path: root/compiler/rustc_infer/src/infer/error_reporting/suggest.rs

use hir::def::CtorKind;
use hir::intravisit::{walk_expr, walk_stmt, Visitor};
use rustc_data_structures::fx::FxIndexSet;
use rustc_errors::{Applicability, Diagnostic};
use rustc_hir as hir;
use rustc_middle::traits::{
    IfExpressionCause, MatchExpressionArmCause, ObligationCause, ObligationCauseCode,
    StatementAsExpression,
};
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::{self as ty, IsSuggestable, Ty, TypeVisitableExt};
use rustc_span::{sym, BytePos, Span};

use crate::errors::{
    ConsiderAddingAwait, SuggAddLetForLetChains, SuggestRemoveSemiOrReturnBinding,
};

use super::TypeErrCtxt;

impl<'tcx> TypeErrCtxt<'_, 'tcx> {
    pub(super) fn suggest_remove_semi_or_return_binding(
        &self,
        first_id: Option<hir::HirId>,
        first_ty: Ty<'tcx>,
        first_span: Span,
        second_id: Option<hir::HirId>,
        second_ty: Ty<'tcx>,
        second_span: Span,
    ) -> Option<SuggestRemoveSemiOrReturnBinding> {
        let remove_semicolon = [
            (first_id, self.resolve_vars_if_possible(second_ty)),
            (second_id, self.resolve_vars_if_possible(first_ty)),
        ]
        .into_iter()
        .find_map(|(id, ty)| {
            let hir::Node::Block(blk) = self.tcx.hir().get(id?) else { return None };
            self.could_remove_semicolon(blk, ty)
        });
        match remove_semicolon {
            Some((sp, StatementAsExpression::NeedsBoxing)) => {
                Some(SuggestRemoveSemiOrReturnBinding::RemoveAndBox {
                    first_lo: first_span.shrink_to_lo(),
                    first_hi: first_span.shrink_to_hi(),
                    second_lo: second_span.shrink_to_lo(),
                    second_hi: second_span.shrink_to_hi(),
                    sp,
                })
            }
            Some((sp, StatementAsExpression::CorrectType)) => {
                Some(SuggestRemoveSemiOrReturnBinding::Remove { sp })
            }
            None => {
                let mut ret = None;
                for (id, ty) in [(first_id, second_ty), (second_id, first_ty)] {
                    if let Some(id) = id
                        && let hir::Node::Block(blk) = self.tcx.hir().get(id)
                        && let Some(diag) = self.consider_returning_binding_diag(blk, ty)
                    {
                        ret = Some(diag);
                        break;
                    }
                }
                ret
            }
        }
    }

    pub(super) fn suggest_boxing_for_return_impl_trait(
        &self,
        err: &mut Diagnostic,
        return_sp: Span,
        arm_spans: impl Iterator<Item = Span>,
    ) {
        err.multipart_suggestion(
            "you could change the return type to be a boxed trait object",
            vec![
                (return_sp.with_hi(return_sp.lo() + BytePos(4)), "Box<dyn".to_string()),
                (return_sp.shrink_to_hi(), ">".to_string()),
            ],
            Applicability::MaybeIncorrect,
        );
        let sugg = arm_spans
            .flat_map(|sp| {
                [(sp.shrink_to_lo(), "Box::new(".to_string()), (sp.shrink_to_hi(), ")".to_string())]
                    .into_iter()
            })
            .collect::<Vec<_>>();
        err.multipart_suggestion(
            "if you change the return type to expect trait objects, box the returned expressions",
            sugg,
            Applicability::MaybeIncorrect,
        );
    }

