macros: Add base functions to check for follow-set ambiguities

Rust does not allow for all macro fragments to be followed by any kind
of tokens: We must check tokens following those fragments that might
contain restrictions and make sure that they are allowed, conforming to
the Macro Follow-Set Ambiguity specification

Co-authored-by: philberty <philip.herron@embecosm.com>

macro-frag-spec: Transform enum into a class

This allows us to add methods on the fragment specifier, which are
needed to make sure that follow-set ambiguities are respected

tests: Add tests for forbidden follow-up tokens

This also fix a test that was previously accepted but invalid: rustc
also rejected it

1 files changed, 11 insertions, 2 deletions

diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index 644e789..1d1b624 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -22,6 +22,7 @@ along with GCC; see the file COPYING3.  If not see
 
 #include "rust-diagnostics.h"
 #include "util/rust-make-unique.h"
+#include <algorithm>
 
 namespace Rust {
 // Left binding powers of operations.
@@ -1767,6 +1768,13 @@ Parser<ManagedTokenSource>::parse_macro_matcher ()
 	  return AST::MacroMatcher::create_error (t->get_locus ());
 	}
 
+      if (matches.size () > 0)
+	{
+	  auto &last_match = matches.back ();
+	  if (!is_match_compatible (*last_match, *match))
+	    return AST::MacroMatcher::create_error (match->get_match_locus ());
+	}
+
       matches.push_back (std::move (match));
 
       // DEBUG
@@ -1955,8 +1963,9 @@ Parser<ManagedTokenSource>::parse_macro_match_fragment ()
   if (t == nullptr)
     return nullptr;
 
-  AST::MacroFragSpec frag = AST::get_frag_spec_from_str (t->get_str ());
-  if (frag == AST::INVALID)
+  AST::MacroFragSpec frag
+    = AST::MacroFragSpec::get_frag_spec_from_str (t->get_str ());
+  if (frag.is_error ())
     {
       Error error (t->get_locus (),
 		   "invalid fragment specifier %qs in fragment macro match",