SONARPY-933 Fix parse error: lambda parameter list can have a trailing comma (#1000)

Author: guillaume-dequenne

python-frontend/src/main/java/org/sonar/python/api/PythonGrammar.java

@@ -314,15 +314,15 @@ public static void grammar(LexerfulGrammarBuilder b) {
     b.rule(NAME).is(IDENTIFIER);
 
     b.rule(VARARGSLIST).is(b.firstOf(
-      b.sequence("**", NAME, b.optional(",")),
-      b.sequence("*", b.optional(NAME), b.zeroOrMore(",", FPDEF, b.optional("=", TEST)), b.optional(",", "**", NAME), b.optional(",")),
+      b.sequence("**", NAME),
+      b.sequence("*", b.optional(NAME), b.zeroOrMore(",", FPDEF, b.optional("=", TEST)), b.optional(",", "**", NAME)),
       b.sequence(FPDEF, b.optional("=", TEST),
         b.zeroOrMore(",", FPDEF, b.optional("=", TEST)),
         b.optional(",", "/", b.zeroOrMore(",", FPDEF, b.optional("=", TEST))),
         b.optional(",", b.firstOf(
           b.sequence("**", NAME),
           b.sequence("*", b.optional(NAME), b.zeroOrMore(",", FPDEF, b.optional("=", TEST)), b.optional(",", "**", NAME))))
-        ), b.optional(",")));
+        )), b.optional(","));
     b.rule(FPDEF).is(b.firstOf(
         NAME,
         b.sequence("(", FPLIST, ")")));

python-frontend/src/test/java/org/sonar/python/tree/PythonTreeMakerTest.java

@@ -1908,6 +1908,7 @@ public void lambda_expr() {
     assertThat(lambda("lambda x, /, *args, **kwargs: x").parameters().all()).hasSize(4);
     assertThat(lambda("lambda *, x: x").parameters().all()).hasSize(2);
     assertThat(lambda("lambda **kwargs: kwargs").parameters().all()).hasSize(1);
+    assertThat(lambda("lambda x, y,: x + y").parameters().all()).hasSize(2);
   }
 
   private LambdaExpression lambda(String code) {