    pub(super) fn suggest_tuple_pattern(
        &self,
        cause: &ObligationCause<'tcx>,
        exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
        diag: &mut Diagnostic,
    ) {
        // Heavily inspired by `FnCtxt::suggest_compatible_variants`, with
        // some modifications due to that being in typeck and this being in infer.
        if let ObligationCauseCode::Pattern { .. } = cause.code() {
            if let ty::Adt(expected_adt, substs) = exp_found.expected.kind() {
                let compatible_variants: Vec<_> = expected_adt
                    .variants()
                    .iter()
                    .filter(|variant| {
                        variant.fields.len() == 1 && variant.ctor_kind() == Some(CtorKind::Fn)
                    })
                    .filter_map(|variant| {
                        let sole_field = &variant.fields[0];
                        let sole_field_ty = sole_field.ty(self.tcx, substs);
                        if self.same_type_modulo_infer(sole_field_ty, exp_found.found) {
                            let variant_path =
                                with_no_trimmed_paths!(self.tcx.def_path_str(variant.def_id));
                            // FIXME #56861: DRYer prelude filtering
                            if let Some(path) = variant_path.strip_prefix("std::prelude::") {
                                if let Some((_, path)) = path.split_once("::") {
                                    return Some(path.to_string());
                                }
                            }
                            Some(variant_path)
                        } else {
                            None
                        }
                    })
                    .collect();
                match &compatible_variants[..] {
                    [] => {}
                    [variant] => {
                        diag.multipart_suggestion_verbose(
                            &format!("try wrapping the pattern in `{}`", variant),
                            vec![
                                (cause.span.shrink_to_lo(), format!("{}(", variant)),
                                (cause.span.shrink_to_hi(), ")".to_string()),
                            ],
                            Applicability::MaybeIncorrect,
                        );
                    }
                    _ => {
                        // More than one matching variant.
                        diag.multipart_suggestions(
                            &format!(
                                "try wrapping the pattern in a variant of `{}`",
                                self.tcx.def_path_str(expected_adt.did())
                            ),
                            compatible_variants.into_iter().map(|variant| {
                                vec![
                                    (cause.span.shrink_to_lo(), format!("{}(", variant)),
                                    (cause.span.shrink_to_hi(), ")".to_string()),
                                ]
                            }),
                            Applicability::MaybeIncorrect,
                        );
                    }
                }
            }
        }
    }

    /// A possible error is to forget to add `.await` when using futures:
    ///
    /// ```compile_fail,E0308
    /// async fn make_u32() -> u32 {
    ///     22
    /// }
    ///
    /// fn take_u32(x: u32) {}
    ///
    /// async fn foo() {
    ///     let x = make_u32();
    ///     take_u32(x);
    /// }
    /// ```
    ///
    /// This routine checks if the found type `T` implements `Future<Output=U>` where `U` is the
    /// expected type. If this is the case, and we are inside of an async body, it suggests adding
    /// `.await` to the tail of the expression.
    pub(super) fn suggest_await_on_expect_found(
        &self,
        cause: &ObligationCause<'tcx>,
        exp_span: Span,
        exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
        diag: &mut Diagnostic,
    ) {
        debug!(
            "suggest_await_on_expect_found: exp_span={:?}, expected_ty={:?}, found_ty={:?}",
            exp_span, exp_found.expected, exp_found.found,
        );

        if let ObligationCauseCode::CompareImplItemObligation { .. } = cause.code() {
            return;
        }

