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Handle associated type shorthand (T::Item)

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This is only allowed for generic parameters (including `Self` in traits), and
special care needs to be taken to not run into cycles while resolving it,
because we use the where clauses of the generic parameter to find candidates for
the trait containing the associated type, but the where clauses may themselves
contain instances of short-hand associated types.

In some cases this is even fine, e.g. we might have `T: Trait<U::Item>, U:
Iterator`. If there is a cycle, we'll currently panic, which isn't great, but
better than overflowing the stack...
This commit is contained in:
Florian Diebold 2019-09-22 20:01:12 +02:00
parent 468e1d14c1
commit 18bf278c25
7 changed files with 538 additions and 392 deletions
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11
crates/ra_hir/src/generics.rs
View file

@ -26,8 +26,9 @@ pub struct GenericParam {
}
/// Data about the generic parameters of a function, struct, impl, etc.
#[derive(Clone, PartialEq, Eq, Debug, Default)]
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct GenericParams {
pub(crate) def: GenericDef,
pub(crate) parent_params: Option<Arc<GenericParams>>,
pub(crate) params: Vec<GenericParam>,
pub(crate) where_predicates: Vec<WherePredicate>,
@ -69,7 +70,6 @@ impl GenericParams {
db: &(impl DefDatabase + AstDatabase),
def: GenericDef,
) -> Arc<GenericParams> {
let mut generics = GenericParams::default();
let parent = match def {
GenericDef::Function(it) => it.container(db).map(GenericDef::from),
GenericDef::TypeAlias(it) => it.container(db).map(GenericDef::from),
@ -77,7 +77,12 @@ impl GenericParams {
GenericDef::Adt(_) | GenericDef::Trait(_) => None,
GenericDef::ImplBlock(_) => None,
};
generics.parent_params = parent.map(|p| db.generic_params(p));
let mut generics = GenericParams {
def,
params: Vec::new(),
parent_params: parent.map(|p| db.generic_params(p)),
where_predicates: Vec::new(),
};
let start = generics.parent_params.as_ref().map(|p| p.params.len()).unwrap_or(0) as u32;
// FIXME: add `: Sized` bound for everything except for `Self` in traits
match def {