--- /dev/null
+use super::FnCtxt;
+
+use crate::errors::{AddReturnTypeSuggestion, ExpectedReturnTypeLabel};
+use rustc_ast::util::parser::{ExprPrecedence, PREC_POSTFIX};
+use rustc_errors::{Applicability, Diagnostic, MultiSpan};
+use rustc_hir as hir;
+use rustc_hir::def::{CtorOf, DefKind};
+use rustc_hir::lang_items::LangItem;
+use rustc_hir::{
+ Expr, ExprKind, GenericBound, Node, Path, QPath, Stmt, StmtKind, TyKind, WherePredicate,
+};
+use rustc_hir_analysis::astconv::AstConv;
+use rustc_infer::infer::{self, TyCtxtInferExt};
+use rustc_infer::traits::{self, StatementAsExpression};
+use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::{self, Binder, IsSuggestable, ToPredicate, Ty};
+use rustc_session::errors::ExprParenthesesNeeded;
+use rustc_span::symbol::sym;
+use rustc_span::Span;
+use rustc_trait_selection::infer::InferCtxtExt;
+use rustc_trait_selection::traits::error_reporting::DefIdOrName;
+use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
+
+impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+ pub(in super::super) fn suggest_semicolon_at_end(&self, span: Span, err: &mut Diagnostic) {
+ err.span_suggestion_short(
+ span.shrink_to_hi(),
+ "consider using a semicolon here",
+ ";",
+ Applicability::MachineApplicable,
+ );
+ }
+
+ /// On implicit return expressions with mismatched types, provides the following suggestions:
+ ///
+ /// - Points out the method's return type as the reason for the expected type.
+ /// - Possible missing semicolon.
+ /// - Possible missing return type if the return type is the default, and not `fn main()`.
+ pub fn suggest_mismatched_types_on_tail(
+ &self,
+ err: &mut Diagnostic,
+ expr: &'tcx hir::Expr<'tcx>,
+ expected: Ty<'tcx>,
+ found: Ty<'tcx>,
+ blk_id: hir::HirId,
+ ) -> bool {
+ let expr = expr.peel_drop_temps();
+ self.suggest_missing_semicolon(err, expr, expected, false);
+ let mut pointing_at_return_type = false;
+ if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
+ let fn_id = self.tcx.hir().get_return_block(blk_id).unwrap();
+ pointing_at_return_type = self.suggest_missing_return_type(
+ err,
+ &fn_decl,
+ expected,
+ found,
+ can_suggest,
+ fn_id,
+ );
+ self.suggest_missing_break_or_return_expr(
+ err, expr, &fn_decl, expected, found, blk_id, fn_id,
+ );
+ }
+ pointing_at_return_type
+ }
+
+ /// When encountering an fn-like type, try accessing the output of the type
+ /// and suggesting calling it if it satisfies a predicate (i.e. if the
+ /// output has a method or a field):
+ /// ```compile_fail,E0308
+ /// fn foo(x: usize) -> usize { x }
+ /// let x: usize = foo; // suggest calling the `foo` function: `foo(42)`
+ /// ```
+ pub(crate) fn suggest_fn_call(
+ &self,
+ err: &mut Diagnostic,
+ expr: &hir::Expr<'_>,
+ found: Ty<'tcx>,
+ can_satisfy: impl FnOnce(Ty<'tcx>) -> bool,
+ ) -> bool {
+ let Some((def_id_or_name, output, inputs)) = self.extract_callable_info(expr, found)
+ else { return false; };
+ if can_satisfy(output) {
+ let (sugg_call, mut applicability) = match inputs.len() {
+ 0 => ("".to_string(), Applicability::MachineApplicable),
+ 1..=4 => (
+ inputs
+ .iter()
+ .map(|ty| {
+ if ty.is_suggestable(self.tcx, false) {
+ format!("/* {ty} */")
+ } else {
+ "/* value */".to_string()
+ }
+ })
+ .collect::<Vec<_>>()
+ .join(", "),
+ Applicability::HasPlaceholders,
+ ),
+ _ => ("/* ... */".to_string(), Applicability::HasPlaceholders),
+ };
+
+ let msg = match def_id_or_name {
+ DefIdOrName::DefId(def_id) => match self.tcx.def_kind(def_id) {
+ DefKind::Ctor(CtorOf::Struct, _) => "construct this tuple struct".to_string(),
+ DefKind::Ctor(CtorOf::Variant, _) => "construct this tuple variant".to_string(),
+ kind => format!("call this {}", kind.descr(def_id)),
+ },
+ DefIdOrName::Name(name) => format!("call this {name}"),
+ };
+
+ let sugg = match expr.kind {
+ hir::ExprKind::Call(..)
+ | hir::ExprKind::Path(..)
+ | hir::ExprKind::Index(..)
+ | hir::ExprKind::Lit(..) => {
+ vec![(expr.span.shrink_to_hi(), format!("({sugg_call})"))]
+ }
+ hir::ExprKind::Closure { .. } => {
+ // Might be `{ expr } || { bool }`
+ applicability = Applicability::MaybeIncorrect;
+ vec![
+ (expr.span.shrink_to_lo(), "(".to_string()),
+ (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
+ ]
+ }
+ _ => {
+ vec![
+ (expr.span.shrink_to_lo(), "(".to_string()),
+ (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
+ ]
+ }
+ };
+
+ err.multipart_suggestion_verbose(
+ format!("use parentheses to {msg}"),
+ sugg,
+ applicability,
+ );
+ return true;
+ }
+ false
+ }
+
+ /// Extracts information about a callable type for diagnostics. This is a
+ /// heuristic -- it doesn't necessarily mean that a type is always callable,
+ /// because the callable type must also be well-formed to be called.
+ pub(in super::super) fn extract_callable_info(
+ &self,
+ expr: &Expr<'_>,
+ found: Ty<'tcx>,
+ ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)> {
+ // Autoderef is useful here because sometimes we box callables, etc.
