2 use crate::astconv::AstConv;
4 use rustc_ast::util::parser::ExprPrecedence;
5 use rustc_span::{self, MultiSpan, Span};
7 use rustc_errors::{Applicability, DiagnosticBuilder};
9 use rustc_hir::def::{CtorOf, DefKind};
10 use rustc_hir::lang_items::LangItem;
11 use rustc_hir::{Expr, ExprKind, ItemKind, Node, Stmt, StmtKind};
12 use rustc_infer::infer;
13 use rustc_middle::lint::in_external_macro;
14 use rustc_middle::ty::{self, Binder, Ty};
15 use rustc_span::symbol::kw;
19 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
20 pub(in super::super) fn suggest_semicolon_at_end(
23 err: &mut DiagnosticBuilder<'_>,
25 err.span_suggestion_short(
27 "consider using a semicolon here",
29 Applicability::MachineApplicable,
33 /// On implicit return expressions with mismatched types, provides the following suggestions:
35 /// - Points out the method's return type as the reason for the expected type.
36 /// - Possible missing semicolon.
37 /// - Possible missing return type if the return type is the default, and not `fn main()`.
38 pub fn suggest_mismatched_types_on_tail(
40 err: &mut DiagnosticBuilder<'_>,
41 expr: &'tcx hir::Expr<'tcx>,
46 let expr = expr.peel_drop_temps();
47 // If the expression is from an external macro, then do not suggest
48 // adding a semicolon, because there's nowhere to put it.
50 if expr.can_have_side_effects() && !in_external_macro(self.tcx.sess, expr.span) {
51 self.suggest_missing_semicolon(err, expr, expected);
53 let mut pointing_at_return_type = false;
54 if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
55 pointing_at_return_type =
56 self.suggest_missing_return_type(err, &fn_decl, expected, found, can_suggest);
57 let fn_id = self.tcx.hir().get_return_block(blk_id).unwrap();
58 self.suggest_missing_break_or_return_expr(
59 err, expr, &fn_decl, expected, found, blk_id, fn_id,
62 pointing_at_return_type
65 /// When encountering an fn-like ctor that needs to unify with a value, check whether calling
66 /// the ctor would successfully solve the type mismatch and if so, suggest it:
68 /// fn foo(x: usize) -> usize { x }
69 /// let x: usize = foo; // suggest calling the `foo` function: `foo(42)`
73 err: &mut DiagnosticBuilder<'_>,
78 let hir = self.tcx.hir();
79 let (def_id, sig) = match *found.kind() {
80 ty::FnDef(def_id, _) => (def_id, found.fn_sig(self.tcx)),
81 ty::Closure(def_id, substs) => (def_id, substs.as_closure().sig()),
85 let sig = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, sig).0;
86 let sig = self.normalize_associated_types_in(expr.span, sig);
87 if self.can_coerce(sig.output(), expected) {
88 let (mut sugg_call, applicability) = if sig.inputs().is_empty() {
89 (String::new(), Applicability::MachineApplicable)
91 ("...".to_string(), Applicability::HasPlaceholders)
93 let mut msg = "call this function";
94 match hir.get_if_local(def_id) {
96 Node::Item(hir::Item { kind: ItemKind::Fn(.., body_id), .. })
97 | Node::ImplItem(hir::ImplItem {
98 kind: hir::ImplItemKind::Fn(_, body_id), ..
