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 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.suggest_block_to_brackets_peeling_refs(err, expr, expr_ty, expected);
43 self.note_type_is_not_clone(err, expected, expr_ty, expr);
44 self.note_need_for_fn_pointer(err, expected, expr_ty);
45 self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
46 self.report_closure_inferred_return_type(err, expected);
49 // Requires that the two types unify, and prints an error message if
51 pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
52 if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
57 pub fn demand_suptype_diag(
62 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
63 self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
66 #[instrument(skip(self), level = "debug")]
67 pub fn demand_suptype_with_origin(
69 cause: &ObligationCause<'tcx>,
72 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
73 match self.at(cause, self.param_env).sup(expected, actual) {
74 Ok(InferOk { obligations, value: () }) => {
75 self.register_predicates(obligations);
78 Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
82 pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
83 if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
88 pub fn demand_eqtype_diag(
93 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
94 self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
97 pub fn demand_eqtype_with_origin(
99 cause: &ObligationCause<'tcx>,
102 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
103 match self.at(cause, self.param_env).eq(expected, actual) {
104 Ok(InferOk { obligations, value: () }) => {
105 self.register_predicates(obligations);
108 Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
112 pub fn demand_coerce(
114 expr: &hir::Expr<'tcx>,
115 checked_ty: Ty<'tcx>,
117 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
118 allow_two_phase: AllowTwoPhase,
121 self.demand_coerce_diag(expr, checked_ty, expected, expected_ty_expr, allow_two_phase);
122 if let Some(mut err) = err {
128 /// Checks that the type of `expr` can be coerced to `expected`.
130 /// N.B., this code relies on `self.diverges` to be accurate. In particular, assignments to `!`
131 /// will be permitted if the diverges flag is currently "always".
132 #[tracing::instrument(level = "debug", skip(self, expr, expected_ty_expr, allow_two_phase))]
133 pub fn demand_coerce_diag(
135 expr: &hir::Expr<'tcx>,
136 checked_ty: Ty<'tcx>,
138 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
139 allow_two_phase: AllowTwoPhase,
140 ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>) {
141 let expected = self.resolve_vars_with_obligations(expected);
143 let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase, None) {
144 Ok(ty) => return (ty, None),
148 self.set_tainted_by_errors();
149 let expr = expr.peel_drop_temps();
150 let cause = self.misc(expr.span);
151 let expr_ty = self.resolve_vars_with_obligations(checked_ty);
152 let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e.clone());
154 let is_insufficiently_polymorphic =
155 matches!(e, TypeError::RegionsInsufficientlyPolymorphic(..));
157 // FIXME(#73154): For now, we do leak check when coercing function
158 // pointers in typeck, instead of only during borrowck. This can lead
159 // to these `RegionsInsufficientlyPolymorphic` errors that aren't helpful.
160 if !is_insufficiently_polymorphic {
161 self.emit_coerce_suggestions(
171 (expected, Some(err))
174 fn annotate_expected_due_to_let_ty(
176 err: &mut Diagnostic,
177 expr: &hir::Expr<'_>,
178 error: Option<TypeError<'_>>,
180 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
181 match (self.tcx.hir().find(parent), error) {
182 (Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })), _)
183 if init.hir_id == expr.hir_id =>
185 // Point at `let` assignment type.
186 err.span_label(ty.span, "expected due to this");
189 Some(hir::Node::Expr(hir::Expr {
190 kind: hir::ExprKind::Assign(lhs, rhs, _), ..
192 Some(TypeError::Sorts(ExpectedFound { expected, .. })),
193 ) if rhs.hir_id == expr.hir_id && !expected.is_closure() => {
194 // We ignore closures explicitly because we already point at them elsewhere.
195 // Point at the assigned-to binding.
