New upstream version 1.66.0+dfsg1

[rustc.git] / compiler / rustc_infer / src / infer / error_reporting / nice_region_error / placeholder_error.rs

use crate::infer::error_reporting::nice_region_error::NiceRegionError;
use crate::infer::lexical_region_resolve::RegionResolutionError;
use crate::infer::ValuePairs;
use crate::infer::{SubregionOrigin, TypeTrace};
use crate::traits::{ObligationCause, ObligationCauseCode};
use rustc_data_structures::intern::Interned;
use rustc_errors::{Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
use rustc_hir::def::Namespace;
use rustc_hir::def_id::DefId;
use rustc_middle::ty::error::ExpectedFound;
use rustc_middle::ty::print::{FmtPrinter, Print, RegionHighlightMode};
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::{self, RePlaceholder, ReVar, Region, TyCtxt};

use std::fmt::{self, Write};

impl<'tcx> NiceRegionError<'_, 'tcx> {
    /// When given a `ConcreteFailure` for a function with arguments containing a named region and
    /// an anonymous region, emit a descriptive diagnostic error.
    pub(super) fn try_report_placeholder_conflict(
        &self,
    ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
        match &self.error {
            ///////////////////////////////////////////////////////////////////////////
            // NB. The ordering of cases in this match is very
            // sensitive, because we are often matching against
            // specific cases and then using an `_` to match all
            // others.

            ///////////////////////////////////////////////////////////////////////////
            // Check for errors from comparing trait failures -- first
            // with two placeholders, then with one.
            Some(RegionResolutionError::SubSupConflict(
                vid,
                _,
                SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                sub_placeholder @ Region(Interned(RePlaceholder(_), _)),
                _,
                sup_placeholder @ Region(Interned(RePlaceholder(_), _)),
                _,
            )) => self.try_report_trait_placeholder_mismatch(
                Some(self.tcx().mk_region(ReVar(*vid))),
                cause,
                Some(*sub_placeholder),
                Some(*sup_placeholder),
                values,
            ),

            Some(RegionResolutionError::SubSupConflict(
                vid,
                _,
                SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                sub_placeholder @ Region(Interned(RePlaceholder(_), _)),
                _,
                _,
                _,
            )) => self.try_report_trait_placeholder_mismatch(
                Some(self.tcx().mk_region(ReVar(*vid))),
                cause,
                Some(*sub_placeholder),
                None,
                values,
            ),

            Some(RegionResolutionError::SubSupConflict(
                vid,
                _,
                SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                _,
                _,
                sup_placeholder @ Region(Interned(RePlaceholder(_), _)),
                _,
            )) => self.try_report_trait_placeholder_mismatch(
                Some(self.tcx().mk_region(ReVar(*vid))),
                cause,
                None,
                Some(*sup_placeholder),
                values,
            ),

            Some(RegionResolutionError::SubSupConflict(
                vid,
                _,
                _,
                _,
                SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                sup_placeholder @ Region(Interned(RePlaceholder(_), _)),
                _,
            )) => self.try_report_trait_placeholder_mismatch(
                Some(self.tcx().mk_region(ReVar(*vid))),
                cause,
                None,
                Some(*sup_placeholder),
                values,
            ),

            Some(RegionResolutionError::UpperBoundUniverseConflict(
                vid,
                _,
                _,
                SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                sup_placeholder @ Region(Interned(RePlaceholder(_), _)),
            )) => self.try_report_trait_placeholder_mismatch(
                Some(self.tcx().mk_region(ReVar(*vid))),
                cause,
                None,
                Some(*sup_placeholder),
                values,
            ),

            Some(RegionResolutionError::ConcreteFailure(
                SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                sub_region @ Region(Interned(RePlaceholder(_), _)),
                sup_region @ Region(Interned(RePlaceholder(_), _)),
            )) => self.try_report_trait_placeholder_mismatch(
                None,
                cause,
                Some(*sub_region),
                Some(*sup_region),
                values,
            ),

            Some(RegionResolutionError::ConcreteFailure(
                SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                sub_region @ Region(Interned(RePlaceholder(_), _)),
                sup_region,
            )) => self.try_report_trait_placeholder_mismatch(
                (!sup_region.has_name()).then_some(*sup_region),
                cause,
                Some(*sub_region),
                None,
                values,
            ),