+ let Some((def_id_or_name, output, inputs)) = self.autoderef(expr.span, found).silence_errors().find_map(|(found, _)| {
+ match *found.kind() {
+ ty::FnPtr(fn_sig) =>
+ Some((DefIdOrName::Name("function pointer"), fn_sig.output(), fn_sig.inputs())),
+ ty::FnDef(def_id, _) => {
+ let fn_sig = found.fn_sig(self.tcx);
+ Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs()))
+ }
+ ty::Closure(def_id, substs) => {
+ let fn_sig = substs.as_closure().sig();
+ Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs().map_bound(|inputs| &inputs[1..])))
+ }
+ ty::Opaque(def_id, substs) => {
+ self.tcx.bound_item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
+ if let ty::PredicateKind::Projection(proj) = pred.kind().skip_binder()
+ && Some(proj.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output()
+ // args tuple will always be substs[1]
+ && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
+ {
+ Some((
+ DefIdOrName::DefId(def_id),
+ pred.kind().rebind(proj.term.ty().unwrap()),
+ pred.kind().rebind(args.as_slice()),
+ ))
+ } else {
+ None
+ }
+ })
+ }
+ ty::Dynamic(data, _, ty::Dyn) => {
+ data.iter().find_map(|pred| {
+ if let ty::ExistentialPredicate::Projection(proj) = pred.skip_binder()
+ && Some(proj.item_def_id) == self.tcx.lang_items().fn_once_output()
+ // for existential projection, substs are shifted over by 1
+ && let ty::Tuple(args) = proj.substs.type_at(0).kind()
+ {
+ Some((
+ DefIdOrName::Name("trait object"),
+ pred.rebind(proj.term.ty().unwrap()),
+ pred.rebind(args.as_slice()),
+ ))
+ } else {
+ None
+ }
+ })
+ }
+ ty::Param(param) => {
+ let def_id = self.tcx.generics_of(self.body_id.owner).type_param(¶m, self.tcx).def_id;
+ self.tcx.predicates_of(self.body_id.owner).predicates.iter().find_map(|(pred, _)| {
+ if let ty::PredicateKind::Projection(proj) = pred.kind().skip_binder()
+ && Some(proj.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output()
+ && proj.projection_ty.self_ty() == found
+ // args tuple will always be substs[1]
+ && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
+ {
+ Some((
+ DefIdOrName::DefId(def_id),
+ pred.kind().rebind(proj.term.ty().unwrap()),
+ pred.kind().rebind(args.as_slice()),
+ ))
+ } else {
+ None
+ }
+ })
+ }
+ _ => None,
+ }
+ }) else { return None; };
+
+ let output = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, output);
+ let inputs = inputs
+ .skip_binder()
+ .iter()
+ .map(|ty| {
+ self.replace_bound_vars_with_fresh_vars(
+ expr.span,
+ infer::FnCall,
+ inputs.rebind(*ty),
+ )
+ })
+ .collect();
+
+ // We don't want to register any extra obligations, which should be
+ // implied by wf, but also because that would possibly result in
+ // erroneous errors later on.
+ let infer::InferOk { value: output, obligations: _ } =
+ self.normalize_associated_types_in_as_infer_ok(expr.span, output);
+
+ if output.is_ty_var() { None } else { Some((def_id_or_name, output, inputs)) }
+ }
+
+ pub fn suggest_two_fn_call(
+ &self,
+ err: &mut Diagnostic,
+ lhs_expr: &'tcx hir::Expr<'tcx>,
+ lhs_ty: Ty<'tcx>,
+ rhs_expr: &'tcx hir::Expr<'tcx>,
+ rhs_ty: Ty<'tcx>,
+ can_satisfy: impl FnOnce(Ty<'tcx>, Ty<'tcx>) -> bool,
+ ) -> bool {
+ let Some((_, lhs_output_ty, lhs_inputs)) = self.extract_callable_info(lhs_expr, lhs_ty)
+ else { return false; };
+ let Some((_, rhs_output_ty, rhs_inputs)) = self.extract_callable_info(rhs_expr, rhs_ty)
+ else { return false; };
+
+ if can_satisfy(lhs_output_ty, rhs_output_ty) {
+ let mut sugg = vec![];
+ let mut applicability = Applicability::MachineApplicable;
+
+ for (expr, inputs) in [(lhs_expr, lhs_inputs), (rhs_expr, rhs_inputs)] {
+ let (sugg_call, this_applicability) = match inputs.len() {
+ 0 => ("".to_string(), Applicability::MachineApplicable),
+ 1..=4 => (
+ inputs
+ .iter()
+ .map(|ty| {
+ if ty.is_suggestable(self.tcx, false) {
+ format!("/* {ty} */")
+ } else {
+ "/* value */".to_string()
+ }
+ })
+ .collect::<Vec<_>>()
+ .join(", "),
+ Applicability::HasPlaceholders,
+ ),
+ _ => ("/* ... */".to_string(), Applicability::HasPlaceholders),
+ };
+
+ applicability = applicability.max(this_applicability);
+
+ match expr.kind {
+ hir::ExprKind::Call(..)
+ | hir::ExprKind::Path(..)
+ | hir::ExprKind::Index(..)