196 let mut primary_span = lhs.span;
197 let mut secondary_span = lhs.span;
198 let mut post_message = "";
200 hir::ExprKind::Path(hir::QPath::Resolved(
205 hir::def::DefKind::Static(_) | hir::def::DefKind::Const,
211 if let Some(hir::Node::Item(hir::Item {
213 kind: hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..),
215 })) = self.tcx.hir().get_if_local(*def_id)
217 primary_span = ty.span;
218 secondary_span = ident.span;
219 post_message = " type";
222 hir::ExprKind::Path(hir::QPath::Resolved(
224 hir::Path { res: hir::def::Res::Local(hir_id), .. },
226 if let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(*hir_id) {
227 let parent = self.tcx.hir().get_parent_node(pat.hir_id);
228 primary_span = pat.span;
229 secondary_span = pat.span;
230 match self.tcx.hir().find(parent) {
231 Some(hir::Node::Local(hir::Local { ty: Some(ty), .. })) => {
232 primary_span = ty.span;
233 post_message = " type";
235 Some(hir::Node::Local(hir::Local { init: Some(init), .. })) => {
236 primary_span = init.span;
237 post_message = " value";
239 Some(hir::Node::Param(hir::Param { ty_span, .. })) => {
240 primary_span = *ty_span;
241 post_message = " parameter type";
250 if primary_span != secondary_span
255 .is_multiline(secondary_span.shrink_to_hi().until(primary_span))
257 // We are pointing at the binding's type or initializer value, but it's pattern
258 // is in a different line, so we point at both.
259 err.span_label(secondary_span, "expected due to the type of this binding");
260 err.span_label(primary_span, &format!("expected due to this{post_message}"));
261 } else if post_message == "" {
262 // We are pointing at either the assignment lhs or the binding def pattern.
263 err.span_label(primary_span, "expected due to the type of this binding");
265 // We are pointing at the binding's type or initializer value.
266 err.span_label(primary_span, &format!("expected due to this{post_message}"));
269 if !lhs.is_syntactic_place_expr() {
270 // We already emitted E0070 "invalid left-hand side of assignment", so we
272 err.downgrade_to_delayed_bug();
279 /// If the expected type is an enum (Issue #55250) with any variants whose
280 /// sole field is of the found type, suggest such variants. (Issue #42764)
281 fn suggest_compatible_variants(
283 err: &mut Diagnostic,
284 expr: &hir::Expr<'_>,
288 if let ty::Adt(expected_adt, substs) = expected.kind() {
289 // If the expression is of type () and it's the return expression of a block,
290 // we suggest adding a separate return expression instead.
291 // (To avoid things like suggesting `Ok(while .. { .. })`.)
292 if expr_ty.is_unit() {
293 let mut id = expr.hir_id;
296 // Unroll desugaring, to make sure this works for `for` loops etc.
298 parent = self.tcx.hir().get_parent_node(id);
299 if let Some(parent_span) = self.tcx.hir().opt_span(parent) {
300 if parent_span.find_ancestor_inside(expr.span).is_some() {
301 // The parent node is part of the same span, so is the result of the
302 // same expansion/desugaring and not the 'real' parent node.
310 if let Some(hir::Node::Block(&hir::Block {
311 span: block_span, expr: Some(e), ..
312 })) = self.tcx.hir().find(parent)
315 if let Some(span) = expr.span.find_ancestor_inside(block_span) {
316 let return_suggestions = if self
318 .is_diagnostic_item(sym::Result, expected_adt.did())
321 } else if self.tcx.is_diagnostic_item(sym::Option, expected_adt.did()) {
322 vec!["None", "Some(())"]
326 if let Some(indent) =
327 self.tcx.sess.source_map().indentation_before(span.shrink_to_lo())
329 // Add a semicolon, except after `}`.
331 match self.tcx.sess.source_map().span_to_snippet(span) {
332 Ok(s) if s.ends_with('}') => "",
335 err.span_suggestions(
337 "try adding an expression at the end of the block",
340 .map(|r| format!("{semicolon}\n{indent}{r}")),
341 Applicability::MaybeIncorrect,
350 let compatible_variants: Vec<String> = expected_adt
354 variant.fields.len() == 1 && variant.ctor_kind == hir::def::CtorKind::Fn
356 .filter_map(|variant| {
357 let sole_field = &variant.fields[0];
358 let sole_field_ty = sole_field.ty(self.tcx, substs);
359 if self.can_coerce(expr_ty, sole_field_ty) {
361 with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
362 // FIXME #56861: DRYer prelude filtering
363 if let Some(path) = variant_path.strip_prefix("std::prelude::")
364 && let Some((_, path)) = path.split_once("::")
366 return Some(path.to_string());
375 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
376 Some(ident) => format!("{ident}: "),
377 None => String::new(),
380 match &compatible_variants[..] {
381 [] => { /* No variants to format */ }
383 // Just a single matching variant.
