Trim at presentation layer

crates/ra_ide/src/completion/presentation.rs

@@ -211,7 +211,7 @@ impl Completions {
             .parameter_names
             .iter()
             .skip(if function_signature.has_self_param { 1 } else { 0 })
-            .cloned()
+            .map(|name| name.trim_start_matches('_').into())
             .collect();
 
         builder = builder.add_call_parens(ctx, name, Params::Named(params));

crates/ra_ide/src/display/function_signature.rs

@@ -237,9 +237,7 @@ impl From<&'_ ast::FnDef> for FunctionSignature {
                                     .descendants()
                                     .find_map(ast::Name::cast)?
                                     .text()
-                                    .to_string()
-                                    .trim_start_matches('_')
-                                    .into(),
+                                    .to_string(),
                             )
                         })
                         .map(|param| param.unwrap_or_default()),