[committed 05/88] gccrs: Implement declarative macro 2.0 parser

[arthur.cohen@embecosm.com]

From: Raiki Tamura <tamaron1203@gmail.com>

gcc/rust/ChangeLog:

	* ast/rust-ast-full-decls.h (class MacroItem): Remove forward declaration.
	* ast/rust-ast-full-test.cc (MacroRulesDefinition):
	Rework MacroRulesDefinition class
	* ast/rust-ast.h (class MacroItem): Remove abstract class.
	* ast/rust-item.h (class MacroItem): Remove forward declaration.
	* ast/rust-macro.h (class MacroItem): Likewise.
	(class MacroRulesDefinition): Add MacroKind enum.
	(class MacroInvocation): Fix inheritance.
	* lex/rust-token.h: Token "macro" is now used.
	* parse/rust-parse-impl.h (Parser::parse_item): Add handling for MACRO.
	(Parser::parse_vis_item): Call into parse_decl_macro_def.
	(Parser::parse_macro_item): Delete function.
	(Parser::parse_macro_rules_def): Return MBE macros only.
	(Parser::parse_decl_macro_def): New function.
	(Parser::parse_stmt): Handle MACRO token.
	(Parser::parse_stmt_or_expr_without_block): Call into parse_macro_rules_def.
	* parse/rust-parse.h: Declare new function.

gcc/testsuite/ChangeLog:

	* rust/compile/decl_macro1.rs: New test.
	* rust/compile/decl_macro2.rs: New test.
	* rust/compile/decl_macro3.rs: New test.
	* rust/compile/decl_macro4.rs: New test.
	* rust/compile/decl_macro5.rs: New test.
	* rust/compile/decl_macro6.rs: New test.
	* rust/compile/decl_macro7.rs: New test.
	* rust/execute/torture/decl_macro1.rs: New test.
	* rust/execute/torture/decl_macro2.rs: New test.
	* rust/execute/torture/decl_macro3.rs: New test.
	* rust/execute/torture/decl_macro4.rs: New test.

Signed-off-by: Raiki Tamura <tamaron1203@gmail.com>
---
 gcc/rust/ast/rust-ast-full-decls.h            |   1 -
 gcc/rust/ast/rust-ast-full-test.cc            |   1 +
 gcc/rust/ast/rust-ast.h                       |   5 -
 gcc/rust/ast/rust-item.h                      |   2 -
 gcc/rust/ast/rust-macro.h                     |  65 +++--
 gcc/rust/lex/rust-token.h                     |   2 +-
 gcc/rust/parse/rust-parse-impl.h              | 229 +++++++++++++-----
 gcc/rust/parse/rust-parse.h                   |   3 +-
 gcc/testsuite/rust/compile/decl_macro1.rs     |   2 +
 gcc/testsuite/rust/compile/decl_macro2.rs     |   2 +
 gcc/testsuite/rust/compile/decl_macro3.rs     |   4 +
 gcc/testsuite/rust/compile/decl_macro4.rs     |   5 +
 gcc/testsuite/rust/compile/decl_macro5.rs     |   5 +
 gcc/testsuite/rust/compile/decl_macro6.rs     |   5 +
 gcc/testsuite/rust/compile/decl_macro7.rs     |   4 +
 .../rust/execute/torture/decl_macro1.rs       |   8 +
 .../rust/execute/torture/decl_macro2.rs       |   8 +
 .../rust/execute/torture/decl_macro3.rs       |  15 ++
 .../rust/execute/torture/decl_macro4.rs       |  15 ++
 19 files changed, 301 insertions(+), 80 deletions(-)
 create mode 100644 gcc/testsuite/rust/compile/decl_macro1.rs
 create mode 100644 gcc/testsuite/rust/compile/decl_macro2.rs
 create mode 100644 gcc/testsuite/rust/compile/decl_macro3.rs
 create mode 100644 gcc/testsuite/rust/compile/decl_macro4.rs
 create mode 100644 gcc/testsuite/rust/compile/decl_macro5.rs
 create mode 100644 gcc/testsuite/rust/compile/decl_macro6.rs
 create mode 100644 gcc/testsuite/rust/compile/decl_macro7.rs
 create mode 100644 gcc/testsuite/rust/execute/torture/decl_macro1.rs
 create mode 100644 gcc/testsuite/rust/execute/torture/decl_macro2.rs
 create mode 100644 gcc/testsuite/rust/execute/torture/decl_macro3.rs
 create mode 100644 gcc/testsuite/rust/execute/torture/decl_macro4.rs