384 err.multipart_suggestion_verbose(
385 &format!("try wrapping the expression in `{variant}`"),
387 (expr.span.shrink_to_lo(), format!("{prefix}{variant}(")),
388 (expr.span.shrink_to_hi(), ")".to_string()),
390 Applicability::MaybeIncorrect,
394 // More than one matching variant.
395 err.multipart_suggestions(
397 "try wrapping the expression in a variant of `{}`",
398 self.tcx.def_path_str(expected_adt.did())
400 compatible_variants.into_iter().map(|variant| {
402 (expr.span.shrink_to_lo(), format!("{prefix}{variant}(")),
403 (expr.span.shrink_to_hi(), ")".to_string()),
406 Applicability::MaybeIncorrect,
413 pub fn get_conversion_methods(
417 checked_ty: Ty<'tcx>,
419 ) -> Vec<AssocItem> {
421 self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
423 self.has_only_self_parameter(m)
426 // This special internal attribute is used to permit
427 // "identity-like" conversion methods to be suggested here.
429 // FIXME (#46459 and #46460): ideally
430 // `std::convert::Into::into` and `std::borrow:ToOwned` would
431 // also be `#[rustc_conversion_suggestion]`, if not for
432 // method-probing false-positives and -negatives (respectively).
434 // FIXME? Other potential candidate methods: `as_ref` and
436 .has_attr(m.def_id, sym::rustc_conversion_suggestion)
442 /// This function checks whether the method is not static and does not accept other parameters than `self`.
443 fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
445 ty::AssocKind::Fn => {
446 method.fn_has_self_parameter
447 && self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
453 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
455 /// Given the following code:
456 /// ```compile_fail,E0308
458 /// fn takes_ref(_: &Foo) {}
459 /// let ref opt = Some(Foo);
461 /// opt.map(|param| takes_ref(param));
463 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
465 /// It only checks for `Option` and `Result` and won't work with
466 /// ```ignore (illustrative)
467 /// opt.map(|param| { takes_ref(param) });
469 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
470 let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind else {
474 let hir::def::Res::Local(local_id) = path.res else {
478 let local_parent = self.tcx.hir().get_parent_node(local_id);
479 let Some(Node::Param(hir::Param { hir_id: param_hir_id, .. })) = self.tcx.hir().find(local_parent) else {
483 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
484 let Some(Node::Expr(hir::Expr {
486 kind: hir::ExprKind::Closure(hir::Closure { fn_decl: closure_fn_decl, .. }),
488 })) = self.tcx.hir().find(param_parent) else {
492 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
493 let hir = self.tcx.hir().find(expr_parent);
494 let closure_params_len = closure_fn_decl.inputs.len();
496 Some(Node::Expr(hir::Expr {
497 kind: hir::ExprKind::MethodCall(method_path, method_expr, _),
501 ) = (hir, closure_params_len) else {
505 let self_ty = self.typeck_results.borrow().expr_ty(&method_expr[0]);
506 let self_ty = format!("{:?}", self_ty);
507 let name = method_path.ident.name;
508 let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
509 || self_ty.starts_with("&std::result::Result")
510 || self_ty.starts_with("std::option::Option")
511 || self_ty.starts_with("std::result::Result"))
512 && (name == sym::map || name == sym::and_then);
513 match (is_as_ref_able, self.sess().source_map().span_to_snippet(method_path.ident.span)) {
515 let suggestion = format!("as_ref().{}", src);
516 Some((method_path.ident.span, "consider using `as_ref` instead", suggestion))
522 pub(crate) fn maybe_get_struct_pattern_shorthand_field(
524 expr: &hir::Expr<'_>,
525 ) -> Option<Symbol> {
526 let hir = self.tcx.hir();
527 let local = match expr {
530 hir::ExprKind::Path(hir::QPath::Resolved(
533 res: hir::def::Res::Local(_),
534 segments: [hir::PathSegment { ident, .. }],
543 match hir.find(hir.get_parent_node(expr.hir_id))? {
544 Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) => {
545 for field in *fields {
546 if field.ident.name == local.name && field.is_shorthand {
547 return Some(local.name);
557 /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
558 pub(crate) fn maybe_get_block_expr(
560 expr: &hir::Expr<'tcx>,
561 ) -> Option<&'tcx hir::Expr<'tcx>> {
563 hir::Expr { kind: hir::ExprKind::Block(block, ..), .. } => block.expr,
568 /// Returns whether the given expression is an `else if`.