        let subdiag = match (
            self.get_impl_future_output_ty(exp_found.expected),
            self.get_impl_future_output_ty(exp_found.found),
        ) {
            (Some(exp), Some(found)) if self.same_type_modulo_infer(exp, found) => match cause
                .code()
            {
                ObligationCauseCode::IfExpression(box IfExpressionCause { then_id, .. }) => {
                    let then_span = self.find_block_span_from_hir_id(*then_id);
                    Some(ConsiderAddingAwait::BothFuturesSugg {
                        first: then_span.shrink_to_hi(),
                        second: exp_span.shrink_to_hi(),
                    })
                }
                ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
                    prior_arms,
                    ..
                }) => {
                    if let [.., arm_span] = &prior_arms[..] {
                        Some(ConsiderAddingAwait::BothFuturesSugg {
                            first: arm_span.shrink_to_hi(),
                            second: exp_span.shrink_to_hi(),
                        })
                    } else {
                        Some(ConsiderAddingAwait::BothFuturesHelp)
                    }
                }
                _ => Some(ConsiderAddingAwait::BothFuturesHelp),
            },
            (_, Some(ty)) if self.same_type_modulo_infer(exp_found.expected, ty) => {
                // FIXME: Seems like we can't have a suggestion and a note with different spans in a single subdiagnostic
                diag.subdiagnostic(ConsiderAddingAwait::FutureSugg {
                    span: exp_span.shrink_to_hi(),
                });
                Some(ConsiderAddingAwait::FutureSuggNote { span: exp_span })
            }
            (Some(ty), _) if self.same_type_modulo_infer(ty, exp_found.found) => match cause.code()
            {
                ObligationCauseCode::Pattern { span: Some(then_span), .. } => {
                    Some(ConsiderAddingAwait::FutureSugg { span: then_span.shrink_to_hi() })
                }
                ObligationCauseCode::IfExpression(box IfExpressionCause { then_id, .. }) => {
                    let then_span = self.find_block_span_from_hir_id(*then_id);
                    Some(ConsiderAddingAwait::FutureSugg { span: then_span.shrink_to_hi() })
                }
                ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
                    ref prior_arms,
                    ..
                }) => Some({
                    ConsiderAddingAwait::FutureSuggMultiple {
                        spans: prior_arms.iter().map(|arm| arm.shrink_to_hi()).collect(),
                    }
                }),
                _ => None,
            },
            _ => None,
        };
        if let Some(subdiag) = subdiag {
            diag.subdiagnostic(subdiag);
        }
    }

    pub fn suggest_await_on_future(&self, diag: &mut Diagnostic, sp: Span) {
        diag.span_suggestion_verbose(
            sp.shrink_to_hi(),
            "consider `await`ing on the `Future`",
            ".await",
            Applicability::MaybeIncorrect,
        );
    }

    pub(super) fn suggest_accessing_field_where_appropriate(
        &self,
        cause: &ObligationCause<'tcx>,
        exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
        diag: &mut Diagnostic,
    ) {
        debug!(
            "suggest_accessing_field_where_appropriate(cause={:?}, exp_found={:?})",
            cause, exp_found
        );
        if let ty::Adt(expected_def, expected_substs) = exp_found.expected.kind() {
            if expected_def.is_enum() {
                return;
            }

            if let Some((name, ty)) = expected_def
                .non_enum_variant()
                .fields
                .iter()
                .filter(|field| field.vis.is_accessible_from(field.did, self.tcx))
                .map(|field| (field.name, field.ty(self.tcx, expected_substs)))
                .find(|(_, ty)| self.same_type_modulo_infer(*ty, exp_found.found))
            {
                if let ObligationCauseCode::Pattern { span: Some(span), .. } = *cause.code() {
                    if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
                        let suggestion = if expected_def.is_struct() {
                            format!("{}.{}", snippet, name)
                        } else if expected_def.is_union() {
                            format!("unsafe {{ {}.{} }}", snippet, name)
                        } else {
                            return;
                        };
                        diag.span_suggestion(
                            span,
                            &format!(
                                "you might have meant to use field `{}` whose type is `{}`",
                                name, ty
                            ),
                            suggestion,
                            Applicability::MaybeIncorrect,
                        );
                    }
                }
            }
        }
    }

    /// When encountering a case where `.as_ref()` on a `Result` or `Option` would be appropriate,
    /// suggests it.
    pub(super) fn suggest_as_ref_where_appropriate(
        &self,
        span: Span,
        exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
        diag: &mut Diagnostic,
    ) {
        if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
            && let Some(msg) = self.should_suggest_as_ref(exp_found.expected, exp_found.found)
        {
            diag.span_suggestion(
                span,
                msg,
                // HACK: fix issue# 100605, suggesting convert from &Option<T> to Option<&T>, remove the extra `&`
                format!("{}.as_ref()", snippet.trim_start_matches('&')),
                Applicability::MachineApplicable,
            );
        }
    }

