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

use rustc_hir as hir;
use rustc_infer::infer::{DefineOpaqueTypes, InferOk, TyCtxtInferExt};
use rustc_infer::traits;
use rustc_middle::ty::{self, ToPredicate};
use rustc_span::def_id::DefId;
use rustc_span::DUMMY_SP;
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;

use thin_vec::ThinVec;

use crate::clean;
use crate::clean::{
    clean_middle_assoc_item, clean_middle_ty, clean_trait_ref_with_bindings, clean_ty_generics,
};
use crate::core::DocContext;

#[instrument(level = "debug", skip(cx))]
pub(crate) fn synthesize_blanket_impls(
    cx: &mut DocContext<'_>,
    item_def_id: DefId,
) -> Vec<clean::Item> {
    let tcx = cx.tcx;
    let ty = tcx.type_of(item_def_id);

    let mut blanket_impls = Vec::new();
    for trait_def_id in tcx.all_traits() {
        if !cx.cache.effective_visibilities.is_reachable(tcx, trait_def_id)
            || cx.generated_synthetics.get(&(ty.skip_binder(), trait_def_id)).is_some()
        {
            continue;
        }
        // NOTE: doesn't use `for_each_relevant_impl` to avoid looking at anything besides blanket impls
        let trait_impls = tcx.trait_impls_of(trait_def_id);
        'blanket_impls: for &impl_def_id in trait_impls.blanket_impls() {
            trace!("considering impl `{impl_def_id:?}` for trait `{trait_def_id:?}`");

            let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
            if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
                continue;
            }
            let infcx = tcx.infer_ctxt().build();
            let args = infcx.fresh_args_for_item(DUMMY_SP, item_def_id);
            let impl_ty = ty.instantiate(tcx, args);
            let param_env = ty::ParamEnv::empty();

            let impl_args = infcx.fresh_args_for_item(DUMMY_SP, impl_def_id);
            let impl_trait_ref = trait_ref.instantiate(tcx, impl_args);

            // Require the type the impl is implemented on to match
            // our type, and ignore the impl if there was a mismatch.
            let Ok(eq_result) = infcx.at(&traits::ObligationCause::dummy(), param_env).eq(
                DefineOpaqueTypes::Yes,
                impl_trait_ref.self_ty(),
                impl_ty,
            ) else {
                continue;
            };
            let InferOk { value: (), obligations } = eq_result;
            // FIXME(eddyb) ignoring `obligations` might cause false positives.
            drop(obligations);

            let predicates = tcx
                .predicates_of(impl_def_id)
                .instantiate(tcx, impl_args)
                .predicates
                .into_iter()
                .chain(Some(ty::Binder::dummy(impl_trait_ref).to_predicate(tcx)));
            for predicate in predicates {
                let obligation = traits::Obligation::new(
                    tcx,
                    traits::ObligationCause::dummy(),
                    param_env,
                    predicate,
                );
                match infcx.evaluate_obligation(&obligation) {
                    Ok(eval_result) if eval_result.may_apply() => {}
                    Err(traits::OverflowError::Canonical) => {}
                    _ => continue 'blanket_impls,
                }
            }
            debug!("found applicable impl for trait ref {trait_ref:?}");

            cx.generated_synthetics.insert((ty.skip_binder(), trait_def_id));

            blanket_impls.push(clean::Item {
                name: None,
                attrs: Default::default(),
                item_id: clean::ItemId::Blanket { impl_id: impl_def_id, for_: item_def_id },
                kind: Box::new(clean::ImplItem(Box::new(clean::Impl {
                    unsafety: hir::Unsafety::Normal,
                    generics: clean_ty_generics(
                        cx,
                        tcx.generics_of(impl_def_id),
                        tcx.explicit_predicates_of(impl_def_id),
                    ),
                    // FIXME(eddyb) compute both `trait_` and `for_` from
                    // the post-inference `trait_ref`, as it's more accurate.
                    trait_: Some(clean_trait_ref_with_bindings(
                        cx,
                        ty::Binder::dummy(trait_ref.instantiate_identity()),
                        ThinVec::new(),
                    )),
                    for_: clean_middle_ty(
                        ty::Binder::dummy(ty.instantiate_identity()),
                        cx,
                        None,
                        None,
                    ),
                    items: tcx
                        .associated_items(impl_def_id)
                        .in_definition_order()
                        .filter(|item| !item.is_impl_trait_in_trait())
                        .map(|item| clean_middle_assoc_item(item, cx))
                        .collect(),
                    polarity: ty::ImplPolarity::Positive,
                    kind: clean::ImplKind::Blanket(Box::new(clean_middle_ty(
                        ty::Binder::dummy(trait_ref.instantiate_identity().self_ty()),
                        cx,
                        None,
                        None,
                    ))),
                }))),
                cfg: None,
                inline_stmt_id: None,
            });
        }
    }

    blanket_impls
}