1 //! Simplification of where-clauses and parameter bounds into a prettier and
2 //! more canonical form.
4 //! Currently all cross-crate-inlined function use `rustc_middle::ty` to reconstruct
5 //! the AST (e.g., see all of `clean::inline`), but this is not always a
6 //! non-lossy transformation. The current format of storage for where-clauses
7 //! for functions and such is simply a list of predicates. One example of this
8 //! is that the AST predicate of: `where T: Trait<Foo = Bar>` is encoded as:
9 //! `where T: Trait, <T as Trait>::Foo = Bar`.
11 //! This module attempts to reconstruct the original where and/or parameter
12 //! bounds by special casing scenarios such as these. Fun!
14 use rustc_data_structures::fx::FxIndexMap;
15 use rustc_hir::def_id::DefId;
19 use crate::clean::GenericArgs as PP;
20 use crate::clean::WherePredicate as WP;
21 use crate::core::DocContext;
23 pub(crate) fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> Vec<WP> {
24 // First, partition the where clause into its separate components.
26 // We use `FxIndexMap` so that the insertion order is preserved to prevent messing up to
27 // the order of the generated bounds.
28 let mut tybounds = FxIndexMap::default();
29 let mut lifetimes = Vec::new();
30 let mut equalities = Vec::new();
32 for clause in clauses {
34 WP::BoundPredicate { ty, bounds, bound_params } => {
35 let (b, p): &mut (Vec<_>, Vec<_>) = tybounds.entry(ty).or_default();
37 p.extend(bound_params);
39 WP::RegionPredicate { lifetime, bounds } => {
40 lifetimes.push((lifetime, bounds));
42 WP::EqPredicate { lhs, rhs } => equalities.push((lhs, rhs)),
46 // Look for equality predicates on associated types that can be merged into
47 // general bound predicates.
48 equalities.retain(|&(ref lhs, ref rhs)| {
49 let Some((ty, trait_did, name)) = lhs.projection() else { return true; };
50 // FIXME(fmease): We don't handle HRTBs correctly here.
51 // Pass `_bound_params` (higher-rank lifetimes) to a modified version of
52 // `merge_bounds`. That vector is currently always empty though since we
53 // don't keep track of late-bound lifetimes when cleaning projection
54 // predicates to cleaned equality predicates while we should first query
55 // them with `collect_referenced_late_bound_regions` and then store them
56 // (or something similar). For prior art, see `clean::auto_trait`.
57 let Some((bounds, _bound_params)) = tybounds.get_mut(ty) else { return true };
58 merge_bounds(cx, bounds, trait_did, name, rhs)
61 // And finally, let's reassemble everything
62 let mut clauses = Vec::new();
64 lifetimes.into_iter().map(|(lt, bounds)| WP::RegionPredicate { lifetime: lt, bounds }),
66 clauses.extend(tybounds.into_iter().map(|(ty, (bounds, bound_params))| WP::BoundPredicate {
71 clauses.extend(equalities.into_iter().map(|(lhs, rhs)| WP::EqPredicate { lhs, rhs }));
75 pub(crate) fn merge_bounds(
76 cx: &clean::DocContext<'_>,
77 bounds: &mut Vec<clean::GenericBound>,
79 assoc: clean::PathSegment,
82 !bounds.iter_mut().any(|b| {
83 let trait_ref = match *b {
84 clean::GenericBound::TraitBound(ref mut tr, _) => tr,
85 clean::GenericBound::Outlives(..) => return false,
87 // If this QPath's trait `trait_did` is the same as, or a supertrait
88 // of, the bound's trait `did` then we can keep going, otherwise
89 // this is just a plain old equality bound.
90 if !trait_is_same_or_supertrait(cx, trait_ref.trait_.def_id(), trait_did) {
93 let last = trait_ref.trait_.segments.last_mut().expect("segments were empty");
95 PP::AngleBracketed { ref mut bindings, .. } => {
96 bindings.push(clean::TypeBinding {
98 kind: clean::TypeBindingKind::Equality { term: rhs.clone() },
101 PP::Parenthesized { ref mut output, .. } => match output {
102 Some(o) => assert_eq!(&clean::Term::Type(o.as_ref().clone()), rhs),
104 if *rhs != clean::Term::Type(clean::Type::Tuple(Vec::new())) {
105 *output = Some(Box::new(rhs.ty().unwrap().clone()));
114 fn trait_is_same_or_supertrait(cx: &DocContext<'_>, child: DefId, trait_: DefId) -> bool {
118 let predicates = cx.tcx.super_predicates_of(child);
119 debug_assert!(cx.tcx.generics_of(child).has_self);
120 let self_ty = cx.tcx.types.self_param;
124 .filter_map(|(pred, _)| {
125 if let ty::PredicateKind::Trait(pred) = pred.kind().skip_binder() {
126 if pred.trait_ref.self_ty() == self_ty { Some(pred.def_id()) } else { None }
131 .any(|did| trait_is_same_or_supertrait(cx, did, trait_))