diff --git a/gcc/rust/ast/rust-ast-full-decls.h b/gcc/rust/ast/rust-ast-full-decls.h
index 136a25ab9aa..58b12a1be0e 100644
--- a/gcc/rust/ast/rust-ast-full-decls.h
+++ b/gcc/rust/ast/rust-ast-full-decls.h
@@ -51,7 +51,6 @@ class Lifetime;
 class GenericParam;
 class LifetimeParam;
 class ConstGenericParam;
-class MacroItem;
 class TraitItem;
 class InherentImplItem;
 class TraitImplItem;
diff --git a/gcc/rust/ast/rust-ast-full-test.cc b/gcc/rust/ast/rust-ast-full-test.cc
index 4f593dcbd49..280f59ffb16 100644
--- a/gcc/rust/ast/rust-ast-full-test.cc
+++ b/gcc/rust/ast/rust-ast-full-test.cc
@@ -1284,6 +1284,7 @@ MacroRulesDefinition::as_string () const
   // get outer attrs
   str += append_attributes (outer_attrs, OUTER);
 
+  // TODO: deal with macro_2_0
   str += "macro_rules!";
 
   str += rule_name;
diff --git a/gcc/rust/ast/rust-ast.h b/gcc/rust/ast/rust-ast.h
index aa86f2f9826..5f18233eb0f 100644
--- a/gcc/rust/ast/rust-ast.h
+++ b/gcc/rust/ast/rust-ast.h
@@ -1350,11 +1350,6 @@ protected:
   }
 };
 
-// A macro item AST node - abstract base class
-class MacroItem : public Item
-{
-};
-
 // Item used in trait declarations - abstract base class
 class TraitItem
 {
diff --git a/gcc/rust/ast/rust-item.h b/gcc/rust/ast/rust-item.h
index 7ea7b86562f..37ed2beabfc 100644
--- a/gcc/rust/ast/rust-item.h
+++ b/gcc/rust/ast/rust-item.h
@@ -4391,8 +4391,6 @@ protected:
   }
 };
 
-// Replaced with forward decls - defined in "rust-macro.h"
-class MacroItem;
 class MacroRulesDefinition;
 } // namespace AST
 } // namespace Rust
diff --git a/gcc/rust/ast/rust-macro.h b/gcc/rust/ast/rust-macro.h
index fc4b5b82fb5..bff8c7ac6fb 100644
--- a/gcc/rust/ast/rust-macro.h
+++ b/gcc/rust/ast/rust-macro.h
@@ -23,13 +23,11 @@
 #include "rust-ast.h"
 #include "rust-ast-fragment.h"
 #include "rust-location.h"
+#include "rust-item.h"
+#include "rust-make-unique.h"
 
 namespace Rust {
 namespace AST {
-
-// Decls as definitions moved to rust-ast.h
-class MacroItem;
-
 class MacroFragSpec
 {
 public:
@@ -446,8 +444,18 @@ public:
 };
 
 // A macro rules definition item AST node
-class MacroRulesDefinition : public MacroItem
+class MacroRulesDefinition : public VisItem
 {
+public:
+  enum MacroKind
+  {
+    // Macro by Example (legacy macro rules)
+    MBE,
+    // Declarative macros 2.0
+    DeclMacro,
+  };
+
+private:
   std::vector<Attribute> outer_attrs;
   Identifier rule_name;
   // MacroRulesDef rules_def;
@@ -460,6 +468,7 @@ class MacroRulesDefinition : public MacroItem
   std::function<Fragment (Location, MacroInvocData &)> associated_transcriber;
   // Since we can't compare std::functions, we need to use an extra boolean
   bool is_builtin_rule;
+  MacroKind kind;
 
