Allow trailing commas in parameter list (#344)

* Add failing test

* Allow trailing commas

src/CSnakes.SourceGeneration/Parser/PythonParser.Parameters.cs

@@ -28,8 +28,8 @@ from defaultValue in Token.EqualTo(PythonToken.Equal).Optional().Then(
 
     public static TokenListParser<PythonToken, PythonFunctionParameter[]> PythonParameterListParser { get; } =
         (from openParen in Token.EqualTo(PythonToken.OpenParenthesis)
-         from parameters in ParameterOrSlashParser.ManyDelimitedBy(Token.EqualTo(PythonToken.Comma))
-         from closeParen in Token.EqualTo(PythonToken.CloseParenthesis)
-         select parameters)
+         from parameters in ParameterOrSlashParser.OptionalOrDefault().ManyDelimitedBy(Token.EqualTo(PythonToken.Comma), Token.EqualTo(PythonToken.CloseParenthesis))
+         select parameters.Where(p => p is not null).ToArray()
+         )
         .Named("Parameter List");
 }

src/CSnakes.Tests/TokenizerTests.cs

@@ -283,6 +283,21 @@ public void ParseFunctionParameterListUntyped()
         Assert.Equal("Any", result.Value[2].Type.Name);
     }
 
+    [Fact]
+    public void ParseFunctionParameterListTrailingComma ()
+    {
+        var code = "(a, b, c, )";
+        var tokens = PythonTokenizer.Instance.Tokenize(code);
+        var result = PythonParser.PythonParameterListParser.TryParse(tokens);
+        Assert.True(result.HasValue);
+        Assert.Equal("a", result.Value[0].Name);
+        Assert.Equal("Any", result.Value[0].Type.Name);
+        Assert.Equal("b", result.Value[1].Name);
+        Assert.Equal("Any", result.Value[1].Type.Name);
+        Assert.Equal("c", result.Value[2].Name);
+        Assert.Equal("Any", result.Value[2].Type.Name);
+    }
+
     [Fact]
     public void ParseFunctionDefinition()
     {