100 | Node::TraitItem(hir::TraitItem {
101 kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Provided(body_id)),
105 let body = hir.body(*body_id);
109 .map(|param| match ¶m.pat.kind {
110 hir::PatKind::Binding(_, _, ident, None)
111 if ident.name != kw::SelfLower =>
115 _ => "_".to_string(),
120 Some(Node::Expr(hir::Expr {
121 kind: ExprKind::Closure(_, _, body_id, _, _),
122 span: full_closure_span,
125 if *full_closure_span == expr.span {
128 msg = "call this closure";
129 let body = hir.body(*body_id);
133 .map(|param| match ¶m.pat.kind {
134 hir::PatKind::Binding(_, _, ident, None)
135 if ident.name != kw::SelfLower =>
139 _ => "_".to_string(),
144 Some(Node::Ctor(hir::VariantData::Tuple(fields, _))) => {
145 sugg_call = fields.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
146 match def_id.as_local().map(|def_id| hir.def_kind(def_id)) {
147 Some(DefKind::Ctor(hir::def::CtorOf::Variant, _)) => {
148 msg = "instantiate this tuple variant";
150 Some(DefKind::Ctor(CtorOf::Struct, _)) => {
151 msg = "instantiate this tuple struct";
156 Some(Node::ForeignItem(hir::ForeignItem {
157 kind: hir::ForeignItemKind::Fn(_, idents, _),
163 if ident.name != kw::SelfLower {
172 Some(Node::TraitItem(hir::TraitItem {
173 kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Required(idents)),
179 if ident.name != kw::SelfLower {
190 err.span_suggestion_verbose(
191 expr.span.shrink_to_hi(),
192 &format!("use parentheses to {}", msg),
193 format!("({})", sugg_call),
201 pub fn suggest_deref_ref_or_into(
203 err: &mut DiagnosticBuilder<'_>,
204 expr: &hir::Expr<'_>,
207 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
209 let expr = expr.peel_blocks();
210 if let Some((sp, msg, suggestion, applicability)) = self.check_ref(expr, found, expected) {
211 err.span_suggestion(sp, msg, suggestion, applicability);
212 } else if let (ty::FnDef(def_id, ..), true) =
213 (&found.kind(), self.suggest_fn_call(err, expr, expected, found))
215 if let Some(sp) = self.tcx.hir().span_if_local(*def_id) {
216 let sp = self.sess().source_map().guess_head_span(sp);
217 err.span_label(sp, &format!("{} defined here", found));
219 } else if !self.check_for_cast(err, expr, found, expected, expected_ty_expr) {
220 let is_struct_pat_shorthand_field =
221 self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, expr.span);
222 let methods = self.get_conversion_methods(expr.span, expected, found, expr.hir_id);
223 if let Ok(expr_text) = self.sess().source_map().span_to_snippet(expr.span) {
224 let mut suggestions = iter::zip(iter::repeat(&expr_text), &methods)
225 .filter_map(|(receiver, method)| {
226 let method_call = format!(".{}()", method.ident);
227 if receiver.ends_with(&method_call) {
228 None // do not suggest code that is already there (#53348)
230 let method_call_list = [".to_vec()", ".to_string()"];
231 let sugg = if receiver.ends_with(".clone()")
232 && method_call_list.contains(&method_call.as_str())
234 let max_len = receiver.rfind('.').unwrap();
235 format!("{}{}", &receiver[..max_len], method_call)
237 if expr.precedence().order() < ExprPrecedence::MethodCall.order() {
238 format!("({}){}", receiver, method_call)
240 format!("{}{}", receiver, method_call)
243 Some(if is_struct_pat_shorthand_field {
244 format!("{}: {}", receiver, sugg)
251 if suggestions.peek().is_some() {
252 err.span_suggestions(
254 "try using a conversion method",
256 Applicability::MaybeIncorrect,
263 /// When encountering the expected boxed value allocated in the stack, suggest allocating it
264 /// in the heap by calling `Box::new()`.
265 pub(in super::super) fn suggest_boxing_when_appropriate(
267 err: &mut DiagnosticBuilder<'_>,
268 expr: &hir::Expr<'_>,
272 if self.tcx.hir().is_inside_const_context(expr.hir_id) {
273 // Do not suggest `Box::new` in const context.