            Some(RegionResolutionError::ConcreteFailure(
                SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                sub_region,
                sup_region @ Region(Interned(RePlaceholder(_), _)),
            )) => self.try_report_trait_placeholder_mismatch(
                (!sub_region.has_name()).then_some(*sub_region),
                cause,
                None,
                Some(*sup_region),
                values,
            ),

            _ => None,
        }
    }

    fn try_report_trait_placeholder_mismatch(
        &self,
        vid: Option<Region<'tcx>>,
        cause: &ObligationCause<'tcx>,
        sub_placeholder: Option<Region<'tcx>>,
        sup_placeholder: Option<Region<'tcx>>,
        value_pairs: &ValuePairs<'tcx>,
    ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
        let (expected_substs, found_substs, trait_def_id) = match value_pairs {
            ValuePairs::TraitRefs(ExpectedFound { expected, found })
                if expected.def_id == found.def_id =>
            {
                (expected.substs, found.substs, expected.def_id)
            }
            ValuePairs::PolyTraitRefs(ExpectedFound { expected, found })
                if expected.def_id() == found.def_id() =>
            {
                // It's possible that the placeholders come from a binder
                // outside of this value pair. Use `no_bound_vars` as a
                // simple heuristic for that.
                (expected.no_bound_vars()?.substs, found.no_bound_vars()?.substs, expected.def_id())
            }
            _ => return None,
        };

        Some(self.report_trait_placeholder_mismatch(
            vid,
            cause,
            sub_placeholder,
            sup_placeholder,
            trait_def_id,
            expected_substs,
            found_substs,
        ))
    }

    // error[E0308]: implementation of `Foo` does not apply to enough lifetimes
    //   --> /home/nmatsakis/tmp/foo.rs:12:5
    //    |
    // 12 |     all::<&'static u32>();
    //    |     ^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    //    |
    //    = note: Due to a where-clause on the function `all`,
    //    = note: `T` must implement `...` for any two lifetimes `'1` and `'2`.
    //    = note: However, the type `T` only implements `...` for some specific lifetime `'2`.
    #[instrument(level = "debug", skip(self))]
    fn report_trait_placeholder_mismatch(
        &self,
        vid: Option<Region<'tcx>>,
        cause: &ObligationCause<'tcx>,
        sub_placeholder: Option<Region<'tcx>>,
        sup_placeholder: Option<Region<'tcx>>,
        trait_def_id: DefId,
        expected_substs: SubstsRef<'tcx>,
        actual_substs: SubstsRef<'tcx>,
    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
        let span = cause.span();
        let msg = format!(
            "implementation of `{}` is not general enough",
            self.tcx().def_path_str(trait_def_id),
        );
        let mut err = self.tcx().sess.struct_span_err(span, &msg);

        let leading_ellipsis = if let ObligationCauseCode::ItemObligation(def_id)
        | ObligationCauseCode::ExprItemObligation(def_id, ..) =
            *cause.code()
        {
            err.span_label(span, "doesn't satisfy where-clause");
            err.span_label(
                self.tcx().def_span(def_id),
                &format!("due to a where-clause on `{}`...", self.tcx().def_path_str(def_id)),
            );
            true
        } else {
            err.span_label(span, &msg);
            false
        };

        let expected_trait_ref = self.cx.resolve_vars_if_possible(ty::TraitRef {
            def_id: trait_def_id,
            substs: expected_substs,
        });
        let actual_trait_ref = self
            .cx
            .resolve_vars_if_possible(ty::TraitRef { def_id: trait_def_id, substs: actual_substs });

        // Search the expected and actual trait references to see (a)
        // whether the sub/sup placeholders appear in them (sometimes
        // you have a trait ref like `T: Foo<fn(&u8)>`, where the
        // placeholder was created as part of an inner type) and (b)
        // whether the inference variable appears. In each case,
        // assign a counter value in each case if so.
        let mut counter = 0;
        let mut has_sub = None;
        let mut has_sup = None;

        let mut actual_has_vid = None;
        let mut expected_has_vid = None;

        self.tcx().for_each_free_region(&expected_trait_ref, |r| {
            if Some(r) == sub_placeholder && has_sub.is_none() {
                has_sub = Some(counter);
                counter += 1;
            } else if Some(r) == sup_placeholder && has_sup.is_none() {
                has_sup = Some(counter);
                counter += 1;
            }

            if Some(r) == vid && expected_has_vid.is_none() {
                expected_has_vid = Some(counter);
                counter += 1;
            }
        });

        self.tcx().for_each_free_region(&actual_trait_ref, |r| {
            if Some(r) == vid && actual_has_vid.is_none() {
                actual_has_vid = Some(counter);
                counter += 1;
            }
        });

        let actual_self_ty_has_vid =
            self.tcx().any_free_region_meets(&actual_trait_ref.self_ty(), |r| Some(r) == vid);

        let expected_self_ty_has_vid =
            self.tcx().any_free_region_meets(&expected_trait_ref.self_ty(), |r| Some(r) == vid);

        let any_self_ty_has_vid = actual_self_ty_has_vid || expected_self_ty_has_vid;

        debug!(
            ?actual_has_vid,
            ?expected_has_vid,
            ?has_sub,
            ?has_sup,
            ?actual_self_ty_has_vid,
            ?expected_self_ty_has_vid,
        );

        self.explain_actual_impl_that_was_found(
            &mut err,
            sub_placeholder,
            sup_placeholder,
            has_sub,
            has_sup,
            expected_trait_ref,
            actual_trait_ref,
            vid,
            expected_has_vid,
            actual_has_vid,
            any_self_ty_has_vid,
            leading_ellipsis,
        );

        err
    }

    /// Add notes with details about the expected and actual trait refs, with attention to cases
    /// when placeholder regions are involved: either the trait or the self type containing
    /// them needs to be mentioned the closest to the placeholders.
    /// This makes the error messages read better, however at the cost of some complexity
    /// due to the number of combinations we have to deal with.
    fn explain_actual_impl_that_was_found(
        &self,
        err: &mut Diagnostic,
        sub_placeholder: Option<Region<'tcx>>,
        sup_placeholder: Option<Region<'tcx>>,
        has_sub: Option<usize>,
        has_sup: Option<usize>,
        expected_trait_ref: ty::TraitRef<'tcx>,
        actual_trait_ref: ty::TraitRef<'tcx>,
        vid: Option<Region<'tcx>>,
        expected_has_vid: Option<usize>,
        actual_has_vid: Option<usize>,
        any_self_ty_has_vid: bool,
        leading_ellipsis: bool,
    ) {
        // HACK(eddyb) maybe move this in a more central location.
        #[derive(Copy, Clone)]
        struct Highlighted<'tcx, T> {
            tcx: TyCtxt<'tcx>,
            highlight: RegionHighlightMode<'tcx>,
            value: T,
        }

        impl<'tcx, T> Highlighted<'tcx, T> {
            fn map<U>(self, f: impl FnOnce(T) -> U) -> Highlighted<'tcx, U> {
                Highlighted { tcx: self.tcx, highlight: self.highlight, value: f(self.value) }
            }
        }

        impl<'tcx, T> fmt::Display for Highlighted<'tcx, T>
        where
            T: for<'a> Print<
                'tcx,
                FmtPrinter<'a, 'tcx>,
                Error = fmt::Error,
                Output = FmtPrinter<'a, 'tcx>,
            >,
        {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                let mut printer = ty::print::FmtPrinter::new(self.tcx, Namespace::TypeNS);
                printer.region_highlight_mode = self.highlight;

                let s = self.value.print(printer)?.into_buffer();
                f.write_str(&s)
            }
        }

        // The weird thing here with the `maybe_highlighting_region` calls and the
        // the match inside is meant to be like this:
        //
        // - The match checks whether the given things (placeholders, etc) appear
        //   in the types are about to print
        // - Meanwhile, the `maybe_highlighting_region` calls set up
        //   highlights so that, if they do appear, we will replace
        //   them `'0` and whatever.  (This replacement takes place
        //   inside the closure given to `maybe_highlighting_region`.)
        //
        // There is some duplication between the calls -- i.e., the
        // `maybe_highlighting_region` checks if (e.g.) `has_sub` is
        // None, an then we check again inside the closure, but this
        // setup sort of minimized the number of calls and so form.