   /**
    * Default function to use as an associated transcriber. This function should
@@ -479,27 +488,51 @@ class MacroRulesDefinition : public MacroItem
    * I am not aware of the implications of this decision. The rustc spec does
    * mention that using the same parser for macro definitions and invocations
    * is "extremely self-referential and non-intuitive". */
-
-public:
-  std::string as_string () const override;
-
   MacroRulesDefinition (Identifier rule_name, DelimType delim_type,
 			std::vector<MacroRule> rules,
-			std::vector<Attribute> outer_attrs, Location locus)
-    : outer_attrs (std::move (outer_attrs)), rule_name (std::move (rule_name)),
+			std::vector<Attribute> outer_attrs, Location locus,
+			MacroKind kind, Visibility vis)
+    : VisItem (std::move (vis), outer_attrs),
+      outer_attrs (std::move (outer_attrs)), rule_name (std::move (rule_name)),
       delim_type (delim_type), rules (std::move (rules)), locus (locus),
-      associated_transcriber (dummy_builtin), is_builtin_rule (false)
+      associated_transcriber (dummy_builtin), is_builtin_rule (false),
+      kind (kind)
   {}
 
   MacroRulesDefinition (
     Identifier builtin_name, DelimType delim_type,
-    std::function<Fragment (Location, MacroInvocData &)> associated_transcriber)
-    : outer_attrs (std::vector<Attribute> ()), rule_name (builtin_name),
+    std::function<Fragment (Location, MacroInvocData &)> associated_transcriber,
+    MacroKind kind, Visibility vis)
+    : VisItem (std::move (vis), std::vector<Attribute> ()),
+      outer_attrs (std::vector<Attribute> ()), rule_name (builtin_name),
       delim_type (delim_type), rules (std::vector<MacroRule> ()),
       locus (Location ()), associated_transcriber (associated_transcriber),
-      is_builtin_rule (true)
+      is_builtin_rule (true), kind (kind)
   {}
 
+public:
+  std::string as_string () const override;
+
+  static std::unique_ptr<MacroRulesDefinition>
+  mbe (Identifier rule_name, DelimType delim_type, std::vector<MacroRule> rules,
+       std::vector<Attribute> outer_attrs, Location locus)
+  {
+    return Rust::make_unique<MacroRulesDefinition> (
+      MacroRulesDefinition (rule_name, delim_type, rules, outer_attrs, locus,
+			    AST::MacroRulesDefinition::MacroKind::MBE,
+			    AST::Visibility::create_error ()));
+  }
+
+  static std::unique_ptr<MacroRulesDefinition>
+  decl_macro (Identifier rule_name, std::vector<MacroRule> rules,
+	      std::vector<Attribute> outer_attrs, Location locus,
+	      Visibility vis)
+  {
+    return Rust::make_unique<MacroRulesDefinition> (MacroRulesDefinition (
+      rule_name, AST::DelimType::CURLY, rules, outer_attrs, locus,
+      AST::MacroRulesDefinition::MacroKind::DeclMacro, vis));
+  }
+
   void accept_vis (ASTVisitor &vis) override;
 
   // Invalid if rule name is empty, so base stripping on that.
@@ -549,7 +582,7 @@ protected:
  * compile time */
 class MacroInvocation : public TypeNoBounds,
 			public Pattern,
-			public MacroItem,
+			public Item,
 			public TraitItem,
 			public TraitImplItem,
 			public InherentImplItem,
diff --git a/gcc/rust/lex/rust-token.h b/gcc/rust/lex/rust-token.h
index 18f1afa664b..0fc55a20beb 100644
--- a/gcc/rust/lex/rust-token.h
+++ b/gcc/rust/lex/rust-token.h
@@ -171,7 +171,7 @@ enum PrimitiveCoreType
   RS_TOKEN_KEYWORD (IN, "in")                                                  \
   RS_TOKEN_KEYWORD (LET, "let")                                                \
   RS_TOKEN_KEYWORD (LOOP, "loop")                                              \
-  RS_TOKEN_KEYWORD (MACRO, "macro") /* unused */                               \
+  RS_TOKEN_KEYWORD (MACRO, "macro")                                            \
   RS_TOKEN_KEYWORD (MATCH_TOK, "match")                                        \
   RS_TOKEN_KEYWORD (MOD, "mod")                                                \
   RS_TOKEN_KEYWORD (MOVE, "move")                                              \
diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index 959e0338a10..d71bafded63 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -1032,11 +1032,6 @@ Parser<ManagedTokenSource>::parse_item (bool called_from_statement)
 
