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|
//! Simplification of where-clauses and parameter bounds into a prettier and
//! more canonical form.
//!
//! Currently all cross-crate-inlined function use `rustc_middle::ty` to reconstruct
//! the AST (e.g., see all of `clean::inline`), but this is not always a
//! non-lossy transformation. The current format of storage for where-clauses
//! for functions and such is simply a list of predicates. One example of this
//! is that the AST predicate of: `where T: Trait<Foo = Bar>` is encoded as:
//! `where T: Trait, <T as Trait>::Foo = Bar`.
//!
//! This module attempts to reconstruct the original where and/or parameter
//! bounds by special casing scenarios such as these. Fun!
use rustc_data_structures::fx::FxIndexMap;
use rustc_hir::def_id::DefId;
use rustc_middle::ty;
use rustc_span::Symbol;
use crate::clean;
use crate::clean::GenericArgs as PP;
use crate::clean::WherePredicate as WP;
use crate::core::DocContext;
pub(crate) fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> Vec<WP> {
// First, partition the where clause into its separate components.
//
// We use `FxIndexMap` so that the insertion order is preserved to prevent messing up to
// the order of the generated bounds.
let mut params: FxIndexMap<Symbol, (Vec<_>, Vec<_>)> = FxIndexMap::default();
let mut lifetimes = Vec::new();
let mut equalities = Vec::new();
let mut tybounds = Vec::new();
for clause in clauses {
match clause {
WP::BoundPredicate { ty, bounds, bound_params } => match ty {
clean::Generic(s) => {
let (b, p) = params.entry(s).or_default();
b.extend(bounds);
p.extend(bound_params);
}
t => tybounds.push((t, (bounds, bound_params))),
},
WP::RegionPredicate { lifetime, bounds } => {
lifetimes.push((lifetime, bounds));
}
WP::EqPredicate { lhs, rhs } => equalities.push((lhs, rhs)),
}
}
// Look for equality predicates on associated types that can be merged into
// general bound predicates
equalities.retain(|&(ref lhs, ref rhs)| {
let Some((self_, trait_did, name)) = lhs.projection() else {
return true;
};
let clean::Generic(generic) = self_ else { return true };
let Some((bounds, _)) = params.get_mut(generic) else { return true };
merge_bounds(cx, bounds, trait_did, name, rhs)
});
// And finally, let's reassemble everything
let mut clauses = Vec::new();
clauses.extend(
lifetimes.into_iter().map(|(lt, bounds)| WP::RegionPredicate { lifetime: lt, bounds }),
);
clauses.extend(params.into_iter().map(|(k, (bounds, params))| WP::BoundPredicate {
ty: clean::Generic(k),
bounds,
bound_params: params,
}));
clauses.extend(tybounds.into_iter().map(|(ty, (bounds, bound_params))| WP::BoundPredicate {
ty,
bounds,
bound_params,
}));
clauses.extend(equalities.into_iter().map(|(lhs, rhs)| WP::EqPredicate { lhs, rhs }));
clauses
}
pub(crate) fn merge_bounds(
cx: &clean::DocContext<'_>,
bounds: &mut Vec<clean::GenericBound>,
trait_did: DefId,
assoc: clean::PathSegment,
rhs: &clean::Term,
) -> bool {
!bounds.iter_mut().any(|b| {
let trait_ref = match *b {
clean::GenericBound::TraitBound(ref mut tr, _) => tr,
clean::GenericBound::Outlives(..) => return false,
};
// If this QPath's trait `trait_did` is the same as, or a supertrait
// of, the bound's trait `did` then we can keep going, otherwise
// this is just a plain old equality bound.
if !trait_is_same_or_supertrait(cx, trait_ref.trait_.def_id(), trait_did) {
return false;
}
let last = trait_ref.trait_.segments.last_mut().expect("segments were empty");
match last.args {
PP::AngleBracketed { ref mut bindings, .. } => {
bindings.push(clean::TypeBinding {
assoc: assoc.clone(),
kind: clean::TypeBindingKind::Equality { term: rhs.clone() },
});
}
PP::Parenthesized { ref mut output, .. } => match output {
Some(o) => assert_eq!(&clean::Term::Type(o.as_ref().clone()), rhs),
None => {
if *rhs != clean::Term::Type(clean::Type::Tuple(Vec::new())) {
*output = Some(Box::new(rhs.ty().unwrap().clone()));
}
}
},
};
true
})
}
fn trait_is_same_or_supertrait(cx: &DocContext<'_>, child: DefId, trait_: DefId) -> bool {
if child == trait_ {
return true;
}
let predicates = cx.tcx.super_predicates_of(child);
debug_assert!(cx.tcx.generics_of(child).has_self);
let self_ty = cx.tcx.types.self_param;
predicates
.predicates
.iter()
.filter_map(|(pred, _)| {
if let ty::PredicateKind::Trait(pred) = pred.kind().skip_binder() {
if pred.trait_ref.self_ty() == self_ty { Some(pred.def_id()) } else { None }
} else {
None
}
})
.any(|did| trait_is_same_or_supertrait(cx, did, trait_))
}
|
