_map(|variant| {
323 let sole_field = &variant.fields[0];
324 let sole_field_ty = sole_field.ty(self.tcx, substs);
325 if self.can_coerce(expr_ty, sole_field_ty) {
327 with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
328 // FIXME #56861: DRYer prelude filtering
329 if let Some(path) = variant_path.strip_prefix("std::prelude::") {
330 if let Some((_, path)) = path.split_once("::") {
331 return Some(path.to_string());
341 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
342 Some(ident) => format!("{}: ", ident),
343 None => String::new(),
346 match &compatible_variants[..] {
347 [] => { /* No variants to format */ }
349 // Just a single matching variant.
350 err.multipart_suggestion_verbose(
351 &format!("try wrapping the expression in `{}`", variant),
353 (expr.span.shrink_to_lo(), format!("{}{}(", prefix, variant)),
354 (expr.span.shrink_to_hi(), ")".to_string()),
356 Applicability::MaybeIncorrect,
360 // More than one matching variant.
361 err.multipart_suggestions(
363 "try wrapping the expression in a variant of `{}`",
364 self.tcx.def_path_str(expected_adt.did)
366 compatible_variants.into_iter().map(|variant| {
368 (expr.span.shrink_to_lo(), format!("{}{}(", prefix, variant)),
369 (expr.span.shrink_to_hi(), ")".to_string()),
372 Applicability::MaybeIncorrect,
379 pub fn get_conversion_methods(
383 checked_ty: Ty<'tcx>,
385 ) -> Vec<AssocItem> {
387 self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
389 self.has_only_self_parameter(m)
394 // This special internal attribute is used to permit
395 // "identity-like" conversion methods to be suggested here.
397 // FIXME (#46459 and #46460): ideally
398 // `std::convert::Into::into` and `std::borrow:ToOwned` would
399 // also be `#[rustc_conversion_suggestion]`, if not for
400 // method-probing false-positives and -negatives (respectively).
402 // FIXME? Other potential candidate methods: `as_ref` and
404 .any(|a| a.has_name(sym::rustc_conversion_suggestion))
410 /// This function checks whether the method is not static and does not accept other parameters than `self`.
411 fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
413 ty::AssocKind::Fn => {
414 method.fn_has_self_parameter
415 && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
421 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
423 /// Given the following code:
426 /// fn takes_ref(_: &Foo) {}
427 /// let ref opt = Some(Foo);
429 /// opt.map(|param| takes_ref(param));
431 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
433 /// It only checks for `Option` and `Result` and won't work with
435 /// opt.map(|param| { takes_ref(param) });
437 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
438 let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
442 let hir::def::Res::Local(local_id) = path.res else {
446 let local_parent = self.tcx.hir().get_parent_node(local_id);
447 let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
451 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
452 let Some(Node::Expr(hir::Expr {
454 kind: hir::ExprKind::Closure(_, closure_fn_decl, ..),
456 })) = self.tcx.hir().find(param_parent) else {
460 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
461 let hir = self.tcx.hir().find(expr_parent);
462 let closure_params_len = closure_fn_decl.inputs.len();
464 Some(Node::Expr(hir::Expr {
465 kind: hir::ExprKind::MethodCall(method_path, method_expr, _),
469 ) = (hir, closure_params_len) else {
473 let self_ty = self.typeck_results.borrow().node_type(method_expr[0].hir_id);
474 let self_ty = format!("{:?}", self_ty);
475 let name = method_path.ident.name;
476 let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
477 || self_ty.starts_with("&std::result::Result")
478 || self_ty.starts_with("std::option::Option")
479 || self_ty.starts_with("std::result::Result"))
480 && (name == sym::map || name == sym::and_then);
481 match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
483 let suggestion = format!("as_ref().{}", src);
484 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
490 crate fn maybe_get_struct_pattern_shorthand_field(
492 expr: &hir::Expr<'_>,
493 ) -> Option<Symbol> {
494 let hir = self.tcx.hir();
495 let local = match expr {
498 hir::ExprKind::Path(hir::QPath::Resolved(
501 res: hir::def::Res::Local(_),
502 segments: [hir::PathSegment { ident, .. }],
511 match hir.find(hir.get_parent_node(expr.hir_id))? {
512 Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) => {
513 for field in *fields {
514 if field.ident.name == local.name && field.is_shorthand {
515 return Some(local.name);
525 /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
526 crate fn maybe_get_block_expr(&self, expr: &hir::Expr<'tcx>) -> Option<&'tcx hir::Expr<'tcx>> {
528 hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
533 /// Returns whether the given expression is an `else if`.