    pub(super) fn suggest_function_pointers(
        &self,
        cause: &ObligationCause<'tcx>,
        span: Span,
        exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
        diag: &mut Diagnostic,
    ) {
        debug!("suggest_function_pointers(cause={:?}, exp_found={:?})", cause, exp_found);
        let ty::error::ExpectedFound { expected, found } = exp_found;
        let expected_inner = expected.peel_refs();
        let found_inner = found.peel_refs();
        if !expected_inner.is_fn() || !found_inner.is_fn() {
            return;
        }
        match (&expected_inner.kind(), &found_inner.kind()) {
            (ty::FnPtr(sig), ty::FnDef(did, substs)) => {
                let expected_sig = &(self.normalize_fn_sig)(*sig);
                let found_sig =
                    &(self.normalize_fn_sig)(self.tcx.fn_sig(*did).subst(self.tcx, substs));

                let fn_name = self.tcx.def_path_str_with_substs(*did, substs);

                if !self.same_type_modulo_infer(*found_sig, *expected_sig)
                    || !sig.is_suggestable(self.tcx, true)
                    || ty::util::is_intrinsic(self.tcx, *did)
                {
                    return;
                }

                let (msg, sug) = match (expected.is_ref(), found.is_ref()) {
                    (true, false) => {
                        let msg = "consider using a reference";
                        let sug = format!("&{fn_name}");
                        (msg, sug)
                    }
                    (false, true) => {
                        let msg = "consider removing the reference";
                        let sug = format!("{fn_name}");
                        (msg, sug)
                    }
                    (true, true) => {
                        diag.note("fn items are distinct from fn pointers");
                        let msg = "consider casting to a fn pointer";
                        let sug = format!("&({fn_name} as {sig})");
                        (msg, sug)
                    }
                    (false, false) => {
                        diag.note("fn items are distinct from fn pointers");
                        let msg = "consider casting to a fn pointer";
                        let sug = format!("{fn_name} as {sig}");
                        (msg, sug)
                    }
                };
                diag.span_suggestion_verbose(span, msg, sug, Applicability::MaybeIncorrect);
            }
            (ty::FnDef(did1, substs1), ty::FnDef(did2, substs2)) => {
                let expected_sig =
                    &(self.normalize_fn_sig)(self.tcx.fn_sig(*did1).subst(self.tcx, substs1));
                let found_sig =
                    &(self.normalize_fn_sig)(self.tcx.fn_sig(*did2).subst(self.tcx, substs2));

                if self.same_type_modulo_infer(*expected_sig, *found_sig) {
                    diag.note("different fn items have unique types, even if their signatures are the same");
                }

                if !self.same_type_modulo_infer(*found_sig, *expected_sig)
                    || !found_sig.is_suggestable(self.tcx, true)
                    || !expected_sig.is_suggestable(self.tcx, true)
                    || ty::util::is_intrinsic(self.tcx, *did1)
                    || ty::util::is_intrinsic(self.tcx, *did2)
                {
                    return;
                }

                let fn_name = self.tcx.def_path_str_with_substs(*did2, substs2);
                let sug = if found.is_ref() {
                    format!("&({fn_name} as {found_sig})")
                } else {
                    format!("{fn_name} as {found_sig}")
                };

                let msg = format!(
                    "consider casting both fn items to fn pointers using `as {expected_sig}`"
                );

                diag.span_suggestion_hidden(span, msg, sug, Applicability::MaybeIncorrect);
            }
            (ty::FnDef(did, substs), ty::FnPtr(sig)) => {
                let expected_sig =
                    &(self.normalize_fn_sig)(self.tcx.fn_sig(*did).subst(self.tcx, substs));
                let found_sig = &(self.normalize_fn_sig)(*sig);

                if !self.same_type_modulo_infer(*found_sig, *expected_sig) {
                    return;
                }

                let fn_name = self.tcx.def_path_str_with_substs(*did, substs);

                let casting = if expected.is_ref() {
                    format!("&({fn_name} as {found_sig})")
                } else {
                    format!("{fn_name} as {found_sig}")
                };

