Re: [PATCH] User-defined fringe tooltips (a request for review)

[Vladimir Kazanov <vekazanov@gmail.com>]

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Hi Eli,

Here is the v4 patch. As we discussed, this is option 3 i.e., looking
up properties in visible text only. In addition to the implementation,
I've fixed the docs, NEWS and TODO files.

Thanks

-- 
Regards,

Vladimir Kazanov

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From e9984a8579bb741c3e37e1eb7941ff33b53df007 Mon Sep 17 00:00:00 2001
From: Vladimir Kazanov <vekazanov@gmail.com>
Date: Sun, 24 Dec 2023 11:13:10 +0000
Subject: [PATCH v4] Tooltips for user-defined fringe indicators

---
 doc/lispref/display.texi |  4 +++
 doc/lispref/text.texi    |  9 ++++++
 etc/NEWS                 |  6 ++++
 etc/TODO                 |  4 ---
 src/frame.c              |  2 ++
 src/xdisp.c              | 61 ++++++++++++++++++++++++++++++++++++++--
 6 files changed, 80 insertions(+), 6 deletions(-)

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index f82c2fad14d..fd083083fd2 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -5501,6 +5501,10 @@ Other Display Specs
 colors are to be used for the bitmap display.  @xref{Fringe Bitmaps},
 for the details.

+It also possible to add context help for fringe bitmaps through the
+@code{show-help-function} mechanism by using @code{left-fringe-help} or
+@code{right-fringe-help} text properties (@pxref{Special Properties}).
+
 @item (space-width @var{factor})
 This display specification affects all the space characters within the
 text that has the specification.  It displays all of these spaces
diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index 18f0ee88fe5..3db82df49b3 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -3663,6 +3663,15 @@ Special Properties
 is displayed as-is by @code{show-help-function}, without being passed
 through @code{substitute-command-keys}.

+@item left-fringe-help
+@itemx right-fringe-help
+@cindex help-echo text on fringes
+If any visible text of a buffer line has @code{left-fringe-help} or
+@code{right-fringe-help} string text property defined on it, then the
+string will be displayed for a corresponding line's fringe through
+@code{show-help-function} (@pxref{Help display}).  This is useful when
+used together with fringe cursors and bitmaps (@pxref{Fringes}).
+
 @item keymap
 @cindex keymap of character
 @kindex keymap @r{(text property)}
diff --git a/etc/NEWS b/etc/NEWS
index 32cec82f970..38fb9819714 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1815,6 +1815,12 @@ the handler code without unwinding the stack, such that we can record
 the backtrace and other dynamic state at the point of the error.  See
 the Info node "(elisp) Handling Errors".

++++
+** Tooltips on fringes.
+It is now possible to provide tooltips on fringes by adding special text
+properties.  See the "Special Properties" Info node in the Emacs Lisp
+Reference Manual.
+
 +++
 ** New 'pop-up-frames' action alist entry for 'display-buffer'.
 This has the same effect as the variable of the same name and takes
diff --git a/etc/TODO b/etc/TODO
index 52c77ccc28d..21b504ad18b 100644
--- a/etc/TODO
+++ b/etc/TODO
@@ -172,10 +172,6 @@ Change them to use report-emacs-bug.
 **** lm-report-bug
 **** tramp-bug
 **** c-submit-bug-report
-
-** Allow fringe indicators to display a tooltip
-Provide a help-echo property?
-
 ** Add a defcustom that supplies a function to name numeric backup files
 Like 'make-backup-file-name-function' for non-numeric backup files.

