TraitImpl blocks have a different CanonicalPath to normal impl blocks

TraitImpls have a canonical path which is a trait projection such as

```rust
pub trait Trait { // ::a::Trait
  fn f(&self); // ::a::Trait::f
}

impl Trait for Struct {
   fn f(&self) {} // <::a::Struct as ::a::Trait>::f
}
```

3 files changed, 29 insertions, 2 deletions

diff --git a/gcc/rust/resolve/rust-ast-resolve-toplevel.h b/gcc/rust/resolve/rust-ast-resolve-toplevel.h
index 0893224..3dd81d8 100644
--- a/gcc/rust/resolve/rust-ast-resolve-toplevel.h
+++ b/gcc/rust/resolve/rust-ast-resolve-toplevel.h
@@ -149,11 +149,19 @@ public:
   {
     bool canonicalize_type_args = !impl_block.has_generics ();
     bool type_resolve_generic_args = false;
-    CanonicalPath impl_type
+
+    CanonicalPath impl_type_seg
       = ResolveTypeToCanonicalPath::resolve (*impl_block.get_type ().get (),
 					     canonicalize_type_args,
 					     type_resolve_generic_args);
-    CanonicalPath impl_prefix = prefix.append (impl_type);
+    CanonicalPath trait_type_seg
+      = ResolveTypeToCanonicalPath::resolve (impl_block.get_trait_path (),
+					     canonicalize_type_args,
+					     type_resolve_generic_args);
+
+    CanonicalPath projection
+      = TraitImplProjection::resolve (trait_type_seg, impl_type_seg);
+    CanonicalPath impl_prefix = prefix.append (projection);
 
     for (auto &impl_item : impl_block.get_impl_items ())
       ResolveToplevelImplItem::go (impl_item.get (), impl_prefix);
diff --git a/gcc/rust/resolve/rust-ast-resolve-type.h b/gcc/rust/resolve/rust-ast-resolve-type.h
index 05b347c3..6d40517 100644
--- a/gcc/rust/resolve/rust-ast-resolve-type.h
+++ b/gcc/rust/resolve/rust-ast-resolve-type.h
@@ -162,6 +162,17 @@ public:
   }
 };
 
+class TraitImplProjection
+{
+public:
+  static CanonicalPath resolve (const CanonicalPath &trait_seg,
+				const CanonicalPath &impl_type_seg)
+  {
+    return CanonicalPath ("<" + impl_type_seg.get () + " as " + trait_seg.get ()
+			  + ">");
+  }
+};
+
 // FIXME: as part of imports and visibility we need to be able to keep a context
 // for handling PathInExpressions segments as they can be local to a particular
 // lexical scope requiring a context to be maintained for resolution
diff --git a/gcc/rust/resolve/rust-name-resolver.h b/gcc/rust/resolve/rust-name-resolver.h
index e45847e..b1f745e 100644
--- a/gcc/rust/resolve/rust-name-resolver.h
+++ b/gcc/rust/resolve/rust-name-resolver.h
@@ -36,6 +36,14 @@ namespace Resolver {
 // impl X<T>   { fn test - path X::test}
 // impl X<i32> { fn test - path X<i32>::test }
 // impl X<f32> { fn test - path X<f32>::test }
+//
+// pub trait Trait { // ::a::Trait
+//   fn f(&self); // ::a::Trait::f
+// }
+//
+// impl Trait for Struct {
+//    fn f(&self) {} // <::a::Struct as ::a::Trait>::f
+// }
 class CanonicalPath
 {
 public: