1 use crate::check::FnCtxt;
2 use rustc::infer::InferOk;
3 use rustc::traits::{self, ObligationCause};
5 use rustc::ty::adjustment::AllowTwoPhase;
6 use rustc::ty::{self, AssocItem, Ty};
7 use rustc_errors::{Applicability, DiagnosticBuilder};
9 use rustc_hir::{is_range_literal, print, Node};
10 use rustc_span::symbol::sym;
12 use syntax::util::parser::PREC_POSTFIX;
14 use super::method::probe;
16 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
17 pub fn emit_coerce_suggestions(
19 err: &mut DiagnosticBuilder<'_>,
24 self.annotate_expected_due_to_let_ty(err, expr);
25 self.suggest_compatible_variants(err, expr, expected, expr_ty);
26 self.suggest_ref_or_into(err, expr, expected, expr_ty);
27 self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
28 self.suggest_missing_await(err, expr, expected, expr_ty);
31 // Requires that the two types unify, and prints an error message if
33 pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
34 self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
37 pub fn demand_suptype_diag(
42 ) -> Option<DiagnosticBuilder<'tcx>> {
43 let cause = &self.misc(sp);
44 match self.at(cause, self.param_env).sup(expected, actual) {
45 Ok(InferOk { obligations, value: () }) => {
46 self.register_predicates(obligations);
49 Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
53 pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
54 if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
59 pub fn demand_eqtype_diag(
64 ) -> Option<DiagnosticBuilder<'tcx>> {
65 self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
68 pub fn demand_eqtype_with_origin(
70 cause: &ObligationCause<'tcx>,
73 ) -> Option<DiagnosticBuilder<'tcx>> {
74 match self.at(cause, self.param_env).eq(expected, actual) {
75 Ok(InferOk { obligations, value: () }) => {
76 self.register_predicates(obligations);
79 Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
88 allow_two_phase: AllowTwoPhase,
90 let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
91 if let Some(mut err) = err {
97 // Checks that the type of `expr` can be coerced to `expected`.
99 // N.B., this code relies on `self.diverges` to be accurate. In
100 // particular, assignments to `!` will be permitted if the
101 // diverges flag is currently "always".
102 pub fn demand_coerce_diag(
104 expr: &hir::Expr<'_>,
105 checked_ty: Ty<'tcx>,
107 allow_two_phase: AllowTwoPhase,
108 ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
109 let expected = self.resolve_vars_with_obligations(expected);
111 let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
112 Ok(ty) => return (ty, None),
116 let expr = expr.peel_drop_temps();
117 let cause = self.misc(expr.span);
118 let expr_ty = self.resolve_vars_with_obligations(checked_ty);
119 let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
121 if self.is_assign_to_bool(expr, expected) {
122 // Error reported in `check_assign` so avoid emitting error again.
124 return (expected, None);
127 self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected);
129 (expected, Some(err))
132 fn annotate_expected_due_to_let_ty(
134 err: &mut DiagnosticBuilder<'_>,
135 expr: &hir::Expr<'_>,
137 let parent = self.tcx.hir().get_parent_node(expr.hir_id);
138 if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
139 self.tcx.hir().find(parent)
141 if init.hir_id == expr.hir_id {
142 // Point at `let` assignment type.
143 err.span_label(ty.span, "expected due to this");
148 /// Returns whether the expected type is `bool` and the expression is `x = y`.