534 crate fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
535 if let hir::ExprKind::If(..) = expr.kind {
536 let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
537 if let Some(Node::Expr(hir::Expr {
538 kind: hir::ExprKind::If(_, _, Some(else_expr)),
540 })) = self.tcx.hir().find(parent_id)
542 return else_expr.hir_id == expr.hir_id;
548 /// This function is used to determine potential "simple" improvements or users' errors and
549 /// provide them useful help. For example:
552 /// fn some_fn(s: &str) {}
554 /// let x = "hey!".to_owned();
555 /// some_fn(x); // error
558 /// No need to find every potential function which could make a coercion to transform a
559 /// `String` into a `&str` since a `&` would do the trick!
561 /// In addition of this check, it also checks between references mutability state. If the
562 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
566 expr: &hir::Expr<'tcx>,
567 checked_ty: Ty<'tcx>,
569 ) -> Option<(Span, &'static str, String, Applicability, bool /* verbose */)> {
570 let sess = self.sess();
573 // If the span is from an external macro, there's no suggestion we can make.
574 if in_external_macro(sess, sp) {
578 let sm = sess.source_map();
580 let replace_prefix = |s: &str, old: &str, new: &str| {
581 s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
584 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
585 let expr = expr.peel_drop_temps();
587 match (&expr.kind, expected.kind(), checked_ty.kind()) {
588 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
589 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
590 if let hir::ExprKind::Lit(_) = expr.kind {
591 if let Ok(src) = sm.span_to_snippet(sp) {
592 if replace_prefix(&src, "b\"", "\"").is_some() {
593 let pos = sp.lo() + BytePos(1);
596 "consider removing the leading `b`",
598 Applicability::MachineApplicable,
605 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
606 if let hir::ExprKind::Lit(_) = expr.kind {
607 if let Ok(src) = sm.span_to_snippet(sp) {
608 if replace_prefix(&src, "\"", "b\"").is_some() {
611 "consider adding a leading `b`",
613 Applicability::MachineApplicable,
622 (_, &ty::Ref(_, _, mutability), _) => {
623 // Check if it can work when put into a ref. For example:
626 // fn bar(x: &mut i32) {}
629 // bar(&x); // error, expected &mut
631 let ref_ty = match mutability {
632 hir::Mutability::Mut => {
633 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
635 hir::Mutability::Not => {
636 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
639 if self.can_coerce(ref_ty, expected) {
640 let mut sugg_sp = sp;
641 if let hir::ExprKind::MethodCall(ref segment, ref args, _) = expr.kind {
643 self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
644 if let ([arg], Some(true), sym::clone) = (
646 self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
648 let ai = self.tcx.associated_item(did);
649 ai.container == ty::TraitContainer(clone_trait)
654 // If this expression had a clone call when suggesting borrowing
655 // we want to suggest removing it because it'd now be unnecessary.
659 if let Ok(src) = sm.span_to_snippet(sugg_sp) {
660 let needs_parens = match expr.kind {
661 // parenthesize if needed (Issue #46756)
662 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
663 // parenthesize borrows of range literals (Issue #54505)
664 _ if is_range_literal(expr) => true,
667 let sugg_expr = if needs_parens { format!("({})", src) } else { src };
669 if let Some(sugg) = self.can_use_as_ref(expr) {
674 Applicability::MachineApplicable,
679 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
680 Some(ident) => format!("{}: ", ident),
681 None => String::new(),
684 if let Some(hir::Node::Expr(hir::Expr {
685 kind: hir::ExprKind::Assign(left_expr, ..),
687 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
689 if mutability == hir::Mutability::Mut {
690 // Found the following case:
691 // fn foo(opt: &mut Option<String>){ opt = None }
694 // consider dereferencing here: `*opt` |
695 // expected mutable reference, found enum `Option`
696 if sm.span_to_snippet(left_expr.span).is_ok() {
698 left_expr.span.shrink_to_lo(),
699 "consider dereferencing here to assign to the mutable \
700 borrowed piece of memory",
702 Applicability::MachineApplicable,
709 return Some(match mutability {
710 hir::Mutability::Mut => (
712 "consider mutably borrowing here",
713 format!("{}&mut {}", prefix, sugg_expr),
714 Applicability::MachineApplicable,
717 hir::Mutability::Not => (
719 "consider borrowing here",
720 format!("{}&{}", prefix, sugg_expr),
721 Applicability::MachineApplicable,
729 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
731 &ty::Ref(_, checked, _),
732 ) if self.infcx.can_sub(self.param_env, checked, expected).is_ok() => {
733 // We have `&T`, check if what was expected was `T`. If so,
734 // we may want to suggest removing a `&`.