569 pub(crate) fn is_else_if_block(&self, expr: &hir::Expr<'_>) -> bool {
570 if let hir::ExprKind::If(..) = expr.kind {
571 let parent_id = self.tcx.hir().get_parent_node(expr.hir_id);
572 if let Some(Node::Expr(hir::Expr {
573 kind: hir::ExprKind::If(_, _, Some(else_expr)),
575 })) = self.tcx.hir().find(parent_id)
577 return else_expr.hir_id == expr.hir_id;
583 /// This function is used to determine potential "simple" improvements or users' errors and
584 /// provide them useful help. For example:
586 /// ```compile_fail,E0308
587 /// fn some_fn(s: &str) {}
589 /// let x = "hey!".to_owned();
590 /// some_fn(x); // error
593 /// No need to find every potential function which could make a coercion to transform a
594 /// `String` into a `&str` since a `&` would do the trick!
596 /// In addition of this check, it also checks between references mutability state. If the
597 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
601 expr: &hir::Expr<'tcx>,
602 checked_ty: Ty<'tcx>,
604 ) -> Option<(Span, String, String, Applicability, bool /* verbose */)> {
605 let sess = self.sess();
608 // If the span is from an external macro, there's no suggestion we can make.
609 if in_external_macro(sess, sp) {
613 let sm = sess.source_map();
615 let replace_prefix = |s: &str, old: &str, new: &str| {
616 s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
619 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
620 let expr = expr.peel_drop_temps();
622 match (&expr.kind, expected.kind(), checked_ty.kind()) {
623 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
624 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
625 if let hir::ExprKind::Lit(_) = expr.kind
626 && let Ok(src) = sm.span_to_snippet(sp)
627 && replace_prefix(&src, "b\"", "\"").is_some()
629 let pos = sp.lo() + BytePos(1);
632 "consider removing the leading `b`".to_string(),
634 Applicability::MachineApplicable,
639 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
640 if let hir::ExprKind::Lit(_) = expr.kind
641 && let Ok(src) = sm.span_to_snippet(sp)
642 && replace_prefix(&src, "\"", "b\"").is_some()
646 "consider adding a leading `b`".to_string(),
648 Applicability::MachineApplicable,
655 (_, &ty::Ref(_, _, mutability), _) => {
656 // Check if it can work when put into a ref. For example:
659 // fn bar(x: &mut i32) {}
662 // bar(&x); // error, expected &mut
664 let ref_ty = match mutability {
665 hir::Mutability::Mut => {
666 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
668 hir::Mutability::Not => {
669 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
672 if self.can_coerce(ref_ty, expected) {
673 let mut sugg_sp = sp;
674 if let hir::ExprKind::MethodCall(ref segment, ref args, _) = expr.kind {
676 self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
677 if let ([arg], Some(true), sym::clone) = (
679 self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
681 let ai = self.tcx.associated_item(did);
682 ai.container == ty::TraitContainer(clone_trait)
687 // If this expression had a clone call when suggesting borrowing
688 // we want to suggest removing it because it'd now be unnecessary.
692 if let Ok(src) = sm.span_to_snippet(sugg_sp) {
693 let needs_parens = match expr.kind {
694 // parenthesize if needed (Issue #46756)
695 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
696 // parenthesize borrows of range literals (Issue #54505)
697 _ if is_range_literal(expr) => true,
700 let sugg_expr = if needs_parens { format!("({src})") } else { src };
702 if let Some(sugg) = self.can_use_as_ref(expr) {
707 Applicability::MachineApplicable,
712 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
713 Some(ident) => format!("{ident}: "),
714 None => String::new(),
717 if let Some(hir::Node::Expr(hir::Expr {
718 kind: hir::ExprKind::Assign(..),
720 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
722 if mutability == hir::Mutability::Mut {
723 // Suppressing this diagnostic, we'll properly print it in `check_expr_assign`
728 return Some(match mutability {
729 hir::Mutability::Mut => (
731 "consider mutably borrowing here".to_string(),
732 format!("{prefix}&mut {sugg_expr}"),
733 Applicability::MachineApplicable,
736 hir::Mutability::Not => (
738 "consider borrowing here".to_string(),
739 format!("{prefix}&{sugg_expr}"),
740 Applicability::MachineApplicable,
748 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
750 &ty::Ref(_, checked, _),
751 ) if self.infcx.can_sub(self.param_env, checked, expected).is_ok() => {
752 // We have `&T`, check if what was expected was `T`. If so,
753 // we may want to suggest removing a `&`.
