Improve error messages for improper plists (Bug#27726)

* src/fns.c (Fplist_put, Flax_plist_get, Flax_plist_put)
(Fplist_member, syms_of_fns): Use ‘plistp’ as pseudo-predicate for
improper plists instead of ‘listp.’

* test/src/fns-tests.el (plist-get/odd-number-of-elements)
(lax-plist-get/odd-number-of-elements)
(plist-put/odd-number-of-elements)
(lax-plist-put/odd-number-of-elements)
(plist-member/improper-list): Add unit tests.

1 files changed, 28 insertions, 0 deletions

diff --git a/test/src/fns-tests.el b/test/src/fns-tests.el
index e294859226c..73c6593caf7 100644
--- a/test/src/fns-tests.el
+++ b/test/src/fns-tests.el
@@ -547,4 +547,32 @@
   (should-error (nconc (cyc1 1) 'tail) :type 'circular-list)
   (should-error (nconc (cyc2 1 2) 'tail) :type 'circular-list))
 
+(ert-deftest plist-get/odd-number-of-elements ()
+  "Test that ‘plist-get’ doesn’t signal an error on degenerate plists."
+  (should-not (plist-get '(:foo 1 :bar) :bar)))
+
+(ert-deftest lax-plist-get/odd-number-of-elements ()
+  "Check for https://debbugs.gnu.org/cgi/bugreport.cgi?bug=27726."
+  (should (equal (should-error (lax-plist-get '(:foo 1 :bar) :bar)
+                               :type 'wrong-type-argument)
+                 '(wrong-type-argument plistp (:foo 1 :bar)))))
+
+(ert-deftest plist-put/odd-number-of-elements ()
+  "Check for https://debbugs.gnu.org/cgi/bugreport.cgi?bug=27726."
+  (should (equal (should-error (plist-put '(:foo 1 :bar) :zot 2)
+                               :type 'wrong-type-argument)
+                 '(wrong-type-argument plistp (:foo 1 :bar)))))
+
+(ert-deftest lax-plist-put/odd-number-of-elements ()
+  "Check for https://debbugs.gnu.org/cgi/bugreport.cgi?bug=27726."
+  (should (equal (should-error (lax-plist-put '(:foo 1 :bar) :zot 2)
+                               :type 'wrong-type-argument)
+                 '(wrong-type-argument plistp (:foo 1 :bar)))))
+
+(ert-deftest plist-member/improper-list ()
+  "Check for https://debbugs.gnu.org/cgi/bugreport.cgi?bug=27726."
+  (should (equal (should-error (plist-member '(:foo 1 . :bar) :qux)
+                               :type 'wrong-type-argument)
+                 '(wrong-type-argument plistp (:foo 1 . :bar)))))
+
 (provide 'fns-tests)