nr: Do prelude resolution for Identifiers

gcc/rust/ChangeLog:

	* resolve/rust-forever-stack.h: New function.
	* resolve/rust-forever-stack.hxx: Implement it.
	* resolve/rust-late-name-resolver-2.0.cc (Late::visit): Call it if the prelude exists
	and we have an unresolved Identifier Call it if the prelude exists and we have
	an unresolved Identifier.

Author: CohenArthur

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

@@ -668,6 +668,8 @@ template <Namespace N> class ForeverStack
   tl::optional<Rib::Definition> get (const Identifier &name);
   tl::optional<Rib::Definition> get_lang_prelude (const Identifier &name);
   tl::optional<Rib::Definition> get_lang_prelude (const std::string &name);
+  tl::optional<Rib::Definition> get_from_prelude (NodeId prelude,
+						  const Identifier &name);
 
   /**
    * Resolve a path to its definition in the current `ForeverStack`

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

@@ -343,6 +343,17 @@ ForeverStack<N>::get_lang_prelude (const std::string &name)
   return lang_prelude.rib.get (name);
 }
 
+template <Namespace N>
+tl::optional<Rib::Definition>
+ForeverStack<N>::get_from_prelude (NodeId prelude, const Identifier &name)
+{
+  auto starting_point = dfs_node (root, prelude);
+  if (!starting_point)
+    return tl::nullopt;
+
+  return get (*starting_point, name);
+}
+
 template <>
 tl::optional<Rib::Definition> inline ForeverStack<Namespace::Labels>::get (
   const Identifier &name)

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

@@ -348,7 +348,17 @@ Late::visit (AST::IdentifierExpr &expr)
 	{
 	  resolved = type;
 	}
-      else
+      else if (!resolved && ctx.prelude)
+	{
+	  resolved
+	    = ctx.values.get_from_prelude (*ctx.prelude, expr.get_ident ());
+
+	  if (!resolved)
+	    resolved
+	      = ctx.types.get_from_prelude (*ctx.prelude, expr.get_ident ());
+	}
+
+      if (!resolved)
 	{
 	  rust_error_at (expr.get_locus (), ErrorCode::E0425,
 			 "cannot find value %qs in this scope",