   // parse outer attributes for item
   AST::AttrVec outer_attrs = parse_outer_attributes ();
-
-  // TODO: decide how to deal with VisItem vs MacroItem dichotomy
-  /* best current solution: catch all keywords that would imply a VisItem in a
-   * switch and have MacroItem as a last resort */
-
   const_TokenPtr t = lexer.peek_token ();
 
   switch (t->get_id ())
@@ -1064,6 +1059,7 @@ Parser<ManagedTokenSource>::parse_item (bool called_from_statement)
     case STATIC_TOK:
     case TRAIT:
     case IMPL:
+    case MACRO:
     /* TODO: implement union keyword but not really because of
      * context-dependence crappy hack way to parse a union written below to
      * separate it from the good code. */
@@ -1078,7 +1074,7 @@ Parser<ManagedTokenSource>::parse_item (bool called_from_statement)
     case CRATE:
     case DOLLAR_SIGN:
       // almost certainly macro invocation semi
-      return parse_macro_item (std::move (outer_attrs));
+      return parse_macro_invocation_semi (std::move (outer_attrs));
       break;
     // crappy hack to do union "keyword"
     case IDENTIFIER:
@@ -1092,19 +1088,18 @@ Parser<ManagedTokenSource>::parse_item (bool called_from_statement)
       else if (t->get_str () == "macro_rules")
 	{
 	  // macro_rules! macro item
-	  return parse_macro_item (std::move (outer_attrs));
+	  return parse_macro_rules_def (std::move (outer_attrs));
 	}
       else if (lexer.peek_token (1)->get_id () == SCOPE_RESOLUTION
 	       || lexer.peek_token (1)->get_id () == EXCLAM)
 	{
 	  /* path (probably) or macro invocation, so probably a macro invocation
 	   * semi */
-	  return parse_macro_item (std::move (outer_attrs));
+	  return parse_macro_invocation_semi (std::move (outer_attrs));
 	}
       gcc_fallthrough ();
     default:
       // otherwise unrecognised
-      // return parse_macro_item(std::move(outer_attrs));
       add_error (Error (t->get_locus (),
 			"unrecognised token %qs for start of %s",
 			t->get_token_description (),
@@ -1335,6 +1330,8 @@ Parser<ManagedTokenSource>::parse_vis_item (AST::AttrVec outer_attrs)
 	  lexer.skip_token (1); // TODO: is this right thing to do?
 	  return nullptr;
 	}
+    case MACRO:
+      return parse_decl_macro_def (std::move (vis), std::move (outer_attrs));
     default:
       // otherwise vis item clearly doesn't exist, which is not an error
       // has a catch-all post-switch return to allow other breaks to occur
@@ -1343,42 +1340,6 @@ Parser<ManagedTokenSource>::parse_vis_item (AST::AttrVec outer_attrs)
   return nullptr;
 }
 
-// Parses a MacroItem (either a MacroInvocationSemi or MacroRulesDefinition).
-template <typename ManagedTokenSource>
-std::unique_ptr<AST::MacroItem>
-Parser<ManagedTokenSource>::parse_macro_item (AST::AttrVec outer_attrs)
-{
-  const_TokenPtr t = lexer.peek_token ();
-
-  /* dodgy way of detecting macro due to weird context-dependence thing.
-   * probably can be improved */
-  // TODO: ensure that string compare works properly
-  if (t->get_id () == IDENTIFIER && t->get_str () == "macro_rules")
-    {
-      return parse_macro_rules_def (std::move (outer_attrs));
-    }
-  else
-    {
-      // DEBUG: TODO: remove
-      rust_debug (
-	"DEBUG - parse_macro_item called and token is not macro_rules");
-      if (t->get_id () == IDENTIFIER)
-	{
-	  rust_debug ("just add to last error: token is not macro_rules and is "
-		      "instead '%s'",
-		      t->get_str ().c_str ());
-	}
-      else
-	{
-	  rust_debug ("just add to last error: token is not macro_rules and is "
-		      "not an identifier either - it is '%s'",
-		      t->get_token_description ());
-	}
-
-      return parse_macro_invocation_semi (std::move (outer_attrs));
-    }
-}
-
 // Parses a macro rules definition syntax extension whatever thing.
 template <typename ManagedTokenSource>
 std::unique_ptr<AST::MacroRulesDefinition>
@@ -1512,16 +1473,16 @@ Parser<ManagedTokenSource>::parse_macro_rules_def (AST::AttrVec outer_attrs)
 	    {
 	      // as this is the end, allow recovery (probably) - may change
 	      return std::unique_ptr<AST::MacroRulesDefinition> (
-		new AST::MacroRulesDefinition (
+		AST::MacroRulesDefinition::mbe (
 		  std::move (rule_name), delim_type, std::move (macro_rules),
 		  std::move (outer_attrs), macro_locus));
 	    }
 	}
 