+ | hir::ExprKind::Lit(..) => {
+ sugg.extend([(expr.span.shrink_to_hi(), format!("({sugg_call})"))]);
+ }
+ hir::ExprKind::Closure { .. } => {
+ // Might be `{ expr } || { bool }`
+ applicability = Applicability::MaybeIncorrect;
+ sugg.extend([
+ (expr.span.shrink_to_lo(), "(".to_string()),
+ (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
+ ]);
+ }
+ _ => {
+ sugg.extend([
+ (expr.span.shrink_to_lo(), "(".to_string()),
+ (expr.span.shrink_to_hi(), format!(")({sugg_call})")),
+ ]);
+ }
+ }
+ }
+
+ err.multipart_suggestion_verbose(
+ format!("use parentheses to call these"),
+ sugg,
+ applicability,
+ );
+
+ true
+ } else {
+ false
+ }
+ }
+
+ pub fn suggest_deref_ref_or_into(
+ &self,
+ err: &mut Diagnostic,
+ expr: &hir::Expr<'tcx>,
+ expected: Ty<'tcx>,
+ found: Ty<'tcx>,
+ expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
+ ) -> bool {
+ let expr = expr.peel_blocks();
+ if let Some((sp, msg, suggestion, applicability, verbose, annotation)) =
+ self.check_ref(expr, found, expected)
+ {
+ if verbose {
+ err.span_suggestion_verbose(sp, &msg, suggestion, applicability);
+ } else {
+ err.span_suggestion(sp, &msg, suggestion, applicability);
+ }
+ if annotation {
+ let suggest_annotation = match expr.peel_drop_temps().kind {
+ hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, _) => "&",
+ hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, _) => "&mut ",
+ _ => return true,
+ };
+ let mut tuple_indexes = Vec::new();
+ let mut expr_id = expr.hir_id;
+ for (parent_id, node) in self.tcx.hir().parent_iter(expr.hir_id) {
+ match node {
+ Node::Expr(&Expr { kind: ExprKind::Tup(subs), .. }) => {
+ tuple_indexes.push(
+ subs.iter()
+ .enumerate()
+ .find(|(_, sub_expr)| sub_expr.hir_id == expr_id)
+ .unwrap()
+ .0,
+ );
+ expr_id = parent_id;
+ }
+ Node::Local(local) => {
+ if let Some(mut ty) = local.ty {
+ while let Some(index) = tuple_indexes.pop() {
+ match ty.kind {
+ TyKind::Tup(tys) => ty = &tys[index],
+ _ => return true,
+ }
+ }
+ let annotation_span = ty.span;
+ err.span_suggestion(
+ annotation_span.with_hi(annotation_span.lo()),
+ format!("alternatively, consider changing the type annotation"),
+ suggest_annotation,
+ Applicability::MaybeIncorrect,
+ );
+ }
+ break;
+ }
+ _ => break,
+ }
+ }
+ }
+ return true;
+ } else if self.suggest_else_fn_with_closure(err, expr, found, expected) {
+ return true;
+ } else if self.suggest_fn_call(err, expr, found, |output| self.can_coerce(output, expected))
+ && let ty::FnDef(def_id, ..) = &found.kind()
+ && let Some(sp) = self.tcx.hir().span_if_local(*def_id)
+ {
+ err.span_label(sp, format!("{found} defined here"));
+ return true;
+ } else if self.check_for_cast(err, expr, found, expected, expected_ty_expr) {
+ return true;
+ } else {
+ let methods = self.get_conversion_methods(expr.span, expected, found, expr.hir_id);
+ if !methods.is_empty() {
+ let mut suggestions = methods.iter()
+ .filter_map(|conversion_method| {
+ let receiver_method_ident = expr.method_ident();
+ if let Some(method_ident) = receiver_method_ident
+ && method_ident.name == conversion_method.name
+ {
+ return None // do not suggest code that is already there (#53348)
+ }
+
+ let method_call_list = [sym::to_vec, sym::to_string];
+ let mut sugg = if let ExprKind::MethodCall(receiver_method, ..) = expr.kind
+ && receiver_method.ident.name == sym::clone
+ && method_call_list.contains(&conversion_method.name)
+ // If receiver is `.clone()` and found type has one of those methods,
+ // we guess that the user wants to convert from a slice type (`&[]` or `&str`)
+ // to an owned type (`Vec` or `String`). These conversions clone internally,
+ // so we remove the user's `clone` call.
+ {
+ vec![(
+ receiver_method.ident.span,
+ conversion_method.name.to_string()
+ )]
+ } else if expr.precedence().order()
+ < ExprPrecedence::MethodCall.order()
+ {
+ vec![
+ (expr.span.shrink_to_lo(), "(".to_string()),
+ (expr.span.shrink_to_hi(), format!(").{}()", conversion_method.name)),
+ ]
+ } else {
+ vec![(expr.span.shrink_to_hi(), format!(".{}()", conversion_method.name))]
+ };
+ let struct_pat_shorthand_field = self.maybe_get_struct_pattern_shorthand_field(expr);
+ if let Some(name) = struct_pat_shorthand_field {
+ sugg.insert(
+ 0,
+ (expr.span.shrink_to_lo(), format!("{}: ", name)),
+ );
+ }
+ Some(sugg)
+ })
+ .peekable();
+ if suggestions.peek().is_some() {
+ err.multipart_suggestions(
+ "try using a conversion method",
+ suggestions,
+ Applicability::MaybeIncorrect,
+ );
+ return true;
+ }
+ } else if let ty::Adt(found_adt, found_substs) = found.kind()
+ && self.tcx.is_diagnostic_item(sym::Option, found_adt.did())
+ && let ty::Adt(expected_adt, expected_substs) = expected.kind()
+ && self.tcx.is_diagnostic_item(sym::Option, expected_adt.did())
+ && let ty::Ref(_, inner_ty, _) = expected_substs.type_at(0).kind()
+ && inner_ty.is_str()
+ {
+ let ty = found_substs.type_at(0);
+ let mut peeled = ty;
+ let mut ref_cnt = 0;
+ while let ty::Ref(_, inner, _) = peeled.kind() {
+ peeled = *inner;
+ ref_cnt += 1;
+ }
+ if let ty::Adt(adt, _) = peeled.kind()
+ && self.tcx.is_diagnostic_item(sym::String, adt.did())
+ {
+ err.span_suggestion_verbose(
+ expr.span.shrink_to_hi(),
+ "try converting the passed type into a `&str`",
+ format!(".map(|x| &*{}x)", "*".repeat(ref_cnt)),
+ Applicability::MaybeIncorrect,
+ );
+ return true;
+ }
+ }
+ }
+
+ false
+ }
+
+ /// When encountering the expected boxed value allocated in the stack, suggest allocating it
+ /// in the heap by calling `Box::new()`.
