fix(fmt): multiline single param only if func definition is multiline…

… for `all_params` (#9187)

* test: adjust single param multiline expected behavior

* fix: `AllParams` single param multiline condition

* refactor: try simplifying the condition logic

crates/fmt/src/formatter.rs

@@ -1638,14 +1638,17 @@ impl<'a, W: Write> Formatter<'a, W> {
                             &params,
                             ",",
                         )?;
-                    // Write new line if we have only one parameter and params first all multi set.
-                    if params.len() == 1 &&
+                    // Write new line if we have only one parameter and params first set,
+                    // or if the function definition is multiline and all params set.
+                    let single_param_multiline = matches!(
+                        fmt.config.multiline_func_header,
+                        MultilineFuncHeaderStyle::ParamsFirst
+                    ) || params_multiline &&
                         matches!(
                             fmt.config.multiline_func_header,
-                            MultilineFuncHeaderStyle::ParamsFirst |
-                                MultilineFuncHeaderStyle::AllParams
-                        )
-                    {
+                            MultilineFuncHeaderStyle::AllParams
+                        );
+                    if params.len() == 1 && single_param_multiline {
                         writeln!(fmt.buf())?;
                     }
                     fmt.write_chunks_separated(&params, ",", params_multiline)?;

crates/fmt/testdata/FunctionDefinition/all-params.fmt.sol

@@ -3,9 +3,7 @@
 interface FunctionInterfaces {
     function noParamsNoModifiersNoReturns();
 
-    function oneParam(
-        uint256 x
-    );
+    function oneParam(uint256 x);
 
     function oneModifier() modifier1;
 
@@ -345,9 +343,7 @@ contract FunctionDefinitions {
         a = 1;
     }
 
-    function oneParam(
-        uint256 x
-    ) {
+    function oneParam(uint256 x) {
         a = 1;
     }