1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165

//! Helper functions corresponding to lifetime errors due to
//! anonymous regions.

use crate::infer::error_reporting::nice_region_error::NiceRegionError;
use crate::infer::TyCtxt;
use rustc_hir as hir;
use rustc_hir::def_id::LocalDefId;
use rustc_middle::ty::{self, Binder, Region, Ty, TypeFoldable};
use rustc_span::Span;

/// Information about the anonymous region we are searching for.
#[derive(Debug)]
pub struct AnonymousParamInfo<'tcx> {
    /// The parameter corresponding to the anonymous region.
    pub param: &'tcx hir::Param<'tcx>,
    /// The type corresponding to the anonymous region parameter.
    pub param_ty: Ty<'tcx>,
    /// The ty::BoundRegionKind corresponding to the anonymous region.
    pub bound_region: ty::BoundRegionKind,
    /// The `Span` of the parameter type.
    pub param_ty_span: Span,
    /// Signals that the argument is the first parameter in the declaration.
    pub is_first: bool,
}

// This method walks the Type of the function body parameters using
// `fold_regions()` function and returns the
// &hir::Param of the function parameter corresponding to the anonymous
// region and the Ty corresponding to the named region.
// Currently only the case where the function declaration consists of
// one named region and one anonymous region is handled.
// Consider the example `fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32`
// Here, we would return the hir::Param for y, we return the type &'a
// i32, which is the type of y but with the anonymous region replaced
// with 'a, the corresponding bound region and is_first which is true if
// the hir::Param is the first parameter in the function declaration.
#[instrument(skip(tcx), level = "debug")]
pub fn find_param_with_region<'tcx>(
    tcx: TyCtxt<'tcx>,
    anon_region: Region<'tcx>,
    replace_region: Region<'tcx>,
) -> Option<AnonymousParamInfo<'tcx>> {
    let (id, bound_region) = match *anon_region {
        ty::ReLateParam(late_param) => (late_param.scope, late_param.bound_region),
        ty::ReEarlyParam(ebr) => {
            (tcx.parent(ebr.def_id), ty::BoundRegionKind::BrNamed(ebr.def_id, ebr.name))
        }
        _ => return None, // not a free region
    };

    let hir = &tcx.hir();
    let def_id = id.as_local()?;

    // FIXME: use def_kind
    // Don't perform this on closures
    match tcx.hir_node_by_def_id(def_id) {
        hir::Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure { .. }, .. }) => {
            return None;
        }
        _ => {}
    }

    let body_id = hir.maybe_body_owned_by(def_id)?;

    let owner_id = hir.body_owner(body_id);
    let fn_decl = hir.fn_decl_by_hir_id(owner_id)?;
    let poly_fn_sig = tcx.fn_sig(id).instantiate_identity();

    let fn_sig = tcx.liberate_late_bound_regions(id, poly_fn_sig);
    let body = hir.body(body_id);
    body.params
        .iter()
        .take(if fn_sig.c_variadic {
            fn_sig.inputs().len()
        } else {
            assert_eq!(fn_sig.inputs().len(), body.params.len());
            body.params.len()
        })
        .enumerate()
        .find_map(|(index, param)| {
            // May return None; sometimes the tables are not yet populated.
            let ty = fn_sig.inputs()[index];
            let mut found_anon_region = false;
            let new_param_ty = tcx.fold_regions(ty, |r, _| {
                if r == anon_region {
                    found_anon_region = true;
                    replace_region
                } else {
                    r
                }
            });
            found_anon_region.then(|| {
                let ty_hir_id = fn_decl.inputs[index].hir_id;
                let param_ty_span = hir.span(ty_hir_id);
                let is_first = index == 0;
                AnonymousParamInfo {
                    param,
                    param_ty: new_param_ty,
                    param_ty_span,
                    bound_region,
                    is_first,
                }
            })
        })
}

impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
    pub(super) fn find_param_with_region(
        &self,
        anon_region: Region<'tcx>,
        replace_region: Region<'tcx>,
    ) -> Option<AnonymousParamInfo<'tcx>> {
        find_param_with_region(self.tcx(), anon_region, replace_region)
    }

    // Here, we check for the case where the anonymous region
    // is in the return type as written by the user.
    // FIXME(#42703) - Need to handle certain cases here.
    pub(super) fn is_return_type_anon(
        &self,
        scope_def_id: LocalDefId,
        br: ty::BoundRegionKind,
        hir_sig: &hir::FnSig<'_>,
    ) -> Option<Span> {
        let fn_ty = self.tcx().type_of(scope_def_id).instantiate_identity();
        if let ty::FnDef(_, _) = fn_ty.kind() {
            let ret_ty = fn_ty.fn_sig(self.tcx()).output();
            let span = hir_sig.decl.output.span();
            let future_output = if hir_sig.header.is_async() {
                ret_ty.map_bound(|ty| self.cx.get_impl_future_output_ty(ty)).transpose()
            } else {
                None
            };
            return match future_output {
                Some(output) if self.includes_region(output, br) => Some(span),
                None if self.includes_region(ret_ty, br) => Some(span),
                _ => None,
            };
        }
        None
    }

    fn includes_region(
        &self,
        ty: Binder<'tcx, impl TypeFoldable<TyCtxt<'tcx>>>,
        region: ty::BoundRegionKind,
    ) -> bool {
        let late_bound_regions = self.tcx().collect_referenced_late_bound_regions(ty);
        // We are only checking is any region meets the condition so order doesn't matter
        #[allow(rustc::potential_query_instability)]
        late_bound_regions.iter().any(|r| *r == region)
    }

    // Here we check for the case where anonymous region
    // corresponds to self and if yes, we display E0312.
    // FIXME(#42700) - Need to format self properly to
    // enable E0621 for it.
    pub(super) fn is_self_anon(&self, is_first: bool, scope_def_id: LocalDefId) -> bool {
        is_first
            && self
                .tcx()
                .opt_associated_item(scope_def_id.to_def_id())
                .is_some_and(|i| i.fn_has_self_parameter)
    }
}