More trait infrastructure

 - make it possible to get parent trait from method
 - add 'obligation' machinery for checking that a type implements a
   trait (and inferring facts about type variables from that)
 - handle type parameters of traits (to a certain degree)
 - improve the hacky implements check to cover enough cases to exercise the
   handling of traits with type parameters
 - basic canonicalization (will probably also be done by Chalk)

1 files changed, 11 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index ecf13fbc3..aa43bc800 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -5,6 +5,7 @@ mod autoderef;
 pub(crate) mod primitive;
 #[cfg(test)]
 mod tests;
+pub(crate) mod traits;
 pub(crate) mod method_resolution;
 mod op;
 mod lower;
@@ -145,6 +146,10 @@ impl Substs {
         Substs(Arc::new([ty]))
     }
 
+    pub fn prefix(&self, n: usize) -> Substs {
+        Substs(self.0.iter().cloned().take(n).collect::<Vec<_>>().into())
+    }
+
     pub fn iter(&self) -> impl Iterator<Item = &Ty> {
         self.0.iter()
     }
@@ -170,6 +175,12 @@ impl Substs {
     }
 }
 
+impl From<Vec<Ty>> for Substs {
+    fn from(v: Vec<Ty>) -> Self {
+        Substs(v.into())
+    }
+}
+
 /// A trait with type parameters. This includes the `Self`, so this represents a concrete type implementing the trait.
 /// Name to be bikeshedded: TraitBound? TraitImplements?
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]