                diag.help(&format!("consider casting the fn item to a fn pointer: `{}`", casting));
            }
            _ => {
                return;
            }
        };
    }

    pub fn should_suggest_as_ref(&self, expected: Ty<'tcx>, found: Ty<'tcx>) -> Option<&str> {
        if let (ty::Adt(exp_def, exp_substs), ty::Ref(_, found_ty, _)) =
            (expected.kind(), found.kind())
        {
            if let ty::Adt(found_def, found_substs) = *found_ty.kind() {
                if exp_def == &found_def {
                    let have_as_ref = &[
                        (
                            sym::Option,
                            "you can convert from `&Option<T>` to `Option<&T>` using \
                        `.as_ref()`",
                        ),
                        (
                            sym::Result,
                            "you can convert from `&Result<T, E>` to \
                        `Result<&T, &E>` using `.as_ref()`",
                        ),
                    ];
                    if let Some(msg) = have_as_ref.iter().find_map(|(name, msg)| {
                        self.tcx.is_diagnostic_item(*name, exp_def.did()).then_some(msg)
                    }) {
                        let mut show_suggestion = true;
                        for (exp_ty, found_ty) in
                            std::iter::zip(exp_substs.types(), found_substs.types())
                        {
                            match *exp_ty.kind() {
                                ty::Ref(_, exp_ty, _) => {
                                    match (exp_ty.kind(), found_ty.kind()) {
                                        (_, ty::Param(_))
                                        | (_, ty::Infer(_))
                                        | (ty::Param(_), _)
                                        | (ty::Infer(_), _) => {}
                                        _ if self.same_type_modulo_infer(exp_ty, found_ty) => {}
                                        _ => show_suggestion = false,
                                    };
                                }
                                ty::Param(_) | ty::Infer(_) => {}
                                _ => show_suggestion = false,
                            }
                        }
                        if show_suggestion {
                            return Some(*msg);
                        }
                    }
                }
            }
        }
        None
    }

    /// Try to find code with pattern `if Some(..) = expr`
    /// use a `visitor` to mark the `if` which its span contains given error span,
    /// and then try to find a assignment in the `cond` part, which span is equal with error span
    pub(super) fn suggest_let_for_letchains(
        &self,
        err: &mut Diagnostic,
        cause: &ObligationCause<'_>,
        span: Span,
    ) {
        let hir = self.tcx.hir();
        if let Some(node) = self.tcx.hir().find_by_def_id(cause.body_id) &&
            let hir::Node::Item(hir::Item {
                    kind: hir::ItemKind::Fn(_sig, _, body_id), ..
                }) = node {
        let body = hir.body(*body_id);

        /// Find the if expression with given span
        struct IfVisitor {
            pub result: bool,
            pub found_if: bool,
            pub err_span: Span,
        }

        impl<'v> Visitor<'v> for IfVisitor {
            fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
                if self.result { return; }
                match ex.kind {
                    hir::ExprKind::If(cond, _, _) => {
                        self.found_if = true;
                        walk_expr(self, cond);
                        self.found_if = false;
                    }
                    _ => walk_expr(self, ex),
                }
            }

            fn visit_stmt(&mut self, ex: &'v hir::Stmt<'v>) {
                if let hir::StmtKind::Local(hir::Local {
                        span, pat: hir::Pat{..}, ty: None, init: Some(_), ..
                    }) = &ex.kind
                    && self.found_if
                    && span.eq(&self.err_span) {
                        self.result = true;
                }
                walk_stmt(self, ex);
            }

            fn visit_body(&mut self, body: &'v hir::Body<'v>) {
                hir::intravisit::walk_body(self, body);
            }
        }

        let mut visitor = IfVisitor { err_span: span, found_if: false, result: false };
        visitor.visit_body(&body);
        if visitor.result {
                err.subdiagnostic(SuggAddLetForLetChains{span: span.shrink_to_lo()});
            }
        }
    }
}