+ pub(in super::super) fn suggest_boxing_when_appropriate(
+ &self,
+ err: &mut Diagnostic,
+ expr: &hir::Expr<'_>,
+ expected: Ty<'tcx>,
+ found: Ty<'tcx>,
+ ) -> bool {
+ if self.tcx.hir().is_inside_const_context(expr.hir_id) {
+ // Do not suggest `Box::new` in const context.
+ return false;
+ }
+ if !expected.is_box() || found.is_box() {
+ return false;
+ }
+ let boxed_found = self.tcx.mk_box(found);
+ if self.can_coerce(boxed_found, expected) {
+ err.multipart_suggestion(
+ "store this in the heap by calling `Box::new`",
+ vec![
+ (expr.span.shrink_to_lo(), "Box::new(".to_string()),
+ (expr.span.shrink_to_hi(), ")".to_string()),
+ ],
+ Applicability::MachineApplicable,
+ );
+ err.note(
+ "for more on the distinction between the stack and the heap, read \
+ https://doc.rust-lang.org/book/ch15-01-box.html, \
+ https://doc.rust-lang.org/rust-by-example/std/box.html, and \
+ https://doc.rust-lang.org/std/boxed/index.html",
+ );
+ true
+ } else {
+ false
+ }
+ }
+
+ /// When encountering a closure that captures variables, where a FnPtr is expected,
+ /// suggest a non-capturing closure
+ pub(in super::super) fn suggest_no_capture_closure(
+ &self,
+ err: &mut Diagnostic,
+ expected: Ty<'tcx>,
+ found: Ty<'tcx>,
+ ) -> bool {
+ if let (ty::FnPtr(_), ty::Closure(def_id, _)) = (expected.kind(), found.kind()) {
+ if let Some(upvars) = self.tcx.upvars_mentioned(*def_id) {
+ // Report upto four upvars being captured to reduce the amount error messages
+ // reported back to the user.
+ let spans_and_labels = upvars
+ .iter()
+ .take(4)
+ .map(|(var_hir_id, upvar)| {
+ let var_name = self.tcx.hir().name(*var_hir_id).to_string();
+ let msg = format!("`{}` captured here", var_name);
+ (upvar.span, msg)
+ })
+ .collect::<Vec<_>>();
+
+ let mut multi_span: MultiSpan =
+ spans_and_labels.iter().map(|(sp, _)| *sp).collect::<Vec<_>>().into();
+ for (sp, label) in spans_and_labels {
+ multi_span.push_span_label(sp, label);
+ }
+ err.span_note(
+ multi_span,
+ "closures can only be coerced to `fn` types if they do not capture any variables"
+ );
+ return true;
+ }
+ }
+ false
+ }
+
+ /// When encountering an `impl Future` where `BoxFuture` is expected, suggest `Box::pin`.
+ #[instrument(skip(self, err))]
+ pub(in super::super) fn suggest_calling_boxed_future_when_appropriate(
+ &self,
+ err: &mut Diagnostic,
+ expr: &hir::Expr<'_>,
+ expected: Ty<'tcx>,
+ found: Ty<'tcx>,
+ ) -> bool {
+ // Handle #68197.
+
+ if self.tcx.hir().is_inside_const_context(expr.hir_id) {
+ // Do not suggest `Box::new` in const context.
+ return false;
+ }
+ let pin_did = self.tcx.lang_items().pin_type();
+ // This guards the `unwrap` and `mk_box` below.
+ if pin_did.is_none() || self.tcx.lang_items().owned_box().is_none() {
+ return false;
+ }
+ let box_found = self.tcx.mk_box(found);
+ let pin_box_found = self.tcx.mk_lang_item(box_found, LangItem::Pin).unwrap();
+ let pin_found = self.tcx.mk_lang_item(found, LangItem::Pin).unwrap();
+ match expected.kind() {
+ ty::Adt(def, _) if Some(def.did()) == pin_did => {
+ if self.can_coerce(pin_box_found, expected) {
+ debug!("can coerce {:?} to {:?}, suggesting Box::pin", pin_box_found, expected);
+ match found.kind() {
+ ty::Adt(def, _) if def.is_box() => {
+ err.help("use `Box::pin`");
+ }
+ _ => {
+ err.multipart_suggestion(
+ "you need to pin and box this expression",
+ vec![
+ (expr.span.shrink_to_lo(), "Box::pin(".to_string()),
+ (expr.span.shrink_to_hi(), ")".to_string()),
+ ],
+ Applicability::MaybeIncorrect,
+ );
+ }
+ }
+ true
+ } else if self.can_coerce(pin_found, expected) {
+ match found.kind() {
+ ty::Adt(def, _) if def.is_box() => {
+ err.help("use `Box::pin`");
+ true
+ }
+ _ => false,
+ }
+ } else {
+ false
+ }
+ }
+ ty::Adt(def, _) if def.is_box() && self.can_coerce(box_found, expected) => {
+ // Check if the parent expression is a call to Pin::new. If it
+ // is and we were expecting a Box, ergo Pin<Box<expected>>, we
+ // can suggest Box::pin.
+ let parent = self.tcx.hir().get_parent_node(expr.hir_id);
+ let Some(Node::Expr(Expr { kind: ExprKind::Call(fn_name, _), .. })) = self.tcx.hir().find(parent) else {
+ return false;
+ };
+ match fn_name.kind {
+ ExprKind::Path(QPath::TypeRelative(
+ hir::Ty {
+ kind: TyKind::Path(QPath::Resolved(_, Path { res: recv_ty, .. })),
+ ..
