Fix comma comments for function definition

src/formatters/functions.rs

@@ -1015,14 +1015,36 @@ fn format_multiline_parameters(
         // Reset the shape (as the parameter is on a newline), and increment the additional indent level
         let shape = shape.reset().increment_additional_indent();
 
-        let parameter = format_parameter(ctx, pair.value(), shape).update_leading_trivia(
+        let mut parameter = format_parameter(ctx, pair.value(), shape).update_leading_trivia(
             FormatTriviaType::Append(vec![create_indent_trivia(ctx, shape)]),
         );
 
-        let punctuation = pair.punctuation().map(|punctuation| {
-            fmt_symbol!(ctx, punctuation, ",", shape)
-                .update_trailing_trivia(FormatTriviaType::Append(vec![create_newline_trivia(ctx)]))
-        });
+        let punctuation = match pair.punctuation() {
+            Some(punctuation) => {
+                // Remove any trailing comments from the parameter if present
+                let mut trailing_comments: Vec<Token> = match &parameter {
+                    Parameter::Name(token) | Parameter::Ellipse(token) => token.trailing_trivia(),
+                    other => panic!("unknown node {:?}", other),
+                }
+                .filter(|token| trivia_util::trivia_is_comment(token))
+                .map(|x| {
+                    // Prepend a single space beforehand
+                    vec![Token::new(TokenType::spaces(1)), x.to_owned()]
+                })
+                .flatten()
+                .collect();
+
+                parameter = parameter.update_trailing_trivia(FormatTriviaType::Replace(vec![]));
+
+                // Add a newline to the end of the trailing comments, then append them all to the end of the comma
+                trailing_comments.push(create_newline_trivia(ctx));
+                Some(
+                    fmt_symbol!(ctx, punctuation, ",", shape)
+                        .update_trailing_trivia(FormatTriviaType::Append(trailing_comments)),
+                )
+            }
+            None => None,
+        };
 
         formatted_parameters.push(Pair::new(parameter, punctuation))
     }

tests/inputs/function-def-comments.lua

@@ -0,0 +1,4 @@
+function func(
+	param_a -- description of a
+	, param_b -- description of b
+) end

tests/snapshots/tests__standard@function-def-comments.lua.snap

@@ -0,0 +1,10 @@
+---
+source: tests/tests.rs
+expression: format(&contents)
+
+---
+function func(
+	param_a, -- description of a
+	param_b -- description of b
+) end
+