754 if sm.is_imported(expr.span) {
755 // Go through the spans from which this span was expanded,
756 // and find the one that's pointing inside `sp`.
758 // E.g. for `&format!("")`, where we want the span to the
759 // `format!()` invocation instead of its expansion.
760 if let Some(call_span) =
761 iter::successors(Some(expr.span), |s| s.parent_callsite())
762 .find(|&s| sp.contains(s))
763 && sm.is_span_accessible(call_span)
766 sp.with_hi(call_span.lo()),
767 "consider removing the borrow".to_string(),
769 Applicability::MachineApplicable,
775 if sp.contains(expr.span)
776 && sm.is_span_accessible(expr.span)
779 sp.with_hi(expr.span.lo()),
780 "consider removing the borrow".to_string(),
782 Applicability::MachineApplicable,
789 &ty::RawPtr(TypeAndMut { ty: ty_b, mutbl: mutbl_b }),
790 &ty::Ref(_, ty_a, mutbl_a),
792 if let Some(steps) = self.deref_steps(ty_a, ty_b)
793 // Only suggest valid if dereferencing needed.
795 // The pointer type implements `Copy` trait so the suggestion is always valid.
796 && let Ok(src) = sm.span_to_snippet(sp)
798 let derefs = "*".repeat(steps);
799 if let Some((span, src, applicability)) = match mutbl_b {
800 hir::Mutability::Mut => {
801 let new_prefix = "&mut ".to_owned() + &derefs;
803 hir::Mutability::Mut => {
804 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
805 let pos = sp.lo() + BytePos(5);
806 let sp = sp.with_lo(pos).with_hi(pos);
807 (sp, derefs, Applicability::MachineApplicable)
810 hir::Mutability::Not => {
811 replace_prefix(&src, "&", &new_prefix).map(|_| {
812 let pos = sp.lo() + BytePos(1);
813 let sp = sp.with_lo(pos).with_hi(pos);
816 format!("mut {derefs}"),
817 Applicability::Unspecified,
823 hir::Mutability::Not => {
824 let new_prefix = "&".to_owned() + &derefs;
826 hir::Mutability::Mut => {
827 replace_prefix(&src, "&mut ", &new_prefix).map(|_| {
828 let lo = sp.lo() + BytePos(1);
829 let hi = sp.lo() + BytePos(5);
830 let sp = sp.with_lo(lo).with_hi(hi);
831 (sp, derefs, Applicability::MachineApplicable)
834 hir::Mutability::Not => {
835 replace_prefix(&src, "&", &new_prefix).map(|_| {
836 let pos = sp.lo() + BytePos(1);
837 let sp = sp.with_lo(pos).with_hi(pos);
838 (sp, derefs, Applicability::MachineApplicable)
846 "consider dereferencing".to_string(),
854 _ if sp == expr.span => {
855 if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
856 let mut expr = expr.peel_blocks();
857 let mut prefix_span = expr.span.shrink_to_lo();
858 let mut remove = String::new();
860 // Try peeling off any existing `&` and `&mut` to reach our target type
862 if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
863 // If the expression has `&`, removing it would fix the error
864 prefix_span = prefix_span.with_hi(inner.span.lo());
866 remove += match mutbl {
867 hir::Mutability::Not => "&",
868 hir::Mutability::Mut => "&mut ",
875 // If we've reached our target type with just removing `&`, then just print now.