       return std::unique_ptr<AST::MacroRulesDefinition> (
-	new AST::MacroRulesDefinition (std::move (rule_name), delim_type,
-				       std::move (macro_rules),
-				       std::move (outer_attrs), macro_locus));
+	AST::MacroRulesDefinition::mbe (std::move (rule_name), delim_type,
+					std::move (macro_rules),
+					std::move (outer_attrs), macro_locus));
     }
   else
     {
@@ -1541,6 +1502,165 @@ Parser<ManagedTokenSource>::parse_macro_rules_def (AST::AttrVec outer_attrs)
     }
 }
 
+// Parses a declarative macro 2.0 definition.
+template <typename ManagedTokenSource>
+std::unique_ptr<AST::MacroRulesDefinition>
+Parser<ManagedTokenSource>::parse_decl_macro_def (AST::Visibility vis,
+						  AST::AttrVec outer_attrs)
+{
+  // ensure that first token is identifier saying "macro"
+  const_TokenPtr t = lexer.peek_token ();
+  if (t->get_id () != MACRO)
+    {
+      Error error (
+	t->get_locus (),
+	"declarative macro definition does not start with %<macro%>");
+      add_error (std::move (error));
+
+      // skip after somewhere?
+      return nullptr;
+    }
+  lexer.skip_token ();
+  Location macro_locus = t->get_locus ();
+
+  // parse macro name
+  const_TokenPtr ident_tok = expect_token (IDENTIFIER);
+  if (ident_tok == nullptr)
+    {
+      return nullptr;
+    }
+  Identifier rule_name = ident_tok->get_str ();
+
+  t = lexer.peek_token ();
+  if (t->get_id () == LEFT_PAREN)
+    {
+      // single definiton of macro rule
+      // e.g. `macro foo($e:expr) {}`
+
+      // parse macro matcher
+      Location locus = lexer.peek_token ()->get_locus ();
+      AST::MacroMatcher matcher = parse_macro_matcher ();
+      if (matcher.is_error ())
+	return nullptr;
+
+      // check delimiter of macro matcher
+      if (matcher.get_delim_type () != AST::DelimType::PARENS)
+	{
+	  Error error (locus, "only parenthesis can be used for a macro "
+			      "matcher in declarative macro definition");
+	  add_error (std::move (error));
+	  return nullptr;
+	}
+
+      Location transcriber_loc = lexer.peek_token ()->get_locus ();
+      AST::DelimTokenTree delim_tok_tree = parse_delim_token_tree ();
+      AST::MacroTranscriber transcriber (delim_tok_tree, transcriber_loc);
+
+      if (transcriber.get_token_tree ().get_delim_type ()
+	  != AST::DelimType::CURLY)
+	{
+	  Error error (transcriber_loc,
+		       "only braces can be used for a macro transcriber "
+		       "in declarative macro definition");
+	  add_error (std::move (error));
+	  return nullptr;
+	}
+
+      AST::MacroRule macro_rule
+	= AST::MacroRule (std::move (matcher), std::move (transcriber), locus);
+      std::vector<AST::MacroRule> macro_rules;
+      macro_rules.push_back (macro_rule);
+
+      return std::unique_ptr<AST::MacroRulesDefinition> (
+	AST::MacroRulesDefinition::decl_macro (std::move (rule_name),
+					       macro_rules,
+					       std::move (outer_attrs),
+					       macro_locus, vis));
+    }
+  else if (t->get_id () == LEFT_CURLY)
+    {
+      // multiple definitions of macro rule separated by comma
+      // e.g. `macro foo { () => {}, ($e:expr) => {}, }`
+
+      // parse left curly
+      const_TokenPtr left_curly = expect_token (LEFT_CURLY);
+      if (left_curly == nullptr)
+	{
+	  return nullptr;
+	}
+
+      // parse actual macro rules
+      std::vector<AST::MacroRule> macro_rules;
+
+      // must be at least one macro rule, so parse it
+      AST::MacroRule initial_rule = parse_macro_rule ();
+      if (initial_rule.is_error ())
+	{
+	  Error error (
+	    lexer.peek_token ()->get_locus (),
+	    "required first macro rule in declarative macro definition "
+	    "could not be parsed");
+	  add_error (std::move (error));
+
+	  // skip after somewhere?
+	  return nullptr;
+	}
+      macro_rules.push_back (std::move (initial_rule));
+
+      t = lexer.peek_token ();
+      // parse macro rules
+      while (t->get_id () == COMMA)
+	{
+	  // skip comma
+	  lexer.skip_token ();
+
+	  // don't parse if end of macro rules