735 if sm.is_imported(expr.span) {
736 // Go through the spans from which this span was expanded,
737 // and find the one that's pointing inside `sp`.
739 // E.g. for `&format!("")`, where we want the span to the
740 // `format!()` invocation instead of its expansion.
741 if let Some(call_span) =
742 iter::successors(Some(expr.span), |s| s.parent_callsite())
743 .find(|&s| sp.contains(s))
745 if sm.span_to_snippet(call_span).is_ok() {
747 sp.with_hi(call_span.lo()),
748 "consider removing the borrow",
750 Applicability::MachineApplicable,
757 if sp.contains(expr.span) {
758 if sm.span_to_snippet(expr.span).is_ok() {
760 sp.with_hi(expr.span.lo()),
761 "consider removing the borrow",
763 Applicability::MachineApplicable,
771 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
772 &ty::Ref(_, ty_a, mutbl_a),
774 if let Some(steps) = self.deref_steps(ty_a, ty_b) {
775 // Only suggest valid if dereferencing needed.
777 // The pointer type implements `Copy` trait so the suggestion is always valid.
778 if let Ok(src) = sm.span_to_snippet(sp) {
779 let derefs = "*".repeat(steps);
780 if let Some((span, src, applicability)) = match mutbl_b {
781 hir::Mutability::Mut => {
782 let new_prefix = "&mut ".to_owned() + &derefs;
784 hir::Mutability::Mut => {
785 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
786 let pos = sp.lo() + BytePos(5);
787 let sp = sp.with_lo(pos).with_hi(pos);
788 (sp, derefs, Applicability::MachineApplicable)
791 hir::Mutability::Not => {
792 replace_prefix(&src, "&", &new_prefix).map(|_| {
793 let pos = sp.lo() + BytePos(1);
794 let sp = sp.with_lo(pos).with_hi(pos);
797 format!("mut {}", derefs),
798 Applicability::Unspecified,
804 hir::Mutability::Not => {
805 let new_prefix = "&".to_owned() + &derefs;
807 hir::Mutability::Mut => {
808 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
809 let lo = sp.lo() + BytePos(1);
810 let hi = sp.lo() + BytePos(5);
811 let sp = sp.with_lo(lo).with_hi(hi);
812 (sp, derefs, Applicability::MachineApplicable)
815 hir::Mutability::Not => {
816 replace_prefix(&src, "&", &new_prefix).map(|_| {
817 let pos = sp.lo() + BytePos(1);
818 let sp = sp.with_lo(pos).with_hi(pos);
819 (sp, derefs, Applicability::MachineApplicable)
827 "consider dereferencing",
837 _ if sp == expr.span => {
838 if let Some(steps) = self.deref_steps(checked_ty, expected) {
839 let expr = expr.peel_blocks();
842 if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
843 // If the expression has `&`, removing it would fix the error
844 let prefix_span = expr.span.with_hi(inner.span.lo());
845 let message = match mutbl {
846 hir::Mutability::Not => "consider removing the `&`",
847 hir::Mutability::Mut => "consider removing the `&mut`",
849 let suggestion = String::new();
854 Applicability::MachineApplicable,
859 // For this suggestion to make sense, the type would need to be `Copy`,
860 // or we have to be moving out of a `Box<T>`
861 if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp)
862 || checked_ty.is_box()
864 let message = if checked_ty.is_box() {
865 "consider unboxing the value"
866 } else if checked_ty.is_region_ptr() {
867 "consider dereferencing the borrow"
869 "consider dereferencing the type"
871 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
872 Some(ident) => format!("{}: ", ident),
873 None => String::new(),
875 let (span, suggestion) = if self.is_else_if_block(expr) {
876 // Don't suggest nonsense like `else *if`
878 } else if let Some(expr) = self.maybe_get_block_expr(expr) {
879 // prefix should be empty here..
880 (expr.span.shrink_to_lo(), "*".to_string())
882 (expr.span.shrink_to_lo(), format!("{}*", prefix))
888 Applicability::MachineApplicable,
900 pub fn check_for_cast(
902 err: &mut Diagnostic,
903 expr: &hir::Expr<'_>,
904 checked_ty: Ty<'tcx>,
905 expected_ty: Ty<'tcx>,
906 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
908 if self.tcx.sess.source_map().is_imported(expr.span) {
909 // Ignore if span is from within a macro.