879 format!("consider removing the `{}`", remove.trim()),
881 // Do not remove `&&` to get to bool, because it might be something like
882 // { a } && b, which we have a separate fixup suggestion that is more
884 if remove.trim() == "&&" && expected == self.tcx.types.bool {
885 Applicability::MaybeIncorrect
887 Applicability::MachineApplicable
893 // For this suggestion to make sense, the type would need to be `Copy`,
894 // or we have to be moving out of a `Box<T>`
895 if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp)
896 // FIXME(compiler-errors): We can actually do this if the checked_ty is
897 // `steps` layers of boxes, not just one, but this is easier and most likely.
898 || (checked_ty.is_box() && steps == 1)
900 let deref_kind = if checked_ty.is_box() {
902 } else if checked_ty.is_region_ptr() {
903 "dereferencing the borrow"
905 "dereferencing the type"
908 // Suggest removing `&` if we have removed any, otherwise suggest just
909 // dereferencing the remaining number of steps.
910 let message = if remove.is_empty() {
911 format!("consider {deref_kind}")
914 "consider removing the `{}` and {} instead",
920 let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
921 Some(ident) => format!("{ident}: "),
922 None => String::new(),
925 let (span, suggestion) = if self.is_else_if_block(expr) {
926 // Don't suggest nonsense like `else *if`
928 } else if let Some(expr) = self.maybe_get_block_expr(expr) {
929 // prefix should be empty here..
930 (expr.span.shrink_to_lo(), "*".to_string())
932 (prefix_span, format!("{}{}", prefix, "*".repeat(steps)))
939 Applicability::MachineApplicable,
950 pub fn check_for_cast(
952 err: &mut Diagnostic,
953 expr: &hir::Expr<'_>,
954 checked_ty: Ty<'tcx>,
955 expected_ty: Ty<'tcx>,
956 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
958 if self.tcx.sess.source_map().is_imported(expr.span) {
959 // Ignore if span is from within a macro.
963 let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) else {
967 // If casting this expression to a given numeric type would be appropriate in case of a type
970 // We want to minimize the amount of casting operations that are suggested, as it can be a
971 // lossy operation with potentially bad side effects, so we only suggest when encountering
972 // an expression that indicates that the original type couldn't be directly changed.
974 // For now, don't suggest casting with `as`.
975 let can_cast = false;
977 let mut sugg = vec![];
979 if let Some(hir::Node::Expr(hir::Expr {
980 kind: hir::ExprKind::Struct(_, fields, _), ..
981 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
983 // `expr` is a literal field for a struct, only suggest if appropriate
986 .find(|field| field.expr.hir_id == expr.hir_id && field.is_shorthand)
988 // This is a field literal
990 sugg.push((field.ident.span.shrink_to_lo(), format!("{}: ", field.ident)));
992 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
993 None => return false,
997 if let hir::ExprKind::Call(path, args) = &expr.kind
998 && let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
999 (&path.kind, args.len())
1000 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
1001 && let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
1002 (&base_ty.kind, path_segment.ident.name)
1004 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
1018 if base_ty_path.segments.len() == 1 =>
1028 "you can convert {} `{}` to {} `{}`",
1029 checked_ty.kind().article(),
1031 expected_ty.kind().article(),
1034 let cast_msg = format!(
1035 "you can cast {} `{}` to {} `{}`",
1036 checked_ty.kind().article(),
1038 expected_ty.kind().article(),
1041 let lit_msg = format!(
1042 "change the type of the numeric literal from `{checked_ty}` to `{expected_ty}`",
1045 let close_paren = if expr.precedence().order() < PREC_POSTFIX {
1046 sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
1052 let mut cast_suggestion = sugg.clone();
1053 cast_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren} as {expected_ty}")));
1054 let mut into_suggestion = sugg.clone();
1055 into_suggestion.push((expr.span.shrink_to_hi(), format!("{close_paren}.into()")));
1056 let mut suffix_suggestion = sugg.clone();
1057 suffix_suggestion.push((
1059 (&expected_ty.kind(), &checked_ty.kind()),
1060 (ty::Int(_) | ty::Uint(_), ty::Float(_))
1062 // Remove fractional part from literal, for example `42.0f32` into `42`
1063 let src = src.trim_end_matches(&checked_ty.to_string());
1064 let len = src.split('.').next().unwrap().len();
1065 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1067 let len = src.trim_end_matches(&checked_ty.to_string()).len();
1068 expr.span.with_lo(expr.span.lo() + BytePos(len as u32))
1070 if expr.precedence().order() < PREC_POSTFIX {
1072 format!("{expected_ty})")
1074 expected_ty.to_string()
1077 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
1078 if let hir::ExprKind::Lit(lit) = &expr.kind { lit.node.is_suffixed() } else { false }
1080 let is_negative_int =
1081 |expr: &hir::Expr<'_>| matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Neg, ..));
1082 let is_uint = |ty: Ty<'_>| matches!(ty.kind(), ty::Uint(..));
1084 let in_const_context = self.tcx.hir().is_inside_const_context(expr.hir_id);
1086 let suggest_fallible_into_or_lhs_from =
1087 |err: &mut Diagnostic, exp_to_found_is_fallible: bool| {
1088 // If we know the expression the expected type is derived from, we might be able
1089 // to suggest a widening conversion rather than a narrowing one (which may
1090 // panic). For example, given x: u8 and y: u32, if we know the span of "x",
1092 // can be given the suggestion "u32::from(x) > y" rather than
1093 // "x > y.try_into().unwrap()".
