add TrailingComma to Record & little formatter refactor

compiler/parse/src/ast.rs

@@ -196,10 +196,12 @@ pub enum Expr<'a> {
     AccessorFunction(&'a str),
 
     // Collection Literals
-    List(&'a [&'a Loc<Expr<'a>>]),
+    List (&'a [&'a Loc<Expr<'a>>]),
+    
     Record {
         update: Option<&'a Loc<Expr<'a>>>,
         fields: &'a [Loc<AssignedField<'a, Expr<'a>>>],
+        trailing_comma: &'a TrailingComma<'a>,
     },
 
     // Lookups
@@ -383,7 +385,23 @@ pub enum AssignedField<'a, Val> {
     Malformed(&'a str),
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq)]
+pub enum TrailingComma<'a> {
+    None,
+    FollowedBy(&'a [CommentOrNewline<'a>]),
+}
+
+impl<'a> TrailingComma<'a> {
+    pub fn is_multiline(&self) -> bool {
+        match self {
+            TrailingComma::None => false,
+            TrailingComma::FollowedBy(comments_or_newlines) =>
+                (*comments_or_newlines).len() > 1
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
 pub enum CommentOrNewline<'a> {
     Newline,
     LineComment(&'a str),