Honor print-charset-text-property value of nil (Bug#31376)

* src/print.c (print_check_string_charset_prop): Move check
for nil Vprint_charset_text_property from here...
(print_prune_string_charset): ... to here.
(syms_of_print) <print-charset-text-property>: Clarify that any
non-boolean values are treated the same as `default'.
* doc/lispref/streams.texi (Output Variables): Add
print-prune-string-charset.
* test/src/print-tests.el (print-charset-text-property-nil)
(print-charset-text-property-default)
(print-charset-text-property-t): New tests.
(print-tests--prints-with-charset-p): New helper function.

1 files changed, 36 insertions, 0 deletions

diff --git a/test/src/print-tests.el b/test/src/print-tests.el
index 01e65028bc7..c96cb5d2b69 100644
--- a/test/src/print-tests.el
+++ b/test/src/print-tests.el
@@ -27,6 +27,42 @@
                      (prin1-to-string "\u00A2\ff"))
                    "\"\\x00a2\\ff\"")))
 
+(defun print-tests--prints-with-charset-p (ch odd-charset)
+  "Return t if `prin1-to-string' prints CH with the `charset' property.
+CH is propertized with a `charset' value according to
+ODD-CHARSET: if nil, then use the one returned by `char-charset',
+otherwise, use a different charset."
+  (integerp
+   (string-match
+    "charset"
+    (prin1-to-string
+     (propertize (string ch)
+                 'charset
+                 (if odd-charset
+                     (cl-find (char-charset ch) charset-list :test-not #'eq)
+                   (char-charset ch)))))))
+
+(ert-deftest print-charset-text-property-nil ()
+  (let ((print-charset-text-property nil))
+    (should-not (print-tests--prints-with-charset-p ?\xf6 t)) ; Bug#31376.
+    (should-not (print-tests--prints-with-charset-p ?a t))
+    (should-not (print-tests--prints-with-charset-p ?\xf6 nil))
+    (should-not (print-tests--prints-with-charset-p ?a nil))))
+
+(ert-deftest print-charset-text-property-default ()
+  (let ((print-charset-text-property 'default))
+    (should (print-tests--prints-with-charset-p ?\xf6 t))
+    (should-not (print-tests--prints-with-charset-p ?a t))
+    (should-not (print-tests--prints-with-charset-p ?\xf6 nil))
+    (should-not (print-tests--prints-with-charset-p ?a nil))))
+
+(ert-deftest print-charset-text-property-t ()
+  (let ((print-charset-text-property t))
+    (should (print-tests--prints-with-charset-p ?\xf6 t))
+    (should (print-tests--prints-with-charset-p ?a t))
+    (should (print-tests--prints-with-charset-p ?\xf6 nil))
+    (should (print-tests--prints-with-charset-p ?a nil))))
+
 (ert-deftest terpri ()
   (should (string= (with-output-to-string
                      (princ 'abc)