impl<'tcx> TypeErrCtxt<'_, 'tcx> {
    /// Be helpful when the user wrote `{... expr; }` and taking the `;` off
    /// is enough to fix the error.
    pub fn could_remove_semicolon(
        &self,
        blk: &'tcx hir::Block<'tcx>,
        expected_ty: Ty<'tcx>,
    ) -> Option<(Span, StatementAsExpression)> {
        let blk = blk.innermost_block();
        // Do not suggest if we have a tail expr.
        if blk.expr.is_some() {
            return None;
        }
        let last_stmt = blk.stmts.last()?;
        let hir::StmtKind::Semi(ref last_expr) = last_stmt.kind else {
            return None;
        };
        let last_expr_ty = self.typeck_results.as_ref()?.expr_ty_opt(*last_expr)?;
        let needs_box = match (last_expr_ty.kind(), expected_ty.kind()) {
            _ if last_expr_ty.references_error() => return None,
            _ if self.same_type_modulo_infer(last_expr_ty, expected_ty) => {
                StatementAsExpression::CorrectType
            }
            (
                ty::Alias(ty::Opaque, ty::AliasTy { def_id: last_def_id, .. }),
                ty::Alias(ty::Opaque, ty::AliasTy { def_id: exp_def_id, .. }),
            ) if last_def_id == exp_def_id => StatementAsExpression::CorrectType,
            (
                ty::Alias(ty::Opaque, ty::AliasTy { def_id: last_def_id, substs: last_bounds, .. }),
                ty::Alias(ty::Opaque, ty::AliasTy { def_id: exp_def_id, substs: exp_bounds, .. }),
            ) => {
                debug!(
                    "both opaque, likely future {:?} {:?} {:?} {:?}",
                    last_def_id, last_bounds, exp_def_id, exp_bounds
                );

                let last_local_id = last_def_id.as_local()?;
                let exp_local_id = exp_def_id.as_local()?;

                match (
                    &self.tcx.hir().expect_item(last_local_id).kind,
                    &self.tcx.hir().expect_item(exp_local_id).kind,
                ) {
                    (
                        hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds: last_bounds, .. }),
                        hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds: exp_bounds, .. }),
                    ) if std::iter::zip(*last_bounds, *exp_bounds).all(|(left, right)| {
                        match (left, right) {
                            (
                                hir::GenericBound::Trait(tl, ml),
                                hir::GenericBound::Trait(tr, mr),
                            ) if tl.trait_ref.trait_def_id() == tr.trait_ref.trait_def_id()
                                && ml == mr =>
                            {
                                true
                            }
                            (
                                hir::GenericBound::LangItemTrait(langl, _, _, argsl),
                                hir::GenericBound::LangItemTrait(langr, _, _, argsr),
                            ) if langl == langr => {
                                // FIXME: consider the bounds!
                                debug!("{:?} {:?}", argsl, argsr);
                                true
                            }
                            _ => false,
                        }
                    }) =>
                    {
                        StatementAsExpression::NeedsBoxing
                    }
                    _ => StatementAsExpression::CorrectType,
                }
            }
            _ => return None,
        };
        let span = if last_stmt.span.from_expansion() {
            let mac_call = rustc_span::source_map::original_sp(last_stmt.span, blk.span);
            self.tcx.sess.source_map().mac_call_stmt_semi_span(mac_call)?
        } else {
            last_stmt.span.with_lo(last_stmt.span.hi() - BytePos(1))
        };
        Some((span, needs_box))
    }

    /// Suggest returning a local binding with a compatible type if the block
    /// has no return expression.
    pub fn consider_returning_binding_diag(
        &self,
        blk: &'tcx hir::Block<'tcx>,
        expected_ty: Ty<'tcx>,
    ) -> Option<SuggestRemoveSemiOrReturnBinding> {
        let blk = blk.innermost_block();
        // Do not suggest if we have a tail expr.
        if blk.expr.is_some() {
            return None;
        }
        let mut shadowed = FxIndexSet::default();
        let mut candidate_idents = vec![];
        let mut find_compatible_candidates = |pat: &hir::Pat<'_>| {
            if let hir::PatKind::Binding(_, hir_id, ident, _) = &pat.kind
                && let Some(pat_ty) = self
                    .typeck_results
                    .as_ref()
                    .and_then(|typeck_results| typeck_results.node_type_opt(*hir_id))
            {
                let pat_ty = self.resolve_vars_if_possible(pat_ty);
                if self.same_type_modulo_infer(pat_ty, expected_ty)
                    && !(pat_ty, expected_ty).references_error()
                    && shadowed.insert(ident.name)
                {
                    candidate_idents.push((*ident, pat_ty));
                }
            }
            true
        };

