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, 15 insertions, 0 deletions

diff --git a/doc/lispref/streams.texi b/doc/lispref/streams.texi
index ebd806601ef..032669cb102 100644
--- a/doc/lispref/streams.texi
+++ b/doc/lispref/streams.texi
@@ -809,6 +809,21 @@ when the output stream is a unibyte buffer or a marker pointing into
 one.
 @end defvar
 
+@defvar print-charset-text-property
+This variable controls printing of `charset' text property on printing
+a string.  The value should be @code{nil}, @code{t}, or
+@code{default}.
+
+If the value is @code{nil}, @code{charset} text properties are never
+printed.  If @code{t}, they are always printed.
+
+If the value is @code{default}, only print @code{charset} text
+properties if there is an ``unexpected'' @code{charset} property.  For
+ascii characters, all charsets are considered ``expected''.
+Otherwise, the expected @code{charset} property of a character is
+given by @code{char-charset}.
+@end defvar
+
 @defvar print-length
 @cindex printing limits
 The value of this variable is the maximum number of elements to print in