149 pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
150 if let hir::ExprKind::Assign(..) = expr.kind {
151 return expected == self.tcx.types.bool;
156 /// If the expected type is an enum (Issue #55250) with any variants whose
157 /// sole field is of the found type, suggest such variants. (Issue #42764)
158 fn suggest_compatible_variants(
160 err: &mut DiagnosticBuilder<'_>,
161 expr: &hir::Expr<'_>,
165 if let ty::Adt(expected_adt, substs) = expected.kind {
166 if !expected_adt.is_enum() {
170 let mut compatible_variants = expected_adt
173 .filter(|variant| variant.fields.len() == 1)
174 .filter_map(|variant| {
175 let sole_field = &variant.fields[0];
176 let sole_field_ty = sole_field.ty(self.tcx, substs);
177 if self.can_coerce(expr_ty, sole_field_ty) {
178 let variant_path = self.tcx.def_path_str(variant.def_id);
179 // FIXME #56861: DRYer prelude filtering
180 Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
187 if compatible_variants.peek().is_some() {
189 self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or_else(|_| {
190 print::to_string(print::NO_ANN, |s| s.print_expr(expr))
192 let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
193 let msg = "try using a variant of the expected enum";
194 err.span_suggestions(expr.span, msg, suggestions, Applicability::MaybeIncorrect);
199 pub fn get_conversion_methods(
203 checked_ty: Ty<'tcx>,
204 ) -> Vec<AssocItem> {
205 let mut methods = self.probe_for_return_type(
207 probe::Mode::MethodCall,
213 self.has_no_input_arg(m)
218 // This special internal attribute is used to whitelist
219 // "identity-like" conversion methods to be suggested here.
221 // FIXME (#46459 and #46460): ideally
222 // `std::convert::Into::into` and `std::borrow:ToOwned` would
223 // also be `#[rustc_conversion_suggestion]`, if not for
224 // method-probing false-positives and -negatives (respectively).
226 // FIXME? Other potential candidate methods: `as_ref` and
228 .find(|a| a.check_name(sym::rustc_conversion_suggestion))
235 // This function checks if the method isn't static and takes other arguments than `self`.
236 fn has_no_input_arg(&self, method: &AssocItem) -> bool {
238 ty::AssocKind::Method => {
239 self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1
245 /// Identify some cases where `as_ref()` would be appropriate and suggest it.
247 /// Given the following code:
250 /// fn takes_ref(_: &Foo) {}
251 /// let ref opt = Some(Foo);
253 /// opt.map(|param| takes_ref(param));
255 /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
257 /// It only checks for `Option` and `Result` and won't work with
259 /// opt.map(|param| { takes_ref(param) });
261 fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
262 let path = match expr.kind {
263 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
267 let local_id = match path.res {
268 hir::def::Res::Local(id) => id,
272 let local_parent = self.tcx.hir().get_parent_node(local_id);
273 let param_hir_id = match self.tcx.hir().find(local_parent) {
274 Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
278 let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
279 let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
280 Some(Node::Expr(hir::Expr {
282 kind: hir::ExprKind::Closure(_, decl, ..),
284 })) => (hir_id, decl),
288 let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
289 let hir = self.tcx.hir().find(expr_parent);
290 let closure_params_len = closure_fn_decl.inputs.len();
291 let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
293 Some(Node::Expr(hir::Expr {
294 kind: hir::ExprKind::MethodCall(path, span, expr),
298 ) => (path, span, expr),
302 let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
303 let self_ty = format!("{:?}", self_ty);
304 let name = method_path.ident.as_str();
305 let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
306 || self_ty.starts_with("&std::result::Result")
307 || self_ty.starts_with("std::option::Option")
308 || self_ty.starts_with("std::result::Result"))
309 && (name == "map" || name == "and_then");
310 match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
312 let suggestion = format!("as_ref().{}", src);
313 Some((*method_span, "consider using `as_ref` instead", suggestion))
319 crate fn is_hir_id_from_struct_pattern_shorthand_field(
324 let cm = self.sess().source_map();
325 let parent_id = self.tcx.hir().get_parent_node(hir_id);
326 if let Some(parent) = self.tcx.hir().find(parent_id) {
327 // Account for fields
328 if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
330 if let Ok(src) = cm.span_to_snippet(sp) {
331 for field in *fields {
332 if field.ident.as_str() == src && field.is_shorthand {
342 /// This function is used to determine potential "simple" improvements or users' errors and
343 /// provide them useful help. For example:
346 /// fn some_fn(s: &str) {}
348 /// let x = "hey!".to_owned();
349 /// some_fn(x); // error
352 /// No need to find every potential function which could make a coercion to transform a
353 /// `String` into a `&str` since a `&` would do the trick!
