gccrs: Fix out of bounds indexing while expanding macros with repetition

gcc/rust/ChangeLog:

	* expand/rust-macro-substitute-ctx.cc
	(SubstituteCtx::substitute_repetition): Fix out-of-bounds.

gcc/testsuite/ChangeLog:

	* rust/compile/macro52.rs: New test.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>

2 files changed, 26 insertions, 3 deletions

diff --git a/gcc/rust/expand/rust-macro-substitute-ctx.cc b/gcc/rust/expand/rust-macro-substitute-ctx.cc
index 9592d2d..eb0f149 100644
--- a/gcc/rust/expand/rust-macro-substitute-ctx.cc
+++ b/gcc/rust/expand/rust-macro-substitute-ctx.cc
@@ -147,15 +147,27 @@ SubstituteCtx::substitute_repetition (
 	{
 	  MatchedFragment sub_fragment;
 
+	  // Hack: A repeating meta variable might not be present in the new
+	  // macro. Don't include this match if the fragment doesn't have enough
+	  // items, as check_repetition_amount should prevent repetition amount
+	  // mismatches anyway.
+	  bool is_used = true;
+
 	  // FIXME: Hack: If a fragment is not repeated, how does it fit in the
 	  // submap? Do we really want to expand it? Is this normal behavior?
 	  if (kv_match.second.is_single_fragment ())
 	    sub_fragment = kv_match.second.get_single_fragment ();
 	  else
-	    sub_fragment = kv_match.second.get_fragments ()[i];
+	    {
+	      if (kv_match.second.get_fragments ().size () > i)
+		sub_fragment = kv_match.second.get_fragments ().at (i);
+	      else
+		is_used = false;
+	    }
 
-	  sub_map.insert (
-	    {kv_match.first, MatchedFragmentContainer::metavar (sub_fragment)});
+	  if (is_used)
+	    sub_map.insert ({kv_match.first,
+			     MatchedFragmentContainer::metavar (sub_fragment)});
 	}
 
       auto substitute_context = SubstituteCtx (input, new_macro, sub_map);
diff --git a/gcc/testsuite/rust/compile/macro52.rs b/gcc/testsuite/rust/compile/macro52.rs
new file mode 100644
index 0000000..31002eb
--- /dev/null
+++ b/gcc/testsuite/rust/compile/macro52.rs
@@ -0,0 +1,11 @@
+macro_rules! multi {
+    ($( $a:ident )? $( + $b:ident )?) => {
+        {
+            $( let $a: u32 )?;
+        }
+    }
+}
+
+pub fn foo() {
+    multi!(_a);
+}