parser: Add 0 sized slice pattern parsing

Check for a closing square bracket before attempting to parse any
pattern within a slice. Also add a new test to verify zero sized
slice parsing.

gcc/rust/ChangeLog:

	* parse/rust-parse-impl.h (Parser::parse_slice_pattern): Add
	closing square bracket check.

gcc/testsuite/ChangeLog:

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

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

2 files changed, 13 insertions, 1 deletions

diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index 15effaa..b17744f 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -11136,8 +11136,16 @@ std::unique_ptr<AST::SlicePattern>
 Parser<ManagedTokenSource>::parse_slice_pattern ()
 {
   Location square_locus = lexer.peek_token ()->get_locus ();
+  std::vector<std::unique_ptr<AST::Pattern>> patterns;
   skip_token (LEFT_SQUARE);
 
+  if (lexer.peek_token ()->get_id () == RIGHT_SQUARE)
+    {
+      skip_token (RIGHT_SQUARE);
+      return std::unique_ptr<AST::SlicePattern> (
+	new AST::SlicePattern (std::move (patterns), square_locus));
+    }
+
   // parse initial pattern (required)
   std::unique_ptr<AST::Pattern> initial_pattern = parse_pattern ();
   if (initial_pattern == nullptr)
@@ -11149,7 +11157,6 @@ Parser<ManagedTokenSource>::parse_slice_pattern ()
       return nullptr;
     }
 
-  std::vector<std::unique_ptr<AST::Pattern>> patterns;
   patterns.push_back (std::move (initial_pattern));
 
   const_TokenPtr t = lexer.peek_token ();
diff --git a/gcc/testsuite/rust/compile/zero_sized_slice.rs b/gcc/testsuite/rust/compile/zero_sized_slice.rs
new file mode 100644
index 0000000..cd1e21e
--- /dev/null
+++ b/gcc/testsuite/rust/compile/zero_sized_slice.rs
@@ -0,0 +1,5 @@
+// { dg-options "-fsyntax-only" }
+
+fn foo() {
+    let [] = [0; 0];
+}