Ensure rustfmt is invoked without edition parameter

Author: apiraino

rust-cargo-tests.el

@@ -21,6 +21,13 @@
        (find-file main-file)
        ,expr)))
 
+(defmacro rust-test--with-snippet-buffer (expr)
+  `(let* ((test-dir (expand-file-name "test-project/" default-directory))
+          (snippet-file (expand-file-name "src/rustfmt-default.rs" test-dir)))
+     (save-current-buffer
+       (find-file snippet-file)
+       ,expr)))
+
 (defun rust-test--find-string (string)
   "Find STRING in current buffer."
   (goto-char (point-min))
@@ -70,3 +77,13 @@
       (should (eq major-mode 'rust-format-mode))
       (should (rust-test--find-string "error:")))
     (kill-buffer "*rustfmt*")))
+
+(ert-deftest rust-test-respect-rustfmt-defaults ()
+  (skip-unless (executable-find "rustfmt"))
+  (rust-test--with-snippet-buffer
+   (let ((old-content (buffer-string))
+             (ret (rust-format-buffer)))
+         (should (string= old-content (buffer-string))))))
+
+(ert-deftest rust-test-ensure-rustfmt-switches-nil ()
+  (should (eq rust-rustfmt-switches nil)))

rust-rustfmt.el

@@ -33,8 +33,10 @@
   :type 'string
   :group 'rust-mode)
 
-(defcustom rust-rustfmt-switches '("--edition" "2024")
-  "Arguments to pass when invoking the `rustfmt' executable."
+(defcustom rust-rustfmt-switches nil
+  "Arguments to pass when invoking the `rustfmt' executable. This variable
+will override any user configuration (e.g. rustfmt.toml). Recommendation
+is to not modify this and rely on declarative configuration instead."
   :type '(repeat string)
   :group 'rust-mode)
 

test-project/src/rustfmt-default.rs

@@ -0,0 +1,5 @@
+// this file ensures that by default rustfmt is invoked without parameters
+// and formats with its default (--edition=2015 as of today)
+
+// With --edition=2024 this import will be reordered
+use std::{i16, i8};