+	  if (token_id_matches_delims (lexer.peek_token ()->get_id (),
+				       AST::CURLY))
+	    {
+	      break;
+	    }
+
+	  // try to parse next rule
+	  AST::MacroRule rule = parse_macro_rule ();
+	  if (rule.is_error ())
+	    {
+	      Error error (
+		lexer.peek_token ()->get_locus (),
+		"failed to parse macro rule in declarative macro definition");
+	      add_error (std::move (error));
+
+	      return nullptr;
+	    }
+
+	  macro_rules.push_back (std::move (rule));
+
+	  t = lexer.peek_token ();
+	}
+
+      // parse right curly
+      const_TokenPtr right_curly = expect_token (RIGHT_CURLY);
+      if (right_curly == nullptr)
+	{
+	  return nullptr;
+	}
+
+      return std::unique_ptr<AST::MacroRulesDefinition> (
+	AST::MacroRulesDefinition::decl_macro (std::move (rule_name),
+					       std::move (macro_rules),
+					       std::move (outer_attrs),
+					       macro_locus, vis));
+    }
+  else
+    {
+      add_error (Error (t->get_locus (),
+			"unexpected token %qs - expecting delimiters "
+			"(for a declarative macro definiton)",
+			t->get_token_description ()));
+      return nullptr;
+    }
+}
+
 // Parses a semi-coloned (except for full block) macro invocation item.
 template <typename ManagedTokenSource>
 std::unique_ptr<AST::MacroInvocation>
@@ -6004,6 +6124,7 @@ Parser<ManagedTokenSource>::parse_stmt (ParseRestrictions restrictions)
     case STATIC_TOK:
     case TRAIT:
     case IMPL:
+    case MACRO:
     /* TODO: implement union keyword but not really because of
      * context-dependence crappy hack way to parse a union written below to
      * separate it from the good code. */
@@ -6019,7 +6140,7 @@ Parser<ManagedTokenSource>::parse_stmt (ParseRestrictions restrictions)
     case CRATE:
     case DOLLAR_SIGN:
       // almost certainly macro invocation semi
-      return parse_macro_item (std::move (outer_attrs));
+      return parse_macro_invocation_semi (std::move (outer_attrs));
       break;
     // crappy hack to do union "keyword"
     case IDENTIFIER:
@@ -6032,7 +6153,7 @@ Parser<ManagedTokenSource>::parse_stmt (ParseRestrictions restrictions)
       else if (t->get_str () == "macro_rules")
 	{
 	  // macro_rules! macro item
-	  return parse_macro_item (std::move (outer_attrs));
+	  return parse_macro_rules_def (std::move (outer_attrs));
 	}
       else if (lexer.peek_token (1)->get_id () == SCOPE_RESOLUTION
 	       || lexer.peek_token (1)->get_id () == EXCLAM)
@@ -6040,7 +6161,7 @@ Parser<ManagedTokenSource>::parse_stmt (ParseRestrictions restrictions)
 	  // FIXME: ensure doesn't take any expressions by mistake
 	  /* path (probably) or macro invocation, so probably a macro
 	   * invocation semi */
-	  return parse_macro_item (std::move (outer_attrs));
+	  return parse_macro_invocation_semi (std::move (outer_attrs));
 	}
       gcc_fallthrough ();
       // TODO: find out how to disable gcc "implicit fallthrough" warning
@@ -11711,8 +11832,8 @@ Parser<ManagedTokenSource>::parse_stmt_or_expr_without_block ()
       else if (t->get_str () == "macro_rules")
 	{
 	  // macro_rules! macro item
-	  std::unique_ptr<AST::MacroItem> item (
-	    parse_macro_item (std::move (outer_attrs)));
+	  std::unique_ptr<AST::Item> item (
+	    parse_macro_rules_def (std::move (outer_attrs)));
 	  return ExprOrStmt (std::move (item));
 	}
       else if (lexer.peek_token (1)->get_id () == SCOPE_RESOLUTION
diff --git a/gcc/rust/parse/rust-parse.h b/gcc/rust/parse/rust-parse.h
index 8449181b12f..5c0fcc3f174 100644
--- a/gcc/rust/parse/rust-parse.h
+++ b/gcc/rust/parse/rust-parse.h
@@ -197,6 +197,8 @@ private:
   AST::DelimTokenTree parse_delim_token_tree ();
   std::unique_ptr<AST::MacroRulesDefinition>
   parse_macro_rules_def (AST::AttrVec outer_attrs);
+  std::unique_ptr<AST::MacroRulesDefinition>
+  parse_decl_macro_def (AST::Visibility vis, AST::AttrVec outer_attrs);
   std::unique_ptr<AST::MacroInvocation>
   parse_macro_invocation_semi (AST::AttrVec outer_attrs);
   std::unique_ptr<AST::MacroInvocation>
@@ -209,7 +211,6 @@ private:
 
