bug#44155: Print integers as characters

["Mattias Engdegård" <mattiase@acm.org>]

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3 nov. 2020 kl. 16.24 skrev Eli Zaretskii <eliz@gnu.org>:

> What is meant by "printable characters" here?  One could think you
> mean [:print:], but that doesn't seem to be what then code does.

Non-control characters (characters other than control characters), in this case. I wanted to keep things simple and not involve the Unicode database in the printer.

(For that matter, [:print:] is a regexp feature and doesn't really define the meaning of 'printable', but your question was valid.)

On the other hand, printing all non-controls using the ?X syntax is maybe not ideal. Attached is a new patch that uses Unicode properties to select only printable base characters.

This patch also removes \a, \v, \e and \d from the characters printed as escaped controls.


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From 3da6d9055b0ae68fc7b3bbee52885113c8c30b6d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Mon, 2 Nov 2020 23:37:16 +0100
Subject: [PATCH] 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
such as ?\n if available, as numbers otherwise (bug#44155).
Done in collaboration with Juri Linkov.

* src/character.c (printable_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.
---
 doc/lispref/streams.texi | 13 +++++----
 etc/NEWS                 | 11 ++++---
 src/character.c          | 21 ++++++++++++++
 src/character.h          |  1 +
 src/print.c              | 63 ++++++++++++++++++++++++++--------------
 test/src/print-tests.el  | 39 +++++++++++++------------
 6 files changed, 96 insertions(+), 52 deletions(-)

diff --git a/doc/lispref/streams.texi b/doc/lispref/streams.texi
index f171f13779..4bc97e4c48 100644
--- a/doc/lispref/streams.texi
+++ b/doc/lispref/streams.texi
@@ -903,10 +903,11 @@ Output Variables
 you can use, see the variable's documentation string.
 @end defvar
 
-@defvar integer-output-format
-This variable specifies how to print integer numbers.  The default is
-@code{nil}, meaning use the decimal format.  When bound to @code{t},
-print integers as characters when an integer represents a character
-(@pxref{Basic Char Syntax}).  When bound to the number @code{16},
-print non-negative integers in the hexadecimal format.
+@defvar print-integers-as-characters
+When this variable is non-@code{nil}, integers that represent
+printable characters or control characters with their own escape
+syntax such as newline will be printed using Lisp character syntax
+(@pxref{Basic Char Syntax}).  Other numbers are printed the usual way.
+For example, the list @code{(4 65 -1 10)} will be printed as
+@samp{(4 ?A -1 ?\n)}.
 @end defvar
diff --git a/etc/NEWS b/etc/NEWS
index e11effc9e8..384c64a91e 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1689,12 +1689,6 @@ ledit.el, lmenu.el, lucid.el and old-whitespace.el.
 \f
 * Lisp Changes in Emacs 28.1
 
-** New variable 'integer-output-format' determines how to print integer values.
-When this variable is bound to the value 't', integers are printed by
-printing functions as characters when an integer represents a character.
-When bound to the number 16, non-negative integers are printed in the
-hexadecimal format.
-
 +++
 ** 'define-globalized-minor-mode' now takes a ':predicate' parameter.
 This can be used to control which major modes the minor mode should be
@@ -1887,6 +1881,11 @@ file can affect code in another.  For details, see the manual section
 'replace-regexp-in-string', 'catch', 'throw', 'error', 'signal'
 and 'play-sound-file'.
 
++++
+** New variable 'print-integers-as-characters' modifies integer printing.
+When this variable is non-nil, character syntax is used for printing
+numbers for which this makes sense, such as '?*' for 42.
+
 \f
 * Changes in Emacs 28.1 on Non-Free Operating Systems
 
diff --git a/src/character.c b/src/character.c
index 5860f6a0c8..6d18e78f26 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 a printable independent character.  */
+bool
+printable_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);
+
+  /* See UTS #18.  */
+  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_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
diff --git a/src/character.h b/src/character.h
index af5023f77c..260c550108 100644
--- a/src/character.h
+++ b/src/character.h
@@ -583,6 +583,7 @@ char_surrogate_p (int c)
 extern bool graphicp (int);
 extern bool printablep (int);
 extern bool blankp (int);
+extern bool printable_base_p (int);
 
 /* Look up the element in char table OBJ at index CH, and return it as
    an integer.  If the element is not a character, return CH itself.  */
diff --git a/src/print.c b/src/print.c
index fa65a3cb26..f7158dbac0 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1848,6 +1848,24 @@ print_vectorlike (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag,
   return true;
 }
 
+static char
+named_escape (int i)
+{
+  switch (i)
+    {
+    case '\b': return 'b';
+    case '\t': return 't';
+    case '\n': return 'n';
+    case '\f': return 'f';
+    case '\r': return 'r';
+    case ' ':  return 's';
+      /* \a, \v, \e and \d are excluded from printing as escapes since
+         they are somewhat rare as characters and more likely to be
+         plain integers. */
+    }
+  return 0;
+}
+
 static void
 print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
 {
@@ -1908,29 +1926,30 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
     {
     case_Lisp_Int:
       {
-	int c;
-	intmax_t i;
+        EMACS_INT i = XFIXNUM (obj);
+        char escaped_name;
 