        let highlight_trait_ref = |trait_ref| Highlighted {
            tcx: self.tcx(),
            highlight: RegionHighlightMode::new(self.tcx()),
            value: trait_ref,
        };

        let same_self_type = actual_trait_ref.self_ty() == expected_trait_ref.self_ty();

        let mut expected_trait_ref = highlight_trait_ref(expected_trait_ref);
        expected_trait_ref.highlight.maybe_highlighting_region(sub_placeholder, has_sub);
        expected_trait_ref.highlight.maybe_highlighting_region(sup_placeholder, has_sup);
        err.note(&{
            let passive_voice = match (has_sub, has_sup) {
                (Some(_), _) | (_, Some(_)) => any_self_ty_has_vid,
                (None, None) => {
                    expected_trait_ref.highlight.maybe_highlighting_region(vid, expected_has_vid);
                    match expected_has_vid {
                        Some(_) => true,
                        None => any_self_ty_has_vid,
                    }
                }
            };

            let mut note = if same_self_type {
                let mut self_ty = expected_trait_ref.map(|tr| tr.self_ty());
                self_ty.highlight.maybe_highlighting_region(vid, actual_has_vid);

                if self_ty.value.is_closure()
                    && self
                        .tcx()
                        .fn_trait_kind_from_lang_item(expected_trait_ref.value.def_id)
                        .is_some()
                {
                    let closure_sig = self_ty.map(|closure| {
                        if let ty::Closure(_, substs) = closure.kind() {
                            self.tcx().signature_unclosure(
                                substs.as_closure().sig(),
                                rustc_hir::Unsafety::Normal,
                            )
                        } else {
                            bug!("type is not longer closure");
                        }
                    });

                    format!(
                        "{}closure with signature `{}` must implement `{}`",
                        if leading_ellipsis { "..." } else { "" },
                        closure_sig,
                        expected_trait_ref.map(|tr| tr.print_only_trait_path()),
                    )
                } else {
                    format!(
                        "{}`{}` must implement `{}`",
                        if leading_ellipsis { "..." } else { "" },
                        self_ty,
                        expected_trait_ref.map(|tr| tr.print_only_trait_path()),
                    )
                }
            } else if passive_voice {
                format!(
                    "{}`{}` would have to be implemented for the type `{}`",
                    if leading_ellipsis { "..." } else { "" },
                    expected_trait_ref.map(|tr| tr.print_only_trait_path()),
                    expected_trait_ref.map(|tr| tr.self_ty()),
                )
            } else {
                format!(
                    "{}`{}` must implement `{}`",
                    if leading_ellipsis { "..." } else { "" },
                    expected_trait_ref.map(|tr| tr.self_ty()),
                    expected_trait_ref.map(|tr| tr.print_only_trait_path()),
                )
            };

            match (has_sub, has_sup) {
                (Some(n1), Some(n2)) => {
                    let _ = write!(
                        note,
                        ", for any two lifetimes `'{}` and `'{}`...",
                        std::cmp::min(n1, n2),
                        std::cmp::max(n1, n2),
                    );
                }
                (Some(n), _) | (_, Some(n)) => {
                    let _ = write!(note, ", for any lifetime `'{}`...", n,);
                }
                (None, None) => {
                    if let Some(n) = expected_has_vid {
                        let _ = write!(note, ", for some specific lifetime `'{}`...", n,);
                    }
                }
            }

            note
        });

        let mut actual_trait_ref = highlight_trait_ref(actual_trait_ref);
        actual_trait_ref.highlight.maybe_highlighting_region(vid, actual_has_vid);
        err.note(&{
            let passive_voice = match actual_has_vid {
                Some(_) => any_self_ty_has_vid,
                None => true,
            };

            let mut note = if same_self_type {
                format!(
                    "...but it actually implements `{}`",
                    actual_trait_ref.map(|tr| tr.print_only_trait_path()),
                )
            } else if passive_voice {
                format!(
                    "...but `{}` is actually implemented for the type `{}`",
                    actual_trait_ref.map(|tr| tr.print_only_trait_path()),
                    actual_trait_ref.map(|tr| tr.self_ty()),
                )
            } else {
                format!(
                    "...but `{}` actually implements `{}`",
                    actual_trait_ref.map(|tr| tr.self_ty()),
                    actual_trait_ref.map(|tr| tr.print_only_trait_path()),
                )
            };

            if let Some(n) = actual_has_vid {
                let _ = write!(note, ", for some specific lifetime `'{}`", n);
            }

            note
        });
    }
}