Forbid writing [,] as list literal

org.lflang.tests/src/org/lflang/tests/LFParsingTest.java

@@ -27,7 +27,7 @@ public class LFParsingTest {
 
 
     @Test
-    public void testLexingEmptyTargetProperties() throws Exception {
+    public void testParsingEmptyTargetProperties() throws Exception {
         assertNoParsingErrorsIn("target C { };      \nreactor Foo {}");
         assertNoParsingErrorsIn("target C {a:b,};   \nreactor Foo {}");
         expectParsingErrorIn("target C {,};      \nreactor Foo {}");
@@ -38,6 +38,13 @@ public void testLexingEmptyTargetProperties() throws Exception {
         // assertNoParsingErrorsIn("target C {x:[,]};  \nreactor Foo {}");
     }
 
+    @Test
+    public void testParsingListLiterals() throws Exception {
+        assertNoParsingErrorsIn("target Python;   \nreactor Foo(p([1,])) {}");
+        // [,] is not an ok list literal
+        expectParsingErrorIn("target Python;      \nreactor Foo(p([,])) {}");
+    }
+
     @Test
     public void testLexingLifetimeAnnots() throws Exception {
         assertNoParsingErrorsIn(makeLfTargetCode("Rust",

org.lflang/src/org/lflang/LinguaFranca.xtext

@@ -387,12 +387,8 @@ SignedInt:
 
 // List literals support even empty lists, and a trailing comma.
 
-// Note: this expansion is weirdly written, but without the
-// emptyList property, Xtext fails to push a ListLiteral node
-// when the list is empty... Another bug of Xtext.
 ListLiteral:
-    '[' (items+=Value (',' items+=Value)* ','? ']'
-        | ','? emptyList?=']')
+    {ListLiteral} '[' ( items+=Value (',' items+=Value)* ','? )? ']'
 ;
 
 Literal:

test/Python/src/ListLiterals.lf

@@ -9,17 +9,18 @@ reactor Sub(seq([1,2])) {
 
 main reactor {
     state l12([1,2]);
+    state l12_trailing([1,2,]);
     state empty([]);
-    state empty2([,]);
+    // doesn't parse state empty2([,]);
 
     sub  = new Sub(seq = [1, 2]);
     sub2 = new Sub(seq = (1, 2));
     sub3 = new Sub(seq = ([1, 2]));
 
     reaction(startup) {=
         assert self.empty == []
-        assert self.empty2 == []
         assert self.l12 == [1, 2]
+        assert self.l12 == self.l12_trailing
         print("Success")
     =}
 }