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 let fn_id = self.tcx.hir().get_return_block(blk_id).unwrap();
56 pointing_at_return_type = self.suggest_missing_return_type(
64 self.suggest_missing_break_or_return_expr(
65 err, expr, &fn_decl, expected, found, blk_id, fn_id,
68 pointing_at_return_type
71 /// When encountering an fn-like ctor that needs to unify with a value, check whether calling
72 /// the ctor would successfully solve the type mismatch and if so, suggest it:
74 /// fn foo(x: usize) -> usize { x }
75 /// let x: usize = foo; // suggest calling the `foo` function: `foo(42)`
79 err: &mut DiagnosticBuilder<'_>,
84 let hir = self.tcx.hir();
85 let (def_id, sig) = match *found.kind() {
86 ty::FnDef(def_id, _) => (def_id, found.fn_sig(self.tcx)),
87 ty::Closure(def_id, substs) => (def_id, substs.as_closure().sig()),
91 let sig = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, sig).0;
92 let sig = self.normalize_associated_types_in(expr.span, sig);
93 if self.can_coerce(sig.output(), expected) {
94 let (mut sugg_call, applicability) = if sig.inputs().is_empty() {
95 (String::new(), Applicability::MachineApplicable)
97 ("...".to_string(), Applicability::HasPlaceholders)
99 let mut msg = "call this function";
100 match hir.get_if_local(def_id) {
102 Node::Item(hir::Item { kind: ItemKind::Fn(.., body_id), .. })
103 | Node::ImplItem(hir::ImplItem {
104 kind: hir::ImplItemKind::Fn(_, body_id), ..
106 | Node::TraitItem(hir::TraitItem {
107 kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Provided(body_id)),
111 let body = hir.body(*body_id);
115 .map(|param| match ¶m.pat.kind {
116 hir::PatKind::Binding(_, _, ident, None)
117 if ident.name != kw::SelfLower =>
121 _ => "_".to_string(),
126 Some(Node::Expr(hir::Expr {
127 kind: ExprKind::Closure(_, _, body_id, _, _),
128 span: full_closure_span,
131 if *full_closure_span == expr.span {
134 msg = "call this closure";
135 let body = hir.body(*body_id);
139 .map(|param| match ¶m.pat.kind {
140 hir::PatKind::Binding(_, _, ident, None)
141 if ident.name != kw::SelfLower =>
145 _ => "_".to_string(),
150 Some(Node::Ctor(hir::VariantData::Tuple(fields, _))) => {
151 sugg_call = fields.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
152 match def_id.as_local().map(|def_id| hir.def_kind(def_id)) {
153 Some(DefKind::Ctor(hir::def::CtorOf::Variant, _)) => {
154 msg = "instantiate this tuple variant";
156 Some(DefKind::Ctor(CtorOf::Struct, _)) => {
157 msg = "instantiate this tuple struct";
162 Some(Node::ForeignItem(hir::ForeignItem {
163 kind: hir::ForeignItemKind::Fn(_, idents, _),
169 if ident.name != kw::SelfLower {
178 Some(Node::TraitItem(hir::TraitItem {
179 kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Required(idents)),
185 if ident.name != kw::SelfLower {
196 err.span_suggestion_verbose(
197 expr.span.shrink_to_hi(),
198 &format!("use parentheses to {}", msg),
199 format!("({})", sugg_call),
207 pub fn suggest_deref_ref_or_into(
209 err: &mut DiagnosticBuilder<'_>,
210 expr: &hir::Expr<'_>,
213 expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
215 let expr = expr.peel_blocks();
216 if let Some((sp, msg, suggestion, applicability)) = self.check_ref(expr, found, expected) {
217 err.span_suggestion(sp, msg, suggestion, applicability);
218 } else if let (ty::FnDef(def_id, ..), true) =
219 (&found.kind(), self.suggest_fn_call(err, expr, expected, found))
221 if let Some(sp) = self.tcx.hir().span_if_local(*def_id) {
222 let sp = self.sess().source_map().guess_head_span(sp);
223 err.span_label(sp, &format!("{} defined here", found));
225 } else if !self.check_for_cast(err, expr, found, expected, expected_ty_expr) {
226 let is_struct_pat_shorthand_field =
227 self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, expr.span);
228 let methods = self.get_conversion_methods(expr.span, expected, found, expr.hir_id);
229 if let Ok(expr_text) = self.sess().source_map().span_to_snippet(expr.span) {
230 let mut suggestions = iter::zip(iter::repeat(&expr_text), &methods)
231 .filter_map(|(receiver, method)| {
232 let method_call = format!(".{}()", method.ident);
233 if receiver.ends_with(&method_call) {
234 None // do not suggest code that is already there (#53348)
236 let method_call_list = [".to_vec()", ".to_string()"];
237 let sugg = if receiver.ends_with(".clone()")
238 && method_call_list.contains(&method_call.as_str())
240 let max_len = receiver.rfind('.').unwrap();
241 format!("{}{}", &receiver[..max_len], method_call)
243 if expr.precedence().order() < ExprPrecedence::MethodCall.order() {
244 format!("({}){}", receiver, method_call)
246 format!("{}{}", receiver, method_call)
249 Some(if is_struct_pat_shorthand_field {
250 format!("{}: {}", receiver, sugg)
257 if suggestions.peek().is_some() {
258 err.span_suggestions(
260 "try using a conversion method",
262 Applicability::MaybeIncorrect,
269 /// When encountering the expected boxed value allocated in the stack, suggest allocating it
270 /// in the heap by calling `Box::new()`.