+ },
+ method,
+ )) if recv_ty.opt_def_id() == pin_did && method.ident.name == sym::new => {
+ err.span_suggestion(
+ fn_name.span,
+ "use `Box::pin` to pin and box this expression",
+ "Box::pin",
+ Applicability::MachineApplicable,
+ );
+ true
+ }
+ _ => false,
+ }
+ }
+ _ => false,
+ }
+ }
+
+ /// A common error is to forget to add a semicolon at the end of a block, e.g.,
+ ///
+ /// ```compile_fail,E0308
+ /// # fn bar_that_returns_u32() -> u32 { 4 }
+ /// fn foo() {
+ /// bar_that_returns_u32()
+ /// }
+ /// ```
+ ///
+ /// This routine checks if the return expression in a block would make sense on its own as a
+ /// statement and the return type has been left as default or has been specified as `()`. If so,
+ /// it suggests adding a semicolon.
+ ///
+ /// If the expression is the expression of a closure without block (`|| expr`), a
+ /// block is needed to be added too (`|| { expr; }`). This is denoted by `needs_block`.
+ pub fn suggest_missing_semicolon(
+ &self,
+ err: &mut Diagnostic,
+ expression: &'tcx hir::Expr<'tcx>,
+ expected: Ty<'tcx>,
+ needs_block: bool,
+ ) {
+ if expected.is_unit() {
+ // `BlockTailExpression` only relevant if the tail expr would be
+ // useful on its own.
+ match expression.kind {
+ ExprKind::Call(..)
+ | ExprKind::MethodCall(..)
+ | ExprKind::Loop(..)
+ | ExprKind::If(..)
+ | ExprKind::Match(..)
+ | ExprKind::Block(..)
+ if expression.can_have_side_effects()
+ // If the expression is from an external macro, then do not suggest
+ // adding a semicolon, because there's nowhere to put it.
+ // See issue #81943.
+ && !in_external_macro(self.tcx.sess, expression.span) =>
+ {
+ if needs_block {
+ err.multipart_suggestion(
+ "consider using a semicolon here",
+ vec![
+ (expression.span.shrink_to_lo(), "{ ".to_owned()),
+ (expression.span.shrink_to_hi(), "; }".to_owned()),
+ ],
+ Applicability::MachineApplicable,
+ );
+ } else {
+ err.span_suggestion(
+ expression.span.shrink_to_hi(),
+ "consider using a semicolon here",
+ ";",
+ Applicability::MachineApplicable,
+ );
+ }
+ }
+ _ => (),
+ }
+ }
+ }
+
+ /// A possible error is to forget to add a return type that is needed:
+ ///
+ /// ```compile_fail,E0308
+ /// # fn bar_that_returns_u32() -> u32 { 4 }
+ /// fn foo() {
+ /// bar_that_returns_u32()
+ /// }
+ /// ```
+ ///
+ /// This routine checks if the return type is left as default, the method is not part of an
+ /// `impl` block and that it isn't the `main` method. If so, it suggests setting the return
+ /// type.
+ pub(in super::super) fn suggest_missing_return_type(
+ &self,
+ err: &mut Diagnostic,
+ fn_decl: &hir::FnDecl<'_>,
+ expected: Ty<'tcx>,
+ found: Ty<'tcx>,
+ can_suggest: bool,
+ fn_id: hir::HirId,
+ ) -> bool {
+ let found =
+ self.resolve_numeric_literals_with_default(self.resolve_vars_if_possible(found));
+ // Only suggest changing the return type for methods that
+ // haven't set a return type at all (and aren't `fn main()` or an impl).
+ match &fn_decl.output {
+ &hir::FnRetTy::DefaultReturn(span) if expected.is_unit() && !can_suggest => {
+ // `fn main()` must return `()`, do not suggest changing return type
+ err.subdiagnostic(ExpectedReturnTypeLabel::Unit { span });
+ return true;
+ }
+ &hir::FnRetTy::DefaultReturn(span) if expected.is_unit() => {
+ if found.is_suggestable(self.tcx, false) {
+ err.subdiagnostic(AddReturnTypeSuggestion::Add { span, found: found.to_string() });
+ return true;
+ } else if let ty::Closure(_, substs) = found.kind()
+ // FIXME(compiler-errors): Get better at printing binders...
+ && let closure = substs.as_closure()
+ && closure.sig().is_suggestable(self.tcx, false)
+ {
+ err.subdiagnostic(AddReturnTypeSuggestion::Add { span, found: closure.print_as_impl_trait().to_string() });
+ return true;
+ } else {
+ // FIXME: if `found` could be `impl Iterator` we should suggest that.
+ err.subdiagnostic(AddReturnTypeSuggestion::MissingHere { span });
+ return true
+ }
+ }
+ &hir::FnRetTy::Return(ref ty) => {
+ // Only point to return type if the expected type is the return type, as if they
+ // are not, the expectation must have been caused by something else.
+ debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
+ let span = ty.span;
+ let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
+ debug!("suggest_missing_return_type: return type {:?}", ty);
+ debug!("suggest_missing_return_type: expected type {:?}", ty);
+ let bound_vars = self.tcx.late_bound_vars(fn_id);
+ let ty = Binder::bind_with_vars(ty, bound_vars);
+ let ty = self.normalize_associated_types_in(span, ty);
+ let ty = self.tcx.erase_late_bound_regions(ty);
+ if self.can_coerce(expected, ty) {
+ err.subdiagnostic(ExpectedReturnTypeLabel::Other { span, expected });
+ self.try_suggest_return_impl_trait(err, expected, ty, fn_id);
+ return true;
+ }
+ }
+ _ => {}
+ }
+ false
+ }
+
+ /// check whether the return type is a generic type with a trait bound
+ /// only suggest this if the generic param is not present in the arguments
+ /// if this is true, hint them towards changing the return type to `impl Trait`
+ /// ```compile_fail,E0308
+ /// fn cant_name_it<T: Fn() -> u32>() -> T {
+ /// || 3
+ /// }
+ /// ```
+ fn try_suggest_return_impl_trait(
+ &self,
+ err: &mut Diagnostic,
+ expected: Ty<'tcx>,
+ found: Ty<'tcx>,
+ fn_id: hir::HirId,
+ ) {
+ // Only apply the suggestion if:
+ // - the return type is a generic parameter
+ // - the generic param is not used as a fn param
+ // - the generic param has at least one bound
+ // - the generic param doesn't appear in any other bounds where it's not the Self type
+ // Suggest:
+ // - Changing the return type to be `impl <all bounds>`
+
+ debug!("try_suggest_return_impl_trait, expected = {:?}, found = {:?}", expected, found);
+
+ let ty::Param(expected_ty_as_param) = expected.kind() else { return };
+
+ let fn_node = self.tcx.hir().find(fn_id);
+
+ let Some(hir::Node::Item(hir::Item {
+ kind:
+ hir::ItemKind::Fn(
+ hir::FnSig { decl: hir::FnDecl { inputs: fn_parameters, output: fn_return, .. }, .. },
+ hir::Generics { params, predicates, .. },
+ _body_id,
+ ),
+ ..
+ })) = fn_node else { return };
+
+ if params.get(expected_ty_as_param.index as usize).is_none() {
+ return;
+ };
+
+ // get all where BoundPredicates here, because they are used in to cases below
+ let where_predicates = predicates
+ .iter()
+ .filter_map(|p| match p {
+ WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
+ bounds,
+ bounded_ty,
+ ..
+ }) => {
+ // FIXME: Maybe these calls to `ast_ty_to_ty` can be removed (and the ones below)
+ let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, bounded_ty);
+ Some((ty, bounds))
+ }
+ _ => None,
+ })
+ .map(|(ty, bounds)| match ty.kind() {
+ ty::Param(param_ty) if param_ty == expected_ty_as_param => Ok(Some(bounds)),
+ // check whether there is any predicate that contains our `T`, like `Option<T>: Send`
+ _ => match ty.contains(expected) {
+ true => Err(()),
+ false => Ok(None),
+ },
+ })
+ .collect::<Result<Vec<_>, _>>();
+
+ let Ok(where_predicates) = where_predicates else { return };
+
+ // now get all predicates in the same types as the where bounds, so we can chain them
+ let predicates_from_where =
+ where_predicates.iter().flatten().flat_map(|bounds| bounds.iter());
+
+ // extract all bounds from the source code using their spans
+ let all_matching_bounds_strs = predicates_from_where
+ .filter_map(|bound| match bound {
+ GenericBound::Trait(_, _) => {
+ self.tcx.sess.source_map().span_to_snippet(bound.span()).ok()
+ }
+ _ => None,
+ })
+ .collect::<Vec<String>>();
+
+ if all_matching_bounds_strs.len() == 0 {
+ return;
+ }
+
+ let all_bounds_str = all_matching_bounds_strs.join(" + ");
+
+ let ty_param_used_in_fn_params = fn_parameters.iter().any(|param| {
+ let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, param);
+ matches!(ty.kind(), ty::Param(fn_param_ty_param) if expected_ty_as_param == fn_param_ty_param)
+ });
+
+ if ty_param_used_in_fn_params {
+ return;
+ }
+
+ err.span_suggestion(
+ fn_return.span(),
+ "consider using an impl return type",
+ format!("impl {}", all_bounds_str),
+ Applicability::MaybeIncorrect,
+ );
+ }
+
+ pub(in super::super) fn suggest_missing_break_or_return_expr(
+ &self,
+ err: &mut Diagnostic,
+ expr: &'tcx hir::Expr<'tcx>,
+ fn_decl: &hir::FnDecl<'_>,
+ expected: Ty<'tcx>,
+ found: Ty<'tcx>,
+ id: hir::HirId,
+ fn_id: hir::HirId,
+ ) {
+ if !expected.is_unit() {
+ return;
+ }
+ let found = self.resolve_vars_with_obligations(found);
+
+ let in_loop = self.is_loop(id)
+ || self.tcx.hir().parent_iter(id).any(|(parent_id, _)| self.is_loop(parent_id));
+
+ let in_local_statement = self.is_local_statement(id)
+ || self
+ .tcx
+ .hir()
+ .parent_iter(id)
+ .any(|(parent_id, _)| self.is_local_statement(parent_id));
+
+ if in_loop && in_local_statement {
+ err.multipart_suggestion(
+ "you might have meant to break the loop with this value",
+ vec![
+ (expr.span.shrink_to_lo(), "break ".to_string()),
+ (expr.span.shrink_to_hi(), ";".to_string()),
+ ],
+ Applicability::MaybeIncorrect,
+ );
+ return;
+ }
+
+ if let hir::FnRetTy::Return(ty) = fn_decl.output {
+ let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
+ let bound_vars = self.tcx.late_bound_vars(fn_id);
+ let ty = self.tcx.erase_late_bound_regions(Binder::bind_with_vars(ty, bound_vars));
+ let ty = self.normalize_associated_types_in(expr.span, ty);
+ let ty = match self.tcx.asyncness(fn_id.owner) {
+ hir::IsAsync::Async => {
+ let infcx = self.tcx.infer_ctxt().build();
+ infcx
+ .get_impl_future_output_ty(ty)
+ .unwrap_or_else(|| {
+ span_bug!(
+ fn_decl.output.span(),
+ "failed to get output type of async function"
+ )
+ })
+ .skip_binder()
+ }
+ hir::IsAsync::NotAsync => ty,
+ };
+ if self.can_coerce(found, ty) {
+ err.multipart_suggestion(
+ "you might have meant to return this value",
+ vec![
+ (expr.span.shrink_to_lo(), "return ".to_string()),
+ (expr.span.shrink_to_hi(), ";".to_string()),
+ ],
+ Applicability::MaybeIncorrect,
+ );
+ }
+ }
+ }
+
+ pub(in super::super) fn suggest_missing_parentheses(
+ &self,
+ err: &mut Diagnostic,
+ expr: &hir::Expr<'_>,
+ ) -> bool {
+ let sp = self.tcx.sess.source_map().start_point(expr.span);
+ if let Some(sp) = self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp) {
+ // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
+ err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
+ true
+ } else {
+ false
+ }
+ }
+
+ /// Given an expression type mismatch, peel any `&` expressions until we get to
+ /// a block expression, and then suggest replacing the braces with square braces
+ /// if it was possibly mistaken array syntax.
