compiler/rustc_infer/src/infer/error_reporting/nice_region_error/different_lifetimes.rs

//! Error Reporting for Anonymous Region Lifetime Errors
//! where both the regions are anonymous.

use crate::errors::AddLifetimeParamsSuggestion;
use crate::errors::LifetimeMismatch;
use crate::errors::LifetimeMismatchLabels;
use crate::infer::error_reporting::nice_region_error::find_anon_type::find_anon_type;
use crate::infer::error_reporting::nice_region_error::util::AnonymousParamInfo;
use crate::infer::error_reporting::nice_region_error::NiceRegionError;
use crate::infer::lexical_region_resolve::RegionResolutionError;
use crate::infer::SubregionOrigin;
use crate::infer::TyCtxt;

use rustc_errors::Subdiagnostic;
use rustc_errors::{Diag, ErrorGuaranteed};
use rustc_hir::Ty;
use rustc_middle::ty::Region;

impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
    /// Print the error message for lifetime errors when both the concerned regions are anonymous.
    ///
    /// Consider a case where we have
    ///
    /// ```compile_fail
    /// fn foo(x: &mut Vec<&u8>, y: &u8) {
    ///     x.push(y);
    /// }
    /// ```
    ///
    /// The example gives
    ///
    /// ```text
    /// fn foo(x: &mut Vec<&u8>, y: &u8) {
    ///                    ---      --- these references are declared with different lifetimes...
    ///     x.push(y);
    ///     ^ ...but data from `y` flows into `x` here
    /// ```
    ///
    /// It has been extended for the case of structs too.
    ///
    /// Consider the example
    ///
    /// ```no_run
    /// struct Ref<'a> { x: &'a u32 }
    /// ```
    ///
    /// ```text
    /// fn foo(mut x: Vec<Ref>, y: Ref) {
    ///                   ---      --- these structs are declared with different lifetimes...
    ///     x.push(y);
    ///     ^ ...but data from `y` flows into `x` here
    /// }
    /// ```
    ///
    /// It will later be extended to trait objects.
    pub(super) fn try_report_anon_anon_conflict(&self) -> Option<ErrorGuaranteed> {
        let (span, sub, sup) = self.regions()?;

        if let Some(RegionResolutionError::ConcreteFailure(
            SubregionOrigin::ReferenceOutlivesReferent(..),
            ..,
        )) = self.error
        {
            // This error doesn't make much sense in this case.
            return None;
        }

        // Determine whether the sub and sup consist of both anonymous (elided) regions.
        let anon_reg_sup = self.tcx().is_suitable_region(sup)?;

        let anon_reg_sub = self.tcx().is_suitable_region(sub)?;
        let scope_def_id_sup = anon_reg_sup.def_id;
        let bregion_sup = anon_reg_sup.bound_region;
        let scope_def_id_sub = anon_reg_sub.def_id;
        let bregion_sub = anon_reg_sub.bound_region;

        let ty_sup = find_anon_type(self.tcx(), sup, &bregion_sup)?;

        let ty_sub = find_anon_type(self.tcx(), sub, &bregion_sub)?;

        debug!(
            "try_report_anon_anon_conflict: found_param1={:?} sup={:?} br1={:?}",
            ty_sub, sup, bregion_sup
        );
        debug!(
            "try_report_anon_anon_conflict: found_param2={:?} sub={:?} br2={:?}",
            ty_sup, sub, bregion_sub
        );

        let (ty_sup, ty_fndecl_sup) = ty_sup;
        let (ty_sub, ty_fndecl_sub) = ty_sub;

        let AnonymousParamInfo { param: anon_param_sup, .. } =
            self.find_param_with_region(sup, sup)?;
        let AnonymousParamInfo { param: anon_param_sub, .. } =
            self.find_param_with_region(sub, sub)?;

        let sup_is_ret_type =
            self.is_return_type_anon(scope_def_id_sup, bregion_sup, ty_fndecl_sup);
        let sub_is_ret_type =
            self.is_return_type_anon(scope_def_id_sub, bregion_sub, ty_fndecl_sub);

        debug!(
            "try_report_anon_anon_conflict: sub_is_ret_type={:?} sup_is_ret_type={:?}",
            sub_is_ret_type, sup_is_ret_type
        );

        let labels = match (sup_is_ret_type, sub_is_ret_type) {
            (ret_capture @ Some(ret_span), _) | (_, ret_capture @ Some(ret_span)) => {
                let param_span =
                    if sup_is_ret_type == ret_capture { ty_sub.span } else { ty_sup.span };
                LifetimeMismatchLabels::InRet {
                    param_span,
                    ret_span,
                    span,
                    label_var1: anon_param_sup.pat.simple_ident(),
                }
            }

            (None, None) => LifetimeMismatchLabels::Normal {
                hir_equal: ty_sup.hir_id == ty_sub.hir_id,
                ty_sup: ty_sup.span,
                ty_sub: ty_sub.span,
                span,
                sup: anon_param_sup.pat.simple_ident(),
                sub: anon_param_sub.pat.simple_ident(),
            },
        };

        let suggestion =
            AddLifetimeParamsSuggestion { tcx: self.tcx(), sub, ty_sup, ty_sub, add_note: true };
        let err = LifetimeMismatch { span, labels, suggestion };
        let reported = self.tcx().dcx().emit_err(err);
        Some(reported)
    }
}

/// Currently only used in rustc_borrowck, probably should be
/// removed in favour of public_errors::AddLifetimeParamsSuggestion
pub fn suggest_adding_lifetime_params<'tcx>(
    tcx: TyCtxt<'tcx>,
    sub: Region<'tcx>,
    ty_sup: &'tcx Ty<'_>,
    ty_sub: &'tcx Ty<'_>,
    err: &mut Diag<'_>,
) {
    let suggestion = AddLifetimeParamsSuggestion { tcx, sub, ty_sup, ty_sub, add_note: false };
    suggestion.add_to_diag(err);
}