271 pub(in super::super) fn suggest_boxing_when_appropriate(
273 err: &mut DiagnosticBuilder<'_>,
274 expr: &hir::Expr<'_>,
278 if self.tcx.hir().is_inside_const_context(expr.hir_id) {
279 // Do not suggest `Box::new` in const context.
282 if !expected.is_box() || found.is_box() {
285 let boxed_found = self.tcx.mk_box(found);
286 if let (true, Ok(snippet)) = (
287 self.can_coerce(boxed_found, expected),
288 self.sess().source_map().span_to_snippet(expr.span),
292 "store this in the heap by calling `Box::new`",
293 format!("Box::new({})", snippet),
294 Applicability::MachineApplicable,
297 "for more on the distinction between the stack and the heap, read \
298 https://doc.rust-lang.org/book/ch15-01-box.html, \
299 https://doc.rust-lang.org/rust-by-example/std/box.html, and \
300 https://doc.rust-lang.org/std/boxed/index.html",
305 /// When encountering a closure that captures variables, where a FnPtr is expected,
306 /// suggest a non-capturing closure
307 pub(in super::super) fn suggest_no_capture_closure(
309 err: &mut DiagnosticBuilder<'_>,
313 if let (ty::FnPtr(_), ty::Closure(def_id, _)) = (expected.kind(), found.kind()) {
314 if let Some(upvars) = self.tcx.upvars_mentioned(*def_id) {
315 // Report upto four upvars being captured to reduce the amount error messages
316 // reported back to the user.
317 let spans_and_labels = upvars
320 .map(|(var_hir_id, upvar)| {
321 let var_name = self.tcx.hir().name(*var_hir_id).to_string();
322 let msg = format!("`{}` captured here", var_name);
325 .collect::<Vec<_>>();
327 let mut multi_span: MultiSpan =
328 spans_and_labels.iter().map(|(sp, _)| *sp).collect::<Vec<_>>().into();
329 for (sp, label) in spans_and_labels {
330 multi_span.push_span_label(sp, label);
332 err.span_note(multi_span, "closures can only be coerced to `fn` types if they do not capture any variables");
337 /// When encountering an `impl Future` where `BoxFuture` is expected, suggest `Box::pin`.
338 pub(in super::super) fn suggest_calling_boxed_future_when_appropriate(
340 err: &mut DiagnosticBuilder<'_>,
341 expr: &hir::Expr<'_>,
347 if self.tcx.hir().is_inside_const_context(expr.hir_id) {
348 // Do not suggest `Box::new` in const context.
351 let pin_did = self.tcx.lang_items().pin_type();
352 match expected.kind() {
353 ty::Adt(def, _) if Some(def.did) != pin_did => return false,
354 // This guards the `unwrap` and `mk_box` below.
355 _ if pin_did.is_none() || self.tcx.lang_items().owned_box().is_none() => return false,
358 let boxed_found = self.tcx.mk_box(found);
359 let new_found = self.tcx.mk_lang_item(boxed_found, LangItem::Pin).unwrap();
360 if let (true, Ok(snippet)) = (
361 self.can_coerce(new_found, expected),
362 self.sess().source_map().span_to_snippet(expr.span),
365 ty::Adt(def, _) if def.is_box() => {
366 err.help("use `Box::pin`");
371 "you need to pin and box this expression",
372 format!("Box::pin({})", snippet),
373 Applicability::MachineApplicable,
383 /// A common error is to forget to add a semicolon at the end of a block, e.g.,
387 /// bar_that_returns_u32()
391 /// This routine checks if the return expression in a block would make sense on its own as a
392 /// statement and the return type has been left as default or has been specified as `()`. If so,
393 /// it suggests adding a semicolon.
394 fn suggest_missing_semicolon(
396 err: &mut DiagnosticBuilder<'_>,
397 expression: &'tcx hir::Expr<'tcx>,
400 if expected.is_unit() {
401 // `BlockTailExpression` only relevant if the tail expr would be
402 // useful on its own.