913 let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
917 // If casting this expression to a given numeric type would be appropriate in case of a type
920 // We want to minimize the amount of casting operations that are suggested, as it can be a
921 // lossy operation with potentially bad side effects, so we only suggest when encountering
922 // an expression that indicates that the original type couldn't be directly changed.
924 // For now, don't suggest casting with `as`.
925 let can_cast = false;
927 let mut sugg = vec![];
929 if let Some(hir::Node::Expr(hir::Expr {
930 kind: hir::ExprKind::Struct(_, fields, _), ..
931 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
933 // `expr` is a literal field for a struct, only suggest if appropriate
936 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
938 // This is a field literal
940 sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
942 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
943 None => return false,
947 if let hir::ExprKind::Call(path, args) = &expr.kind {
948 if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
949 (&path.kind, args.len())
951 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
952 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
953 (&base_ty.kind, path_segment.ident.name)
955 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
969 if base_ty_path.segments.len() == 1 =>
981 "you can convert {} `{}` to {} `{}`",
982 checked_ty.kind().article(),
984 expected_ty.kind().article(),
987 let cast_msg = format!(
988 "you can cast {} `{}` to {} `{}`",
989 checked_ty.kind().article(),
991 expected_ty.kind().article(),
994 let lit_msg = format!(
995 "change the type of the numeric literal from `{}` to `{}`",
996 checked_ty, expected_ty,
999 let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1000 sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1006 let mut cast_suggestion = sugg.clone();
1008 .push((expr.span.shrink_to_hi(), format!("{} as {}", close_paren, expected_ty)));
1009 let mut into_suggestion = sugg.clone();
1010 into_suggestion.push((expr.span.shrink_to_hi(), format!("{}.into()", close_paren)));
1011 let mut suffix_suggestion = sugg.clone();
1012 suffix_suggestion.push((
1014 (&expected_ty.kind(), &checked_ty.kind()),
1015 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1017 // Remove fractional part from literal, for example `42.0f32` into `42`
1018 let src = src.trim_end_matches(&checked_ty.to_string());
1019 let len = src.split('.').next().unwrap().len();
1020 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1022 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1023 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1025 if expr.precedence().order() < PREC_POSTFIX {
1027 format!("{})", expected_ty)
1029 expected_ty.to_string()
1032 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1033 if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1035 let is_negative_int =
1036 |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1037 let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1039 let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1041 let suggest_fallible_into_or_lhs_from =
1042 |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1043 // If we know the expression the expected type is derived from, we might be able
1044 // to suggest a widening conversion rather than a narrowing one (which may
1045 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1047 // can be given the suggestion "u32::from(x) > y" rather than
1048 // "x > y.try_into().unwrap()".
1049 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1053 .span_to_snippet(expr.span)
1055 .map(|src| (expr, src))
1057 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1058 (lhs_expr_and_src, exp_to_found_is_fallible)
1061 "you can convert `{}` from `{}` to `{}`, matching the type of `{}`",
1062 lhs_src, expected_ty, checked_ty, src
1064 let suggestion = vec![
1065 (lhs_expr.span.shrink_to_lo(), format!("{}::from(", checked_ty)),
1066 (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1070 let msg = format!("{} and panic if the converted value doesn't fit", msg);
1071 let mut suggestion = sugg.clone();
1073 expr.span.shrink_to_hi(),
1074 format!("{}.try_into().unwrap()", close_paren),
1078 err.multipart_suggestion_verbose(
1081 Applicability::MachineApplicable,
1085 let suggest_to_change_suffix_or_into =
1086 |err: &mut Diagnostic,
1087 found_to_exp_is_fallible: bool,
1088 exp_to_found_is_fallible: bool| {
1090 expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1096 let always_fallible = found_to_exp_is_fallible
1097 && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1098 let msg = if literal_is_ty_suffixed(expr) {
1100 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1101 // We now know that converting either the lhs or rhs is fallible. Before we
1102 // suggest a fallible conversion, check if the value can never fit in the
1104 let msg = format!("`{}` cannot fit into type `{}`", src, expected_ty);
1107 } else if in_const_context {
1108 // Do not recommend `into` or `try_into` in const contexts.
