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

use rustc_infer::traits::{TraitEngine, TraitEngineExt};

use crate::infer::canonical::OriginalQueryValues;
use crate::infer::InferCtxt;
use crate::traits::{EvaluationResult, OverflowError, PredicateObligation, SelectionContext};

pub trait InferCtxtExt<'tcx> {
    fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool;

    fn predicate_must_hold_considering_regions(
        &self,
        obligation: &PredicateObligation<'tcx>,
    ) -> bool;

    fn predicate_must_hold_modulo_regions(&self, obligation: &PredicateObligation<'tcx>) -> bool;

    fn evaluate_obligation(
        &self,
        obligation: &PredicateObligation<'tcx>,
    ) -> Result<EvaluationResult, OverflowError>;

    // Helper function that canonicalizes and runs the query. If an
    // overflow results, we re-run it in the local context so we can
    // report a nice error.
    /*crate*/
    fn evaluate_obligation_no_overflow(
        &self,
        obligation: &PredicateObligation<'tcx>,
    ) -> EvaluationResult;
}

impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
    /// Evaluates whether the predicate can be satisfied (by any means)
    /// in the given `ParamEnv`.
    fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool {
        self.evaluate_obligation_no_overflow(obligation).may_apply()
    }

    /// Evaluates whether the predicate can be satisfied in the given
    /// `ParamEnv`, and returns `false` if not certain. However, this is
    /// not entirely accurate if inference variables are involved.
    ///
    /// This version may conservatively fail when outlives obligations
    /// are required.
    fn predicate_must_hold_considering_regions(
        &self,
        obligation: &PredicateObligation<'tcx>,
    ) -> bool {
        self.evaluate_obligation_no_overflow(obligation).must_apply_considering_regions()
    }

    /// Evaluates whether the predicate can be satisfied in the given
    /// `ParamEnv`, and returns `false` if not certain. However, this is
    /// not entirely accurate if inference variables are involved.
    ///
    /// This version ignores all outlives constraints.
    fn predicate_must_hold_modulo_regions(&self, obligation: &PredicateObligation<'tcx>) -> bool {
        self.evaluate_obligation_no_overflow(obligation).must_apply_modulo_regions()
    }

    /// Evaluate a given predicate, capturing overflow and propagating it back.
    fn evaluate_obligation(
        &self,
        obligation: &PredicateObligation<'tcx>,
    ) -> Result<EvaluationResult, OverflowError> {
        let mut _orig_values = OriginalQueryValues::default();

        let param_env = obligation.param_env;

        if self.next_trait_solver() {
            self.probe(|snapshot| {
                let mut fulfill_cx = crate::solve::FulfillmentCtxt::new(self);
                fulfill_cx.register_predicate_obligation(self, obligation.clone());
                // True errors
                // FIXME(-Ztrait-solver=next): Overflows are reported as ambig here, is that OK?
                if !fulfill_cx.select_where_possible(self).is_empty() {
                    Ok(EvaluationResult::EvaluatedToErr)
                } else if !fulfill_cx.select_all_or_error(self).is_empty() {
                    Ok(EvaluationResult::EvaluatedToAmbig)
                } else if self.opaque_types_added_in_snapshot(snapshot) {
                    Ok(EvaluationResult::EvaluatedToOkModuloOpaqueTypes)
                } else if self.region_constraints_added_in_snapshot(snapshot) {
                    Ok(EvaluationResult::EvaluatedToOkModuloRegions)
                } else {
                    Ok(EvaluationResult::EvaluatedToOk)
                }
            })
        } else {
            assert!(!self.intercrate);
            let c_pred = self.canonicalize_query_keep_static(
                param_env.and(obligation.predicate),
                &mut _orig_values,
            );
            self.tcx.at(obligation.cause.span()).evaluate_obligation(c_pred)
        }
    }

    // Helper function that canonicalizes and runs the query. If an
    // overflow results, we re-run it in the local context so we can
    // report a nice error.
    fn evaluate_obligation_no_overflow(
        &self,
        obligation: &PredicateObligation<'tcx>,
    ) -> EvaluationResult {
        // Run canonical query. If overflow occurs, rerun from scratch but this time
        // in standard trait query mode so that overflow is handled appropriately
        // within `SelectionContext`.
        match self.evaluate_obligation(obligation) {
            Ok(result) => result,
            Err(OverflowError::Canonical) => {
                let mut selcx = SelectionContext::new(&self);
                selcx.evaluate_root_obligation(obligation).unwrap_or_else(|r| match r {
                    OverflowError::Canonical => {
                        span_bug!(
                            obligation.cause.span,
                            "Overflow should be caught earlier in standard query mode: {:?}, {:?}",
                            obligation,
                            r,
                        )
                    }
                    OverflowError::ErrorReporting => EvaluationResult::EvaluatedToErr,
                    OverflowError::Error(_) => EvaluationResult::EvaluatedToErr,
                })
            }
            Err(OverflowError::ErrorReporting) => EvaluationResult::EvaluatedToErr,
            Err(OverflowError::Error(_)) => EvaluationResult::EvaluatedToErr,
        }
    }
}