+ pub(crate) fn suggest_block_to_brackets_peeling_refs(
+ &self,
+ diag: &mut Diagnostic,
+ mut expr: &hir::Expr<'_>,
+ mut expr_ty: Ty<'tcx>,
+ mut expected_ty: Ty<'tcx>,
+ ) -> bool {
+ loop {
+ match (&expr.kind, expr_ty.kind(), expected_ty.kind()) {
+ (
+ hir::ExprKind::AddrOf(_, _, inner_expr),
+ ty::Ref(_, inner_expr_ty, _),
+ ty::Ref(_, inner_expected_ty, _),
+ ) => {
+ expr = *inner_expr;
+ expr_ty = *inner_expr_ty;
+ expected_ty = *inner_expected_ty;
+ }
+ (hir::ExprKind::Block(blk, _), _, _) => {
+ self.suggest_block_to_brackets(diag, *blk, expr_ty, expected_ty);
+ break true;
+ }
+ _ => break false,
+ }
+ }
+ }
+
+ pub(crate) fn suggest_copied_or_cloned(
+ &self,
+ diag: &mut Diagnostic,
+ expr: &hir::Expr<'_>,
+ expr_ty: Ty<'tcx>,
+ expected_ty: Ty<'tcx>,
+ ) -> bool {
+ let ty::Adt(adt_def, substs) = expr_ty.kind() else { return false; };
+ let ty::Adt(expected_adt_def, expected_substs) = expected_ty.kind() else { return false; };
+ if adt_def != expected_adt_def {
+ return false;
+ }
+
+ let mut suggest_copied_or_cloned = || {
+ let expr_inner_ty = substs.type_at(0);
+ let expected_inner_ty = expected_substs.type_at(0);
+ if let ty::Ref(_, ty, hir::Mutability::Not) = expr_inner_ty.kind()
+ && self.can_eq(self.param_env, *ty, expected_inner_ty).is_ok()
+ {
+ let def_path = self.tcx.def_path_str(adt_def.did());
+ if self.type_is_copy_modulo_regions(self.param_env, *ty, expr.span) {
+ diag.span_suggestion_verbose(
+ expr.span.shrink_to_hi(),
+ format!(
+ "use `{def_path}::copied` to copy the value inside the `{def_path}`"
+ ),
+ ".copied()",
+ Applicability::MachineApplicable,
+ );
+ return true;
+ } else if let Some(clone_did) = self.tcx.lang_items().clone_trait()
+ && rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions(
+ self,
+ self.param_env,
+ *ty,
+ clone_did,
+ expr.span
+ )
+ {
+ diag.span_suggestion_verbose(
+ expr.span.shrink_to_hi(),
+ format!(
+ "use `{def_path}::cloned` to clone the value inside the `{def_path}`"
+ ),
+ ".cloned()",
+ Applicability::MachineApplicable,
+ );
+ return true;
+ }
+ }
+ false
+ };
+
+ if let Some(result_did) = self.tcx.get_diagnostic_item(sym::Result)
+ && adt_def.did() == result_did
+ // Check that the error types are equal
+ && self.can_eq(self.param_env, substs.type_at(1), expected_substs.type_at(1)).is_ok()
+ {
+ return suggest_copied_or_cloned();
+ } else if let Some(option_did) = self.tcx.get_diagnostic_item(sym::Option)
+ && adt_def.did() == option_did
+ {
+ return suggest_copied_or_cloned();
+ }
+
+ false
+ }
+
+ pub(crate) fn suggest_into(
+ &self,
+ diag: &mut Diagnostic,
+ expr: &hir::Expr<'_>,
+ expr_ty: Ty<'tcx>,
+ expected_ty: Ty<'tcx>,
+ ) -> bool {
+ let expr = expr.peel_blocks();
+
+ // We have better suggestions for scalar interconversions...
+ if expr_ty.is_scalar() && expected_ty.is_scalar() {
+ return false;
+ }
+
+ // Don't suggest turning a block into another type (e.g. `{}.into()`)
+ if matches!(expr.kind, hir::ExprKind::Block(..)) {
+ return false;
+ }
+
+ // We'll later suggest `.as_ref` when noting the type error,
+ // so skip if we will suggest that instead.
+ if self.err_ctxt().should_suggest_as_ref(expected_ty, expr_ty).is_some() {
+ return false;
+ }
+
+ if let Some(into_def_id) = self.tcx.get_diagnostic_item(sym::Into)
+ && self.predicate_must_hold_modulo_regions(&traits::Obligation::new(
+ self.misc(expr.span),
+ self.param_env,
+ ty::Binder::dummy(ty::TraitRef {
+ def_id: into_def_id,
+ substs: self.tcx.mk_substs_trait(expr_ty, &[expected_ty.into()]),
+ })
+ .to_poly_trait_predicate()
+ .to_predicate(self.tcx),
+ ))
+ {
+ let sugg = if expr.precedence().order() >= PREC_POSTFIX {
+ vec![(expr.span.shrink_to_hi(), ".into()".to_owned())]
+ } else {
+ vec![(expr.span.shrink_to_lo(), "(".to_owned()), (expr.span.shrink_to_hi(), ").into()".to_owned())]
+ };
+ diag.multipart_suggestion(
+ format!("call `Into::into` on this expression to convert `{expr_ty}` into `{expected_ty}`"),
+ sugg,
+ Applicability::MaybeIncorrect
+ );
+ return true;
+ }
+
+ false
+ }
+
+ /// Suggest wrapping the block in square brackets instead of curly braces
+ /// in case the block was mistaken array syntax, e.g. `{ 1 }` -> `[ 1 ]`.
