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::hir::def_id::DefId;
use rustc::ty;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sync::Lrc;
use super::constraints::*;
use super::terms::*;
use super::terms::VarianceTerm::*;
use super::xform::*;
struct SolveContext<'a, 'tcx: 'a> {
terms_cx: TermsContext<'a, 'tcx>,
constraints: Vec<Constraint<'a>>,
solutions: Vec<ty::Variance>,
}
pub fn solve_constraints(constraints_cx: ConstraintContext) -> ty::CrateVariancesMap {
let ConstraintContext { terms_cx, constraints, .. } = constraints_cx;
let mut solutions = vec![ty::Bivariant; terms_cx.inferred_terms.len()];
for &(id, ref variances) in &terms_cx.lang_items {
let InferredIndex(start) = terms_cx.inferred_starts[&id];
for (i, &variance) in variances.iter().enumerate() {
solutions[start + i] = variance;
}
}
let mut solutions_cx = SolveContext {
terms_cx,
constraints,
solutions,
};
solutions_cx.solve();
let variances = solutions_cx.create_map();
let empty_variance = Lrc::new(Vec::new());
ty::CrateVariancesMap { variances, empty_variance }
}
impl<'a, 'tcx> SolveContext<'a, 'tcx> {
fn solve(&mut self) {
let mut changed = true;
while changed {
changed = false;
for constraint in &self.constraints {
let Constraint { inferred, variance: term } = *constraint;
let InferredIndex(inferred) = inferred;
let variance = self.evaluate(term);
let old_value = self.solutions[inferred];
let new_value = glb(variance, old_value);
if old_value != new_value {
debug!("Updating inferred {} \
from {:?} to {:?} due to {:?}",
inferred,
old_value,
new_value,
term);
self.solutions[inferred] = new_value;
changed = true;
}
}
}
}
fn create_map(&self) -> FxHashMap<DefId, Lrc<Vec<ty::Variance>>> {
let tcx = self.terms_cx.tcx;
let solutions = &self.solutions;
self.terms_cx.inferred_starts.iter().map(|(&id, &InferredIndex(start))| {
let def_id = tcx.hir.local_def_id(id);
let generics = tcx.generics_of(def_id);
let mut variances = solutions[start..start+generics.count()].to_vec();
debug!("id={} variances={:?}", id, variances);
if let ty::TyFnDef(..) = tcx.type_of(def_id).sty {
for variance in &mut variances {
if *variance == ty::Bivariant {
*variance = ty::Invariant;
}
}
}
(def_id, Lrc::new(variances))
}).collect()
}
fn evaluate(&self, term: VarianceTermPtr<'a>) -> ty::Variance {
match *term {
ConstantTerm(v) => v,
TransformTerm(t1, t2) => {
let v1 = self.evaluate(t1);
let v2 = self.evaluate(t2);
v1.xform(v2)
}
InferredTerm(InferredIndex(index)) => self.solutions[index],
}
}
}