eieio-core.el: Allow assignment to cl-structs through `slot-value`

* lisp/emacs-lisp/eieio-core.el (eieio--validate-slot-value):
Obey the `:read-only` property of the slot.
(eieio-oset): Allow use on cl-structs as well.
(eieio-read-only): New error.

* test/lisp/emacs-lisp/eieio-tests/eieio-tests.el (eieio-test--struct):
Make the last field read-only.
(eieio-test-defstruct-slot-value): Test that cl-struct slots can be
assigned via `slot-value`.

1 files changed, 5 insertions, 2 deletions

diff --git a/test/lisp/emacs-lisp/eieio-tests/eieio-tests.el b/test/lisp/emacs-lisp/eieio-tests/eieio-tests.el
index dfdfb63b584..6f6a1f4f19a 100644
--- a/test/lisp/emacs-lisp/eieio-tests/eieio-tests.el
+++ b/test/lisp/emacs-lisp/eieio-tests/eieio-tests.el
@@ -971,7 +971,7 @@ Subclasses to override slot attributes.")
 
 ;;;; Interaction with defstruct
 
-(cl-defstruct eieio-test--struct a b c)
+(cl-defstruct eieio-test--struct a b (c nil :read-only t))
 
 (ert-deftest eieio-test-defstruct-slot-value ()
   (let ((x (make-eieio-test--struct :a 'A :b 'B :c 'C)))
@@ -980,7 +980,10 @@ Subclasses to override slot attributes.")
     (should (eq (eieio-test--struct-b x)
                 (slot-value x 'b)))
     (should (eq (eieio-test--struct-c x)
-                (slot-value x 'c)))))
+                (slot-value x 'c)))
+    (setf (slot-value x 'a) 1)
+    (should (eq (eieio-test--struct-a x) 1))
+    (should-error (setf (slot-value x 'c) 3) :type 'eieio-read-only)))
 
 (provide 'eieio-tests)