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.

4 files changed, 75 insertions, 14 deletions

diff --git a/gcc/rust/expand/rust-macro-expand.cc b/gcc/rust/expand/rust-macro-expand.cc
index 0b01ede..7829757 100644
--- a/gcc/rust/expand/rust-macro-expand.cc
+++ b/gcc/rust/expand/rust-macro-expand.cc
@@ -23,6 +23,7 @@
 #include "rust-ast-full.h"
 #include "rust-ast-visitor.h"
 #include "rust-diagnostics.h"
+#include "rust-macro.h"
 #include "rust-parse.h"
 #include "rust-cfg-strip.h"
 #include "rust-early-name-resolver.h"
@@ -118,7 +119,7 @@ MacroExpander::expand_decl_macro (location_t invoc_locus,
   for (auto &ent : matched_fragments)
     matched_fragments_ptr.emplace (ent.first, ent.second.get ());
 
-  return transcribe_rule (*matched_rule, invoc_token_tree,
+  return transcribe_rule (rules_def, *matched_rule, invoc_token_tree,
 			  matched_fragments_ptr, semicolon, peek_context ());
 }
 
@@ -1023,7 +1024,8 @@ tokens_to_str (std::vector<std::unique_ptr<AST::Token>> &tokens)
 
 AST::Fragment
 MacroExpander::transcribe_rule (
-  AST::MacroRule &match_rule, AST::DelimTokenTree &invoc_token_tree,
+  AST::MacroRulesDefinition &definition, AST::MacroRule &match_rule,
+  AST::DelimTokenTree &invoc_token_tree,
   std::map<std::string, MatchedFragmentContainer *> &matched_fragments,
   AST::InvocKind invoc_kind, ContextType ctx)
 {
@@ -1037,8 +1039,8 @@ MacroExpander::transcribe_rule (
   auto invoc_stream = invoc_token_tree.to_token_stream ();
   auto macro_rule_tokens = transcribe_tree.to_token_stream ();
 
-  auto substitute_context
-    = SubstituteCtx (invoc_stream, macro_rule_tokens, matched_fragments);
+  auto substitute_context = SubstituteCtx (invoc_stream, macro_rule_tokens,
+					   matched_fragments, definition);
   std::vector<std::unique_ptr<AST::Token>> substituted_tokens
     = substitute_context.substitute_tokens ();
 
diff --git a/gcc/rust/expand/rust-macro-expand.h b/gcc/rust/expand/rust-macro-expand.h
index c186f3d..3948e44 100644
--- a/gcc/rust/expand/rust-macro-expand.h
+++ b/gcc/rust/expand/rust-macro-expand.h
@@ -331,7 +331,8 @@ struct MacroExpander
 		       AST::DelimTokenTree &invoc_token_tree);
 
   AST::Fragment transcribe_rule (
-    AST::MacroRule &match_rule, AST::DelimTokenTree &invoc_token_tree,
+    AST::MacroRulesDefinition &definition, AST::MacroRule &match_rule,
+    AST::DelimTokenTree &invoc_token_tree,
     std::map<std::string, MatchedFragmentContainer *> &matched_fragments,
     AST::InvocKind invoc_kind, ContextType ctx);
 
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
diff --git a/gcc/rust/expand/rust-macro-substitute-ctx.h b/gcc/rust/expand/rust-macro-substitute-ctx.h
index 835f48a..7e0175a 100644
--- a/gcc/rust/expand/rust-macro-substitute-ctx.h
+++ b/gcc/rust/expand/rust-macro-substitute-ctx.h
@@ -18,6 +18,7 @@
 
 #include "rust-ast.h"
 #include "rust-macro-expand.h"
+#include "rust-macro.h"
 
 namespace Rust {
 class SubstituteCtx
@@ -25,6 +26,7 @@ class SubstituteCtx
   std::vector<std::unique_ptr<AST::Token>> &input;
   std::vector<std::unique_ptr<AST::Token>> &macro;
   std::map<std::string, MatchedFragmentContainer *> &fragments;
+  AST::MacroRulesDefinition &definition;
 
   /**
    * Find the repetition amount to use when expanding a repetition, and
@@ -40,11 +42,28 @@ class SubstituteCtx
 public:
   SubstituteCtx (std::vector<std::unique_ptr<AST::Token>> &input,
 		 std::vector<std::unique_ptr<AST::Token>> &macro,
-		 std::map<std::string, MatchedFragmentContainer *> &fragments)
-    : input (input), macro (macro), fragments (fragments)
+		 std::map<std::string, MatchedFragmentContainer *> &fragments,
+		 AST::MacroRulesDefinition &definition)
+    : input (input), macro (macro), fragments (fragments),
+      definition (definition)
   {}
 
   /**
+   * Special-case the $crate metavar to expand to the name of the crate in which
+   * the macro was defined.
+   *
+   * https://doc.rust-lang.org/reference/macros-by-example.html#r-macro.decl.hygiene.crate
+   *
+   *
+   * @param expanded Reference to a vector upon which expanded tokens will be
+   * pushed
+   *
+   * @return True if the substitution succeeded
+   */
+  bool
+  substitute_dollar_crate (std::vector<std::unique_ptr<AST::Token>> &expanded);
+
+  /**
    * Substitute a metavariable by its given fragment in a transcribing context,
    * i.e. replacing $var with the associated fragment.
    *
@@ -52,7 +71,7 @@ public:
    * @param expanded Reference to a vector upon which expanded tokens will be
    * pushed
    *
-   * @return True iff the substitution succeeded
+   * @return True if the substitution succeeded
    */
   bool substitute_metavar (std::unique_ptr<AST::Token> &metavar,
 			   std::vector<std::unique_ptr<AST::Token>> &expanded);