[elpa] externals/compat db9321e222 1/3: Add provided-mode-derived-p from Emacs 27

[ELPA Syncer]

branch: externals/compat
commit db9321e222352c5c276c5df60b921999034264bf
Author: Philip Kaludercic <philipk@posteo.net>
Commit: Philip Kaludercic <philipk@posteo.net>

    Add provided-mode-derived-p from Emacs 27
---
 compat-27.el    | 17 +++++++++++++++++
 compat-tests.el | 23 +++++++++++++++++++++++
 compat.texi     |  7 +++++++
 3 files changed, 47 insertions(+)

diff --git a/compat-27.el b/compat-27.el
index fdc81c93c8..89ed286954 100644
--- a/compat-27.el
+++ b/compat-27.el
@@ -399,6 +399,23 @@ where USER is a valid login name."
               body)))
     (cons 'progn (nreverse body))))
 
+(compat-defun provided-mode-derived-p (mode &rest modes)
+  "Non-nil if MODE is derived from one of MODES.
+Uses the `derived-mode-parent' property of the symbol to trace backwards.
+If you just want to check `major-mode', use `derived-mode-p'."
+  :realname compat--provided-mode-derived-p
+  ;; If MODE is an alias, then look up the real mode function first.
+  (when-let ((alias (symbol-function mode)))
+    (when (symbolp alias)
+      (setq mode alias)))
+  (while
+      (and
+       (not (memq mode modes))
+       (let* ((parent (get mode 'derived-mode-parent))
+              (parentfn (symbol-function parent)))
+         (setq mode (if (and parentfn (symbolp parentfn)) parentfn parent)))))
+  mode)
+
 ;;* UNTESTED
 (compat-defmacro ignore-error (condition &rest body)
   "Execute BODY; if the error CONDITION occurs, return nil.
diff --git a/compat-tests.el b/compat-tests.el
index b2940cfbd8..0794b76972 100644
--- a/compat-tests.el
+++ b/compat-tests.el
@@ -1838,5 +1838,28 @@ being compared against."
   (ought t "~root/")
   (ought t "~root/file"))
 
+(let ((one (make-symbol "1"))
+      (two (make-symbol "2"))
+      (three (make-symbol "3"))
+      (one.5 (make-symbol "1.5"))
+      (eins (make-symbol "𝟙")))
+  (put two 'derived-mode-parent one)
+  (put one.5 'derived-mode-parent one)
+  (put three 'derived-mode-parent two)
+  (compat-deftests provided-mode-derived-p
+    (ought one one one)
+    (ought one two one)
+    (ought one three one)
+    (ought nil one eins)
+    (ought nil two eins)
+    (ought nil two one.5)
+    (ought one two one.5 one)
+    (ought two two one.5 two)
+    (ought one three one.5 one)
+    (ought two three one.5 one two)
+    (ought two three one.5 two one)
+    (ought three three one.5 two one three)
+    (ought three three one.5 three two one)))
+
 (provide 'compat-tests)
 ;;; compat-tests.el ends here
diff --git a/compat.texi b/compat.texi
index 7e70fd9d61..27b00337c4 100644
--- a/compat.texi
+++ b/compat.texi
@@ -1468,6 +1468,13 @@ of @env{PATH} can lead to confusing results.
 @xref{Subprocess Creation,,,elisp}.
 @end defopt
 
+@c based on lisp/modes.el
+@defun provided-mode-derived-p mode &rest modes
+This function returns non-@code{nil} if @var{mode} is derived from any
+of the major modes given by the symbols @var{modes}.
+@end defun
+
+
 @subsection Prefixed Definitions
 These functions are prefixed with @code{compat} prefix, and are only
 loaded when @code{compat-27} is required: