Fixing issue with a trailing comma being added after a trailing comme…

…nt (belav#1370)

closes belav#1354

---------

Co-authored-by: Lasath Fernando <devel@lasath.org>

Src/CSharpier.Tests/FormattingTests/TestFiles/cs/TrailingComma_TrailingComments.expected.test

@@ -0,0 +1,19 @@
+var someObject = new SomeObject()
+{
+    Property1 = 1,
+    Property2 = 2, // Trailing Comment
+};
+
+var someObject = new SomeObject()
+{
+    Property1 = 1,
+    Property2 = [], // Trailing Comment
+};
+
+var someObject = new SomeObject()
+{
+    Property1 = 1,
+    Property2 =
+    [ /* this formatting isn't ideal, but this probably won't happen in the real world */
+    ], // Trailing Comment
+};

Src/CSharpier.Tests/FormattingTests/TestFiles/cs/TrailingComma_TrailingComments.test

@@ -0,0 +1,17 @@
+var someObject = new SomeObject()
+{
+    Property1 = 1,
+    Property2 = 2 // Trailing Comment
+};
+
+var someObject = new SomeObject()
+{
+    Property1 = 1,
+    Property2 = [] // Trailing Comment
+};
+
+var someObject = new SomeObject()
+{
+    Property1 = 1,
+    Property2 = [/* this formatting isn't ideal, but this probably won't happen in the real world */ ] // Trailing Comment
+};

Src/CSharpier/SyntaxPrinter/FormattingContext.cs

@@ -31,9 +31,19 @@ internal class FormattingContext
     // we also need to keep track if we move around usings with disabledText
     public bool ReorderedUsingsWithDisabledText { get; set; }
 
+    public TrailingCommaContext? TrailingComma { get; set; }
+
     public FormattingContext WithSkipNextLeadingTrivia()
     {
         this.SkipNextLeadingTrivia = true;
         return this;
     }
+
+    public FormattingContext WithTrailingComma(SyntaxTrivia syntaxTrivia, Doc doc)
+    {
+        this.TrailingComma = new TrailingCommaContext(syntaxTrivia, doc);
+        return this;
+    }
+
+    public record TrailingCommaContext(SyntaxTrivia TrailingComment, Doc PrintedTrailingComma);
 }

Src/CSharpier/SyntaxPrinter/SeparatedSyntaxList.cs

@@ -74,12 +74,30 @@ private static Doc Print<T>(
                 continue;
             }
 
+            var firstTrailingComment = list[x]
+                .GetTrailingTrivia()
+                .FirstOrDefault(o => o.IsComment());
+
+            // we want a trailing comma, but we need to get it printed in place before a trailing comment
+            // shove it in the context so the token printing can pick it up and put it in place
+            if (
+                x >= list.SeparatorCount
+                && closingToken is not null
+                && firstTrailingComment != default
+            )
+            {
+                context.WithTrailingComma(
+                    firstTrailingComment,
+                    TrailingComma.Print(closingToken.Value, context, true)
+                );
+            }
+
             docs.Add(printFunc(list[x], context));
 
             // if the syntax tree doesn't have a trailing comma but we want want, then add it
             if (x >= list.SeparatorCount)
             {
-                if (closingToken != null)
+                if (closingToken != null && firstTrailingComment == default)
                 {
                     docs.Add(TrailingComma.Print(closingToken.Value, context));
                 }

Src/CSharpier/SyntaxPrinter/Token.cs

@@ -125,6 +125,16 @@ or SyntaxKind.InterpolatedRawStringEndToken
             var trailingTrivia = PrintTrailingTrivia(syntaxToken);
             if (trailingTrivia != Doc.Null)
             {
+                if (
+                    context.TrailingComma is not null
+                    && syntaxToken.TrailingTrivia.FirstOrDefault(o => o.IsComment())
+                        == context.TrailingComma.TrailingComment
+                )
+                {
+                    docs.Add(context.TrailingComma.PrintedTrailingComma);
+                    context.TrailingComma = null;
+                }
+
                 docs.Add(trailingTrivia);
             }
         }

Src/CSharpier/SyntaxPrinter/TrailingComma.cs

@@ -2,18 +2,21 @@ namespace CSharpier.SyntaxPrinter;
 
 internal static class TrailingComma
 {
-    public static Doc Print(SyntaxToken closingToken, FormattingContext context)
+    public static Doc Print(
+        SyntaxToken closingToken,
+        FormattingContext context,
+        bool skipIfBreak = false
+    )
     {
         if (!context.UsePrettierStyleTrailingCommas)
         {
             return Doc.Null;
         }
 
-        return closingToken.LeadingTrivia.Any(o => o.IsDirective)
-            ? Doc.Null
-            : Doc.IfBreak(
-                Token.Print(SyntaxFactory.Token(SyntaxKind.CommaToken), context),
-                Doc.Null
-            );
+        var printedToken = Token.Print(SyntaxFactory.Token(SyntaxKind.CommaToken), context);
+
+        return closingToken.LeadingTrivia.Any(o => o.IsDirective) ? Doc.Null
+            : skipIfBreak ? printedToken
+            : Doc.IfBreak(printedToken, Doc.Null);
     }
 }