rustc_trait_selection/
opaque_types.rs

1use rustc_data_structures::fx::FxIndexMap;
2use rustc_hir::OpaqueTyOrigin;
3use rustc_hir::def_id::LocalDefId;
4use rustc_infer::infer::outlives::env::OutlivesEnvironment;
5use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
6use rustc_middle::ty::{
7    self, DefiningScopeKind, GenericArgKind, GenericArgs, OpaqueTypeKey, TyCtxt, TypeVisitableExt,
8    TypingMode, fold_regions,
9};
10use rustc_span::{ErrorGuaranteed, Span};
11
12use crate::errors::NonGenericOpaqueTypeParam;
13use crate::regions::OutlivesEnvironmentBuildExt;
14use crate::traits::ObligationCtxt;
15
16#[derive(Debug)]
17pub enum InvalidOpaqueTypeArgs<'tcx> {
18    AlreadyReported(ErrorGuaranteed),
19    NotAParam { opaque_type_key: OpaqueTypeKey<'tcx>, param_index: usize, span: Span },
20    DuplicateParam { opaque_type_key: OpaqueTypeKey<'tcx>, param_indices: Vec<usize>, span: Span },
21}
22impl From<ErrorGuaranteed> for InvalidOpaqueTypeArgs<'_> {
23    fn from(guar: ErrorGuaranteed) -> Self {
24        InvalidOpaqueTypeArgs::AlreadyReported(guar)
25    }
26}
27impl<'tcx> InvalidOpaqueTypeArgs<'tcx> {
28    pub fn report(self, infcx: &InferCtxt<'tcx>) -> ErrorGuaranteed {
29        let tcx = infcx.tcx;
30        match self {
31            InvalidOpaqueTypeArgs::AlreadyReported(guar) => guar,
32            InvalidOpaqueTypeArgs::NotAParam { opaque_type_key, param_index, span } => {
33                let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
34                let opaque_param = opaque_generics.param_at(param_index, tcx);
35                let kind = opaque_param.kind.descr();
36                infcx.dcx().emit_err(NonGenericOpaqueTypeParam {
37                    arg: opaque_type_key.args[param_index],
38                    kind,
39                    span,
40                    param_span: tcx.def_span(opaque_param.def_id),
41                })
42            }
43            InvalidOpaqueTypeArgs::DuplicateParam { opaque_type_key, param_indices, span } => {
44                let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
45                let descr = opaque_generics.param_at(param_indices[0], tcx).kind.descr();
46                let spans: Vec<_> = param_indices
47                    .into_iter()
48                    .map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id))
49                    .collect();
50                infcx
51                    .dcx()
52                    .struct_span_err(span, "non-defining opaque type use in defining scope")
53                    .with_span_note(spans, format!("{descr} used multiple times"))
54                    .emit()
55            }
56        }
57    }
58}
59
60/// Opaque type parameter validity check as documented in the [rustc-dev-guide chapter].
61///
62/// [rustc-dev-guide chapter]:
63/// https://rustc-dev-guide.rust-lang.org/opaque-types-region-infer-restrictions.html
64pub fn check_opaque_type_parameter_valid<'tcx>(
65    infcx: &InferCtxt<'tcx>,
66    opaque_type_key: OpaqueTypeKey<'tcx>,
67    span: Span,
68    defining_scope_kind: DefiningScopeKind,
69) -> Result<(), InvalidOpaqueTypeArgs<'tcx>> {
70    let tcx = infcx.tcx;
71    let opaque_env = LazyOpaqueTyEnv::new(tcx, opaque_type_key.def_id);
72    let mut seen_params: FxIndexMap<_, Vec<_>> = FxIndexMap::default();
73
74    // Avoid duplicate errors in case the opaque has already been malformed in
75    // HIR typeck.
76    if let DefiningScopeKind::MirBorrowck = defining_scope_kind {
77        infcx
78            .tcx
79            .type_of_opaque_hir_typeck(opaque_type_key.def_id)
80            .instantiate_identity()
81            .error_reported()?;
82    }
83
84    for (i, arg) in opaque_type_key.iter_captured_args(tcx) {
85        let arg_is_param = match arg.kind() {
86            GenericArgKind::Lifetime(lt) => match defining_scope_kind {
87                DefiningScopeKind::HirTypeck => continue,
88                DefiningScopeKind::MirBorrowck => {
89                    matches!(lt.kind(), ty::ReEarlyParam(_) | ty::ReLateParam(_))
90                        || (lt.is_static() && opaque_env.param_equal_static(i))
91                }
92            },
93            GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
94            GenericArgKind::Const(ct) => matches!(ct.kind(), ty::ConstKind::Param(_)),
95        };
96
97        if arg_is_param {
98            // Register if the same lifetime appears multiple times in the generic args.
