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-edition-2015-file-buffer (expr)
+  `(let* ((test-dir (expand-file-name "test-project/" default-directory))
+          (main-file (expand-file-name "src/edition-2015.rs" test-dir)))
+     (save-current-buffer
+       (find-file main-file)
+       ,expr)))
+
 (defun rust-test--find-string (string)
   "Find STRING in current buffer."
   (goto-char (point-min))
@@ -70,3 +77,10 @@
       (should (eq major-mode 'rust-format-mode))
       (should (rust-test--find-string "error:")))
     (kill-buffer "*rustfmt*")))
+
+(ert-deftest rust-test-rustfmt-ensure-edition-2015 ()
+  (skip-unless (executable-find "rustfmt"))
+  (rust-test--with-edition-2015-file-buffer
+   (let ((old-content (buffer-string))
+             (ret (rust-format-buffer)))
+         (should (string= old-content (buffer-string))))))

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/edition-2015.rs

@@ -0,0 +1,4 @@
+// this file ensures that by default rustfmt is invoked without parameters
+// and formats with its default --edition=2015
+// (with --edition=2024 this import would be reordered)
+use anyhow::{anyhow, Context};