   // Top-level item-related
   std::unique_ptr<AST::VisItem> parse_vis_item (AST::AttrVec outer_attrs);
-  std::unique_ptr<AST::MacroItem> parse_macro_item (AST::AttrVec outer_attrs);
 
   // VisItem subclass-related
   std::unique_ptr<AST::Module> parse_module (AST::Visibility vis,
diff --git a/gcc/testsuite/rust/compile/decl_macro1.rs b/gcc/testsuite/rust/compile/decl_macro1.rs
new file mode 100644
index 00000000000..4a81a71e500
--- /dev/null
+++ b/gcc/testsuite/rust/compile/decl_macro1.rs
@@ -0,0 +1,2 @@
+#![feature(decl_macro)]
+macro m() {}
diff --git a/gcc/testsuite/rust/compile/decl_macro2.rs b/gcc/testsuite/rust/compile/decl_macro2.rs
new file mode 100644
index 00000000000..cbe19b0c14b
--- /dev/null
+++ b/gcc/testsuite/rust/compile/decl_macro2.rs
@@ -0,0 +1,2 @@
+#![feature(decl_macro)]
+pub macro m($e: expr) { $e + $e }
diff --git a/gcc/testsuite/rust/compile/decl_macro3.rs b/gcc/testsuite/rust/compile/decl_macro3.rs
new file mode 100644
index 00000000000..d48da7835f9
--- /dev/null
+++ b/gcc/testsuite/rust/compile/decl_macro3.rs
@@ -0,0 +1,4 @@
+#![feature(decl_macro)]
+macro foo {
+    () => {}
+}
diff --git a/gcc/testsuite/rust/compile/decl_macro4.rs b/gcc/testsuite/rust/compile/decl_macro4.rs
new file mode 100644
index 00000000000..b8576cf0dd8
--- /dev/null
+++ b/gcc/testsuite/rust/compile/decl_macro4.rs
@@ -0,0 +1,5 @@
+#![feature(decl_macro)]
+macro foo {
+    () => { 0 },
+    ($n: expr) => { $n + 1 },
+}
\ No newline at end of file
diff --git a/gcc/testsuite/rust/compile/decl_macro5.rs b/gcc/testsuite/rust/compile/decl_macro5.rs
new file mode 100644
index 00000000000..b4ea20ffa74
--- /dev/null
+++ b/gcc/testsuite/rust/compile/decl_macro5.rs
@@ -0,0 +1,5 @@
+#![feature(decl_macro)]
+macro foo {
+    () => [],
+    ($h: expr, $(t: expr),*) => ($h),
+}
diff --git a/gcc/testsuite/rust/compile/decl_macro6.rs b/gcc/testsuite/rust/compile/decl_macro6.rs
new file mode 100644
index 00000000000..5c5e7002a98
--- /dev/null
+++ b/gcc/testsuite/rust/compile/decl_macro6.rs
@@ -0,0 +1,5 @@
+#![feature(decl_macro)]
+macro m {}
+// { dg-error "unexpected token .\}. - expecting delimiters .for a macro matcher." "" { target *-*-* } .-1 }
+// { dg-error "required first macro rule in declarative macro definition could not be parsed" "" { target *-*-* } .-2 }