1110 } else if found_to_exp_is_fallible {
1111 return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1115 let suggestion = if literal_is_ty_suffixed(expr) {
1116 suffix_suggestion.clone()
1118 into_suggestion.clone()
1120 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1123 match (&expected_ty.kind(), &checked_ty.kind()) {
1124 (&ty::Int(ref exp), &ty::Int(ref found)) => {
1125 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1127 (Some(exp), Some(found)) if exp < found => (true, false),
1128 (Some(exp), Some(found)) if exp > found => (false, true),
1129 (None, Some(8 | 16)) => (false, true),
1130 (Some(8 | 16), None) => (true, false),
1131 (None, _) | (_, None) => (true, true),
1132 _ => (false, false),
1134 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1137 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1138 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1140 (Some(exp), Some(found)) if exp < found => (true, false),
1141 (Some(exp), Some(found)) if exp > found => (false, true),
1142 (None, Some(8 | 16)) => (false, true),
1143 (Some(8 | 16), None) => (true, false),
1144 (None, _) | (_, None) => (true, true),
1145 _ => (false, false),
1147 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1150 (&ty::Int(exp), &ty::Uint(found)) => {
1151 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1153 (Some(exp), Some(found)) if found < exp => (false, true),
1154 (None, Some(8)) => (false, true),
1157 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1160 (&ty::Uint(exp), &ty::Int(found)) => {
1161 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1163 (Some(exp), Some(found)) if found > exp => (true, false),
1164 (Some(8), None) => (true, false),
1167 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1170 (&ty::Float(ref exp), &ty::Float(ref found)) => {
1171 if found.bit_width() < exp.bit_width() {
1172 suggest_to_change_suffix_or_into(err, false, true);
1173 } else if literal_is_ty_suffixed(expr) {
1174 err.multipart_suggestion_verbose(
1177 Applicability::MachineApplicable,
1179 } else if can_cast {
1180 // Missing try_into implementation for `f64` to `f32`
1181 err.multipart_suggestion_verbose(
1182 &format!("{}, producing the closest possible value", cast_msg),
1184 Applicability::MaybeIncorrect, // lossy conversion
1189 (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1190 if literal_is_ty_suffixed(expr) {
1191 err.multipart_suggestion_verbose(
1194 Applicability::MachineApplicable,
1196 } else if can_cast {
1197 // Missing try_into implementation for `{float}` to `{integer}`
1198 err.multipart_suggestion_verbose(
1199 &format!("{}, rounding the float towards zero", msg),
1201 Applicability::MaybeIncorrect, // lossy conversion
1206 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1207 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1208 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1209 err.multipart_suggestion_verbose(
1211 "{}, producing the floating point representation of the integer",
1215 Applicability::MachineApplicable,
1217 } else if literal_is_ty_suffixed(expr) {
1218 err.multipart_suggestion_verbose(
1221 Applicability::MachineApplicable,
1224 // Missing try_into implementation for `{integer}` to `{float}`
1225 err.multipart_suggestion_verbose(
1227 "{}, producing the floating point representation of the integer, \
1228 rounded if necessary",
1232 Applicability::MaybeIncorrect, // lossy conversion
1237 (&ty::Float(ref exp), &ty::Int(ref found)) => {
1238 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1239 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1240 err.multipart_suggestion_verbose(
1242 "{}, producing the floating point representation of the integer",
1246 Applicability::MachineApplicable,
1248 } else if literal_is_ty_suffixed(expr) {
1249 err.multipart_suggestion_verbose(
1252 Applicability::MachineApplicable,
1255 // Missing try_into implementation for `{integer}` to `{float}`
1256 err.multipart_suggestion_verbose(
1258 "{}, producing the floating point representation of the integer, \
1259 rounded if necessary",
1263 Applicability::MaybeIncorrect, // lossy conversion
1269 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1270 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1273 err.multipart_suggestion_verbose(
1274 &format!("{}, since a `char` always occupies 4 bytes", cast_msg,),
1276 Applicability::MachineApplicable,
1284 // Report the type inferred by the return statement.
1285 fn report_closure_inferred_return_type(&self, err: &mut Diagnostic, expected: Ty<'tcx>) {
1286 if let Some(sp) = self.ret_coercion_span.get() {
1287 // If the closure has an explicit return type annotation, or if
1288 // the closure's return type has been inferred from outside
1289 // requirements (such as an Fn* trait bound), then a type error
1290 // may occur at the first return expression we see in the closure
1291 // (if it conflicts with the declared return type). Skip adding a
1292 // note in this case, since it would be incorrect.
1293 if !self.return_type_pre_known {
1297 "return type inferred to be `{}` here",
1298 self.resolve_vars_if_possible(expected)