Resolve module final self segment in use decls

Lowercase self suffix with path was not resolved properly, this should
point to the module right before.

gcc/rust/ChangeLog:

	* resolve/rust-forever-stack.hxx: Add a new specialized function
	to retrieve the last "real" segment depending on the namespace.
	* resolve/rust-forever-stack.h: Add new function prototype.
	* resolve/rust-early-name-resolver-2.0.cc (Early::finalize_rebind_import):
	Set declared name according to the selected segment, if there is a self
	suffix in the use declaration then select the previous segment.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

Author: P-E-P

gcc/rust/resolve/rust-early-name-resolver-2.0.cc

@@ -417,10 +417,19 @@ Early::finalize_rebind_import (const Early::ImportPair &mapping)
       declared_name = rebind.get_identifier ().as_string ();
       locus = rebind.get_identifier ().get_locus ();
       break;
-    case AST::UseTreeRebind::NewBindType::NONE:
-      declared_name = path.get_final_segment ().as_string ();
-      locus = path.get_final_segment ().get_locus ();
-      break;
+      case AST::UseTreeRebind::NewBindType::NONE: {
+	const auto &segments = path.get_segments ();
+	// We don't want to insert `self` with `use module::self`
+	if (path.get_final_segment ().is_lower_self_seg ())
+	  {
+	    rust_assert (segments.size () > 1);
+	    declared_name = segments[segments.size () - 2].as_string ();
+	  }
+	else
+	  declared_name = path.get_final_segment ().as_string ();
+	locus = path.get_final_segment ().get_locus ();
+	break;
+      }
     case AST::UseTreeRebind::NewBindType::WILDCARD:
       rust_unreachable ();
       break;

gcc/rust/resolve/rust-forever-stack.h

@@ -795,6 +795,10 @@ template <Namespace N> class ForeverStack
     SegIterator<S> iterator,
     std::function<void (const S &, NodeId)> insert_segment_resolution);
 
+  tl::optional<Rib::Definition> resolve_final_segment (Node &final_node,
+						       std::string &seg_name,
+						       bool is_lower_self);
+
   /* Helper functions for forward resolution (to_canonical_path, to_rib...) */
   struct DfsResult
   {

gcc/rust/resolve/rust-forever-stack.hxx

@@ -594,6 +594,26 @@ ForeverStack<N>::resolve_segments (
   return *current_node;
 }
 
+template <>
+inline tl::optional<Rib::Definition>
+ForeverStack<Namespace::Types>::resolve_final_segment (Node &final_node,
+						       std::string &seg_name,
+						       bool is_lower_self)
+{
+  if (is_lower_self)
+    return Rib::Definition::NonShadowable (final_node.id);
+  else
+    return final_node.rib.get (seg_name);
+}
+
+template <Namespace N>
+tl::optional<Rib::Definition>
+ForeverStack<N>::resolve_final_segment (Node &final_node, std::string &seg_name,
+					bool is_lower_self)
+{
+  return final_node.rib.get (seg_name);
+}
+
 template <Namespace N>
 template <typename S>
 tl::optional<Rib::Definition>
@@ -643,12 +663,13 @@ ForeverStack<N>::resolve_path (
       if (final_node.rib.kind == Rib::Kind::TraitOrImpl)
 	return tl::nullopt;
 
-      std::string seg_name
-	= unwrap_type_segment (segments.back ()).as_string ();
+      auto &seg = unwrap_type_segment (segments.back ());
+      std::string seg_name = seg.as_string ();
 
       // assuming this can't be a lang item segment
-      tl::optional<Rib::Definition> res = final_node.rib.get (seg_name);
-
+      tl::optional<Rib::Definition> res
+	= resolve_final_segment (final_node, seg_name,
+				 seg.is_lower_self_seg ());
       // Ok we didn't find it in the rib, Lets try the prelude...
       if (!res)
 	res = get_prelude (seg_name);