276 if !expected.is_box() || found.is_box() {
279 let boxed_found = self.tcx.mk_box(found);
280 if let (true, Ok(snippet)) = (
281 self.can_coerce(boxed_found, expected),
282 self.sess().source_map().span_to_snippet(expr.span),
286 "store this in the heap by calling `Box::new`",
287 format!("Box::new({})", snippet),
288 Applicability::MachineApplicable,
291 "for more on the distinction between the stack and the heap, read \
292 https://doc.rust-lang.org/book/ch15-01-box.html, \
293 https://doc.rust-lang.org/rust-by-example/std/box.html, and \
294 https://doc.rust-lang.org/std/boxed/index.html",
299 /// When encountering a closure that captures variables, where a FnPtr is expected,
300 /// suggest a non-capturing closure
301 pub(in super::super) fn suggest_no_capture_closure(
303 err: &mut DiagnosticBuilder<'_>,
307 if let (ty::FnPtr(_), ty::Closure(def_id, _)) = (expected.kind(), found.kind()) {
308 if let Some(upvars) = self.tcx.upvars_mentioned(*def_id) {
309 // Report upto four upvars being captured to reduce the amount error messages
310 // reported back to the user.
311 let spans_and_labels = upvars
314 .map(|(var_hir_id, upvar)| {
315 let var_name = self.tcx.hir().name(*var_hir_id).to_string();
316 let msg = format!("`{}` captured here", var_name);
319 .collect::<Vec<_>>();
321 let mut multi_span: MultiSpan =
322 spans_and_labels.iter().map(|(sp, _)| *sp).collect::<Vec<_>>().into();
323 for (sp, label) in spans_and_labels {
324 multi_span.push_span_label(sp, label);
326 err.span_note(multi_span, "closures can only be coerced to `fn` types if they do not capture any variables");
331 /// When encountering an `impl Future` where `BoxFuture` is expected, suggest `Box::pin`.
332 pub(in super::super) fn suggest_calling_boxed_future_when_appropriate(
334 err: &mut DiagnosticBuilder<'_>,
335 expr: &hir::Expr<'_>,
341 if self.tcx.hir().is_inside_const_context(expr.hir_id) {
342 // Do not suggest `Box::new` in const context.
345 let pin_did = self.tcx.lang_items().pin_type();
346 match expected.kind() {
347 ty::Adt(def, _) if Some(def.did) != pin_did => return false,
348 // This guards the `unwrap` and `mk_box` below.
349 _ if pin_did.is_none() || self.tcx.lang_items().owned_box().is_none() => return false,
352 let boxed_found = self.tcx.mk_box(found);
353 let new_found = self.tcx.mk_lang_item(boxed_found, LangItem::Pin).unwrap();
354 if let (true, Ok(snippet)) = (
355 self.can_coerce(new_found, expected),
356 self.sess().source_map().span_to_snippet(expr.span),
359 ty::Adt(def, _) if def.is_box() => {
360 err.help("use `Box::pin`");
365 "you need to pin and box this expression",
366 format!("Box::pin({})", snippet),
367 Applicability::MachineApplicable,
377 /// A common error is to forget to add a semicolon at the end of a block, e.g.,
381 /// bar_that_returns_u32()
385 /// This routine checks if the return expression in a block would make sense on its own as a
386 /// statement and the return type has been left as default or has been specified as `()`. If so,
387 /// it suggests adding a semicolon.
388 fn suggest_missing_semicolon(
390 err: &mut DiagnosticBuilder<'_>,
391 expression: &'tcx hir::Expr<'tcx>,
394 if expected.is_unit() {
395 // `BlockTailExpression` only relevant if the tail expr would be
396 // useful on its own.
397 match expression.kind {
399 | ExprKind::MethodCall(..)
402 | ExprKind::Match(..)
403 | ExprKind::Block(..)
404 if expression.can_have_side_effects() =>
407 expression.span.shrink_to_hi(),
408 "consider using a semicolon here",
410 Applicability::MachineApplicable,
418 /// A possible error is to forget to add a return type that is needed:
422 /// bar_that_returns_u32()
426 /// This routine checks if the return type is left as default, the method is not part of an
427 /// `impl` block and that it isn't the `main` method. If so, it suggests setting the return
429 pub(in super::super) fn suggest_missing_return_type(
431 err: &mut DiagnosticBuilder<'_>,
432 fn_decl: &hir::FnDecl<'_>,
437 // Only suggest changing the return type for methods that
438 // haven't set a return type at all (and aren't `fn main()` or an impl).
439 match (&fn_decl.output, found.is_suggestable(), can_suggest, expected.is_unit()) {
440 (&hir::FnRetTy::DefaultReturn(span), true, true, true) => {
443 "try adding a return type",
444 format!("-> {} ", self.resolve_vars_with_obligations(found)),
445 Applicability::MachineApplicable,
449 (&hir::FnRetTy::DefaultReturn(span), false, true, true) => {
450 err.span_label(span, "possibly return type missing here?");
453 (&hir::FnRetTy::DefaultReturn(span), _, false, true) => {
454 // `fn main()` must return `()`, do not suggest changing return type
455 err.span_label(span, "expected `()` because of default return type");
458 // expectation was caused by something else, not the default return
459 (&hir::FnRetTy::DefaultReturn(_), _, _, false) => false,
460 (&hir::FnRetTy::Return(ref ty), _, _, _) => {
461 // Only point to return type if the expected type is the return type, as if they
462 // are not, the expectation must have been caused by something else.
463 debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
465 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
466 debug!("suggest_missing_return_type: return type {:?}", ty);
467 debug!("suggest_missing_return_type: expected type {:?}", ty);
468 if ty.kind() == expected.kind() {
469 err.span_label(sp, format!("expected `{}` because of return type", expected));
477 pub(in super::super) fn suggest_missing_break_or_return_expr(
479 err: &mut DiagnosticBuilder<'_>,
480 expr: &'tcx hir::Expr<'tcx>,
481 fn_decl: &hir::FnDecl<'_>,
487 if !expected.is_unit() {
490 let found = self.resolve_vars_with_obligations(found);
492 let in_loop = self.is_loop(id)
493 || self.tcx.hir().parent_iter(id).any(|(parent_id, _)| self.is_loop(parent_id));
495 let in_local_statement = self.is_local_statement(id)
500 .any(|(parent_id, _)| self.is_local_statement(parent_id));
502 if in_loop && in_local_statement {
503 err.multipart_suggestion(
504 "you might have meant to break the loop with this value",
506 (expr.span.shrink_to_lo(), "break ".to_string()),
507 (expr.span.shrink_to_hi(), ";".to_string()),
509 Applicability::MaybeIncorrect,
514 if let hir::FnRetTy::Return(ty) = fn_decl.output {
515 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
516 let bound_vars = self.tcx.late_bound_vars(fn_id);
517 let ty = self.tcx.erase_late_bound_regions(Binder::bind_with_vars(ty, bound_vars));
518 let ty = self.normalize_associated_types_in(expr.span, ty);
519 if self.can_coerce(found, ty) {
520 err.multipart_suggestion(
521 "you might have meant to return this value",
523 (expr.span.shrink_to_lo(), "return ".to_string()),
524 (expr.span.shrink_to_hi(), ";".to_string()),
526 Applicability::MaybeIncorrect,
532 pub(in super::super) fn suggest_missing_parentheses(
534 err: &mut DiagnosticBuilder<'_>,
535 expr: &hir::Expr<'_>,
537 let sp = self.tcx.sess.source_map().start_point(expr.span);
538 if let Some(sp) = self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp) {
539 // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
540 self.tcx.sess.parse_sess.expr_parentheses_needed(err, *sp, None);
544 fn is_loop(&self, id: hir::HirId) -> bool {
545 let node = self.tcx.hir().get(id);
546 matches!(node, Node::Expr(Expr { kind: ExprKind::Loop(..), .. }))
549 fn is_local_statement(&self, id: hir::HirId) -> bool {
550 let node = self.tcx.hir().get(id);
551 matches!(node, Node::Stmt(Stmt { kind: StmtKind::Local(..), .. }))