        let hir = self.tcx.hir();
        for stmt in blk.stmts.iter().rev() {
            let hir::StmtKind::Local(local) = &stmt.kind else { continue; };
            local.pat.walk(&mut find_compatible_candidates);
        }
        match hir.find_parent(blk.hir_id) {
            Some(hir::Node::Expr(hir::Expr { hir_id, .. })) => match hir.find_parent(*hir_id) {
                Some(hir::Node::Arm(hir::Arm { pat, .. })) => {
                    pat.walk(&mut find_compatible_candidates);
                }
                Some(
                    hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body), .. })
                    | hir::Node::ImplItem(hir::ImplItem {
                        kind: hir::ImplItemKind::Fn(_, body), ..
                    })
                    | hir::Node::TraitItem(hir::TraitItem {
                        kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body)),
                        ..
                    })
                    | hir::Node::Expr(hir::Expr {
                        kind: hir::ExprKind::Closure(hir::Closure { body, .. }),
                        ..
                    }),
                ) => {
                    for param in hir.body(*body).params {
                        param.pat.walk(&mut find_compatible_candidates);
                    }
                }
                Some(hir::Node::Expr(hir::Expr {
                    kind:
                        hir::ExprKind::If(
                            hir::Expr { kind: hir::ExprKind::Let(let_), .. },
                            then_block,
                            _,
                        ),
                    ..
                })) if then_block.hir_id == *hir_id => {
                    let_.pat.walk(&mut find_compatible_candidates);
                }
                _ => {}
            },
            _ => {}
        }

        match &candidate_idents[..] {
            [(ident, _ty)] => {
                let sm = self.tcx.sess.source_map();
                let (span, sugg) = if let Some(stmt) = blk.stmts.last() {
                    let stmt_span = sm.stmt_span(stmt.span, blk.span);
                    let sugg = if sm.is_multiline(blk.span)
                        && let Some(spacing) = sm.indentation_before(stmt_span)
                    {
                        format!("\n{spacing}{ident}")
                    } else {
                        format!(" {ident}")
                    };
                    (stmt_span.shrink_to_hi(), sugg)
                } else {
                    let sugg = if sm.is_multiline(blk.span)
                        && let Some(spacing) = sm.indentation_before(blk.span.shrink_to_lo())
                    {
                        format!("\n{spacing}    {ident}\n{spacing}")
                    } else {
                        format!(" {ident} ")
                    };
                    let left_span = sm.span_through_char(blk.span, '{').shrink_to_hi();
                    (
                        sm.span_extend_while(left_span, |c| c.is_whitespace()).unwrap_or(left_span),
                        sugg,
                    )
                };
                Some(SuggestRemoveSemiOrReturnBinding::Add { sp: span, code: sugg, ident: *ident })
            }
            values if (1..3).contains(&values.len()) => {
                let spans = values.iter().map(|(ident, _)| ident.span).collect::<Vec<_>>();
                Some(SuggestRemoveSemiOrReturnBinding::AddOne { spans: spans.into() })
            }
            _ => None,
        }
    }

    pub fn consider_returning_binding(
        &self,
        blk: &'tcx hir::Block<'tcx>,
        expected_ty: Ty<'tcx>,
        err: &mut Diagnostic,
    ) -> bool {
        let diag = self.consider_returning_binding_diag(blk, expected_ty);
        match diag {
            Some(diag) => {
                err.subdiagnostic(diag);
                true
            }
            None => false,
        }
    }
}