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bug#63825: 29.0.90; The header line should be hidden when empty
From: |
Eshel Yaron |
Subject: |
bug#63825: 29.0.90; The header line should be hidden when empty |
Date: |
Fri, 02 Jun 2023 09:19:17 +0300 |
User-agent: |
Gnus/5.13 (Gnus v5.13) |
Spencer Baugh <sbaugh@janestreet.com> writes:
> Eli Zaretskii <eliz@gnu.org> writes:
>> Specifically, if the header-line-format is just a single cons cell,
>> and the car of that cons cell is either :eval or a symbol, and the
>> result of evaluation those yields nil, don't display the header line.
>> (I don't really like the idea of not displaying the mode line under
>> the same conditions.)
>>
>> Patches welcome.
>
> Ok, the easy way to achieve that is to run format-mode-line on the
> header-line-format and if it evaluates to "", don't display the header
> line. That also ignores the cases where header-line-format is multiple
> cons cells, all of which evaluate to nil, and other such scenarios. Is
> that an acceptable approach to you?
This might be a bit too coarse IMO, because it would make it a lot
harder to create an empty header line. Namely, setting
`header-line-format` to an empty string would no longer create an empty
header line.
I'm far from fluent in Emacs's internals, but AFAIU from skimming
src/xdisp.c there's another issue which is that Emacs checks whether a
window should have a header line in many circumstances, as it affects
the window's effective dimensions. So formatting the entire header line
each time Emacs just wants to know whether there is or isn't a header
line might not be ideal in terms of efficiency.
The way I read Eli's above message, it boils down to extending the C
function `window_wants_mode_line` with a couple of special cases.
Something like the following (mildly tested):
diff --git a/src/window.c b/src/window.c
index f4e09f49eae..10bccc6df65 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5471,6 +5471,36 @@ window_wants_mode_line (struct window *w)
}
+/**
+ * null_header_line_format:
+ *
+ * Return 1 when header line format F indicates that the header line
+ * should not be displayed at all.
+ *
+ * This is when F is nil, or F is a cons cell and either its car is a
+ * symbol whose value as a variable is nil, or its car is the symbol
+ * ':eval' and its cddr evaluates to nil.
+ */
+static bool
+null_header_line_format (Lisp_Object f)
+{
+ Lisp_Object car;
+
+ if (NILP (f))
+ return 1;
+
+ if (CONSP (f)) {
+ car = XCAR (f);
+ return (SYMBOLP (car)
+ && ((EQ (car, QCeval)
+ && NILP (Feval (XCAR (XCDR (f)), Qnil)))
+ || NILP (find_symbol_value (car))));
+ }
+
+ return 0;
+}
+
+
/**
* window_wants_header_line:
*
@@ -5495,8 +5525,8 @@ window_wants_header_line (struct window *w)
&& !MINI_WINDOW_P (w)
&& !WINDOW_PSEUDO_P (w)
&& !EQ (window_header_line_format, Qnone)
- && (!NILP (window_header_line_format)
- || !NILP (BVAR (XBUFFER (WINDOW_BUFFER (w)), header_line_format)))
+ && (!null_header_line_format (window_header_line_format)
+ || !null_header_line_format (BVAR (XBUFFER (WINDOW_BUFFER (w)),
header_line_format)))
&& (WINDOW_PIXEL_HEIGHT (w)
> (window_wants_mode_line (w)
? 2 * WINDOW_FRAME_LINE_HEIGHT (w)
- bug#63825: 29.0.90; The header line should be hidden when empty, Spencer Baugh, 2023/06/01
- bug#63825: 29.0.90; The header line should be hidden when empty, Eli Zaretskii, 2023/06/01
- bug#63825: 29.0.90; The header line should be hidden when empty, Eshel Yaron, 2023/06/01
- bug#63825: 29.0.90; The header line should be hidden when empty, Spencer Baugh, 2023/06/01
- bug#63825: 29.0.90; The header line should be hidden when empty, Eli Zaretskii, 2023/06/01
- bug#63825: 29.0.90; The header line should be hidden when empty, Spencer Baugh, 2023/06/01
- bug#63825: 29.0.90; The header line should be hidden when empty,
Eshel Yaron <=
- bug#63825: 29.0.90; The header line should be hidden when empty, Eli Zaretskii, 2023/06/02
- bug#63825: 29.0.90; The header line should be hidden when empty, Eshel Yaron, 2023/06/02
- bug#63825: 29.0.90; The header line should be hidden when empty, Eli Zaretskii, 2023/06/03
- bug#63825: 29.0.90; The header line should be hidden when empty, Eshel Yaron, 2023/06/03
- bug#63825: 29.0.90; The header line should be hidden when empty, Eli Zaretskii, 2023/06/04
- bug#63825: 29.0.90; The header line should be hidden when empty, Eshel Yaron, 2023/06/04
- bug#63825: 29.0.90; The header line should be hidden when empty, Eli Zaretskii, 2023/06/06
- bug#63825: 29.0.90; The header line should be hidden when empty, Eshel Yaron, 2023/06/06
- bug#63825: 29.0.90; The header line should be hidden when empty, Eli Zaretskii, 2023/06/02