different_lifetimes.rs

// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Error Reporting for Anonymous Region Lifetime Errors
//! where both the regions are anonymous.
use hir;
use infer::InferCtxt;
use ty::{self, Region};
use infer::region_inference::RegionResolutionError::*;
use infer::region_inference::RegionResolutionError;
use hir::map as hir_map;
use middle::resolve_lifetime as rl;
use hir::intravisit::{self, Visitor, NestedVisitorMap};

impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
    // This method prints the error message for lifetime errors when both the concerned regions
    // are anonymous.
    // Consider a case where we have
    // fn foo(x: &mut Vec<&u8>, y: &u8)
    //    { x.push(y); }.
    // The example gives
    // 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
    // struct Ref<'a> { x: &'a u32 }
    // 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 fn try_report_anon_anon_conflict(&self, error: &RegionResolutionError<'tcx>) -> bool {
        let (span, sub, sup) = match *error {
            ConcreteFailure(ref origin, sub, sup) => (origin.span(), sub, sup),
            _ => return false, // inapplicable
        };

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

        let anon_reg_sub = or_false!(self.is_suitable_region(sub));
        let scope_def_id_sup = anon_reg_sup.def_id;
        let bregion_sup = anon_reg_sup.boundregion;
        let scope_def_id_sub = anon_reg_sub.def_id;
        let bregion_sub = anon_reg_sub.boundregion;

        let ty_sup = or_false!(self.find_anon_type(sup, &bregion_sup));

        let ty_sub = or_false!(self.find_anon_type(sub, &bregion_sub));
        debug!("try_report_anon_anon_conflict: found_arg1={:?} sup={:?} br1={:?}",
               ty_sub,
               sup,
               bregion_sup);
        debug!("try_report_anon_anon_conflict: found_arg2={:?} sub={:?} br2={:?}",
               ty_sup,
               sub,
               bregion_sub);

        let (main_label, label1, label2) = if let (Some(sup_arg), Some(sub_arg)) =
            (self.find_arg_with_region(sup, sup), self.find_arg_with_region(sub, sub)) {

            let (anon_arg_sup, is_first_sup, anon_arg_sub, is_first_sub) =
                (sup_arg.arg, sup_arg.is_first, sub_arg.arg, sub_arg.is_first);
            if self.is_self_anon(is_first_sup, scope_def_id_sup) ||
               self.is_self_anon(is_first_sub, scope_def_id_sub) {
                return false;
            }

            if self.is_return_type_anon(scope_def_id_sup, bregion_sup) ||
               self.is_return_type_anon(scope_def_id_sub, bregion_sub) {
                return false;
            }

            if anon_arg_sup == anon_arg_sub {
                (format!("this type was declared with multiple lifetimes..."),
                 format!(" with one lifetime"),
                 format!(" into the other"))
            } else {
                let span_label_var1 = if let Some(simple_name) = anon_arg_sup.pat.simple_name() {
                    format!(" from `{}`", simple_name)
                } else {
                    format!("")
                };

                let span_label_var2 = if let Some(simple_name) = anon_arg_sub.pat.simple_name() {
                    format!(" into `{}`", simple_name)
                } else {
                    format!("")
                };

                let span_label =
                    format!("these two types are declared with different lifetimes...",);

                (span_label, span_label_var1, span_label_var2)
            }
        } else {
            debug!("no arg with anon region found");
            debug!("try_report_anon_anon_conflict: is_suitable(sub) = {:?}",
                   self.is_suitable_region(sub));
            debug!("try_report_anon_anon_conflict: is_suitable(sup) = {:?}",
                   self.is_suitable_region(sup));
            return false;
        };

        struct_span_err!(self.tcx.sess, span, E0623, "lifetime mismatch")
            .span_label(ty_sup.span, main_label)
            .span_label(ty_sub.span, format!(""))
            .span_label(span, format!("...but data{} flows{} here", label1, label2))
            .emit();
        return true;
    }

    /// This function calls the `visit_ty` method for the parameters
    /// corresponding to the anonymous regions. The `nested_visitor.found_type`
    /// contains the anonymous type.
    ///
    /// # Arguments
    /// region - the anonymous region corresponding to the anon_anon conflict
    /// br - the bound region corresponding to the above region which is of type `BrAnon(_)`
    ///
    /// # Example
    /// ```
    /// fn foo(x: &mut Vec<&u8>, y: &u8)
    ///    { x.push(y); }
    /// ```
    /// The function returns the nested type corresponding to the anonymous region
    /// for e.g. `&u8` and Vec<`&u8`.
    pub fn find_anon_type(&self, region: Region<'tcx>, br: &ty::BoundRegion) -> Option<&hir::Ty> {
        if let Some(anon_reg) = self.is_suitable_region(region) {
            let def_id = anon_reg.def_id;
            if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
                let inputs: &[_] = match self.tcx.hir.get(node_id) {
                    hir_map::NodeItem(&hir::Item { node: hir::ItemFn(ref fndecl, ..), .. }) => {
                        &fndecl.inputs
                    }
                    hir_map::NodeTraitItem(&hir::TraitItem {
                                               node: hir::TraitItemKind::Method(ref fndecl, ..), ..
                                           }) => &fndecl.decl.inputs,
                    hir_map::NodeImplItem(&hir::ImplItem {
                                              node: hir::ImplItemKind::Method(ref fndecl, ..), ..
                                          }) => &fndecl.decl.inputs,

