fix: function returns formatting

crates/fmt/src/formatter.rs

@@ -1497,12 +1497,27 @@ impl<'a, W: Write> Formatter<'a, W> {
                 if fmt.inline_config.is_disabled(returns_loc) {
                     fmt.indented(1, |fmt| fmt.visit_source(returns_loc))?;
                 } else {
-                    let returns = fmt.items_to_chunks(
+                    let mut returns = fmt.items_to_chunks(
                         returns_end,
                         func.returns
                             .iter_mut()
                             .filter_map(|(loc, param)| param.as_mut().map(|param| (*loc, param))),
                     )?;
+
+                    // there's an issue with function return value that would lead to indent issues because those can be formatted with line breaks <https://github.com/foundry-rs/foundry/issues/4080>
+                    for function_chunk in
+                        returns.iter_mut().filter(|chunk| chunk.content.starts_with("function("))
+                    {
+                        // this will bypass the recursive indent that was applied when the function
+                        // content was formatted in the chunk
+                        function_chunk.content = function_chunk
+                            .content
+                            .split('\n')
+                            .map(|s| s.trim_start())
+                            .collect::<Vec<_>>()
+                            .join("\n");
+                    }
+
                     fmt.write_postfix_comments_before(returns_loc.start())?;
                     fmt.write_whitespace_separator(multiline)?;
                     fmt.indented(1, |fmt| {

crates/fmt/testdata/FunctionDefinitionWithFunctionReturns/fmt.sol

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
+
+contract ReturnFnFormat {
+    function returnsFunction()
+        internal
+        pure
+        returns (
+            function()
+            internal pure returns (uint256)
+        )
+    {}
+}

crates/fmt/testdata/FunctionDefinitionWithFunctionReturns/original.sol

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
+
+contract ReturnFnFormat {
+    function returnsFunction()
+    internal
+    pure
+    returns (
+        function()
+        internal pure returns (uint256)
+    )
+    {}
+}

crates/fmt/tests/formatter.rs

@@ -160,6 +160,7 @@ test_directories! {
     ErrorDefinition,
     EventDefinition,
     FunctionDefinition,
+    FunctionDefinitionWithFunctionReturns,
     FunctionType,
     ImportDirective,
     ModifierDefinition,