Check for inline comments that will force hanging in function arguments

CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Added flag `--no-ignore-vcs` to continue formatting files listed in a `.gitignore` file, instead of skipping over them ([#895](https://github.com/JohnnyMorganz/StyLua/issues/895))
 
+### Fixed
+
+- Fixed malformed formatting when a binary expression inside of a function call with comments around the operators is incorrectly collapsed onto one line ([#996](https://github.com/JohnnyMorganz/StyLua/issues/996))
+
 ## [2.3.1] - 2025-11-01
 
 ### Fixed

src/formatters/functions.rs

@@ -147,11 +147,13 @@ fn function_args_contains_comments(
         true
     } else {
         arguments.pairs().any(|argument| {
-            // Leading / Trailing trivia of expression (ignore inline comments)
+            // Leading / Trailing trivia of expression
             argument.value().leading_trivia()
                 .iter()
                 .chain(argument.value().trailing_trivia().iter())
                 .any(function_trivia_contains_comments)
+            // Inline comments that will force hanging
+            || argument.value().has_inline_comments()
             // Punctuation contains comments
             || argument
                 .punctuation()

src/formatters/trivia_util.rs

@@ -1172,7 +1172,11 @@ impl HasInlineComments for Expression {
     fn has_inline_comments(&self) -> bool {
         match self {
             Expression::BinaryOperator { lhs, binop, rhs } => {
-                contains_comments(binop) || contains_comments(lhs) || rhs.has_inline_comments()
+                contains_comments(binop)
+                    || lhs.has_trailing_comments(CommentSearch::Single)
+                    || rhs.has_leading_comments(CommentSearch::Single)
+                    || lhs.has_inline_comments()
+                    || rhs.has_inline_comments()
             }
             Expression::UnaryOperator { unop, expression } => {
                 let op_contains_comments = match unop {

tests/inputs/hang-binop-comments-3.lua

@@ -0,0 +1,10 @@
+-- https://github.com/JohnnyMorganz/StyLua/issues/996
+
+local function f()
+  local a = "ab"
+  a = a:gsub("a".. -- "
+    'b', function() return "c" end)
+  print(a)
+end
+
+f()

tests/snapshots/tests__standard@hang-binop-comments-3.lua.snap

@@ -0,0 +1,20 @@
+---
+source: tests/tests.rs
+expression: "format(&contents, LuaVersion::Lua51)"
+input_file: tests/inputs/hang-binop-comments-3.lua
+---
+-- https://github.com/JohnnyMorganz/StyLua/issues/996
+
+local function f()
+	local a = "ab"
+	a = a:gsub(
+		"a" -- "
+			.. "b",
+		function()
+			return "c"
+		end
+	)
+	print(a)
+end
+
+f()