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use rustc::ty;
use std::rc::Rc;
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) {
let ConstraintContext { terms_cx, constraints, .. } = constraints_cx;
let solutions = terms_cx.inferred_infos
.iter()
.map(|ii| ii.initial_variance)
.collect();
let mut solutions_cx = SolveContext {
terms_cx: terms_cx,
constraints: constraints,
solutions: solutions,
};
solutions_cx.solve();
solutions_cx.write();
}
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 {} (node {}) \
from {:?} to {:?} due to {:?}",
inferred,
self.terms_cx
.inferred_infos[inferred]
.param_id,
old_value,
new_value,
term);
self.solutions[inferred] = new_value;
changed = true;
}
}
}
}
fn write(&self) {
let tcx = self.terms_cx.tcx;
let _ignore = tcx.dep_graph.in_ignore();
let solutions = &self.solutions;
let inferred_infos = &self.terms_cx.inferred_infos;
let mut index = 0;
let num_inferred = self.terms_cx.num_inferred();
while index < num_inferred {
let item_id = inferred_infos[index].item_id;
let mut item_variances = vec![];
while index < num_inferred && inferred_infos[index].item_id == item_id {
let info = &inferred_infos[index];
let variance = solutions[index];
debug!("Index {} Info {} Variance {:?}",
index,
info.index,
variance);
assert_eq!(item_variances.len(), info.index);
item_variances.push(variance);
index += 1;
}
debug!("item_id={} item_variances={:?}", item_id, item_variances);
let item_def_id = tcx.hir.local_def_id(item_id);
if tcx.has_attr(item_def_id, "rustc_variance") {
span_err!(tcx.sess,
tcx.hir.span(item_id),
E0208,
"{:?}",
item_variances);
}
tcx.maps.variances
.borrow_mut()
.insert(item_def_id, Rc::new(item_variances));
}
}
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],
}
}
}