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::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!
15 use std::collections::BTreeMap;
17 use rustc::hir::def_id::DefId;
20 use crate::clean::GenericArgs as PP;
21 use crate::clean::WherePredicate as WP;
23 use crate::core::DocContext;
25 pub fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> Vec<WP> {
26 // First, partition the where clause into its separate components
27 let mut params: BTreeMap<_, Vec<_>> = BTreeMap::new();
28 let mut lifetimes = Vec::new();
29 let mut equalities = Vec::new();
30 let mut tybounds = Vec::new();
32 for clause in clauses {
34 WP::BoundPredicate { ty, bounds } => {
36 clean::Generic(s) => params.entry(s).or_default()
38 t => tybounds.push((t, bounds)),
41 WP::RegionPredicate { lifetime, bounds } => {
42 lifetimes.push((lifetime, bounds));
44 WP::EqPredicate { lhs, rhs } => equalities.push((lhs, rhs)),
48 // Look for equality predicates on associated types that can be merged into
49 // general bound predicates
50 equalities.retain(|&(ref lhs, ref rhs)| {
51 let (self_, trait_did, name) = if let Some(p) = lhs.projection() {
56 let generic = match self_ {
57 clean::Generic(s) => s,
60 let bounds = match params.get_mut(generic) {
65 merge_bounds(cx, bounds, trait_did, name, rhs)
68 // And finally, let's reassemble everything
69 let mut clauses = Vec::new();
70 clauses.extend(lifetimes.into_iter().map(|(lt, bounds)| {
71 WP::RegionPredicate { lifetime: lt, bounds }
73 clauses.extend(params.into_iter().map(|(k, v)| {
75 ty: clean::Generic(k),
79 clauses.extend(tybounds.into_iter().map(|(ty, bounds)| {
80 WP::BoundPredicate { ty, bounds }
82 clauses.extend(equalities.into_iter().map(|(lhs, rhs)| {
83 WP::EqPredicate { lhs, rhs }
89 cx: &clean::DocContext<'_>,
90 bounds: &mut Vec<clean::GenericBound>,
95 !bounds.iter_mut().any(|b| {
96 let trait_ref = match *b {
97 clean::GenericBound::TraitBound(ref mut tr, _) => tr,
98 clean::GenericBound::Outlives(..) => return false,
100 let (did, path) = match trait_ref.trait_ {
101 clean::ResolvedPath { did, ref mut path, ..} => (did, path),
104 // If this QPath's trait `trait_did` is the same as, or a supertrait
105 // of, the bound's trait `did` then we can keep going, otherwise
106 // this is just a plain old equality bound.
107 if !trait_is_same_or_supertrait(cx, did, trait_did) {
110 let last = path.segments.last_mut().expect("segments were empty");
112 PP::AngleBracketed { ref mut bindings, .. } => {
113 bindings.push(clean::TypeBinding {
114 name: name.to_string(),
115 kind: clean::TypeBindingKind::Equality {
120 PP::Parenthesized { ref mut output, .. } => match output {
121 Some(o) => assert_eq!(o, rhs),
122 None => if *rhs != clean::Type::Tuple(Vec::new()) {
123 *output = Some(rhs.clone());
131 pub fn ty_params(mut params: Vec<clean::GenericParamDef>) -> Vec<clean::GenericParamDef> {
132 for param in &mut params {
134 clean::GenericParamDefKind::Type { ref mut bounds, .. } => {
135 *bounds = mem::take(bounds);
137 _ => panic!("expected only type parameters"),
143 fn trait_is_same_or_supertrait(cx: &DocContext<'_>, child: DefId,
144 trait_: DefId) -> bool {
148 let predicates = cx.tcx.super_predicates_of(child);
149 debug_assert!(cx.tcx.generics_of(child).has_self);
150 let self_ty = cx.tcx.types.self_param;
151 predicates.predicates.iter().filter_map(|(pred, _)| {
152 if let ty::Predicate::Trait(ref pred) = *pred {
153 if pred.skip_binder().trait_ref.self_ty() == self_ty {
161 }).any(|did| trait_is_same_or_supertrait(cx, did, trait_))