Keep multiline function arguments hugged with Input collapse mode

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed function calls with a multiline anonymous function argument being expanded when `collapse_simple_statement = "Input"`, instead of keeping the function hugged to the call parentheses ([#1175](https://github.com/JohnnyMorganz/StyLua/issues/1175))
+
 ## [2.6.0] - 2026-10-10
 
 ### Added

src/formatters/functions.rs

@@ -260,12 +260,17 @@ fn function_args_multiline_heuristic(
     // Use state values to determine the type of arguments we have seen so far
     let mut current_state = ArgumentState::new();
 
-    for pair in first_iter_formatted_arguments {
+    for (pair, original_argument) in first_iter_formatted_arguments.zip(arguments.iter()) {
         let argument = pair.value();
         match argument {
             Expression::Function(anonymous_function) => {
-                // Check to see whether it has been expanded
-                let is_expanded = !should_collapse_function_body(ctx, anonymous_function.body());
+                // Check to see whether it has been expanded. Use the original function body where possible:
+                // the formatted one has lost the input positions that `CollapseSimpleStatement::Input` relies on
+                let function_body = match original_argument {
+                    Expression::Function(original_function) => original_function.body(),
+                    _ => anonymous_function.body(),
+                };
+                let is_expanded = !should_collapse_function_body(ctx, function_body);
                 if is_expanded {
                     // If we have a mixture of multiline args, and other arguments
                     // Then the function args should be expanded

tests/tests.rs

@@ -263,6 +263,68 @@ end)
     );
 }
 
+const COLLAPSE_FUNCTION_ARGUMENT_INPUT: &str = r#"pcall(function()
+	return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb
+end, 5)
+pcall(function() return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb end, 5)
+foo(1, function()
+	return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb
+end)
+pcall(function() return x end, 5)
+"#;
+
+#[test]
+fn test_collapse_simple_statement_input_keeps_multiline_function_argument_hug() {
+    let config = Config {
+        collapse_simple_statement: CollapseSimpleStatement::Input,
+        ..Config::default()
+    };
+
+    insta::assert_snapshot!(
+        format_code(COLLAPSE_FUNCTION_ARGUMENT_INPUT, config, None, OutputVerification::None).unwrap(),
+        @r###"
+    pcall(function()
+    	return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb
+    end, 5)
+    pcall(
+    	function() return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb end,
+    	5
+    )
+    foo(1, function()
+    	return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb
+    end)
+    pcall(function() return x end, 5)
+    "###
+    );
+}
+
+#[test]
+fn test_collapse_simple_statement_always_function_argument_hug() {
+    let config = Config {
+        collapse_simple_statement: CollapseSimpleStatement::Always,
+        ..Config::default()
+    };
+
+    insta::assert_snapshot!(
+        format_code(COLLAPSE_FUNCTION_ARGUMENT_INPUT, config, None, OutputVerification::None).unwrap(),
+        @r###"
+    pcall(
+    	function() return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb end,
+    	5
+    )
+    pcall(
+    	function() return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb end,
+    	5
+    )
+    foo(
+    	1,
+    	function() return aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa == bbb end
+    )
+    pcall(function() return x end, 5)
+    "###
+    );
+}
+
 #[test]
 fn test_preserve_block_newline_gaps() {
     insta::glob!("inputs-preserve-block-newline-gaps/*.lua", |path| {