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;
17 use rustc_span::Symbol;
20 use crate::clean::GenericArgs as PP;
21 use crate::clean::WherePredicate as WP;
22 use crate::core::DocContext;
24 crate fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> Vec<WP> {
25 // First, partition the where clause into its separate components.
27 // We use `FxIndexMap` so that the insertion order is preserved to prevent messing up to
28 // the order of the generated bounds.
29 let mut params: FxIndexMap<Symbol, (Vec<_>, Vec<_>)> = FxIndexMap::default();
30 let mut lifetimes = Vec::new();
31 let mut equalities = Vec::new();
32 let mut tybounds = Vec::new();
34 for clause in clauses {
36 WP::BoundPredicate { ty, bounds, bound_params } => match ty {
37 clean::Generic(s) => {
38 let (b, p) = params.entry(s).or_default();
40 p.extend(bound_params);
42 t => tybounds.push((t, (bounds, bound_params))),
44 WP::RegionPredicate { lifetime, bounds } => {
45 lifetimes.push((lifetime, bounds));
47 WP::EqPredicate { lhs, rhs } => equalities.push((lhs, rhs)),
51 // Look for equality predicates on associated types that can be merged into
52 // general bound predicates
53 equalities.retain(|&(ref lhs, ref rhs)| {
54 let (self_, trait_did, name) = if let Some(p) = lhs.projection() {
59 let generic = match self_ {
60 clean::Generic(s) => s,
63 let (bounds, _) = match params.get_mut(generic) {
68 merge_bounds(cx, bounds, trait_did, name, rhs)
71 // And finally, let's reassemble everything
72 let mut clauses = Vec::new();
74 lifetimes.into_iter().map(|(lt, bounds)| WP::RegionPredicate { lifetime: lt, bounds }),
76 clauses.extend(params.into_iter().map(|(k, (bounds, params))| WP::BoundPredicate {
77 ty: clean::Generic(k),
81 clauses.extend(tybounds.into_iter().map(|(ty, (bounds, bound_params))| WP::BoundPredicate {
86 clauses.extend(equalities.into_iter().map(|(lhs, rhs)| WP::EqPredicate { lhs, rhs }));
90 crate fn merge_bounds(
91 cx: &clean::DocContext<'_>,
92 bounds: &mut Vec<clean::GenericBound>,
97 !bounds.iter_mut().any(|b| {
98 let trait_ref = match *b {
99 clean::GenericBound::TraitBound(ref mut tr, _) => tr,
100 clean::GenericBound::Outlives(..) => return false,
102 // If this QPath's trait `trait_did` is the same as, or a supertrait
103 // of, the bound's trait `did` then we can keep going, otherwise
104 // this is just a plain old equality bound.
105 if !trait_is_same_or_supertrait(cx, trait_ref.trait_.def_id(), trait_did) {
108 let last = trait_ref.trait_.segments.last_mut().expect("segments were empty");
110 PP::AngleBracketed { ref mut bindings, .. } => {
111 bindings.push(clean::TypeBinding {
113 kind: clean::TypeBindingKind::Equality { term: rhs.clone() },
116 PP::Parenthesized { ref mut output, .. } => match output {
117 Some(o) => assert_eq!(&clean::Term::Type(o.as_ref().clone()), rhs),
119 if *rhs != clean::Term::Type(clean::Type::Tuple(Vec::new())) {
120 *output = Some(Box::new(rhs.ty().unwrap().clone()));
129 fn trait_is_same_or_supertrait(cx: &DocContext<'_>, child: DefId, trait_: DefId) -> bool {
133 let predicates = cx.tcx.super_predicates_of(child);
134 debug_assert!(cx.tcx.generics_of(child).has_self);
135 let self_ty = cx.tcx.types.self_param;
139 .filter_map(|(pred, _)| {
140 if let ty::PredicateKind::Trait(pred) = pred.kind().skip_binder() {
141 if pred.trait_ref.self_ty() == self_ty { Some(pred.def_id()) } else { None }
146 .any(|did| trait_is_same_or_supertrait(cx, did, trait_))