                    _ => &[],
                };

                return inputs
                           .iter()
                           .filter_map(|arg| self.find_component_for_bound_region(&**arg, br))
                           .next();
            }
        }
        None
    }

    // This method creates a FindNestedTypeVisitor which returns the type corresponding
    // to the anonymous region.
    fn find_component_for_bound_region(&self,
                                       arg: &'gcx hir::Ty,
                                       br: &ty::BoundRegion)
                                       -> Option<(&'gcx hir::Ty)> {
        let mut nested_visitor = FindNestedTypeVisitor {
            infcx: &self,
            hir_map: &self.tcx.hir,
            bound_region: *br,
            found_type: None,
            depth: 1,
        };
        nested_visitor.visit_ty(arg);
        nested_visitor.found_type
    }
}

// The FindNestedTypeVisitor captures the corresponding `hir::Ty` of the
// anonymous region. The example above would lead to a conflict between
// the two anonymous lifetimes for &u8 in x and y respectively. This visitor
// would be invoked twice, once for each lifetime, and would
// walk the types like &mut Vec<&u8> and &u8 looking for the HIR
// where that lifetime appears. This allows us to highlight the
// specific part of the type in the error message.
struct FindNestedTypeVisitor<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
    infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
    hir_map: &'a hir::map::Map<'gcx>,
    // The bound_region corresponding to the Refree(freeregion)
    // associated with the anonymous region we are looking for.
    bound_region: ty::BoundRegion,
    // The type where the anonymous lifetime appears
    // for e.g. Vec<`&u8`> and <`&u8`>
    found_type: Option<&'gcx hir::Ty>,
    depth: u32,
}

impl<'a, 'gcx, 'tcx> Visitor<'gcx> for FindNestedTypeVisitor<'a, 'gcx, 'tcx> {
    fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
        NestedVisitorMap::OnlyBodies(&self.hir_map)
    }

    fn visit_ty(&mut self, arg: &'gcx hir::Ty) {
        match arg.node {
            hir::TyBareFn(_) => {
                self.depth += 1;
                intravisit::walk_ty(self, arg);
                self.depth -= 1;
                return;
            }

            hir::TyTraitObject(ref bounds, _) => {
                for bound in bounds {
                    self.depth += 1;
                    self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
                    self.depth -= 1;
                }
            }

            hir::TyRptr(ref lifetime, _) => {
                // the lifetime of the TyRptr
                let hir_id = self.infcx.tcx.hir.node_to_hir_id(lifetime.id);
                match (self.infcx.tcx.named_region(hir_id), self.bound_region) {
                    // Find the index of the anonymous region that was part of the
                    // error. We will then search the function parameters for a bound
                    // region at the right depth with the same index
                    (Some(rl::Region::LateBoundAnon(debruijn_index, anon_index)),
                     ty::BrAnon(br_index)) => {
                        debug!("LateBoundAnon depth = {:?} anon_index = {:?} br_index={:?}",
                               debruijn_index.depth,
                               anon_index,
                               br_index);
                        if debruijn_index.depth == self.depth && anon_index == br_index {
                            self.found_type = Some(arg);
                            return; // we can stop visiting now
                        }
                    }

                    // Find the index of the named region that was part of the
                    // error. We will then search the function parameters for a bound
                    // region at the right depth with the same index
                    (Some(rl::Region::EarlyBound(_, id)), ty::BrNamed(def_id, _)) => {
                        debug!("EarlyBound self.infcx.tcx.hir.local_def_id(id)={:?} \
                                        def_id={:?}",
                               self.infcx.tcx.hir.local_def_id(id),
                               def_id);
                        if self.infcx.tcx.hir.local_def_id(id) == def_id {
                            self.found_type = Some(arg);
                            return; // we can stop visiting now
                        }
                    }