355 /// In addition of this check, it also checks between references mutability state. If the
356 /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
360 expr: &hir::Expr<'_>,
361 checked_ty: Ty<'tcx>,
363 ) -> Option<(Span, &'static str, String)> {
364 let cm = self.sess().source_map();
366 if !cm.span_to_filename(sp).is_real() {
367 // Ignore if span is from within a macro #41858, #58298. We previously used the macro
368 // call span, but that breaks down when the type error comes from multiple calls down.
372 let is_struct_pat_shorthand_field =
373 self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
375 // If the span is from a macro, then it's hard to extract the text
376 // and make a good suggestion, so don't bother.
377 let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
379 // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
380 let expr = expr.peel_drop_temps();
382 match (&expr.kind, &expected.kind, &checked_ty.kind) {
383 (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
384 (&ty::Str, &ty::Array(arr, _)) | (&ty::Str, &ty::Slice(arr))
385 if arr == self.tcx.types.u8 =>
387 if let hir::ExprKind::Lit(_) = expr.kind {
388 if let Ok(src) = cm.span_to_snippet(sp) {
389 if src.starts_with("b\"") {
392 "consider removing the leading `b`",
393 src[1..].to_string(),
399 (&ty::Array(arr, _), &ty::Str) | (&ty::Slice(arr), &ty::Str)
400 if arr == self.tcx.types.u8 =>
402 if let hir::ExprKind::Lit(_) = expr.kind {
403 if let Ok(src) = cm.span_to_snippet(sp) {
404 if src.starts_with("\"") {
407 "consider adding a leading `b`",
416 (_, &ty::Ref(_, _, mutability), _) => {
417 // Check if it can work when put into a ref. For example:
420 // fn bar(x: &mut i32) {}
423 // bar(&x); // error, expected &mut
425 let ref_ty = match mutability {
426 hir::Mutability::Mut => {
427 self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
429 hir::Mutability::Not => {
430 self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
433 if self.can_coerce(ref_ty, expected) {
434 let mut sugg_sp = sp;
435 if let hir::ExprKind::MethodCall(segment, _sp, args) = &expr.kind {
436 let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
437 if let ([arg], Some(true), sym::clone) = (
439 self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
440 let ai = self.tcx.associated_item(did);
441 ai.container == ty::TraitContainer(clone_trait)
445 // If this expression had a clone call when suggesting borrowing
446 // we want to suggest removing it because it'd now be unnecessary.
450 if let Ok(src) = cm.span_to_snippet(sugg_sp) {
451 let needs_parens = match expr.kind {
452 // parenthesize if needed (Issue #46756)
453 hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
454 // parenthesize borrows of range literals (Issue #54505)
455 _ if is_range_literal(self.tcx.sess.source_map(), expr) => true,
458 let sugg_expr = if needs_parens { format!("({})", src) } else { src };
460 if let Some(sugg) = self.can_use_as_ref(expr) {
463 let field_name = if is_struct_pat_shorthand_field {
464 format!("{}: ", sugg_expr)
468 if let Some(hir::Node::Expr(hir::Expr {
469 kind: hir::ExprKind::Assign(left_expr, ..),
471 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
473 if mutability == hir::Mutability::Mut {
474 // Found the following case:
475 // fn foo(opt: &mut Option<String>){ opt = None }
478 // consider dereferencing here: `*opt` |
479 // expected mutable reference, found enum `Option`
480 if let Ok(src) = cm.span_to_snippet(left_expr.span) {
483 "consider dereferencing here to assign to the mutable \
484 borrowed piece of memory",
491 return Some(match mutability {
492 hir::Mutability::Mut => (
494 "consider mutably borrowing here",
495 format!("{}&mut {}", field_name, sugg_expr),
497 hir::Mutability::Not => (
499 "consider borrowing here",
500 format!("{}&{}", field_name, sugg_expr),
507 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
509 &ty::Ref(_, checked, _),
511 self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
514 // We have `&T`, check if what was expected was `T`. If so,
515 // we may want to suggest removing a `&`.
