From d2efef7bff85da7f27d7eb2c3931cb23f0eda26a Mon Sep 17 00:00:00 2001
From: George Dietrich <dev@dietrich.pub>
Date: Fri, 14 Jun 2024 13:18:53 -0400
Subject: [PATCH] Ensure trailing commas are not written when parameters are
 not multi-line

---
 spec/compiler/formatter/formatter_spec.cr | 35 +++++++++++++++++++++++
 src/compiler/crystal/tools/formatter.cr   |  4 +--
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/spec/compiler/formatter/formatter_spec.cr b/spec/compiler/formatter/formatter_spec.cr
index e4e76279f4d5..7bb7a1034e72 100644
--- a/spec/compiler/formatter/formatter_spec.cr
+++ b/spec/compiler/formatter/formatter_spec.cr
@@ -1120,6 +1120,41 @@ describe Crystal::Formatter do
       )
       end
       CRYSTAL
+
+    assert_format <<-CRYSTAL, flags: %w[def_trailing_comma]
+      def foo(a)
+      end
+      CRYSTAL
+
+    assert_format <<-CRYSTAL, flags: %w[def_trailing_comma]
+      def foo(a, b)
+      end
+      CRYSTAL
+
+    assert_format <<-CRYSTAL, flags: %w[def_trailing_comma]
+      def foo(a, *args)
+      end
+      CRYSTAL
+
+    assert_format <<-CRYSTAL, flags: %w[def_trailing_comma]
+      def foo(a, *args, &block)
+      end
+      CRYSTAL
+
+    assert_format <<-CRYSTAL, flags: %w[def_trailing_comma]
+      def foo(a, **kwargs)
+      end
+      CRYSTAL
+
+    assert_format <<-CRYSTAL, flags: %w[def_trailing_comma]
+      def foo(a, **kwargs, &block)
+      end
+      CRYSTAL
+
+    assert_format <<-CRYSTAL, flags: %w[def_trailing_comma]
+      def foo(a, &block)
+      end
+      CRYSTAL
   end
 
   assert_format "1   +   2", "1 + 2"
diff --git a/src/compiler/crystal/tools/formatter.cr b/src/compiler/crystal/tools/formatter.cr
index 614ecc836637..dc14c70a90ad 100644
--- a/src/compiler/crystal/tools/formatter.cr
+++ b/src/compiler/crystal/tools/formatter.cr
@@ -1562,7 +1562,7 @@ module Crystal
 
       args.each_with_index do |arg, i|
         has_more = !last?(i, args) || double_splat || block_arg || yields || variadic
-        wrote_newline = format_def_arg(wrote_newline, has_more, true) do
+        wrote_newline = format_def_arg(wrote_newline, has_more, found_first_newline && !has_more) do
           if i == splat_index
             write_token :OP_STAR
             skip_space_or_newline
@@ -1577,7 +1577,7 @@ module Crystal
       end
 
       if double_splat
-        wrote_newline = format_def_arg(wrote_newline, block_arg || yields, true) do
+        wrote_newline = format_def_arg(wrote_newline, block_arg || yields, found_first_newline) do
           write_token :OP_STAR_STAR
           skip_space_or_newline