Fix encoding with 'utf-8-auto'

* src/coding.c (encode_coding_utf_8): Fix encoding with
'utf-8-auto': it should produce BOM, per the documentation of
the :bom attribute.  (Bug#60750)

* lisp/international/mule.el (define-coding-system): Doc fix.

* test/src/coding-tests.el (coding-tests): Use
'with-coding-priority' instead of 'prefer-coding-system', as the
latter has global persistent effect and affects further tests.

1 files changed, 15 insertions, 15 deletions

diff --git a/test/src/coding-tests.el b/test/src/coding-tests.el
index 6bd8d1ae6c4..b27907027ba 100644
--- a/test/src/coding-tests.el
+++ b/test/src/coding-tests.el
@@ -148,21 +148,21 @@
 
 (defun coding-tests (content-type write-coding read-coding detected-coding
                                    &optional translator)
-  (prefer-coding-system 'utf-8-auto)
-  (let ((filename (coding-tests-filename content-type write-coding)))
-    (with-temp-buffer
-      (let ((coding-system-for-read read-coding)
-            (contents (coding-tests-file-contents content-type))
-            (disable-ascii-optimization nil))
-        (if translator
-            (setq contents (funcall translator contents)))
-        (insert-file-contents filename)
-        (if (and (coding-system-equal buffer-file-coding-system detected-coding)
-                 (string= (buffer-string) contents))
-            nil
-          (list buffer-file-coding-system
-                (string-to-list (buffer-string))
-                (string-to-list contents)))))))
+  (with-coding-priority '(utf-8-auto)
+    (let ((filename (coding-tests-filename content-type write-coding)))
+      (with-temp-buffer
+        (let ((coding-system-for-read read-coding)
+              (contents (coding-tests-file-contents content-type))
+              (disable-ascii-optimization nil))
+          (if translator
+              (setq contents (funcall translator contents)))
+          (insert-file-contents filename)
+          (if (and (coding-system-equal buffer-file-coding-system detected-coding)
+                   (string= (buffer-string) contents))
+              nil
+            (list buffer-file-coding-system
+                  (string-to-list (buffer-string))
+                  (string-to-list contents))))))))
 
 (ert-deftest ert-test-coding-ascii ()
   (unwind-protect