403 match expression.kind {
405 | ExprKind::MethodCall(..)
408 | ExprKind::Match(..)
409 | ExprKind::Block(..)
410 if expression.can_have_side_effects() =>
413 expression.span.shrink_to_hi(),
414 "consider using a semicolon here",
416 Applicability::MachineApplicable,
424 /// A possible error is to forget to add a return type that is needed:
428 /// bar_that_returns_u32()
432 /// This routine checks if the return type is left as default, the method is not part of an
433 /// `impl` block and that it isn't the `main` method. If so, it suggests setting the return
435 pub(in super::super) fn suggest_missing_return_type(
437 err: &mut DiagnosticBuilder<'_>,
438 fn_decl: &hir::FnDecl<'_>,
444 // Only suggest changing the return type for methods that
445 // haven't set a return type at all (and aren't `fn main()` or an impl).
446 match (&fn_decl.output, found.is_suggestable(), can_suggest, expected.is_unit()) {
447 (&hir::FnRetTy::DefaultReturn(span), true, true, true) => {
450 "try adding a return type",
451 format!("-> {} ", self.resolve_vars_with_obligations(found)),
452 Applicability::MachineApplicable,
456 (&hir::FnRetTy::DefaultReturn(span), false, true, true) => {
457 err.span_label(span, "possibly return type missing here?");
460 (&hir::FnRetTy::DefaultReturn(span), _, false, true) => {
461 // `fn main()` must return `()`, do not suggest changing return type
462 err.span_label(span, "expected `()` because of default return type");
465 // expectation was caused by something else, not the default return
466 (&hir::FnRetTy::DefaultReturn(_), _, _, false) => false,
467 (&hir::FnRetTy::Return(ref ty), _, _, _) => {
468 // Only point to return type if the expected type is the return type, as if they
469 // are not, the expectation must have been caused by something else.
470 debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
472 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
473 debug!("suggest_missing_return_type: return type {:?}", ty);
474 debug!("suggest_missing_return_type: expected type {:?}", ty);
475 let bound_vars = self.tcx.late_bound_vars(fn_id);
476 let ty = self.tcx.erase_late_bound_regions(Binder::bind_with_vars(ty, bound_vars));
477 let ty = self.normalize_associated_types_in(sp, ty);
478 if self.can_coerce(expected, ty) {
479 err.span_label(sp, format!("expected `{}` because of return type", expected));
487 pub(in super::super) fn suggest_missing_break_or_return_expr(
489 err: &mut DiagnosticBuilder<'_>,
490 expr: &'tcx hir::Expr<'tcx>,
491 fn_decl: &hir::FnDecl<'_>,
497 if !expected.is_unit() {
500 let found = self.resolve_vars_with_obligations(found);
502 let in_loop = self.is_loop(id)
503 || self.tcx.hir().parent_iter(id).any(|(parent_id, _)| self.is_loop(parent_id));
505 let in_local_statement = self.is_local_statement(id)
510 .any(|(parent_id, _)| self.is_local_statement(parent_id));
512 if in_loop && in_local_statement {
513 err.multipart_suggestion(
514 "you might have meant to break the loop with this value",
516 (expr.span.shrink_to_lo(), "break ".to_string()),
517 (expr.span.shrink_to_hi(), ";".to_string()),
519 Applicability::MaybeIncorrect,
524 if let hir::FnRetTy::Return(ty) = fn_decl.output {
525 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
526 let bound_vars = self.tcx.late_bound_vars(fn_id);
527 let ty = self.tcx.erase_late_bound_regions(Binder::bind_with_vars(ty, bound_vars));
528 let ty = self.normalize_associated_types_in(expr.span, ty);
529 if self.can_coerce(found, ty) {
530 err.multipart_suggestion(
531 "you might have meant to return this value",
533 (expr.span.shrink_to_lo(), "return ".to_string()),
534 (expr.span.shrink_to_hi(), ";".to_string()),
536 Applicability::MaybeIncorrect,
542 pub(in super::super) fn suggest_missing_parentheses(
544 err: &mut DiagnosticBuilder<'_>,
545 expr: &hir::Expr<'_>,
547 let sp = self.tcx.sess.source_map().start_point(expr.span);
548 if let Some(sp) = self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp) {
549 // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
550 self.tcx.sess.parse_sess.expr_parentheses_needed(err, *sp, None);
554 fn is_loop(&self, id: hir::HirId) -> bool {
555 let node = self.tcx.hir().get(id);
556 matches!(node, Node::Expr(Expr { kind: ExprKind::Loop(..), .. }))
559 fn is_local_statement(&self, id: hir::HirId) -> bool {
560 let node = self.tcx.hir().get(id);
561 matches!(node, Node::Stmt(Stmt { kind: StmtKind::Local(..), .. }))