blob: 82103c5a03b6e04fe52fcf2ba3ba2af3ed57b1f5 (
plain)
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
|
//! Module for inferring the variance of type and lifetime parameters. See the [rustc dev guide]
//! chapter for more info.
//!
//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/variance.html
use rustc_arena::DroplessArena;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::{self, CrateVariancesMap, TyCtxt};
/// Defines the `TermsContext` basically houses an arena where we can
/// allocate terms.
mod terms;
/// Code to gather up constraints.
mod constraints;
/// Code to solve constraints and write out the results.
mod solve;
/// Code to write unit tests of variance.
pub mod test;
/// Code for transforming variances.
mod xform;
pub fn provide(providers: &mut Providers) {
*providers = Providers { variances_of, crate_variances, ..*providers };
}
fn crate_variances(tcx: TyCtxt<'_>, (): ()) -> CrateVariancesMap<'_> {
let arena = DroplessArena::default();
let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &arena);
let constraints_cx = constraints::add_constraints_from_crate(terms_cx);
solve::solve_constraints(constraints_cx)
}
fn variances_of(tcx: TyCtxt<'_>, item_def_id: DefId) -> &[ty::Variance] {
// Skip items with no generics - there's nothing to infer in them.
if tcx.generics_of(item_def_id).count() == 0 {
return &[];
}
match tcx.def_kind(item_def_id) {
DefKind::Fn
| DefKind::AssocFn
| DefKind::Enum
| DefKind::Struct
| DefKind::Union
| DefKind::Variant
| DefKind::Ctor(..) => {}
_ => {
// Variance not relevant.
span_bug!(tcx.def_span(item_def_id), "asked to compute variance for wrong kind of item")
}
}
// Everything else must be inferred.
let crate_map = tcx.crate_variances(());
crate_map.variances.get(&item_def_id).copied().unwrap_or(&[])
}
|