1094 let lhs_expr_and_src = expected_ty_expr.and_then(|expr| {
1098 .span_to_snippet(expr.span)
1100 .map(|src| (expr, src))
1102 let (msg, suggestion) = if let (Some((lhs_expr, lhs_src)), false) =
1103 (lhs_expr_and_src, exp_to_found_is_fallible)
1106 "you can convert `{lhs_src}` from `{expected_ty}` to `{checked_ty}`, matching the type of `{src}`",
1108 let suggestion = vec![
1109 (lhs_expr.span.shrink_to_lo(), format!("{checked_ty}::from(")),
1110 (lhs_expr.span.shrink_to_hi(), ")".to_string()),
1114 let msg = format!("{msg} and panic if the converted value doesn't fit");
1115 let mut suggestion = sugg.clone();
1117 expr.span.shrink_to_hi(),
1118 format!("{close_paren}.try_into().unwrap()"),
1122 err.multipart_suggestion_verbose(
1125 Applicability::MachineApplicable,
1129 let suggest_to_change_suffix_or_into =
1130 |err: &mut Diagnostic,
1131 found_to_exp_is_fallible: bool,
1132 exp_to_found_is_fallible: bool| {
1134 expected_ty_expr.map(|e| self.tcx.hir().is_lhs(e.hir_id)).unwrap_or(false);
1140 let always_fallible = found_to_exp_is_fallible
1141 && (exp_to_found_is_fallible || expected_ty_expr.is_none());
1142 let msg = if literal_is_ty_suffixed(expr) {
1144 } else if always_fallible && (is_negative_int(expr) && is_uint(expected_ty)) {
1145 // We now know that converting either the lhs or rhs is fallible. Before we
1146 // suggest a fallible conversion, check if the value can never fit in the
1148 let msg = format!("`{src}` cannot fit into type `{expected_ty}`");
1151 } else if in_const_context {
1152 // Do not recommend `into` or `try_into` in const contexts.
