Allow trailing comma in vectors. Closes #2482.

src/libsyntax/parse/parser.rs

@@ -805,7 +805,7 @@ class parser {
             self.bump();
             let mutbl = self.parse_mutability();
             let es = self.parse_seq_to_end(
-                token::RBRACKET, seq_sep_trailing_disallowed(token::COMMA),
+                token::RBRACKET, seq_sep_trailing_allowed(token::COMMA),
                 {|p| p.parse_expr()});
             hi = self.span.hi;
             ex = expr_vec(es, mutbl);

src/test/compile-fail/empty-vec-trailing-comma.rs

@@ -0,0 +1,3 @@
+fn main() {
+    let v = [,]; //! ERROR unexpected token: ','
+}

src/test/run-pass/vec-trailing-comma.rs

@@ -0,0 +1,10 @@
+// Issue #2482.
+
+fn main() {
+    let v1: [int] = [10, 20, 30,];
+    let v2: [int] = [10, 20, 30];
+    assert (v1[2] == v2[2]);
+    let v3: [int] = [10,];
+    let v4: [int] = [10];
+    assert (v3[0] == v4[0]);
+}