-	if (EQ (Vinteger_output_format, Qt) && CHARACTERP (obj)
-	    && (c = XFIXNUM (obj)))
+	if (print_integers_as_characters && i >= 0 && i <= MAX_UNICODE_CHAR
+            && ((escaped_name = named_escape (i))
+                || printable_base_p (i)))
 	  {
 	    printchar ('?', printcharfun);
-	    if (escapeflag
-		&& (c == ';' || c == '(' || c == ')' || c == '{' || c == '}'
-		    || c == '[' || c == ']' || c == '\"' || c == '\'' || c == '\\'))
+            if (escaped_name)
+              {
+                printchar ('\\', printcharfun);
+                i = escaped_name;
+              }
+            else if (escapeflag
+                     && (i == ';' || i == '\"' || i == '\'' || i == '\\'
+                         || i == '(' || i == ')'
+                         || i == '{' || i == '}'
+                         || i == '[' || i == ']'))
 	      printchar ('\\', printcharfun);
-	    printchar (c, printcharfun);
-	  }
-	else if (INTEGERP (Vinteger_output_format)
-		 && integer_to_intmax (Vinteger_output_format, &i)
-		 && i == 16 && !NILP (Fnatnump (obj)))
-	  {
-	    int len = sprintf (buf, "#x%"pI"x", (EMACS_UINT) XFIXNUM (obj));
-	    strout (buf, len, len, printcharfun);
+	    printchar (i, printcharfun);
 	  }
 	else
 	  {
-	    int len = sprintf (buf, "%"pI"d", XFIXNUM (obj));
+	    int len = sprintf (buf, "%"pI"d", i);
 	    strout (buf, len, len, printcharfun);
 	  }
       }
@@ -2270,12 +2289,12 @@ syms_of_print (void)
 that represents the number without losing information.  */);
   Vfloat_output_format = Qnil;
 
-  DEFVAR_LISP ("integer-output-format", Vinteger_output_format,
-	       doc: /* The format used to print integers.
-When t, print characters from integers that represent a character.
-When a number 16, print non-negative integers in the hexadecimal format.
-Otherwise, by default print integers in the decimal format.  */);
-  Vinteger_output_format = Qnil;
+  DEFVAR_BOOL ("print-integers-as-characters", print_integers_as_characters,
+	       doc: /* Non-nil means integers are printed using characters syntax.
+Only printable characters, and control characters with named escape
+sequences such as newline, are printed this way.  Other integers,
+including those corresponding to raw bytes, are not affected.  */);
+  print_integers_as_characters = Qnil;
 
   DEFVAR_LISP ("print-length", Vprint_length,
 	       doc: /* Maximum length of list to print before abbreviating.
diff --git a/test/src/print-tests.el b/test/src/print-tests.el
index 7b026b6b21..05b1e4e6e4 100644
--- a/test/src/print-tests.el
+++ b/test/src/print-tests.el
@@ -383,25 +383,28 @@ print-hash-table-test
       (let ((print-length 1))
         (format "%S" h))))))
 
-(print-tests--deftest print-integer-output-format ()
+(print-tests--deftest print-integers-as-characters ()
   ;; Bug#44155.
-  (let ((integer-output-format t)
-        (syms (list ?? ?\; ?\( ?\) ?\{ ?\} ?\[ ?\] ?\" ?\' ?\\ ?Á)))
-    (should (equal (read (print-tests--prin1-to-string syms)) syms))
-    (should (equal (print-tests--prin1-to-string syms)
-                   (concat "(" (mapconcat #'prin1-char syms " ") ")"))))
-  (let ((integer-output-format t)
-        (syms (list -1 0 1 ?\120 4194175 4194176 (max-char) (1+ (max-char)))))
-    (should (equal (read (print-tests--prin1-to-string syms)) syms)))
-  (let ((integer-output-format 16)
-        (syms (list -1 0 1 most-positive-fixnum (1+ most-positive-fixnum))))
-    (should (equal (read (print-tests--prin1-to-string syms)) syms))
-    (should (equal (print-tests--prin1-to-string syms)
-                   (concat "(" (mapconcat
-                                (lambda (i)
-                                  (if (and (>= i 0) (<= i most-positive-fixnum))
-                                      (format "#x%x" i) (format "%d" i)))
-                                syms " ") ")")))))
+  (let* ((print-integers-as-characters t)
+         (chars '(?? ?\; ?\( ?\) ?\{ ?\} ?\[ ?\] ?\" ?\' ?\\ ?f ?~ ?Á 32
+                  ?\n ?\r ?\t ?\b ?\f ?\a ?\v ?\e ?\d))
+         (nums '(-1 -65 0 1 31 #x80 #x9f #x110000 #x3fff80 #x3fffff))
+         (nonprints '(#xd800 #xdfff #x030a #xffff #x200c))
+         (printed-chars (print-tests--prin1-to-string chars))
+         (printed-nums (print-tests--prin1-to-string nums))
+         (printed-nonprints (print-tests--prin1-to-string nonprints)))
+    (should (equal (read printed-chars) chars))
+    (should (equal
+             printed-chars
+             (concat
+              "(?? ?\\; ?\\( ?\\) ?\\{ ?\\} ?\\[ ?\\] ?\\\" ?\\' ?\\\\"
+              " ?f ?~ ?Á ?\\s ?\\n ?\\r ?\\t ?\\b ?\\f 7 11 27 127)")))
+    (should (equal (read printed-nums) nums))
+    (should (equal printed-nums
+                   "(-1 -65 0 1 31 128 159 1114112 4194176 4194303)"))
+    (should (equal (read printed-nonprints) nonprints))
+    (should (equal printed-nonprints
+                   "(55296 57343 778 65535 8204)"))))
 
 (provide 'print-tests)
 ;;; print-tests.el ends here
-- 
2.21.1 (Apple Git-122.3)