[PATCH] [gdb/build] Remove dependency on _rl_term_autowrap

[Tom de Vries <tdevries@suse.de>]

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[ was: Re: [pushed] [gdb/tui] Fix TUI resizing for TERM=ansi ]

On 4/30/23 21:15, Tom Tromey wrote:
>>>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes:
> 
> Tom> As it happens, when TERM is set to ansi, readline decides that the terminal
> Tom> cannot auto-wrap lines, and reserves one column to deal with that, and as a
> Tom> result reports back one less than the actual screen width:
> ...
> Tom> This is currently not causing trouble in testing because we have a workaround
> Tom> in place in proc Term::resize.  If we disable the workaround:
> 
> Thank you for tracking this down.
> I never even considered this might be a readline issue.
> 
> Tom> +      readline_hidden_cols = _rl_term_autowrap ? 0 : 1;
> 
> I hate to have a new dependency on a readline internal variable.

Agreed, it's ugly.

> Don't some distros mark these as hidden in libreadline.so?
> I feel like there was another bug along these lines.
> 

That's probably PR10723 - "Dependency on readline internal variable" ( 
https://sourceware.org/bugzilla/show_bug.cgi?id=10723 ).

> However, I don't see another way to do it.

I had an earlier version of the patch that used the COLUMNS env variable 
instead.  It felt a bit hacky, so I went for _rl_term_autowrap, but 
patch attached below goes back to the COLUMNS approach.  WDYT?

> Maybe some official API could be added by the upstream readline.
> Would you want to bring it up there?
> 

If we commit the patch below, then this is solved for _rl_term_autowrap, 
but not for the other instances.

I expect bringing it up will will need to be done per instance, with a 
detailed explanation of why we need it, so that sounds like project I 
don't have time for atm.

> Anyway it seems ok to me.

Thanks for the review.

- Tom

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From dbb4a6b592df08d6263af38c4857c55acb540352 Mon Sep 17 00:00:00 2001
From: Tom de Vries <tdevries@suse.de>
Date: Mon, 1 May 2023 07:19:33 +0200
Subject: [PATCH] [gdb/build] Remove dependency on _rl_term_autowrap

Commit deb1ba4e38b ("[gdb/tui] Fix TUI resizing for TERM=ansi") introduced a
dependency on readline private variable _rl_term_autowrap.

There is precedent for this, but it's something we want to get rid of
(PR build/10723).

Remove the dependency on _rl_term_autowrap, and instead calculate
readline_hidden_cols by comparing the environment variable COLS with cols as
returned by rl_get_screen_size.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=10723
---
 gdb/utils.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/gdb/utils.c b/gdb/utils.c
index e10198accd0..8738d3fc7e4 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -1116,10 +1116,6 @@ static bool filter_initialized = false;
 
 \f
 
-/* See readline's rlprivate.h.  */
-
-EXTERN_C int _rl_term_autowrap;
-
 /* See utils.h.  */
 
 int readline_hidden_cols = 0;
@@ -1160,10 +1156,17 @@ init_page_info (void)
 	   (because rl_change_environment defaults to 1)
 	 - may report one less than the detected screen width in
 	   rl_get_screen_size (when _rl_term_autowrap == 0).
-	 We could set readline_hidden_cols by comparing COLUMNS to cols as
-	 returned by rl_get_screen_size, but instead simply use
-	 _rl_term_autowrap.  */
-      readline_hidden_cols = _rl_term_autowrap ? 0 : 1;
+	 We could use _rl_term_autowrap, but we want to avoid introducing
+	 another dependency on readline private variables, so set
+	 readline_hidden_cols by comparing COLUMNS to cols as returned by
+	 rl_get_screen_size.  */
+      char *columns_env_str = getenv ("COLUMNS");
+      gdb_assert (columns_env_str != nullptr);
+      int columns_env_val = atoi (columns_env_str);
+      gdb_assert (columns_env_val != 0);
+      readline_hidden_cols = columns_env_val - cols;
+      gdb_assert (readline_hidden_cols >= 0);
+      gdb_assert (readline_hidden_cols <= 1);
 
       lines_per_page = rows;
       chars_per_line = cols;

base-commit: 077a1f08485e88f3b234af1dbb8b907b16045e6a
-- 
2.35.3