+// { dg-error "failed to parse item in crate" "" { target *-*-* } .-3 }
diff --git a/gcc/testsuite/rust/compile/decl_macro7.rs b/gcc/testsuite/rust/compile/decl_macro7.rs
new file mode 100644
index 00000000000..7327fb56782
--- /dev/null
+++ b/gcc/testsuite/rust/compile/decl_macro7.rs
@@ -0,0 +1,4 @@
+#![feature(decl_macro)]
+pub macro hello() [ "Hello" ]
+// { dg-error "only braces can be used for a macro transcriber in declarative macro definition" "" { target *-*-* } .-1 }
+// { dg-error "failed to parse item in crate" }
\ No newline at end of file
diff --git a/gcc/testsuite/rust/execute/torture/decl_macro1.rs b/gcc/testsuite/rust/execute/torture/decl_macro1.rs
new file mode 100644
index 00000000000..accc8b1db8e
--- /dev/null
+++ b/gcc/testsuite/rust/execute/torture/decl_macro1.rs
@@ -0,0 +1,8 @@
+#![feature(decl_macro)]
+macro one() {
+    1
+}
+
+fn main() -> i32 {
+    one!() - 1
+}
diff --git a/gcc/testsuite/rust/execute/torture/decl_macro2.rs b/gcc/testsuite/rust/execute/torture/decl_macro2.rs
new file mode 100644
index 00000000000..f42b96262fe
--- /dev/null
+++ b/gcc/testsuite/rust/execute/torture/decl_macro2.rs
@@ -0,0 +1,8 @@
+#![feature(decl_macro)]
+macro one {
+    () => { 1 }
+}
+
+fn main() -> i32 {
+    one!() - 1
+}
diff --git a/gcc/testsuite/rust/execute/torture/decl_macro3.rs b/gcc/testsuite/rust/execute/torture/decl_macro3.rs
new file mode 100644
index 00000000000..fa2cf793cf2
--- /dev/null
+++ b/gcc/testsuite/rust/execute/torture/decl_macro3.rs
@@ -0,0 +1,15 @@
+#![feature(decl_macro)]
+macro add {
+    ($e:expr) => {
+        $e
+    },
+    ($h:expr, $($t:expr),*) => {
+        $h + add!($($t),*)
+    },
+}
+
+fn main() -> i32 {
+    let a = add!(1, 2, 3);
+
+    a - 6
+}
diff --git a/gcc/testsuite/rust/execute/torture/decl_macro4.rs b/gcc/testsuite/rust/execute/torture/decl_macro4.rs
new file mode 100644
index 00000000000..e700e63161d
--- /dev/null
+++ b/gcc/testsuite/rust/execute/torture/decl_macro4.rs
@@ -0,0 +1,15 @@
+#![feature(decl_macro)]
+pub macro add {
+    ($e:expr) => {
+        $e
+    },
+    ($h:expr, $($t:expr),*) => {
+        $h + add!($($t),*)
+    },
+}
+
+fn main() -> i32 {
+    let a = add!(1, 2, 3);
+
+    a - 6
+}
-- 
2.40.0