+ pub(crate) fn suggest_block_to_brackets(
+ &self,
+ diag: &mut Diagnostic,
+ blk: &hir::Block<'_>,
+ blk_ty: Ty<'tcx>,
+ expected_ty: Ty<'tcx>,
+ ) {
+ if let ty::Slice(elem_ty) | ty::Array(elem_ty, _) = expected_ty.kind() {
+ if self.can_coerce(blk_ty, *elem_ty)
+ && blk.stmts.is_empty()
+ && blk.rules == hir::BlockCheckMode::DefaultBlock
+ {
+ let source_map = self.tcx.sess.source_map();
+ if let Ok(snippet) = source_map.span_to_snippet(blk.span) {
+ if snippet.starts_with('{') && snippet.ends_with('}') {
+ diag.multipart_suggestion_verbose(
+ "to create an array, use square brackets instead of curly braces",
+ vec![
+ (
+ blk.span
+ .shrink_to_lo()
+ .with_hi(rustc_span::BytePos(blk.span.lo().0 + 1)),
+ "[".to_string(),
+ ),
+ (
+ blk.span
+ .shrink_to_hi()
+ .with_lo(rustc_span::BytePos(blk.span.hi().0 - 1)),
+ "]".to_string(),
+ ),
+ ],
+ Applicability::MachineApplicable,
+ );
+ }
+ }
+ }
+ }
+ }
+
+ fn is_loop(&self, id: hir::HirId) -> bool {
+ let node = self.tcx.hir().get(id);
+ matches!(node, Node::Expr(Expr { kind: ExprKind::Loop(..), .. }))
+ }
+
+ fn is_local_statement(&self, id: hir::HirId) -> bool {
+ let node = self.tcx.hir().get(id);
+ matches!(node, Node::Stmt(Stmt { kind: StmtKind::Local(..), .. }))
+ }
+
+ /// Suggest that `&T` was cloned instead of `T` because `T` does not implement `Clone`,
+ /// which is a side-effect of autoref.
+ pub(crate) fn note_type_is_not_clone(
+ &self,
+ diag: &mut Diagnostic,
+ expected_ty: Ty<'tcx>,
+ found_ty: Ty<'tcx>,
+ expr: &hir::Expr<'_>,
+ ) {
+ let hir::ExprKind::MethodCall(segment, callee_expr, &[], _) = expr.kind else { return; };
+ let Some(clone_trait_did) = self.tcx.lang_items().clone_trait() else { return; };
+ let ty::Ref(_, pointee_ty, _) = found_ty.kind() else { return };
+ let results = self.typeck_results.borrow();
+ // First, look for a `Clone::clone` call
+ if segment.ident.name == sym::clone
+ && results.type_dependent_def_id(expr.hir_id).map_or(
+ false,
+ |did| {
+ let assoc_item = self.tcx.associated_item(did);
+ assoc_item.container == ty::AssocItemContainer::TraitContainer
+ && assoc_item.container_id(self.tcx) == clone_trait_did
+ },
+ )
+ // If that clone call hasn't already dereferenced the self type (i.e. don't give this
+ // diagnostic in cases where we have `(&&T).clone()` and we expect `T`).
+ && !results.expr_adjustments(callee_expr).iter().any(|adj| matches!(adj.kind, ty::adjustment::Adjust::Deref(..)))
+ // Check that we're in fact trying to clone into the expected type
+ && self.can_coerce(*pointee_ty, expected_ty)
+ // And the expected type doesn't implement `Clone`
+ && !self.predicate_must_hold_considering_regions(&traits::Obligation {
+ cause: traits::ObligationCause::dummy(),
+ param_env: self.param_env,
+ recursion_depth: 0,
+ predicate: ty::Binder::dummy(ty::TraitRef {
+ def_id: clone_trait_did,
+ substs: self.tcx.mk_substs([expected_ty.into()].iter()),
+ })
+ .without_const()
+ .to_predicate(self.tcx),
+ })
+ {
+ diag.span_note(
+ callee_expr.span,
+ &format!(
+ "`{expected_ty}` does not implement `Clone`, so `{found_ty}` was cloned instead"
+ ),
+ );
+ }
+ }
+
+ /// A common error is to add an extra semicolon:
+ ///
+ /// ```compile_fail,E0308
+ /// fn foo() -> usize {
+ /// 22;
+ /// }
+ /// ```
+ ///
+ /// This routine checks if the final statement in a block is an
+ /// expression with an explicit semicolon whose type is compatible
+ /// with `expected_ty`. If so, it suggests removing the semicolon.
+ pub(crate) fn consider_removing_semicolon(
+ &self,
+ blk: &'tcx hir::Block<'tcx>,
+ expected_ty: Ty<'tcx>,
+ err: &mut Diagnostic,
+ ) -> bool {
+ if let Some((span_semi, boxed)) = self.err_ctxt().could_remove_semicolon(blk, expected_ty) {
+ if let StatementAsExpression::NeedsBoxing = boxed {
+ err.span_suggestion_verbose(
+ span_semi,
+ "consider removing this semicolon and boxing the expression",
+ "",
+ Applicability::HasPlaceholders,
+ );
+ } else {
+ err.span_suggestion_short(
+ span_semi,
+ "remove this semicolon to return this value",
+ "",
+ Applicability::MachineApplicable,
+ );
+ }
+ true
+ } else {
+ false
+ }
+ }
+}
projects / rustc.git / blobdiff