expansion: Correctly expand $crate metavar

gcc/rust/ChangeLog:

	* expand/rust-macro-expand.cc: Use new SubstituteCtx API.
	* expand/rust-macro-expand.h: Likewise.
	* expand/rust-macro-substitute-ctx.cc: Implement proper expansion of $crate.
	* expand/rust-macro-substitute-ctx.h: Adapt APIs to take macro definition when
	substituting.
	* util/rust-hir-map.cc (Mappings::insert_macro_def): Store crate information when
	inserting macro definition in mappings.
	(Mappings::lookup_macro_def_crate): New.
	* util/rust-hir-map.h: Adapt mappings to store crate in which macros were defined.

gcc/testsuite/ChangeLog:

	* rust/execute/crate-metavar1.rs: New test.
	* rust/compile/crate-metavar1.rs: New test.

1 files changed, 45 insertions, 6 deletions

diff --git a/gcc/rust/expand/rust-macro-substitute-ctx.cc b/gcc/rust/expand/rust-macro-substitute-ctx.cc
index 03709a1..9eb2d92 100644
--- a/gcc/rust/expand/rust-macro-substitute-ctx.cc
+++ b/gcc/rust/expand/rust-macro-substitute-ctx.cc
@@ -17,10 +17,47 @@
 // <http://www.gnu.org/licenses/>.
 
 #include "rust-macro-substitute-ctx.h"
+#include "input.h"
+#include "rust-hir-map.h"
+#include "rust-token.h"
 
 namespace Rust {
 
 bool
+SubstituteCtx::substitute_dollar_crate (
+  std::vector<std::unique_ptr<AST::Token>> &expanded)
+{
+  auto &mappings = Analysis::Mappings::get ();
+
+  auto def_crate = mappings.lookup_macro_def_crate (definition.get_node_id ());
+  auto current_crate = mappings.get_current_crate ();
+
+  rust_assert (def_crate);
+
+  // If we're expanding a macro defined in the current crate which uses $crate,
+  // we can just replace the metavar with the `crate` path segment. Otherwise,
+  // use the fully qualified extern-crate lookup path `::<crate_name>`
+  if (*def_crate == current_crate)
+    {
+      expanded.push_back (std::make_unique<AST::Token> (
+	Rust::Token::make_identifier (UNKNOWN_LOCATION, "crate")));
+    }
+  else
+    {
+      auto name = mappings.get_crate_name (*def_crate);
+
+      rust_assert (name);
+
+      expanded.push_back (std::make_unique<AST::Token> (
+	Rust::Token::make (SCOPE_RESOLUTION, UNKNOWN_LOCATION)));
+      expanded.push_back (std::make_unique<AST::Token> (
+	Rust::Token::make_identifier (UNKNOWN_LOCATION, std::string (*name))));
+    }
+
+  return true;
+}
+
+bool
 SubstituteCtx::substitute_metavar (
   std::unique_ptr<AST::Token> &metavar,
   std::vector<std::unique_ptr<AST::Token>> &expanded)
@@ -30,14 +67,15 @@ SubstituteCtx::substitute_metavar (
   auto it = fragments.find (metavar_name);
   if (it == fragments.end ())
     {
-      // fail to substitute
+      // fail to substitute, unless we are dealing with a special-case metavar
+      // like $crate
 
-      // HACK: substitute ($ crate) => (crate)
-      if (metavar->get_id () != CRATE)
-	return false;
+      if (metavar->get_id () == CRATE)
+	return substitute_dollar_crate (expanded);
 
       expanded.push_back (metavar->clone_token ());
-      return true;
+
+      return false;
     }
   else
     {
@@ -187,7 +225,8 @@ SubstituteCtx::substitute_repetition (
 			     kv_match.second->get_fragments ().at (i).get ());
 	}
 
-      auto substitute_context = SubstituteCtx (input, new_macro, sub_map);
+      auto substitute_context
+	= SubstituteCtx (input, new_macro, sub_map, definition);
       auto new_tokens = substitute_context.substitute_tokens ();
 
       // Skip the first repetition, but add the separator to the expanded