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

//! Common logic for borrowck use-after-move errors when moved into a `fn(self)`,
//! as well as errors when attempting to call a non-const function in a const
//! context.

use rustc_hir::def_id::DefId;
use rustc_hir::{lang_items, LangItem};
use rustc_span::symbol::Ident;
use rustc_span::{sym, DesugaringKind, Span};
use tracing::debug;

use crate::ty::{AssocItemContainer, GenericArgsRef, Instance, ParamEnv, Ty, TyCtxt};

#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum CallDesugaringKind {
    /// for _ in x {} calls x.into_iter()
    ForLoopIntoIter,
    /// x? calls x.branch()
    QuestionBranch,
    /// x? calls type_of(x)::from_residual()
    QuestionFromResidual,
    /// try { ..; x } calls type_of(x)::from_output(x)
    TryBlockFromOutput,
    /// `.await` calls `IntoFuture::into_future`
    Await,
}

impl CallDesugaringKind {
    pub fn trait_def_id(self, tcx: TyCtxt<'_>) -> DefId {
        match self {
            Self::ForLoopIntoIter => tcx.get_diagnostic_item(sym::IntoIterator).unwrap(),
            Self::QuestionBranch | Self::TryBlockFromOutput => {
                tcx.require_lang_item(LangItem::Try, None)
            }
            Self::QuestionFromResidual => tcx.get_diagnostic_item(sym::FromResidual).unwrap(),
            Self::Await => tcx.get_diagnostic_item(sym::IntoFuture).unwrap(),
        }
    }
}

#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum CallKind<'tcx> {
    /// A normal method call of the form `receiver.foo(a, b, c)`
    Normal {
        self_arg: Option<Ident>,
        desugaring: Option<(CallDesugaringKind, Ty<'tcx>)>,
        method_did: DefId,
        method_args: GenericArgsRef<'tcx>,
    },
    /// A call to `Fn(..)::call(..)`, desugared from `my_closure(a, b, c)`
    FnCall { fn_trait_id: DefId, self_ty: Ty<'tcx> },
    /// A call to an operator trait, desugared from operator syntax (e.g. `a << b`)
    Operator { self_arg: Option<Ident>, trait_id: DefId, self_ty: Ty<'tcx> },
    DerefCoercion {
        /// The `Span` of the `Target` associated type
        /// in the `Deref` impl we are using.
        deref_target: Span,
        /// The type `T::Deref` we are dereferencing to
        deref_target_ty: Ty<'tcx>,
        self_ty: Ty<'tcx>,
    },
}

pub fn call_kind<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    method_did: DefId,
    method_args: GenericArgsRef<'tcx>,
    fn_call_span: Span,
    from_hir_call: bool,
    self_arg: Option<Ident>,
) -> CallKind<'tcx> {
    let parent = tcx.opt_associated_item(method_did).and_then(|assoc| {
        let container_id = assoc.container_id(tcx);
        match assoc.container {
            AssocItemContainer::ImplContainer => tcx.trait_id_of_impl(container_id),
            AssocItemContainer::TraitContainer => Some(container_id),
        }
    });

    let fn_call = parent.and_then(|p| {
        lang_items::FN_TRAITS.iter().filter_map(|&l| tcx.lang_items().get(l)).find(|&id| id == p)
    });

    let operator = if !from_hir_call && let Some(p) = parent {
        lang_items::OPERATORS.iter().filter_map(|&l| tcx.lang_items().get(l)).find(|&id| id == p)
    } else {
        None
    };

    let is_deref = !from_hir_call && tcx.is_diagnostic_item(sym::deref_method, method_did);

    // Check for a 'special' use of 'self' -
    // an FnOnce call, an operator (e.g. `<<`), or a
    // deref coercion.
    let kind = if let Some(trait_id) = fn_call {
        Some(CallKind::FnCall { fn_trait_id: trait_id, self_ty: method_args.type_at(0) })
    } else if let Some(trait_id) = operator {
        Some(CallKind::Operator { self_arg, trait_id, self_ty: method_args.type_at(0) })
    } else if is_deref {
        let deref_target = tcx.get_diagnostic_item(sym::deref_target).and_then(|deref_target| {
            Instance::try_resolve(tcx, param_env, deref_target, method_args).transpose()
        });
        if let Some(Ok(instance)) = deref_target {
            let deref_target_ty = instance.ty(tcx, param_env);
            Some(CallKind::DerefCoercion {
                deref_target: tcx.def_span(instance.def_id()),
                deref_target_ty,
                self_ty: method_args.type_at(0),
            })
        } else {
            None
        }
    } else {
        None
    };

    kind.unwrap_or_else(|| {
        // This isn't a 'special' use of `self`
        debug!(?method_did, ?fn_call_span);
        let desugaring = if tcx.is_lang_item(method_did, LangItem::IntoIterIntoIter)
            && fn_call_span.desugaring_kind() == Some(DesugaringKind::ForLoop)
        {
            Some((CallDesugaringKind::ForLoopIntoIter, method_args.type_at(0)))
        } else if fn_call_span.desugaring_kind() == Some(DesugaringKind::QuestionMark) {
            if tcx.is_lang_item(method_did, LangItem::TryTraitBranch) {
                Some((CallDesugaringKind::QuestionBranch, method_args.type_at(0)))
            } else if tcx.is_lang_item(method_did, LangItem::TryTraitFromResidual) {
                Some((CallDesugaringKind::QuestionFromResidual, method_args.type_at(0)))
            } else {
                None
            }
        } else if tcx.is_lang_item(method_did, LangItem::TryTraitFromOutput)
            && fn_call_span.desugaring_kind() == Some(DesugaringKind::TryBlock)
        {
            Some((CallDesugaringKind::TryBlockFromOutput, method_args.type_at(0)))
        } else if fn_call_span.is_desugaring(DesugaringKind::Await) {
            Some((CallDesugaringKind::Await, method_args.type_at(0)))
        } else {
            None
        };
        CallKind::Normal { self_arg, desugaring, method_did, method_args }
    })
}