1154 } else if found_to_exp_is_fallible {
1155 return suggest_fallible_into_or_lhs_from(err, exp_to_found_is_fallible);
1159 let suggestion = if literal_is_ty_suffixed(expr) {
1160 suffix_suggestion.clone()
1162 into_suggestion.clone()
1164 err.multipart_suggestion_verbose(msg, suggestion, Applicability::MachineApplicable);
1167 match (&expected_ty.kind(), &checked_ty.kind()) {
1168 (&ty::Int(ref exp), &ty::Int(ref found)) => {
1169 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1171 (Some(exp), Some(found)) if exp < found => (true, false),
1172 (Some(exp), Some(found)) if exp > found => (false, true),
1173 (None, Some(8 | 16)) => (false, true),
1174 (Some(8 | 16), None) => (true, false),
1175 (None, _) | (_, None) => (true, true),
1176 _ => (false, false),
1178 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1181 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
1182 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1184 (Some(exp), Some(found)) if exp < found => (true, false),
1185 (Some(exp), Some(found)) if exp > found => (false, true),
1186 (None, Some(8 | 16)) => (false, true),
1187 (Some(8 | 16), None) => (true, false),
1188 (None, _) | (_, None) => (true, true),
1189 _ => (false, false),
1191 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1194 (&ty::Int(exp), &ty::Uint(found)) => {
1195 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1197 (Some(exp), Some(found)) if found < exp => (false, true),
1198 (None, Some(8)) => (false, true),
1201 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1204 (&ty::Uint(exp), &ty::Int(found)) => {
1205 let (f2e_is_fallible, e2f_is_fallible) = match (exp.bit_width(), found.bit_width())
1207 (Some(exp), Some(found)) if found > exp => (true, false),
1208 (Some(8), None) => (true, false),
1211 suggest_to_change_suffix_or_into(err, f2e_is_fallible, e2f_is_fallible);
1214 (&ty::Float(ref exp), &ty::Float(ref found)) => {
1215 if found.bit_width() < exp.bit_width() {
1216 suggest_to_change_suffix_or_into(err, false, true);
1217 } else if literal_is_ty_suffixed(expr) {
1218 err.multipart_suggestion_verbose(
1221 Applicability::MachineApplicable,
1223 } else if can_cast {
1224 // Missing try_into implementation for `f64` to `f32`
1225 err.multipart_suggestion_verbose(
1226 &format!("{cast_msg}, producing the closest possible value"),
1228 Applicability::MaybeIncorrect, // lossy conversion
1233 (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
1234 if literal_is_ty_suffixed(expr) {
1235 err.multipart_suggestion_verbose(
1238 Applicability::MachineApplicable,
1240 } else if can_cast {
1241 // Missing try_into implementation for `{float}` to `{integer}`
1242 err.multipart_suggestion_verbose(
1243 &format!("{msg}, rounding the float towards zero"),
1245 Applicability::MaybeIncorrect, // lossy conversion
1250 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
1251 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
1252 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1253 err.multipart_suggestion_verbose(
1255 "{msg}, producing the floating point representation of the integer",
1258 Applicability::MachineApplicable,
1260 } else if literal_is_ty_suffixed(expr) {
1261 err.multipart_suggestion_verbose(
1264 Applicability::MachineApplicable,
1267 // Missing try_into implementation for `{integer}` to `{float}`
1268 err.multipart_suggestion_verbose(
1270 "{cast_msg}, producing the floating point representation of the integer, \
1271 rounded if necessary",
1274 Applicability::MaybeIncorrect, // lossy conversion
1279 (&ty::Float(ref exp), &ty::Int(ref found)) => {
1280 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
1281 if exp.bit_width() > found.bit_width().unwrap_or(256) {
1282 err.multipart_suggestion_verbose(
1284 "{}, producing the floating point representation of the integer",
1288 Applicability::MachineApplicable,
1290 } else if literal_is_ty_suffixed(expr) {
1291 err.multipart_suggestion_verbose(
1294 Applicability::MachineApplicable,
1297 // Missing try_into implementation for `{integer}` to `{float}`
1298 err.multipart_suggestion_verbose(
1300 "{}, producing the floating point representation of the integer, \
1301 rounded if necessary",
1305 Applicability::MaybeIncorrect, // lossy conversion
1311 &ty::Uint(ty::UintTy::U32 | ty::UintTy::U64 | ty::UintTy::U128)
1312 | &ty::Int(ty::IntTy::I32 | ty::IntTy::I64 | ty::IntTy::I128),
1315 err.multipart_suggestion_verbose(
1316 &format!("{cast_msg}, since a `char` always occupies 4 bytes"),
1318 Applicability::MachineApplicable,
1326 // Report the type inferred by the return statement.
1327 fn report_closure_inferred_return_type(&self, err: &mut Diagnostic, expected: Ty<'tcx>) {
1328 if let Some(sp) = self.ret_coercion_span.get()
1329 // If the closure has an explicit return type annotation, or if
1330 // the closure's return type has been inferred from outside
1331 // requirements (such as an Fn* trait bound), then a type error
1332 // may occur at the first return expression we see in the closure
1333 // (if it conflicts with the declared return type). Skip adding a
1334 // note in this case, since it would be incorrect.
1335 && !self.return_type_pre_known
1340 "return type inferred to be `{}` here",
1341 self.resolve_vars_if_possible(expected)