rustc_next_trait_solver/solve/
search_graph.rs

1use std::convert::Infallible;
2use std::marker::PhantomData;
3
4use rustc_type_ir::data_structures::ensure_sufficient_stack;
5use rustc_type_ir::search_graph::{self, PathKind};
6use rustc_type_ir::solve::{
7    AccessedOpaques, CanonicalInput, Certainty, NoSolution, QueryResult, RerunResultExt,
8};
9use rustc_type_ir::{Interner, MayBeErased, TypingMode};
10
11use crate::canonical::response_no_constraints_raw;
12use crate::delegate::SolverDelegate;
13use crate::solve::{
14    EvalCtxt, FIXPOINT_STEP_LIMIT, has_no_inference_or_external_constraints, inspect,
15};
16
17/// This type is never constructed. We only use it to implement `search_graph::Delegate`
18/// for all types which impl `SolverDelegate` and doing it directly fails in coherence.
19pub(super) struct SearchGraphDelegate<D: SolverDelegate> {
20    _marker: PhantomData<D>,
21}
22pub(super) type SearchGraph<D> = search_graph::SearchGraph<SearchGraphDelegate<D>>;
23impl<D, I> search_graph::Delegate for SearchGraphDelegate<D>
24where
25    D: SolverDelegate<Interner = I>,
26    I: Interner,
27{
28    type Cx = D::Interner;
29
30    const ENABLE_PROVISIONAL_CACHE: bool = true;
31    type ValidationScope = Infallible;
32    fn enter_validation_scope(
33        _cx: Self::Cx,
34        _input: CanonicalInput<I>,
35    ) -> Option<Self::ValidationScope> {
36        None
37    }
38
39    const FIXPOINT_STEP_LIMIT: usize = FIXPOINT_STEP_LIMIT;
40
41    type ProofTreeBuilder = inspect::ProofTreeBuilder<D>;
42    fn inspect_is_noop(inspect: &mut Self::ProofTreeBuilder) -> bool {
43        inspect.is_noop()
44    }
45
46    const DIVIDE_AVAILABLE_DEPTH_ON_OVERFLOW: usize = 4;
47
48    fn initial_provisional_result(
49        cx: I,
50        kind: PathKind,
51        input: CanonicalInput<I>,
52    ) -> (QueryResult<I>, AccessedOpaques<I>) {
53        match kind {
54            PathKind::Coinductive => response_no_constraints(cx, input, Certainty::Yes),
55            PathKind::Unknown | PathKind::ForcedAmbiguity => {
56                response_no_constraints(cx, input, Certainty::overflow(false))
57            }
58            // Even though we know these cycles to be unproductive, we still return
59            // overflow during coherence. This is both as we are not 100% confident in
60            // the implementation yet and any incorrect errors would be unsound there.
61            // The affected cases are also fairly artificial and not necessarily desirable
62            // so keeping this as ambiguity is fine for now.
63            //
64            // See `tests/ui/traits/next-solver/cycles/unproductive-in-coherence.rs` for an
65            // example where this would matter. We likely should change these cycles to `NoSolution`
66            // even in coherence once this is a bit more settled.
67            PathKind::Inductive => match input.typing_mode.0 {
68                TypingMode::Coherence => {
69                    response_no_constraints(cx, input, Certainty::overflow(false))
70                }
71                TypingMode::Typeck { .. }
72                | TypingMode::PostTypeckUntilBorrowck { .. }
73                | TypingMode::Reflection
74                | TypingMode::PostBorrowck { .. }
75                | TypingMode::PostAnalysis
76                | TypingMode::Codegen
77                | TypingMode::ErasedNotCoherence(MayBeErased) => {
78                    (Err(NoSolution), AccessedOpaques::default())
79                }
80            },
81        }
82    }
83
84    fn is_initial_provisional_result(
85        result: (QueryResult<I>, AccessedOpaques<I>),
86    ) -> Option<PathKind> {
87        match result.0 {
88            Ok(response) => {
89                if has_no_inference_or_external_constraints(response) {
90                    if response.value.certainty == Certainty::Yes {
91                        return Some(PathKind::Coinductive);
92                    } else if response.value.certainty == Certainty::overflow(false) {
93                        return Some(PathKind::Unknown);
94                    }
95                }
96
97                None
98            }
99            Err(NoSolution) => Some(PathKind::Inductive),
100        }
101    }
102
103    fn stack_overflow_result(
104        cx: I,
105        input: CanonicalInput<I>,
106    ) -> (QueryResult<I>, AccessedOpaques<I>) {
107        response_no_constraints(cx, input, Certainty::overflow(true))
108    }
109
110    const FIXPOINT_OVERFLOW_AMBIGUITY_KIND: Certainty = Certainty::overflow(false);
111    fn fixpoint_overflow_result(
112        cx: I,
113        input: CanonicalInput<I>,
114    ) -> (QueryResult<I>, AccessedOpaques<I>) {
115        response_no_constraints(cx, input, Certainty::overflow(false))
116    }
117
118    fn is_ambiguous_result(result: (QueryResult<I>, AccessedOpaques<I>)) -> Option<Certainty> {
119        result.0.ok().and_then(|response| {
120            if has_no_inference_or_external_constraints(response)
121                && #[allow(non_exhaustive_omitted_patterns)] match response.value.certainty {
    Certainty::Maybe { .. } => true,
    _ => false,
}matches!(response.value.certainty, Certainty::Maybe { .. })
122            {
123                Some(response.value.certainty)
124            } else {
125                None
126            }
127        })
128    }
129
130    fn compute_goal(
131        search_graph: &mut SearchGraph<D>,
132        cx: I,
133        input: CanonicalInput<I>,
134        inspect: &mut Self::ProofTreeBuilder,
135    ) -> (QueryResult<I>, AccessedOpaques<I>) {
136        ensure_sufficient_stack(|| {
137            EvalCtxt::enter_canonical(cx, search_graph, input, inspect, |ecx, goal| {
138                // if we're in `RerunNonErased`, don't even bother with inspect, and immediately return
139                let result = ecx.compute_goal(goal).map_err_to_rerun()?;
140
141                ecx.inspect.query_result(result);
142                result.map_err(Into::into)
143            })
144        })
145    }
146}
147
148fn response_no_constraints<I: Interner>(
149    cx: I,
150    input: CanonicalInput<I>,
151    certainty: Certainty,
152) -> (QueryResult<I>, AccessedOpaques<I>) {
153    (
154        Ok(response_no_constraints_raw(
155            cx,
156            input.canonical.max_universe,
157            input.canonical.var_kinds,
158            certainty,
159        )),
160        AccessedOpaques::default(),
161    )
162}
rustc_next_trait_solver/solve/search_graph.rs

rustc_next_trait_solver/solve/
search_graph.rs
