line.
@end defvar
+Emacs displays the header line for a window unless
+@code{header-line-format} is either @code{nil}, or it's a list whose
+@sc{car} is a symbol, and either that symbol is @code{:eval} and the
+second list element evaluates to @code{nil} or the symbol's value as a
+variable is @code{nil} or void. Note that there are other possible
+values @code{header-line-format} that result in an empty header line
+(for example, @code{""}), but all other values tell Emacs to display a
+header line, whether or not it is empty.
+
If @code{display-line-numbers-mode} is turned on in a buffer
(@pxref{Display Custom, display-line-numbers-mode,, emacs, The GNU
Emacs Manual}), the buffer text is indented on display by the amount
+++
** 'copy-tree' now copies records when its optional 2nd argument is non-nil.
++++
+** Certain values of 'header-line-format' now inhibit empty header line.
+Emacs now avoids displaying a header line, instead of displaying an
+empty one, when 'header-line-format' is a list whose 'car' is a
+symbol, and either that symbol is ':eval' and the second element of
+the list evaluates to 'nil' or the symbol's value as a variable is
+'nil' or void.
+
\f
* Lisp Changes in Emacs 30.1
extern void syms_of_xdisp (void);
extern void init_xdisp (void);
extern Lisp_Object safe_eval (Lisp_Object);
+extern Lisp_Object safe_eval_inhibit_quit (Lisp_Object);
extern bool pos_visible_p (struct window *, ptrdiff_t, int *,
int *, int *, int *, int *, int *);
}
+/**
+ * null_header_line_format:
+ *
+ * Return non-zero when header line format FMT indicates that the
+ * header line should not be displayed at all.
+ *
+ * This is when FMT is nil, or if FMT is a cons cell and either its
+ * car is a symbol whose value as a variable is nil or void, or its
+ * car is the symbol ':eval' and its cadr evaluates to nil.
+ */
+static bool
+null_header_line_format (Lisp_Object fmt, struct frame * f)
+{
+ Lisp_Object car;
+ Lisp_Object val;
+
+ if (NILP (fmt))
+ return true;
+
+ if (CONSP (fmt))
+ {
+ car = XCAR (fmt);
+ if (SYMBOLP (car))
+ {
+ if (EQ (car, QCeval))
+ {
+ val = safe_eval_inhibit_quit (XCAR (XCDR (fmt)));
+ if (!FRAME_LIVE_P (f))
+ signal_error (":eval deleted the frame being displayed", fmt);
+ return NILP (val);
+ }
+ val = find_symbol_value (car);
+ return (SYMBOLP (car)
+ && (EQ (val, Qunbound)
+ || NILP (val)));
+ }
+ }
+
+ return false;
+}
+
+
/**
* window_wants_header_line:
*
Lisp_Object window_header_line_format =
window_parameter (w, Qheader_line_format);
+ struct frame * f = WINDOW_XFRAME(w);
+
return (WINDOW_LEAF_P (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, f)
+ || !null_header_line_format (BVAR (XBUFFER (WINDOW_BUFFER (w)),
+ header_line_format),
+ f))
&& (WINDOW_PIXEL_HEIGHT (w)
> (window_wants_mode_line (w)
? 2 * WINDOW_FRAME_LINE_HEIGHT (w)
return safe__call1 (inhibit_quit, Qeval, sexpr);
}
+Lisp_Object
+safe_eval_inhibit_quit (Lisp_Object sexpr)
+{
+ return safe__eval (true, sexpr);
+}
+
/* Call function FN with two arguments ARG1 and ARG2.
Return the result, or nil if something went wrong. */