Reduce integer-output-format to print-integers-as-characters

The variable now only controls whether characters are printed, not
the radix.  Control chars are printed in human-readable syntax
only when special escapes such as ?\n are available.  Spaces,
formatting and combining chars are excluded (bug#44155).
Done in collaboration with Juri Linkov.

* src/character.c (graphic_base_p):
* src/print.c (named_escape): New functions.
(print_object): Change semantics as described above.
(syms_of_print): Rename integer-output-format.  Update doc string.
* doc/lispref/streams.texi (Output Variables):
* etc/NEWS:
* test/src/print-tests.el (print-integers-as-characters):
Rename and update according to new semantics.  The test now passes.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/character.c b/src/character.c
index 5860f6a0c8c..00b73293a3f 100644
--- a/src/character.c
+++ b/src/character.c
@@ -982,6 +982,27 @@ printablep (int c)
 	    || gen_cat == UNICODE_CATEGORY_Cn)); /* unassigned */
 }
 
+/* Return true if C is graphic character that can be printed independently.  */
+bool
+graphic_base_p (int c)
+{
+  Lisp_Object category = CHAR_TABLE_REF (Vunicode_category_table, c);
+  if (! FIXNUMP (category))
+    return false;
+  EMACS_INT gen_cat = XFIXNUM (category);
+
+  return (!(gen_cat == UNICODE_CATEGORY_Mn       /* mark, nonspacing */
+            || gen_cat == UNICODE_CATEGORY_Mc    /* mark, combining */
+            || gen_cat == UNICODE_CATEGORY_Me    /* mark, enclosing */
+            || gen_cat == UNICODE_CATEGORY_Zs    /* separator, space */
+            || gen_cat == UNICODE_CATEGORY_Zl    /* separator, line */
+            || gen_cat == UNICODE_CATEGORY_Zp    /* separator, paragraph */
+            || gen_cat == UNICODE_CATEGORY_Cc    /* other, control */
+            || gen_cat == UNICODE_CATEGORY_Cs    /* other, surrogate */
+            || gen_cat == UNICODE_CATEGORY_Cf    /* other, format */
+            || gen_cat == UNICODE_CATEGORY_Cn)); /* other, unassigned */
+}
+
 /* Return true if C is a horizontal whitespace character, as defined
    by https://www.unicode.org/reports/tr18/tr18-19.html#blank.  */
 bool