Support lower bound on hscrolling when only current line scrolls

* doc/emacs/display.texi (Horizontal Scrolling): Document the new
mode of auto-hscrolling only the current line.

* src/xdisp.c (init_iterator): When hscrolling only the
current line, apply the	window's min_hscroll here, so that
non-current lines will be hscrolled by that minimum.
Suggested by Stephen Berman <stephen.berman@gmx.net>.
(hscroll_window_tree): Account for window's min_hscroll when
deciding whether to recompute the hscroll.
(display_line): Subtract window's min_hscroll from x_incr, as that
was already accounted for in init_iterator.  (Bug#27008)

1 files changed, 9 insertions, 2 deletions

diff --git a/doc/emacs/display.texi b/doc/emacs/display.texi
index d07913cefbe..a0d0792eacc 100644
--- a/doc/emacs/display.texi
+++ b/doc/emacs/display.texi
@@ -308,7 +308,11 @@ displayed.  When the text in a window is scrolled horizontally, text
 lines are truncated rather than continued (@pxref{Line Truncation}).
 If a window shows truncated lines, Emacs performs automatic horizontal
 scrolling whenever point moves off the left or right edge of the
-screen.  To disable automatic horizontal scrolling, set the variable
+screen.  By default, all the lines in the window are scrolled
+horizontally together, but if you set the variable
+@code{auto-hscroll-mode} to the special value of @code{current-line},
+only the line showing the cursor will be scrolled.  To disable
+automatic horizontal scrolling entirely, set the variable
 @code{auto-hscroll-mode} to @code{nil}.  Note that when the automatic
 horizontal scrolling is turned off, if point moves off the edge of the
 screen, the cursor disappears to indicate that.  (On text terminals,
@@ -366,7 +370,10 @@ sufficiently large argument will restore the normal display.
   If you use those commands to scroll a window horizontally, that sets
 a lower bound for automatic horizontal scrolling.  Automatic scrolling
 will continue to scroll the window, but never farther to the right
-than the amount you previously set by @code{scroll-left}.
+than the amount you previously set by @code{scroll-left}.  When
+@code{auto-hscroll-mode} is set to @code{current-line}, all the lines
+other than the one showing the cursor will be scrolled by that minimal
+amount.
 
 @node Narrowing
 @section Narrowing