99            // There is an exception when the opaque type *requires* the lifetimes to be equal.
100            // See [rustc-dev-guide chapter] § "An exception to uniqueness rule".
101            let seen_where = seen_params.entry(arg).or_default();
102            if !seen_where.first().is_some_and(|&prev_i| opaque_env.params_equal(i, prev_i)) {
103                seen_where.push(i);
104            }
105        } else {
106            // Prevent `fn foo() -> Foo<u32>` from being defining.
107            opaque_env.param_is_error(i)?;
108            return Err(InvalidOpaqueTypeArgs::NotAParam { opaque_type_key, param_index: i, span });
109        }
110    }
111
112    for (_, param_indices) in seen_params {
113        if param_indices.len() > 1 {
114            return Err(InvalidOpaqueTypeArgs::DuplicateParam {
115                opaque_type_key,
116                param_indices,
117                span,
118            });
119        }
120    }
121
122    Ok(())
123}
124
125/// Computes if an opaque type requires a lifetime parameter to be equal to
126/// another one or to the `'static` lifetime.
127/// These requirements are derived from the explicit and implied bounds.
128struct LazyOpaqueTyEnv<'tcx> {
129    tcx: TyCtxt<'tcx>,
130    def_id: LocalDefId,
131
132    /// Equal parameters will have the same name. Computed Lazily.
133    /// Example:
134    ///     `type Opaque<'a: 'static, 'b: 'c, 'c: 'b> = impl Sized;`
135    ///     Identity args: `['a, 'b, 'c]`
136    ///     Canonical args: `['static, 'b, 'b]`
137    canonical_args: std::cell::OnceCell<ty::GenericArgsRef<'tcx>>,
138}
139
140impl<'tcx> LazyOpaqueTyEnv<'tcx> {
141    fn new(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self {
142        Self { tcx, def_id, canonical_args: std::cell::OnceCell::new() }
143    }
144
145    fn param_equal_static(&self, param_index: usize) -> bool {
146        self.get_canonical_args()[param_index].expect_region().is_static()
147    }
148
149    fn params_equal(&self, param1: usize, param2: usize) -> bool {
150        let canonical_args = self.get_canonical_args();
151        canonical_args[param1] == canonical_args[param2]
152    }
153
154    fn param_is_error(&self, param_index: usize) -> Result<(), ErrorGuaranteed> {
155        self.get_canonical_args()[param_index].error_reported()
156    }
157
158    fn get_canonical_args(&self) -> ty::GenericArgsRef<'tcx> {
159        if let Some(&canonical_args) = self.canonical_args.get() {
160            return canonical_args;
161        }
162
163        let &Self { tcx, def_id, .. } = self;
164        let origin = tcx.local_opaque_ty_origin(def_id);
165        let parent = match origin {
166            OpaqueTyOrigin::FnReturn { parent, .. }
167            | OpaqueTyOrigin::AsyncFn { parent, .. }
168            | OpaqueTyOrigin::TyAlias { parent, .. } => parent,
169        };
170        let param_env = tcx.param_env(parent);
171        let args = GenericArgs::identity_for_item(tcx, parent).extend_to(
172            tcx,
173            def_id.to_def_id(),
174            |param, _| {
175                tcx.map_opaque_lifetime_to_parent_lifetime(param.def_id.expect_local()).into()
176            },
177        );
178
179        // FIXME(#132279): It feels wrong to use `non_body_analysis` here given that we're
180        // in a body here.
181        let infcx = tcx.infer_ctxt().build(TypingMode::non_body_analysis());
182        let ocx = ObligationCtxt::new(&infcx);
183
184        let wf_tys = ocx.assumed_wf_types(param_env, parent).unwrap_or_else(|_| {
185            tcx.dcx().span_delayed_bug(tcx.def_span(def_id), "error getting implied bounds");
186            Default::default()
187        });
188        let outlives_env = OutlivesEnvironment::new(&infcx, parent, param_env, wf_tys);
189
190        let mut seen = vec![tcx.lifetimes.re_static];
191        let canonical_args = fold_regions(tcx, args, |r1, _| {
192            if r1.is_error() {
193                r1
194            } else if let Some(&r2) = seen.iter().find(|&&r2| {
195                let free_regions = outlives_env.free_region_map();
196                free_regions.sub_free_regions(tcx, r1, r2)
197                    && free_regions.sub_free_regions(tcx, r2, r1)
198            }) {
199                r2
200            } else {
201                seen.push(r1);
202                r1
203            }
204        });
205        self.canonical_args.set(canonical_args).unwrap();
206        canonical_args
207    }
208}
rustc_trait_selection/opaque_types.rs

rustc_trait_selection/
opaque_types.rs