516 if !cm.span_to_filename(expr.span).is_real() {
517 if let Ok(code) = cm.span_to_snippet(sp) {
518 if code.chars().next() == Some('&') {
521 "consider removing the borrow",
522 code[1..].to_string(),
528 if let Ok(code) = cm.span_to_snippet(expr.span) {
529 return Some((sp, "consider removing the borrow", code));
532 _ if sp == expr.span && !is_macro => {
533 // Check for `Deref` implementations by constructing a predicate to
534 // prove: `<T as Deref>::Output == U`
535 let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
536 let item_def_id = self
538 .associated_items(deref_trait)
539 .find(|item| item.kind == ty::AssocKind::Type)
543 ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
544 // `<T as Deref>::Output`
545 projection_ty: ty::ProjectionTy {
547 substs: self.tcx.intern_substs(&[checked_ty.into()]),
554 let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
555 let impls_deref = self.infcx.predicate_may_hold(&obligation);
557 // For a suggestion to make sense, the type would need to be `Copy`.
558 let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
560 if is_copy && impls_deref {
561 if let Ok(code) = cm.span_to_snippet(sp) {
562 let message = if checked_ty.is_region_ptr() {
563 "consider dereferencing the borrow"
565 "consider dereferencing the type"
567 let suggestion = if is_struct_pat_shorthand_field {
568 format!("{}: *{}", code, code)
572 return Some((sp, message, suggestion));
581 pub fn check_for_cast(
583 err: &mut DiagnosticBuilder<'_>,
584 expr: &hir::Expr<'_>,
585 checked_ty: Ty<'tcx>,
586 expected_ty: Ty<'tcx>,
588 if self.tcx.hir().is_const_context(expr.hir_id) {
589 // Shouldn't suggest `.into()` on `const`s.
590 // FIXME(estebank): modify once we decide to suggest `as` casts
593 if !self.tcx.sess.source_map().span_to_filename(expr.span).is_real() {
594 // Ignore if span is from within a macro.
598 // If casting this expression to a given numeric type would be appropriate in case of a type
601 // We want to minimize the amount of casting operations that are suggested, as it can be a
602 // lossy operation with potentially bad side effects, so we only suggest when encountering
603 // an expression that indicates that the original type couldn't be directly changed.
605 // For now, don't suggest casting with `as`.
606 let can_cast = false;
608 let mut prefix = String::new();
609 if let Some(hir::Node::Expr(hir::Expr {
610 kind: hir::ExprKind::Struct(_, fields, _), ..
611 })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
613 // `expr` is a literal field for a struct, only suggest if appropriate
614 for field in *fields {
615 if field.expr.hir_id == expr.hir_id && field.is_shorthand {
616 // This is a field literal
617 prefix = format!("{}: ", field.ident);
622 // Likely a field was meant, but this field wasn't found. Do not suggest anything.
