Support mode aliases in 'provided-mode-derived-p'

* lisp/subr.el (provided-mode-derived-p): Check aliases of
MODES as well as MODES themselves.  (Bug#32795)

* test/lisp/subr-tests.el (provided-mode-derived-p): New test.

Copyright-paperwork-exempt: yes

1 files changed, 12 insertions, 0 deletions

diff --git a/test/lisp/subr-tests.el b/test/lisp/subr-tests.el
index 86938d5dbe0..f218a7663e0 100644
--- a/test/lisp/subr-tests.el
+++ b/test/lisp/subr-tests.el
@@ -61,6 +61,18 @@
                      (quote
                       (0 font-lock-keyword-face))))))))
 
+(ert-deftest provided-mode-derived-p ()
+  ;; base case: `derived-mode' directly derives `prog-mode'
+  (should (progn
+            (define-derived-mode derived-mode prog-mode "test")
+            (provided-mode-derived-p 'derived-mode 'prog-mode)))
+  ;; edge case: `derived-mode' derives an alias of `prog-mode'
+  (should (progn
+            (defalias 'parent-mode
+              (if (fboundp 'prog-mode) 'prog-mode 'fundamental-mode))
+            (define-derived-mode derived-mode parent-mode "test")
+            (provided-mode-derived-p 'derived-mode 'prog-mode))))
+
 (ert-deftest number-sequence-test ()
   (should (= (length
               (number-sequence (1- most-positive-fixnum) most-positive-fixnum))