Re: Puzzling behavior from echo area: truncates prompt string at 100 characters?

Re: Puzzling behavior from echo area: truncates prompt string at 100 characters?

[Eli Zaretskii]

[Moved here from help-gnu-emacs.]

> Date: Tue, 20 Dec 2011 20:29:57 -0500
> From: Tom Davey <tdavey@gmail.com>
> 
> I'm using Emacs 24.0.50.1. The following "message" command, with an
> arbitrarily chosen argument string of exactly 150 characters --
> 
> (message "0123456789 123456789 223456789 323456789 423456789 523456789
> 623456789 723456789 823456789 923456789 023456789 123456789 223456789
> 323456789 423456789")
> 
> -- displays the entire length of the string (all 150 characters) in
> the minibuffer's echo area, as one would expect. In fact, I find that
> the echo area frame will expand in height to display even much longer
> messages. (The variable "message-truncate-lines" is nil.)
> 
> However, if the same 150-character string becomes an argument to an
> "(interactive)" declaration in a defun() function, like this --
> 
> (interactive "c0123456789 123456789 223456789 323456789 423456789
> 523456789 623456789 723456789 823456789 923456789 023456789 123456789
> 223456789 323456789 423456789")
> 
> -- then the display of the prompt string in the echo area is
> truncated. Only the first 99 characters display; the remainder of the
> echo area (to the right) is unused and empty. Nor does the echo area's
> frame expand in height, as it does with the "message" function.
> 
> Naturally, in a real-world application my prompt string would not be
> composed of integers but of helpful alphanumeric text. However, no
> matter what form of a prompt string I supply to the "interactive"
> declaration, the echo area truncates it at the 100th character.
> 
> Does anybody have an idea how I might get a long prompt in an
> interactive declaration to fully display in the echo area?

This happens because call-interactively arbitrarily truncates the
prompt at the 99th character:

  char prompt1[100];
  ...
      strncpy (prompt1, tem + 1, sizeof prompt1 - 1);
      prompt1[sizeof prompt1 - 1] = 0;
      tem1 = strchr (prompt1, '\n');
      if (tem1) *tem1 = 0;

      visargs[0] = build_string (prompt1);
      if (strchr (prompt1, '%'))
	callint_message = Fformat (i, visargs);
      else
	callint_message = visargs[0];
  ...
        case 'c':		/* Character */
	  /* Prompt in `minibuffer-prompt' face.  */
	  Fput_text_property (make_number (0),
			      make_number (SCHARS (callint_message)),
			      Qface, Qminibuffer_prompt, callint_message);
	  args[i] = Fread_char (callint_message, Qnil, Qnil);

This limitation was there since 1991, but AFAICS it is not documented
anywhere.

Do we want to keep this limitation?  If so, it should be at least
documented.

Re: Puzzling behavior from echo area: truncates prompt string at 100 characters?

[Andreas Schwab]

Eli Zaretskii <eliz@gnu.org> writes:

> This limitation was there since 1991, but AFAICS it is not documented
> anywhere.

I don't think this was a deliberate decision, just sloppy coding.

> Do we want to keep this limitation?  If so, it should be at least
> documented.

I can trivially be lifted:

diff --git a/src/callint.c b/src/callint.c
index 80e24f6..8dcf9a6 100644
--- a/src/callint.c
+++ b/src/callint.c
@@ -274,7 +274,6 @@ invoke it.  If KEYS is omitted or nil, the return value of
 
   ptrdiff_t i, nargs;
   int foo;
-  char prompt1[100];
   char *tem1;
   int arg_from_tty = 0;
   struct gcpro gcpro1, gcpro2, gcpro3, gcpro4, gcpro5;
@@ -491,13 +490,8 @@ invoke it.  If KEYS is omitted or nil, the return value of
   tem = string;
   for (i = 1; *tem; i++)
     {
-      strncpy (prompt1, tem + 1, sizeof prompt1 - 1);
-      prompt1[sizeof prompt1 - 1] = 0;
-      tem1 = strchr (prompt1, '\n');
-      if (tem1) *tem1 = 0;
-
-      visargs[0] = build_string (prompt1);
-      if (strchr (prompt1, '%'))
+      visargs[0] = make_string (tem + 1, strcspn (tem + 1, "\n"));
+      if (strchr (SSDATA (visargs[0]), '%'))
 	callint_message = Fformat (i, visargs);
       else
 	callint_message = visargs[0];

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Puzzling behavior from echo area: truncates prompt string at 100 characters?

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: Tom Davey <tdavey@gmail.com>,  emacs-devel@gnu.org
> Date: Sat, 24 Dec 2011 11:59:36 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > This limitation was there since 1991, but AFAICS it is not documented
> > anywhere.
> 
> I don't think this was a deliberate decision, just sloppy coding.

Most probably.

> > Do we want to keep this limitation?  If so, it should be at least
> > documented.
> 
> I can trivially be lifted:

Assuming Stefan and Chong approve, I think you should install this.

Thanks.

Re: Puzzling behavior from echo area: truncates prompt string at 100 characters?

[Tom Davey]

Eli Zaretskii writes to Andreas Schwab:

> Assuming Stefan and Chong approve, I think you should install this.

I am not a programmer, just an IT business guy. That my little
question might result in a useful patch to Emacs is beyond gratifying.
Thanks for making my day.

Tom Davey

--
Tom Davey
tom@tomdavey.com
New York NY USA

Re: Puzzling behavior from echo area: truncates prompt string at 100 characters?

[Chong Yidong]

Eli Zaretskii <eliz@gnu.org> writes:

>> > Do we want to keep this limitation?  If so, it should be at least
>> > documented.
>>
>> I can trivially be lifted:
>
> Assuming Stefan and Chong approve, I think you should install this.

Absolutely: please to commit, and thanks.