626 if let hir::ExprKind::Call(path, args) = &expr.kind {
627 if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
628 (&path.kind, args.len())
630 // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
631 if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
632 (&base_ty.kind, path_segment.ident.name)
634 if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
648 if base_ty_path.segments.len() == 1 =>
659 let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
660 let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
661 let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
662 let lit_msg = format!(
663 "change the type of the numeric literal from `{}` to `{}`",
664 checked_ty, expected_ty,
667 let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
669 if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
670 let cast_suggestion = format!(
673 if needs_paren { "(" } else { "" },
675 if needs_paren { ")" } else { "" },
678 let try_into_suggestion = format!(
679 "{}{}{}{}.try_into().unwrap()",
681 if needs_paren { "(" } else { "" },
683 if needs_paren { ")" } else { "" },
685 let into_suggestion = format!(
688 if needs_paren { "(" } else { "" },
690 if needs_paren { ")" } else { "" },
692 let suffix_suggestion = format!(
694 if needs_paren { "(" } else { "" },
695 if let (ty::Int(_), ty::Float(_)) | (ty::Uint(_), ty::Float(_)) =
696 (&expected_ty.kind, &checked_ty.kind,)
698 // Remove fractional part from literal, for example `42.0f32` into `42`
699 let src = src.trim_end_matches(&checked_ty.to_string());
700 src.split(".").next().unwrap()
702 src.trim_end_matches(&checked_ty.to_string())
705 if needs_paren { ")" } else { "" },
707 let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
708 if let hir::ExprKind::Lit(lit) = &expr.kind {
709 lit.node.is_suffixed()
715 let suggest_to_change_suffix_or_into =
716 |err: &mut DiagnosticBuilder<'_>, is_fallible: bool| {
717 let into_sugg = into_suggestion.clone();
720 if literal_is_ty_suffixed(expr) {
722 } else if is_fallible {
727 if literal_is_ty_suffixed(expr) {
728 suffix_suggestion.clone()
729 } else if is_fallible {
734 Applicability::MachineApplicable,
738 match (&expected_ty.kind, &checked_ty.kind) {
739 (&ty::Int(ref exp), &ty::Int(ref found)) => {
740 let is_fallible = match (found.bit_width(), exp.bit_width()) {
741 (Some(found), Some(exp)) if found > exp => true,
742 (None, _) | (_, None) => true,
745 suggest_to_change_suffix_or_into(err, is_fallible);
748 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
749 let is_fallible = match (found.bit_width(), exp.bit_width()) {
750 (Some(found), Some(exp)) if found > exp => true,
751 (None, _) | (_, None) => true,
754 suggest_to_change_suffix_or_into(err, is_fallible);
757 (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
758 suggest_to_change_suffix_or_into(err, true);
761 (&ty::Float(ref exp), &ty::Float(ref found)) => {
762 if found.bit_width() < exp.bit_width() {
763 suggest_to_change_suffix_or_into(err, false);
764 } else if literal_is_ty_suffixed(expr) {
769 Applicability::MachineApplicable,
772 // Missing try_into implementation for `f64` to `f32`
775 &format!("{}, producing the closest possible value", cast_msg),
777 Applicability::MaybeIncorrect, // lossy conversion
782 (&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
783 if literal_is_ty_suffixed(expr) {
788 Applicability::MachineApplicable,
791 // Missing try_into implementation for `{float}` to `{integer}`
794 &format!("{}, rounding the float towards zero", msg),
796 Applicability::MaybeIncorrect, // lossy conversion
799 "if the rounded value cannot be represented by the target \
800 integer type, including `Inf` and `NaN`, casting will cause \
802 (https://github.com/rust-lang/rust/issues/10184)",
807 (&ty::Float(ref exp), &ty::Uint(ref found)) => {
808 // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
809 if exp.bit_width() > found.bit_width().unwrap_or(256) {
813 "{}, producing the floating point representation of the integer",
817 Applicability::MachineApplicable,
819 } else if literal_is_ty_suffixed(expr) {
824 Applicability::MachineApplicable,
827 // Missing try_into implementation for `{integer}` to `{float}`
831 "{}, producing the floating point representation of the integer,
832 rounded if necessary",
836 Applicability::MaybeIncorrect, // lossy conversion
841 (&ty::Float(ref exp), &ty::Int(ref found)) => {
842 // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
843 if exp.bit_width() > found.bit_width().unwrap_or(256) {
847 "{}, producing the floating point representation of the integer",
851 Applicability::MachineApplicable,
853 } else if literal_is_ty_suffixed(expr) {
858 Applicability::MachineApplicable,
861 // Missing try_into implementation for `{integer}` to `{float}`
865 "{}, producing the floating point representation of the integer, \
866 rounded if necessary",
870 Applicability::MaybeIncorrect, // lossy conversion