src/librustdoc/clean/simplify.rs

   1 //! Simplification of where-clauses and parameter bounds into a prettier and
   2 //! more canonical form.
   3 //!
   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`.
  10 //!
  11 //! This module attempts to reconstruct the original where and/or parameter
  12 //! bounds by special casing scenarios such as these. Fun!
  13
  14 use rustc_data_structures::fx::FxIndexMap;
  15 use rustc_hir::def_id::DefId;
  16 use rustc_middle::ty;
  17 use rustc_span::Symbol;
  18
  19 use crate::clean;
  20 use crate::clean::GenericArgs as PP;
  21 use crate::clean::WherePredicate as WP;
  22 use crate::core::DocContext;
  23
  24 crate fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> Vec<WP> {
  25     // First, partition the where clause into its separate components.
  26     //
  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();
  33
  34     for clause in clauses {
  35         match clause {
  36             WP::BoundPredicate { ty, bounds, bound_params } => match ty {
  37                 clean::Generic(s) => {
  38                     let (b, p) = params.entry(s).or_default();
  39                     b.extend(bounds);
  40                     p.extend(bound_params);
  41                 }
  42                 t => tybounds.push((t, (bounds, bound_params))),
  43             },
  44             WP::RegionPredicate { lifetime, bounds } => {
  45                 lifetimes.push((lifetime, bounds));
  46             }
  47             WP::EqPredicate { lhs, rhs } => equalities.push((lhs, rhs)),
  48         }
  49     }
  50
  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 Some((self_, trait_did, name)) = lhs.projection() else {
  55             return true;
  56         };
  57         let clean::Generic(generic) = self_ else { return true };
  58         let Some((bounds, _)) = params.get_mut(generic) else { return true };
  59
  60         merge_bounds(cx, bounds, trait_did, name, rhs)
  61     });
  62
  63     // And finally, let's reassemble everything
  64     let mut clauses = Vec::new();
  65     clauses.extend(
  66         lifetimes.into_iter().map(|(lt, bounds)| WP::RegionPredicate { lifetime: lt, bounds }),
  67     );
  68     clauses.extend(params.into_iter().map(|(k, (bounds, params))| WP::BoundPredicate {
  69         ty: clean::Generic(k),
  70         bounds,
  71         bound_params: params,
  72     }));
  73     clauses.extend(tybounds.into_iter().map(|(ty, (bounds, bound_params))| WP::BoundPredicate {
  74         ty,
  75         bounds,
  76         bound_params,
  77     }));
  78     clauses.extend(equalities.into_iter().map(|(lhs, rhs)| WP::EqPredicate { lhs, rhs }));
  79     clauses
  80 }
  81
  82 crate fn merge_bounds(
  83     cx: &clean::DocContext<'_>,
  84     bounds: &mut Vec<clean::GenericBound>,
  85     trait_did: DefId,
  86     assoc: clean::PathSegment,
  87     rhs: &clean::Term,
  88 ) -> bool {
  89     !bounds.iter_mut().any(|b| {
  90         let trait_ref = match *b {
  91             clean::GenericBound::TraitBound(ref mut tr, _) => tr,
  92             clean::GenericBound::Outlives(..) => return false,
  93         };
  94         // If this QPath's trait `trait_did` is the same as, or a supertrait
  95         // of, the bound's trait `did` then we can keep going, otherwise
  96         // this is just a plain old equality bound.
  97         if !trait_is_same_or_supertrait(cx, trait_ref.trait_.def_id(), trait_did) {
  98             return false;
  99         }
 100         let last = trait_ref.trait_.segments.last_mut().expect("segments were empty");
 101         match last.args {
 102             PP::AngleBracketed { ref mut bindings, .. } => {
 103                 bindings.push(clean::TypeBinding {
 104                     assoc: assoc.clone(),
 105                     kind: clean::TypeBindingKind::Equality { term: rhs.clone() },
 106                 });
 107             }
 108             PP::Parenthesized { ref mut output, .. } => match output {
 109                 Some(o) => assert_eq!(&clean::Term::Type(o.as_ref().clone()), rhs),
 110                 None => {
 111                     if *rhs != clean::Term::Type(clean::Type::Tuple(Vec::new())) {
 112                         *output = Some(Box::new(rhs.ty().unwrap().clone()));
 113                     }
 114                 }
 115             },
 116         };
 117         true
 118     })
 119 }
 120
 121 fn trait_is_same_or_supertrait(cx: &DocContext<'_>, child: DefId, trait_: DefId) -> bool {
 122     if child == trait_ {
 123         return true;
 124     }
 125     let predicates = cx.tcx.super_predicates_of(child);
 126     debug_assert!(cx.tcx.generics_of(child).has_self);
 127     let self_ty = cx.tcx.types.self_param;
 128     predicates
 129         .predicates
 130         .iter()
 131         .filter_map(|(pred, _)| {
 132             if let ty::PredicateKind::Trait(pred) = pred.kind().skip_binder() {
 133                 if pred.trait_ref.self_ty() == self_ty { Some(pred.def_id()) } else { None }
 134             } else {
 135                 None
 136             }
 137         })
 138         .any(|did| trait_is_same_or_supertrait(cx, did, trait_))
 139 }