diff --git a/src/frame.c b/src/frame.c
index abd6ef00901..ff99b0353af 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -6383,6 +6383,7 @@ syms_of_frame (void)
   DEFSYM (Qchild_frame_border_width, "child-frame-border-width");
   DEFSYM (Qinternal_border_width, "internal-border-width");
   DEFSYM (Qleft_fringe, "left-fringe");
+  DEFSYM (Qleft_fringe_help, "left-fringe-help");
   DEFSYM (Qline_spacing, "line-spacing");
   DEFSYM (Qmenu_bar_lines, "menu-bar-lines");
   DEFSYM (Qtab_bar_lines, "tab-bar-lines");
@@ -6390,6 +6391,7 @@ syms_of_frame (void)
   DEFSYM (Qname, "name");
   DEFSYM (Qright_divider_width, "right-divider-width");
   DEFSYM (Qright_fringe, "right-fringe");
+  DEFSYM (Qright_fringe_help, "right-fringe-help");
   DEFSYM (Qscreen_gamma, "screen-gamma");
   DEFSYM (Qscroll_bar_background, "scroll-bar-background");
   DEFSYM (Qscroll_bar_foreground, "scroll-bar-foreground");
diff --git a/src/xdisp.c b/src/xdisp.c
index 140d71129f3..b4d57b5b6f2 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -35730,6 +35730,59 @@ note_mode_line_or_margin_highlight (Lisp_Object window, int x, int y,
 }


+/* Take proper action when mouse has moved to the window WINDOW, with
+   window-local x-position X and y-position Y. This is only used for
+   displaying user-defined fringe indicator help-echo messages.  */
+
+static void
+note_fringe_highlight (Lisp_Object window, int x, int y,
+		       enum window_part part)
+{
+  if (!NILP (help_echo_string))
+    return;
+
+  /* Find a message to display through the help-echo mechanism whenever
+     the mouse hovers over a fringe indicator.  Both text properties and
+     overlays have to be checked.  */
+
+  /* Check the text property symbol to use.  */
+  Lisp_Object sym;
+  if (part == ON_LEFT_FRINGE)
+    sym = Qleft_fringe_help;
+  else
+    sym = Qright_fringe_help;
+
+  /* Translate windows coordinates into a vertical window position.  */
+  int hpos, vpos, area;
+  struct window *w = XWINDOW (window);
+  x_y_to_hpos_vpos (w, x, y, &hpos, &vpos, 0, 0, &area);
+
+  /* Get to the first glyph of a text row based on the vertical position
+     of the fringe.  */
+  struct glyph *glyph = MATRIX_ROW_GLYPH_START(w->current_matrix, vpos);
+  int glyph_num = MATRIX_ROW_USED(w->current_matrix, vpos);
+
+  /* Check all glyphs while looking for fringe tooltips.  */
+
+  /* NOTE: iterating over glyphs can only find text properties coming
+     from visible text.  This means that zero-length overlays and
+     invisibile text are NOT inspected.  */
+  for (;glyph_num; glyph_num--, glyph++)
+    {
+      Lisp_Object pos = make_fixnum(glyph->charpos);
+      Lisp_Object help_echo = Qnil;
+
+      if (STRINGP(glyph->object) || BUFFERP(glyph->object))
+	help_echo = get_char_property_and_overlay (pos, sym, glyph->object, NULL);
+
+      if (STRINGP (help_echo))
+	{
+	  help_echo_string = help_echo;
+	  break;
+	}
+    }
+}
+
 /* EXPORT:
    Take proper action when the mouse has moved to position X, Y on
    frame F with regards to highlighting portions of display that have
@@ -35957,8 +36010,12 @@ note_mouse_highlight (struct frame *f, int x, int y)
       }
     else
       cursor = FRAME_OUTPUT_DATA (f)->nontext_cursor;
-  else if (part == ON_LEFT_FRINGE || part == ON_RIGHT_FRINGE
-	   || part == ON_VERTICAL_SCROLL_BAR
+  else if (part == ON_LEFT_FRINGE || part == ON_RIGHT_FRINGE)
+    {
+      cursor = FRAME_OUTPUT_DATA (f)->nontext_cursor;
+      note_fringe_highlight (window, x, y, part);
+    }
+  else if (part == ON_VERTICAL_SCROLL_BAR
 	   || part == ON_HORIZONTAL_SCROLL_BAR)
     cursor = FRAME_OUTPUT_DATA (f)->nontext_cursor;
   else
--
2.34.1