                    // Find the index of the named region that was part of the
                    // error. We will then search the function parameters for a bound
                    // region at the right depth with the same index
                    (Some(rl::Region::LateBound(debruijn_index, id)), ty::BrNamed(def_id, _)) => {
                        debug!("FindNestedTypeVisitor::visit_ty: LateBound depth = {:?}",
                               debruijn_index.depth);
                        debug!("self.infcx.tcx.hir.local_def_id(id)={:?}",
                               self.infcx.tcx.hir.local_def_id(id));
                        debug!("def_id={:?}", def_id);
                        if debruijn_index.depth == self.depth &&
                           self.infcx.tcx.hir.local_def_id(id) == def_id {
                            self.found_type = Some(arg);
                            return; // we can stop visiting now
                        }
                    }

                    (Some(rl::Region::Static), _) |
                    (Some(rl::Region::Free(_, _)), _) |
                    (Some(rl::Region::EarlyBound(_, _)), _) |
                    (Some(rl::Region::LateBound(_, _)), _) |
                    (Some(rl::Region::LateBoundAnon(_, _)), _) |
                    (None, _) => {
                        debug!("no arg found");
                    }
                }
            }
            // Checks if it is of type `hir::TyPath` which corresponds to a struct.
            hir::TyPath(_) => {
                let subvisitor = &mut TyPathVisitor {
                                          infcx: self.infcx,
                                          found_it: false,
                                          bound_region: self.bound_region,
                                          hir_map: self.hir_map,
                                      };
                intravisit::walk_ty(subvisitor, arg); // call walk_ty; as visit_ty is empty,
                // this will visit only outermost type
                if subvisitor.found_it {
                    self.found_type = Some(arg);
                }
            }
            _ => {}
        }
        // walk the embedded contents: e.g., if we are visiting `Vec<&Foo>`,
        // go on to visit `&Foo`
        intravisit::walk_ty(self, arg);
    }
}

// The visitor captures the corresponding `hir::Ty` of the anonymous region
// in the case of structs ie. `hir::TyPath`.
// This visitor would be invoked for each lifetime corresponding to a struct,
// and would walk the types like Vec<Ref> in the above example and Ref looking for the HIR
// where that lifetime appears. This allows us to highlight the
// specific part of the type in the error message.
struct TyPathVisitor<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
    infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
    hir_map: &'a hir::map::Map<'gcx>,
    found_it: bool,
    bound_region: ty::BoundRegion,
}

impl<'a, 'gcx, 'tcx> Visitor<'gcx> for TyPathVisitor<'a, 'gcx, 'tcx> {
    fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
        NestedVisitorMap::OnlyBodies(&self.hir_map)
    }

    fn visit_lifetime(&mut self, lifetime: &hir::Lifetime) {

        let hir_id = self.infcx.tcx.hir.node_to_hir_id(lifetime.id);
        match (self.infcx.tcx.named_region(hir_id), self.bound_region) {
            // the lifetime of the TyPath!
            (Some(rl::Region::LateBoundAnon(debruijn_index, anon_index)), ty::BrAnon(br_index)) => {
                if debruijn_index.depth == 1 && anon_index == br_index {
                    self.found_it = true;
                    return;
                }
            }

            (Some(rl::Region::EarlyBound(_, id)), ty::BrNamed(def_id, _)) => {
                debug!("EarlyBound self.infcx.tcx.hir.local_def_id(id)={:?} \
                                        def_id={:?}",
                       self.infcx.tcx.hir.local_def_id(id),
                       def_id);
                if self.infcx.tcx.hir.local_def_id(id) == def_id {
                    self.found_it = true;
                    return; // we can stop visiting now
                }
            }

            (Some(rl::Region::LateBound(debruijn_index, id)), ty::BrNamed(def_id, _)) => {
                debug!("FindNestedTypeVisitor::visit_ty: LateBound depth = {:?}",
                       debruijn_index.depth);
                debug!("self.infcx.tcx.hir.local_def_id(id)={:?}",
                       self.infcx.tcx.hir.local_def_id(id));
                debug!("def_id={:?}", def_id);
                if debruijn_index.depth == 1 && self.infcx.tcx.hir.local_def_id(id) == def_id {
                    self.found_it = true;
                    return; // we can stop visiting now
                }
            }

            (Some(rl::Region::Static), _) |
            (Some(rl::Region::EarlyBound(_, _)), _) |
            (Some(rl::Region::LateBound(_, _)), _) |
            (Some(rl::Region::LateBoundAnon(_, _)), _) |
            (Some(rl::Region::Free(_, _)), _) |
            (None, _) => {
                debug!("no arg found");
            }
        }
    }

    fn visit_ty(&mut self, arg: &'gcx hir::Ty) {
        // ignore nested types
        //
        // If you have a type like `Foo<'a, &Ty>` we
        // are only interested in the immediate lifetimes ('a).
        //
        // Making `visit_ty` empty will ignore the `&Ty` embedded
        // inside, it will get reached by the outer visitor.
        debug!("`Ty` corresponding to a struct is {:?}", arg);
    }
}